New Alpha Chatter

[weslambe]

As you all know I just got my machine. I've been having problems with chatter and Dirk Hazeleger (sorry Dirk, I can't spell your name) came out to help me get things going.

We worked all day and found that my machine had a couple of issues. Chatter being the main bugaboo. After leaning up against the rail and getting a grease rack mark on my shirt we matched it up to the chatter marks on the doors. They matched! Turns out that my racks are causing chatter. The answer was to exercise the machine by running it back and forth many times. I found that my racks on my x car are serpentine. I put a dial indicator on my x car and hung it over to the outside of the rack just above the teeth and ran it the length of the machine. One side is out by 25 thousanths and the other side is out by 8 one way and 15 the other to make a 23 thou difference.

I made a little file that jogs to 97,49 then back to 0,0 and have run it over 500 times to try to break in the machine. As I am writing this, the machine is doing another 200 passes over the machine.

The chatter has decreased, but I still get it on x ramping moves and at speeds over about 6ips. The y ramps seem to be ok.

I can't cut at the speeds that I thought I would be able to with this machine. To get relatively smooth cuts I have to cut my vbit paths at 2ips. I should have bought a prs standard and saved the extra 7,000.00

I have doors to deliver Monday and will be sanding, sanding, sanding the chatter.

BTW. The ramping is making a grumbling noise as it comes up to speed no matter what the settings. X only.

[harryball]

Sorry to hear it, wish I could be more help... but I can ask a lot of questions :-)

Is a pinion loose? Make sure you check the pinions are tight, I had a loose one on my Z and couldn't even tell it until I pulled it loose to take a look. I couldn't move it with my hand as it was jambing back and forth, but as soon as I tried to loose a jamb nut it popped free and started moving. Installed it properly and all my Z axis problems (depth and noise) went away.

As for the doors, have you tried cutting in climb and conventional to see which gives you the best final cut on the product?

Are you running a spindle or a router? A spindle is far more stable at speed.

How large are your vbits? Are you seeing chatter or bit vibration when cutting fast? Larger diameter vbits might help. You might also run a roughing pass at higher speed then come back with a slower finishing pass. You'll have speed and final finish quality.

Again, wish I could be more help.

Robert

[weslambe]

Robert,

Thanks for the help.

We took the motors off, and checked the pinions and rolled the x car back and forth. Both were seem ok although I think I feel some bumpyness that Dirk said he couldn't feel when rolling the xcar (sans motors) very slowly.

As for which direction to cut I've been making doors on other machines for over 4 years with no issues related to cut direction.

I am running a Colombo 5hp spindle with a delta VFD-B. Before I returned my last machine to the other manufacturer I cut some doors. No chatter except on arches and that's why I returned it. I feel confident that the spindle isn't the issue although I do have a loaner Porter Cable here to rule that out. (thanks again Stan) I guess I will have to make a PC mounting bracket out of wood to test this. I did ask SB to lend me one and they said they would but I haven't seen it yet.

My vbit is a large one from Her-Saf. The insert is fairly new. New enough to cut without chatter. I have 4 or 5 other vbits from CMT, Whiteside, Grizzly, and Freud. All get the same result, chatter. I am getting the chatter at all speeds but it is much more pronounced at higher speeds. At slow speeds the bit will clean up after itself for the most part.

As for a finishing pass, if I have to do that, I have defeated the purpose of buying a machine that costs twice as much as it's slower counterpart. The purpose of buying an alpha was to cut my time in the shop down by boosting the production speed. If I have to cut every path twice, I would have been better off keeping my old prt96.

Things that were checked:

Grounded spindle and table
communications
y car rails were out of spec. Dirk fixed this.
distance between rails is ok

I am willing to try anything to get this machine up to speed. I cannot continue to be forced to get up at 2:30 every day because I have to sand chatter away.

I am keeping count on how many times I have run the break-in jogs. I am now at 650 times back and forth. That means I've jogged across the machine and back 1300 times. My pinion will be toothless before long.

[richards]

Wes,
Sorry to hear that you're still working out the kinks. I've found with my Alpha that setting the speed to the higher numbers is mostly an exercise in wishful thinking. Unless I'm using my machine like a panel saw to make full length and full width cuts, the actual time to cut parts whether I set the speed to 5-ips or to 10-ips is usually very close. Because of the part geometry, ramping usually plays a major factor in the total time to cut a part vs the highest possible speed. It's kind of like having a 60-mph speed limit but then having a stop sign every block. The constant acceleration/deceleration would keep us from ever attaining 60-mph. Ramping has that same effect on my machine (depending on the part).

Since you're having problems with chatter in the ramping portion of the cut, why not play with the ramp settings until you get a nice gentle movement? I've done that with my machine. Granted, that's one of the factors that slows down through-put, but, if more modest ramping eliminates 'chatter' then the results might be worth the trade-off. The car analogy fits here too. 'Chatter' caused by too fast ramping would be the same as 'burning rubber'; lots of noise, lots of smoke, lots of wear and tear on the engine and gear train, but very little progress on actually going anywhere.

You might find some other factor that is at the root of the problem, but the SB3 help section on ramping is very thorough, and, changing values and running tests on those changed values is quick and easy.

[weslambe]

While Mike was writing to tell me to check my ramping values I was working on them. I went and messed with the ramping values and did get some positive results. A lot of the chatter is gone, but I can't go any farther down on the settings for some of them. .05 is the minimum on the xy move ramp speed and jog ramp speed.

Here's what my settings are now.
xy move ramp speed = .05
z move ramp speed = .4
a move ramp speed = .4
b move ramp speed = .4
xy jog ramp speed = .05
z jog ramp speed = .4
a jog ramp speed = .4
b jog ramp speed = .4
Move ramp rate = .2
Jog ramp rate = .2
3D threshold = 300
Minimum Dist to check = .75
Slow Corner speed = 35


I am getting better results by doing this and setting my z move speed to .5ips

I am still getting some rack chatter and think that the x motors rumble too much on ramping.

Maybe I can make doors with this machine. I hope to have something positive to post later today.

[richards]

Wes,
It's good to see some progress. I'm wondering though, if some more tweaking might be necessary? (Please keep in mind that I've only seen the PRS model at the Jamboree and that I've never operated one. So what I'm suggesting relates mostly to my PRT-Alpha.)

I would try using a higher xy move ramp speed of .2 and I would also try a much higher Move ramp rate of .8 or higher. The xy jog ramp speed and Jog ramp rate can probably be left at factory defaults, since you're not cutting while jogging.

If I understand ramping properly, the xy MOVE ramp speed is the starting speed for the ramp. Stepper motors have a nasty habit of running rough at very low speeds (harmonics), so setting the xy move ramp speed higher might actually start the motor at a pulse rate above the harmonic problem area. Secondly, the Move Ramp Rate, I believe, is the distance moved to increase or decrease 2 units of speed. In other words, a higher number means that the ramping period will be longer (and smoother) and a lower number will mean that the ramping period will be shorter (and choppier).

Your Slow Corner Speed is right where Brady recommends (and where I have mine set on my Alpha).

[Brady Watson]

Wes,
Don't mess with the ramps above the '3D Thershold' value. Leave them be or you'll wind up taking away from your experience rather than enhancing it. For your 7.2:1 tool, and *most* types of cutting, you'll want to use these settings:

Here's what my settings are now.
xy move ramp speed = .4
z move ramp speed = .4
a move ramp speed = .4
b move ramp speed = .4
xy jog ramp speed = .4
z jog ramp speed = .4
a jog ramp speed = .4
b jog ramp speed = .4
Move ramp rate = .4
Jog ramp rate = .4
3D threshold = 150
Minimum Dist to check = .08
Slow Corner speed = 35 to 50

Some of the values that you have listed are WAY out of whack. Leave the default values alone, except for the last 3, until you have a better handle on tuning them. Values that are too far out of the norm will make your machine run rough.

-B

[srwtlc]

Wes, How much force did you apply to the X motors when pushing them up into the rack before tightening them down? I found that if I used to much force on them that I would get growling/vibrating when traveling at a higher rate. If too little, then you can get some extra backlash if the rack has any variance. Such as at the ends where the one set screw can be pulling the rack closer to the rail.

Personally I would still prefer the spring loaded scenario.

[weslambe]

I hope to have pictures as soon as my batteries get charged.

Brady,
Anything above .05 on jog and ramp move rates causes a noticable bumping as the motors ramp up or down in speed.

Scott,
Any idea how often we should be checking our motor/pinion gear clearance? Should we be loosening and tightening our motors frequently? I can only imagine how long the threads will last.
I'm not forcing the motor up into the rack. I guess I could try a little less tension from pinion to rack though.

Also, I'm not ruling out my spindle or collets, but I get the bumpy road feeling from the machine without the spindle running. If I had to try to try to describe the how the table feels to the touch when it's running (without the spindle running) it would be like an ice cream maker when it gets stuck on some ice.

The table noticably shakes when running. Worse on ramps though.

[Brady Watson]

Wes,
I would back up a few steps before looking into adjusting ramps etc. Setting the ramp rate as low as you have is just masking the problem, not fixing it. Some of your other settings can also prevent you from correctly diagnosing what is going on with the machine. It sounds to me like you have a mechanical problem for sure. You must be absolutely sure of the following:

1) Pinion gears are aligned to the rack, in & out so that the entire footprint of the pinion is engaged into the footprint of the rack. Eye-ball the rack to make sure that it is parallel to the machine all the way down on all axes.

2) Pinion grub screw *must* be absolutely without a doubt, cranked down as hard as you can. When you bend the long portion of the hex key, you know you're in the right range. This is why SB gives you 3 hex wrenches.

3) Pinion to rack lash is easier to achieve than the old spring-type setup. Loosen up the hold-down bolts and use both hands to wiggle the motor into the rack. Don't pull the butt end of the motor too high, resulting in an off-axis alignment. Tighten hold-down bolts.

4) Wiggle YZ car with control box on. Listen for noise. Grab it and push and pull in every direction. You should hear nothing. If you hear 'ticking' when you wiggle it, find out where it is coming from and adjust the eccentric bushing on the v-roller bearings. Take care not to move the Z axis out of perpendicular with the spoilboard.

-B

[weslambe]

Brady,

I mentioned earlier that the racks are "S" shaped on one side and bowed on the other. The "S" side is 8 thousandths out in one direction and 15 thousandths out in the other for a total of 22 thousanths out in an "S" shape. The other side is out by 25 thousanths in one direction only making it a bow in the center.

This is directly under the hardened rails which measure 77 13/16th exactly all the way down. They could be out by the measurements mentioned above. I will try another tact to see if I can get them perfectly straight.

Dirk: I think you got my long hex wrench.

[richards]

Wes,
I was just leaving to handle a computer emergency when I last posted, so I didn't read all of your parameter settings properly nor did I compare them to default settings. Brady caught the parameters that I overlooked - especially the Minimum Distance to Check.

I don't doubt that you're getting the best cut at 0.05 xy move ramp speed, but that particular value may be effected by another parameter. It might be best to set all of the ramping values to default settings and then change one at a time, perhaps starting with the Slow Corner Speed and then the Move Ramp Rate and then, if necessary the other parameters. The good part about changing ramp speeds is that you can hear, feel and see the effects while air cutting.

On my machine, all of the ramp values are at default settings except Move Ramp Rate and Slow Corner Speed. Currently, I have the Move Ramp Rate set to .8 and the Slow Corner Speed set to 35. I found those settings by air cutting a 6" square until the machine sounded and felt smooth. I used PartWizard to generate the 6" square and then ran the test at 2-ips, 4-ips, 6-ips and 8-ips. When the machine sounded and felt smooth, I cut the square to verify the settings. There was no visible chatter marks on the part.

Just to make sure that semantics aren't getting in the way, I define 'chatter' as hills and valleys that repeat about every 1/8" with a height of 0.025", more or less, kind of a wash-board effect. Using that definition, there was no chatter on the parts that Bill Young cut with the PRS-Alpha at the Jamboree. I watched for about an hour as he cut kit parts out of plywood. As he stacked up the parts, I picked up piece after piece, looked at it and ran my finger tip along the edge. Inside circles were round and smooth. Outside circles were round and smooth. Straight cuts were straight and smooth. One part matched another part when one was stacked on top of the other. All of this happened while a room full of curious people stood around the machine. Many of us were bumping the machine and leaning against the rails to get a better view. All of that makes me think that you're going to get perfect cuts once you have things tuned optimally.

Edited: Brady and Wes, you both posted while I was slowly composing (and running checks on some networked computers here at a customer's site). Wes, I'm leaning towards following Brady's suggestions first. It doesn't seem probable that the bowing that you've described would cause the chatter. Having 0.025" deviation along a 10 foot length isn't perfect, but I don't think that it would cause a repeating chatter pattern.

[weslambe]

Here's a picture across the Y axis. The spacing on these chatter marks are .125 to .135 or so apart. I could take a picture of my shirt's rack mark next to this so that you can the correlation.


3719

This chatter is everywhere using every bit at every speed except for 2ips or less.

BTW. This picture is a little out of focus due to dead batteries.

[bleeth]

Brady, as you may recall, the last couple of years saw my prt being used in the custom shop for cutting templates, etc. and I've been pretty hands off when it comes to operating it. I did however, upgrade the control box to the Agek which is pretty much the same as the 4-g. I have the 3.2 (3.6?) geared motors. Do you feel the above suggested values are a good place for mine as well? I just spent the day re-shimming, straightening and squaring the rails and am milling the new spoil board now.
Having good clean square corners and maximum output is now critical as I will be using it for boxes on a production basis and they need to be right.

Dave

[richards]

Wes,

I just got back to the shop and saw your photo of the chatter marks. You said they mirrored the rack marks on your shirt so I measured the rack teeth on my machine and found them to be a little more than 1/8" apart. You wrote that the photo is of cuts made with the Y-axis, which has only one motor, eliminating the possibility of the two X-axis motors fighting each other. That leads me to suspect that Brady has already described the cause of the problem being related to the way the motors are physically connected to the machine. Luckily, on your machine it's very easy to adjust the tightness of the motor to the rack. Following Brady's outline, I would check that the spur gear is very securely fastened to the motor's gear box and then reseat the Y-axis motor (probably a tad little looser than it is right now) and then try the cut again.

As long as there is a distinct clue like you have the old adage of Akum's Razor will probably hold true: All things being equal the simplest explanation is probably the correct explanation . . .

[weslambe]

I will loosen the motors.

[ted]

Ryan and I took a crack at duplicating Wes's difficulty this afternoon. We were using the same PRSalpha tool, and as I understand it, the same type of Her-Saf v-bit. We did not have any trouble finding a feed rate and spindle speed that gave us some of the same type marks [in this case, 4ips and 12K RPM]. However, it was also fairly easy to adjust the feed parameters to produce a pretty smooth cut [the samples here are 8ips and 18K RPM].

In the photos below, the cut on the right (marked A) is the slower one that shows the problematic finish. The one on the right (marked B) is the faster and smooth cut.

Since Dirk has paid the tool a visit and has a pretty good eye for how they should be set up, I'm thinking I'd like to see how Wes's cuts will look with a new collet and collet nut. It's also the case, that our tool here has run quite a bit and that it could be that a little wear on the pinions is not a bad thing. It's possible they start off being a little stiff and tight; such that there may be merit in the suggestions above to reduce the tension a bit as well as get a little grease and wear on them.

We are very interested in figuring out what is going on.


3720

3721

3722

3723

3724

3725

3726

[ted]

Ooops, also forgot to mention we did a circle at the higher feed rate which is also shown in the pictures above.

Ted Hall, ShopBot Tools

[weslambe]

I bought another shopbot for a reason and that reason is that Ted stands behind his machine. I have no doubt that I will be running smoothly soon.

I will order the new collet and nut on Monday but I still go back to the 3 doors I created on my other machine. They were perfectly smooth except for the arches. That was my reason for returning it. Those three doors were created on April the 22nd and I returned the machine on the 24th. I didn't cut anything with my Colombo until I got my Shopbot. I have cut about 5 hours on the Colombo since I received my new Shobot. I don't think that's the issue but I'm willing to try anything so that I can get back in business.

By the way Ted, Dirk's visit was a real morale booster but he said this was the first time he had left a site without fixing the problem.

EDIT: The pictures I took above were of a cut made by a 2 flute Amana bit, not a Her-saf. I have taken to trying all of my bits. I have had to drop everything to watch my 3 year old twins while the older sisters are playing a softball tournament. Then I have to cook. I may be able to continue testing later tonight.

Regardless of the outcome, I have doors to deliver Monday. Looks like I will be sanding unless I see a miracle.

Ted, if the collets are bad, wouldn't the chatter be random?

[harryball]

Wes... I was sitting here remembering a situation I faced in the past with a harmonic vibration in a 30m uplink dish many years past.

I'd be curious how the bot felt to the hand as it moved from 0 to 96 with the spindle running. Use speeds that you would like be cutting, i.e. 5 ips at 18k or something. With it sitting still and spindle only do you notice periodic or constant vibrations? With it moving? Then with it moving making a test cut? If I can't help I can at least ask questions eh? ;-) It's my nature to love brain teasers and you've got one. When Ted works out what the problem is it'll probably be something so obvious we just can't see it.

Robert

[weslambe]

Ted,

One more question so that I can be on the same sheet of music as you.

On your cuts above "A and B". Did you use an old collet for the "A" cut or did you simply change cut speeds? Because if you didn't change collets then collets are probably not the reason for the chatter at your shop or mine for that matter. Regardless, I am willing to buy new equipment to test the theory.

I would bet that a pencil taped to the spindle would create a wiggly line. I will try that later tonight.

[weslambe]

Robert,

I get a bumpy ride with my bot up and down the x and y. A little less so on the y. All with the spindle turned off.

With the spindle turned off and jogging back and forth I can actually see the table shake as it ramps up to speed.

At fast move speeds you can see the table shake on ramping moves also.

Maybe when I finish this job I will tear the machine down to little pieces and start over from scratch.

I am disappointed. If it were just ramping, Dirk would have found that yesterday.

[harryball]

I wonder if the motor shaft is perpendicular to the track. That would keep the pinions trying to ride up the teeth and that would make for a rough ride. After all your running what kind of wear do you see on the pinions?

Robert

[richards]

Wes,
Is there any chance that the shaft hole on one or more of the spur gears was bored a little off-center? I've done that more than once when I've bored out a gear on the lathe. If the hole is not concentric to the edge, no amount of twiddling will make that motor run smoothly, especially when the new design eliminates the spring tensioner. (In my opinion, the new system is vastly superior to the older spring system, but having a non-concentric hole would be one instance that would make the new system fail.)

[weslambe]

this morning I continued running my door job. I tried cuts at various spindle speeds and feed rates. Nothing helps much.

I made a little file that moves the y back and forth and increases the move speed as it goes along.
ms,3
my,49
my,0
ms,4
my,49
my,0
ms,5
my,49
my,0

all the way up to 8 ips.

What I noticed while holding onto the bit (spindle off) as it traverses the machine:

3 ips, slight rumbling, noticable though
4 ips, major rumbling, very, very noticable
5 ips, major rumbling but less than at 4 ips
6 ips, somewhat like 3 ips
7 ips, again, like 3
8 ips, again, like 3

I have done 10 ips too and it feels like Ka-ka. It's as bad as 4 if not worse.

I took the y motor off and pushed the y car back and forth on the gantry (something that wasn't done when Dirk was here). At the home position you can push the car and let go of it and it will roll down the gantry about 1 foot before it starts binding up. From that point on, if you push the car and let go, in the + direction, it will not roll any farther than your fingertips. Therefore, I have concluded that the rails are not properly aligned. I will go to Harbor Freight today and buy a 12" dial indicator and some new hex wrenches. The ones I had a few days ago have gone missing. My shop is a mess but I hope they will turn up.

I cleaned the pinion gear and looked at the wear on it. It is uneven wear. I can see where the rack has polished the pinion. It has a polished look about 2/3rds of the way across the pinion.

I didn't look to see how it was wearing on the other side of the pinion teeth.

If Ted's machine shakes at 4 ips and mine does too, what gives? Ted, did you guys try and run the machine at 4 ips and hold onto the spindle as it moved?

I am just barely hanging onto my business after the fiasco with my last machine. Now I've got to figure out what's going on here?

Maybe tension springs would be a better solution because they would allow the pinions to ride up and down on the rack when there is a slight warp in the rack?

How about making the motor mounts into little z cars and push them up with a tensioning spring? That would be a little difficult with the current z motor since it's right against the z car.

Sorry, I went off on a tangent.

I know that I probably need new collets and collet nut since I have about 150 hours on my current ones and they are a little loose in the nut. (Colombo recommends replacement at 700 hours) They don't fall out though.

But why spend the money when my machine shakes without the spindle turned on?

Mike,

I haven't checked to see if they are bored off center. I will though.

[weslambe]

For clarity's sake, my last machine was made by another manufacturer. I didn't make that clear in my last post.

[richards]

Wes,
I've just run a spreadsheet on the actual RPM that your steppers would be running at various feed speeds. To do that, I've made some assumptions that I think are correct:

30-tooth pinion gear
7.2:1 gear ratio
1000 steps per rotation for your motors

If those assumptions are correct and if my math is correct, here is a list of RPMs at various feed speeds:

IPS - RPM
---------
3 - 275.02
4 - 366.69
5 - 458.37
6 - 550.04
7 - 641.71
8 - 733.39
9 - 825.06
10 - 916.73

That shows that somebody at Shopbot made a perfect match when selecting motors and gear boxes for the PRS-Alpha. My testing has shown that most steppers run almost perfectly in the RPM range from 200 to 1000.

That chart only shows that the motors should not have problems with harmonics at those speeds. So, that would make me look even more carefully at the alignment of the V-rollers to V-rails, gears to racks, proper boring of the pulley or any other mechanical problem that would keep the motors from doing their job.

[weslambe]

Mike,

Ted showed us pictures of his chatter at 4 ips. His machine is the same as mine. Is this an indicator that there is a systemic problem with the new Alpha series? I hope not. Now I am at my wit's end. I bought the machine so that I could spend more time with my family and give my parents a break from babysitting my 3 year old twins as often as they have had to recently.

Now, I have to get up every morning at 2:30 so that I can have time to sand chatter after cutting during the day. Getting up at that hour means I don't get to sleep in the same room as my wife since she doesn't need to get up at 2:30 every day with me.

I do trust that Shopbot is making every effort to resolve this problem, but I cannot afford to waste my life waiting for a solution. When my machine stops shaking while doing air cuts I will consider buying replacement collets. Collets may well have something to do with the overall cut quality, but the collets have no bearing on how the machine air cuts. I am on my way to Jackson, which is 45 miles away, to buy some 12" calipers so that I can check the y rails. I cannot continue to bleed green trying to get machines running correctly.

[paco]

Almost chatter free cut can be obtain from tweaking CAD/CAM strategies, machine hardware, control software settings (ramps), cutter selection, hold down method, types of materials and so on (obvious stuff) but ""perfectly"" chatter free cut can obtain with a 100 000$ (and more) machine upgrade... I believe. Still, one wont be free of any issues with 100 000$ and up machines... I do know.

[carlcnc]

Mike,Wes, et al

[carlcnc]

Mike,Wes, et al,

once "tracked" down I think you will find the source of these"jitters" to be something in the 2 slaved motors/reducers/pinion driving gantry.
can be ,pulse smoothness,noise or capacitance on cables of different lengths,pinions with several thousandths of variation, a major difference in the pressure each pinion is held to the rack could do it.
just my opinion,but:
Mis alignment [out of parallel] vee tracks will cause binding and slop but not jitter.

carl

[harryball]

Wes, from everything you describe it just seems there must be some fundimental physical problem. I wish I lived closer and could come take a peek myself.

I'm just thinking outloud here...

I wonder if I could run the bot on a single X motor, leave the other disengaged and floating. Keeping the spindle close to the single engaged motor. This would let me see if it ran smoother with one X or the other.

I might consider swapping the Y motor, which if I understand runs smoothly (or smoother) with an X and see if the problem moved.

Of course, double checking all the alignments would be logical as well.

If the pinions are wearing uneven, that means uneven pressure. I'm still wondering if the shaft is perpendicular to the track or as Mike suggested, one or more of the pinions is machined offcenter or out of square.

Hang in there Wes, I'm sure shopbot will figure this out.

Robert

[weslambe]

I just got back from Jackson. Let's see 10:40 was my last post and that's when I walked out the door. It's now 1:10. That's a good example of wasted time and money. I bought a 12" digital caliper for about $50.00 and will make measurments along the y axis. 50 bucks for one set of measurments.

I believe that I am correct on the pinion/rack alignment. If they are not perfect, then the results will be amplified on the spindle. I just might hang the motors from one of the upper hex screws and attach a spring like the old machines to see if it makes a difference.

Paco, this isn't my first machine. It's my forth. My first was a shopbot and it cut almost perfectly. I sold it because it was too slow. The man who owns it now would say the same about it today and it cost him a little over 5 grand.
Cutter selection, speed, ramping, material and cam package do make a difference. I have been cutting the same doors using the same software, materials, and cutters for over 4 years. Many of those years were chatter free. Yes, the expensive machines have issues too. I was considering purchasing a Flexicam last year for about 70 grand. I didn't because I saw some issues related to depth of cut while at the IWF in Atlanta last year. I chose another brand based on its fine components. THK ball screws and linear rails and guides. I still own the 10' rails and bearing blocks. I also helped a friend of mine set up a 60 thousand dollar CNC Automation moving table machine. Two 10 HP spindles and 8 position tool changer. Centroid based. I'd never seen this before and had his machine picking up tools and running correctly in a day. He still needed to get some guidance on ramping into his corners on his doors so I know what other expensive machines are capable of. I also know that the shopbot SHOULD be capable of cutting a straight line WITHOUT chatter marks.

I am worried but I continue to have faith that this will be corrected and I will be able to get back to business before I completely lose my arse.

[richards]

Wes,
One thing that I don't think has been tried is to have someone else with a PRS-Alpha run your file. I'm sure that anyone you asked would be willing to do that for the price of a sheet of MDF. At the same time, they could run the file that Ted and Ryan used to test for chatter. That would show whether the machine has a 'sore' spot somewhere in its design (which I very much doubt would be the case), whether there is something that needs tweaking on your machine or whether the file itself should be tweaked (which I also doubt, since the V-cuts that you're doing are fairly shallow). In any case, at a certain point it might be good to get a second opinion from a fellow shopbotter.

I would be happy to run your files, but it wouldn't really prove anything since my machine is the PRT-Alpha that I've modified with belt-driven transmissions. This much I do know, the PRT-Alpha with direct drive (at least mine) had chatter problems. I cut a bunch of drawer fronts for my shop with the factory configuration that I've left unsanded and unpainted. They're just drawer fronts for a working shop, so I 'm not too particular. People who see them with their brushed pewter pull-knobs have always been amazed at how nice they look. When I point out the chatter marks, they aren't too concerned. In fact that has led to a lot of sales where friends and neighbors want the same thing for their garage or laundry room. When I show them their drawer fronts without chatter marks, they're even more pleased. The only difference is that with geared belt transmission, chatter took a leave of absence. The point that I guess that I'm trying to make is that my problem was strictly mechanical. My machine has soft iron V-rails, not hardened rails like yours. My machine only has 3:1 gearing not 7.2:1 gearing like yours. My machine has a lot more flex when compared with yours. So, even though the birthing of a new machine can be a royal pain, you have a machine that is much superior to the one that I have. It won't be long until the birthing process is just a memory and you'll be wondering what to do with all the extra free time that you have.

Edited: Wes, I forgot to address the 4-ips issue. I have several feed speed/spindle speed zones that I don't use on my machine. Although I have very little knowledge of mechanical engineering, I have read extensively about 'harmonics'. I know that stepper motors have that problem at certain speeds (usually less that 100 RPM), but I've also read that almost any thing mechanical that moves will develop harmonics at specific speeds. In fact, I've never owned a car/truck yet that didn't get the shakes at certain moderate speeds. Since I once drove at least 70,000 miles a year, I've had lots of experience with that natural shaking. My solution was to speed up 5 MPH or slow down 5 MPH. It almost always worked. Basically the same thing happens with my Alpha. When the machine sounds rough, I just fiddle with the Shift > keys or Shift < keys to adjust the speed just a little. It works for me.

[weslambe]

Looks like the gantry wasn't set up correctly. Here is a picture of the last couple of inches of my 5' straight edge and the upper rail of the gantry. I have a picture of the other side of the straight edge on the rail to make sure the straight edge was really straight.

3727

3728

I put the end of the straight edge all the way to the far side and this is the gap that I got. I also have the same gap under the rail but it's harder to get the 60" straight edge under there and take pictures due to the gussets.

Should I take apart the top rail? Should I loosen the top rail until it's straight then make sure the bottom matches? Shouldn't this have been checked at the factory? I think my machine shipped on a Friday. I wonder if it was made that day.

Mike, you left out one thing on the "new machine birthing process", it's a pain in the a@@.

[bleeth]

Wes: I totally understand your needs to cut back on sanding. It is a major pain. That being said, please note that all parts cutters have to do it. At Enkbol, the carved ornament company, they have a full team that does nothing but apply sanding sealer and hand detail each piece. All the large door companies either have teams of hand sanders or very expensive butfering sanding machines. Having ordered hardwood five piece doors from many different suppliers around the country over the years, I can always tell just by looking whether they have been through this process or not. Some have an automatic mark-up of 15-25% to ship "Totally ready to finish" doors. Others, who refuse to ship unless they are perfectly sanded, simply charge more in their base pricing to cover this.

I have the following concerns with your symptoms:
1. Software version-Run either 3.4...or 3.53. I just updated to 3.53 and noticed improved smoothness immediately.
2. I can't personally speak for the new motor mount system, but unless the pinions and rack are absolutely perfectly machined and square then a stiff mount of the motors will translate anomalies. It seems to me that the teeth should be firmly, but not tightly in contact with each other.
3. The higher degree of machining the more important perfect levelling and alignment of the components becomes. Besides checking the precision of the y rails with your new calipers, I would do the same thing with a good jig for the x's as well. A good rig to do so can be made from a set of trammel points and hardwood carrier. Properly levelling everything can take some time and needs at a minimum a top quality level such as stabila and preferrably a bubble level or quality laser transit. If you or a friend don't have one, then one can be rented reasonably. The "el cheapo" laser levellors from Home Depot are useless for precision work. For verifying straightness that same transit will give you good results and I have verified it with extruded straight edges. The nature of the new x rails should make straightness a none issue, but only a tiny amount of lateral bowing will throw things off.
4. Collett and spindle-Even a low hour collett can get you if it has been overstressed just once. If you have one of a size you have not hardly used, try it for some test cutting. You may get a pleasant surprise. If your spindle has any vibration when not running under load and with no collet in it then you may have a bent shaft in it. That would be bad news.
5. Always allow at least several days and more like a week to install any serious piece of equipment and shake out the bugs. I have seen it take a month to get a brand new Giben Beam saw running just right. The pressure of getting a job out on a schedule only makes it worse. I know. I have not only been there before, but I am there now with a full office suite to deliver by July 1 and organizing a complete shop for production only since June 1. I just spent 2 days tweaking my machine to re-balance it to my standards and had a tough time ignoring the clock and concentrating on the issues one at a time regardless of time required.
5. This last is a rule that must always be followed to avoid turmoil: Make the time to get/keep all parts and tools organized. More time, aggravation, and money is wasted looking for misplaced tools in an environment that is allowed to slip due to pressure to "get the job done" then any factor I can think of.

I bet your faith is well placed that these issues will be resolved, particularly if you handle them systematically.

Dave

[bleeth]

Wes: You posted your gantry shots while I was composing-Get the top rail straight and level first and then align the bottom one. You also should start with the alignment of the x rails before attacking the gantry. Don't forget to verify the squareness of the spindle after the other two are right.

[weslambe]

Dave,

Thanks for the input. I didn't have to sand the doors I made on the prt 96 much at all and have a video that I made when I sold Doorbot showing how much sanding was needed. I spent about 1 to 2 minutes per door mostly because of machine flex in the corners.

I'm kind of getting a wierd vibe here. I have a machine that is out of whack and came that way. I show pictures of chatter and gaps and people keep going back to my collets. The machine SHAKES WITHOUT THE SPINDLE TURNED ON!!!!

Yes, I think it can be fixed. If I didn't, I would be in Durham Tuesday with the machine on a pallet.

Sorry Dave, I don't mean to direct this at you.

I've had 2 other shopbotters look at my machine. Stan Holt and Dirk. Dirk left telling me that this was the first time he'd left without fixing the problem and Stan was the one who noticed that the racks didn't seem straight, not me.

Feel free to come to Mississippi and help me if you'd like. I have plenty of room for you to stay. I even have a 31 ft camper that I use when I have to get up at 2:30 that you could use. It has a very comfortable queen sized bed and all of the other comforts of home without a bill. Please come. I'll even feed you. I'll buy the beer and hookers if that's what it takes. I am getting desperate. BTW, I don't know any hookers but if there were any around, they probably wouldn't have any teeth. This is Mississippi after all.

I am trying hard to keep a sense of humor.

Feel free to call with advice or criticism.

601 374-0148

Dave, one more thing, Dirk was here! He checked all of this with me. I purchased a 78" level just for this job. I checked this level's edge against some very, very expensive ones and it was just as good. I also have a digital 4' level and another non-digital johnson level that is accurate to within .005mm over a meter. I used all three together when getting the machine level. I can call in the calvary. My bro is a jig and fixture man at Goodyear aviation and can come "shoot" my machine if need be. I don't think I'm there yet.

[srwtlc]

Wes,

I agree with Dave. Take care of the top one first and then the bottom one.

I had problems with mine also. The top one appeared to be fine (parallel and perpendicular YZ), but the bottom one was out of parallel with the top from one side to the other by about 0.060".

I use several precision cut blocks (miter saw cut maple checked with a caliper was the best I could do at the time) and clamped them between the rails themselves not the stock that they're mounted to. I then tightened the lower rail from the center out rechecking for parallel afterwards.

I don't know it that would cause the bumpy ride your seeing, but if it was binding enough, it may. Mine was so tight at one end that I was getting almost what felt like galling on the rails, but cleaned up with a little mineral spirits and a scotch bright.

How does the rail compare to the bar stock that they're screwed to. Could there be a couple of screws that are forcing the rail off centerline.

Man, I wish I was closer, I'd let you use my machine and I'd do some sanding for ya!

Whether or not this is the problem, I would agree that it's something that shouldn't get past QC.

[srwtlc]

What about dialing the distance between the top of the rail and the teeth on the rack. Who's to say that the double stick tape is consistent in it's thickness or could there be some foreign object between the tape and the bar stock that it's mounted too. What's to say that we aren't slightly compressing that tape by forcing the motors into the rack. Get that carriage so it free wheels (with slight resistance) without the motor attached first and then try with the motor on. I got mine so that I could push with slight resistance to Y48 and the wire guide would push it back.

[harryball]

I do wish I was closer too or I had the time right now to come visit... though I don't need hookers. My wife would be packing to head out now, she loves seeing new places. Not that it helps, but I feel your pain. I just did a maintenance yesterday on my bot as I have about 100 bat houses and 100 kits to complete for a festival in a couple of months all on top of normal productions. Things must go right or I'll be up at 2AM working as well.

I'm glad your sense of humor is returning, that generally means you're having some hope in the future.

I agree with Mike, if a PRS Alpha owner out there was willing to run one of your door files on a sheet of MDF and send you some pictures of nice very low to no chatter doors I bet that would improve your morale just a little. I have a PRT Alpha myself so I can't offer much help there.

Robert

[bleeth]

Wes: Good speaking with you. For the benefit of others I will summarize conclusions:
1. The y carriage extrusion is bowed. This means the rails need shimming to be flattened. This is step one. Then level the top one and set the bottom one parallel. That should get the car running smoothly.
2. The rack is not perfectly straight and probably not flat. I think the 4 bolt system needs to be re-thought at SB and a tensioner spring and pivot needs to be re-introduced.

The photos by Ted and Ryan prove that there is still some R & D needed in Durham for this model to perform at the increased performance expected. There is no way that a machine for 13K is going to do what a 250K machine will, nor should anyone expect it to, but there really shouldn't be chatter at 4ips when v carving less than 1/2" through mdf with the stiffness of the steel skeleton in the PRS. Chatter has been the bane of all of us who actually use our tools to compete in the real world with larger and wealthier shops and the main reason for the upgrades from the PRT bolted together gantry to PRS and the movement from SB Drivers to Geckos. We know the Gecko's have solved the electronic part of things, and now, the new structure probably just needs some mild tweaking in design and more strict quality control to finish the job. I have a feeling the next one may be the PRX!!! Ted: You are welcome to use that designation without royalty!

Dave

[srwtlc]

If that extrusion is bowed, shimming both top and bottom rails to be the same without making them wavy is going to be a pain! On top of that, your end plates could be (more than likely) toed in/out and then you'd have to shim them too.

I think SB should be loading the truck for a road trip Monday morning.

[weslambe]

I need to double check the extrusion to see if it's bowed or the hardened rail is the only thing bowed. I have some more doors to make tonight and will be able to remove the z car afterwards. That will make it a little easier to actually measure the whole thing I think.

At any rate, if the rails are the only thing bowed I would be well served to make the adjustments with the z car on the table.

Thats one problem. Now on to the next.

EDIT: It's not the aluminum extrusion that is bowed on the y car. Whoever put my gantry together didn't do a very good job. There is a huge bow upward in the center of the y car's rails. So much that I can rock my little 4' level on it like a see-saw.

That could be some of my problem with chatter on the y. I will fix this tonight or tomorrow assuming there is enough room left in the t-slot to move the rails that far. It may be about a 16th of an inch high in the middle.

What concerned me before about bows was the x car rails. They were (if I recall correctly) bowed but putting the table together seemed to pull them straight.

My spindle still drops to the table when I power down. Maybe I can find some after market springs that are strong enough to hold up a 5 hp colombo spindle.

[weslambe]

Carl,

Mis-alignment of the v-rail can not only cause slop, but chatter because any variation causes the roller bearing to climb off of the rail. When the bearing climbs the result is that the pinion gear is pressed tighter into the rack since it's bolted to the gantry. Not only is it in the rack tighter, but it now has a slight angle. It's not much, but I am seeking to make perfect doors for my customers who pay for perfect doors.

Pinions pressed too tightly causes chatter. Pinions at an angle to the rack causes chatter. Vbearings riding up the rails causes both of these at the same time.

I had a customer who wouldn't buy doors if they were more than 1mm out of spec because he makes frameless cabinets. Thank God he moved to New York because I am sanding more than 1mm away now. Slop is normal on half inch overlay doors because they almost never are closer than 1/8th of an inch. More likely they are almost an inch apart or better all of the time.

Frameless and inset had better be right or you lose your customer and your reputation.

I would rather do no business right now than to jeopardize all future business because of slop.

[conceptmachine]

Wes,
You havn't posted on how thing's are going,Did you get your problem's resolved?
shawn

[mthomas]

I would also like to know how this has been (has it been?) resovled.

[mthomas]

Does anyone who's been in contact with Wes know how this was (was it?) resolved?

[henrik_o]

A bump and aye on knowing how this was resolved, if it was.

[bleeth]

I cannot personally verify this but I have heard that Ted has volunteered to repurchase Wes's machine and Wes is designing his own to suit his needs.

[weslambe]

Dave is right.

After 2 days of tweeking by shopbot, they offered me a refund. Dirk came to my shop one day then Ryan came another. Neither of them could make the machine quit chattering.

I am building my own machine.

[richards]

It's too bad that the only option seems to be a home-built machine. It seems to me that designing something from scratch is going to take a lot of time and a lot of money before that machine is running.

Yesterday I cut a bunch of doors on my PRT-Alpha and had chatter-free cuts that were as good as the photos that Ted posted higher up in this thread. They ran at 6-ips and 15,000 RPM. Before that I had an easy job cutting some ultra-light MDF for a customer that just wanted a bunch of sheets cut with multiple grooves that he could cut down into dentil moulding. That stuff cut at 7.5-ips and 15,000 RPM.

In every case, the material dictated the feed speed and the spindle speed. It's kind of like tilling the garden in early spring every year. The condition of the ground dictates the speed that I use to till the soil. Just because my tiller can cut through the soil faster than I can follow doesn't mean that I should pulverise the soil just to get the job done. Jeez! That little 85' x 45' garden spot has taken twenty-five years to convert from lifeless clay into rich garden soil. I'm not going to let a machine dictate to me the speed and method of tilling.

That's my philosophy on CNC routing also. The material and the type of cut dicates my cutting speed. I get pretty good results with a machine that is vastly inferior to the new PRS series. The machine is just a faily simple mechanical tool. It ran 'alright' as it came from the factory. With a few simple mods and a lot of practice, it runs more than just 'alright'. My Delta Uni-saw is another tool that took some tweaking before it cut properly. As it came from the factory, it would cut wood, but after buying $300 worth of tools to align the saw, it really cuts wood. Tender loving care works for gardens, for tools and for people.

[weslambe]

Here's a quote from Mike Richards on the Mechmate.com forum on his PRT.

http://www.mechmate.com/forums/newreply.php?do=newreply&p=3590

"Why not ask someone to make some sample cuts for you in the kind of material that you will be cutting? If someone with geared motors cuts the part(s) and someone with non-geared motors cuts the part(s), you'll have side-by-side comparison. The cost to do that should be minimal and then you would have peace of mind. (That's exactly what I should have done before buying the PRT-Alpha. As much as I like the machine now, it took the better part of two years to adjust/modify the machine before I was satisfied.)"

You stated above: " It ran 'alright' as it came from the factory. With a few simple mods and a lot of practice, it runs more than just 'alright'."

You speak like man with forked tongue.

After cutting several thousand cabinet doors on my PRT 96, a friends CNC Automation, my Shopsabres and the new PRS, I know what to expect. I know what feed speeds and spindle rpms to use with each bit. Since I only use about 6 different bits to create all of my doors, I know each one's particular parameters very well.

A also find it laughable that Brady would imply in another thread that I don't have enough seat time on CNC machines to know how to use them well enough to create chatter free cuts! The combined 20+ years of CNC time from 4 different people (two from Shopbot) who cut at all ranges of speeds using a Porter Cable and my Colombo spindle produced similar results. The ONLY speed that produced ALMOST chatter free cuts was 6 ips. I have the test sheets with all of the cuts made in my shop. I'm keeping them until after I get my machine built so that I can do a side by side comparison. All of the cut's data is written next to each cut.

One more small thing.

I like Dirk. He's a nice guy. He bought my machine from Shopbot and picked it up on Monday. He said he was taking it back to his shop and was going to make it work. Dirk was the second person to come and look at my machine (Stan Holt was the first) and he left without fixing it. If it can be "fixed" at Dirk's shop then why wasn't it fixed at mine?

[richards]

Wes,
We are talking about 'chatter' aren't we? You wrote that you got 'almost' chatter free cuts at 6-ips. I get chatter-free cuts at 6-ips, so that's the speed that I use when I cut MDF and want chatter free cuts. The quality of cut that is required dictates the feed speed and spindle speed parameters that I can use. I'm free to choose any feed speed and spindle speed that I want, but I'm not free to use any feed speed and spindle speed and still expect to get the required quality. It's not rocket science, just very basic physics.

Before adding the belt-drive gearboxes to my PRT-Alpha, I cut tens of thousands of parts where chatter was not an issue. Some of those parts were cut at 10-ips or faster. The point is that the PRT-Alpha, from the factory, has certain characteristics that determined how I would use the machine and what I could cut using that particular machine. Modifications extended the usefulnes of the machine into areas that were/are important to me. I've never yet bought a major piece of equipment that didn't need careful adjustment and/or slight modifications before I felt that it was giving me all that I could desire. And, you'll notice that I'm implying that I have machines other than my PRT-Alpha in my shop. I use the machine that best suits my needs for the project. Sometimes the PRT-Alpha is not the best machine for the job.

I am constantly getting sample parts from people who stop by to see if I can cut something for them. The quality of those sample parts ranges from terrible to very good and all of those parts were cut on $150,000+ machines. When it comes to quality, I know how to make my PRT-Alpha sing and dance just the way that I want it to.

One thing is certain. When it comes time to upgrade or replace my PRT-Alpha, I'll choose the PRS-Standard or PRS-Alpha. I'll probably spend a few weeks or months tweaking it until it sings and dances to my tune, but that's just part of life. It's taken my good wife thirty-five years to adjust and tweak me until, finally, I'm somewhat usable to her and (hopefully) finally tuned to the point that she's not going to send me back to the factory for a replacement.

Good luck on your quest to build a machine that meets your requirements. I hope that you're able to make it all work in a timely and cost efficient manner.

-Mike

[Forum Admin]

OK - this thread has drifted away from discussion of the ShopBot into personal comments that don't serve a useful purpose here. Time to move on.