Multipass Cut Through - Not Retracing in the same spot.

[TNWALKINGHORSE]

Hello, I am a new owner of a used PRT 32x24 ShopBot running version 1 of PartWorks. I am still learning the machine and it is quite fun and quite a challenge at the same time. Today I was playing around with cutouts and was using a 1/8" upspiral to cut though a piece of 3/4 select pine. I set it up to cut .20" inches per pass. It did cut though...(I also used 4 tabs). However, the second, third and final pass did not retrace over the 1st pass. It shifted slightly. I was using a small 9" x 9" piece of scrap screwed to the table with 4 screws. The letter "M" seen in the pic below is only about 2.25" tall. Anyone no what is causing this? If you need more info, please let me know. -Matt


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[scottp55]

Almost looks like "Lost Steps" in 1 axis?
Just out of curiosity can you post pics of the complete letter And rotate 1 pic 90 degrees?
Also maybe try one with a .06" Pass Depth and show comparison pic?
Sure others will chime in shortly with better opinions.
scott

[bleeth]

Looks to me like one or more of a couple things:
Loose or worn pinion gears or the tension not correct on the motor mount springs.
Also tram your router to ensure it is truly perpendicular to the table.

[harryball]

A 1/8" bit is kind of small for that so I thought it might be bit deflection at first, but what you have going on is a lot more than that. On the inside of the M, the cuts opposite the top, did the bit correctly trace the path or did it cut into the entire block? If it is only off in one direction it rules out lost steps as once you loose a step it will look like your entire cut file moved over on the material. For lost steps to happen, the insides of the M would be cut for the entire depth when the bit was running inside. I don't know if a 1/8 bit would take the pressure if that happened.

Check your pinions, make sure one is not loose. With the Buddy it would mean in one direction you could be dead on but in the other you could be off as the shaft turned in the pinion to bind before beginning to turn in the other direction.

/RB

[TNWALKINGHORSE]

I am going to try the same cut file with the same bit on HDU to see if the softer material makes a difference (less deflection.) If it cuts fine there, is it safe to assume that the z-axis is square and all pinions, etc are OK?

[bleeth]

Go ahead-and when you're done and see the same thing read the suggestions and follow through.
(you can lead a TWH to water but you..........) LOL

[MogulTx]

I think Dave is trying to tell you that you asked for, and got, good tips from some experienced people. If you want to go off and do something different, then do it... but you are ignoring the logical path toward tracking down this cut issue. And sooner or later you need to check out the things that the people with experience - from whom you solicited input- have told you that you should check out.

If that were deflection: The amount of "deflection" you are seeing would have snapped that bit. THAT is not deflection. You may very well have had some deflection due to depth of cut ( max depth of cut should be about the diameter of the bit unless the material is exceedingly soft- like foam). But you can clearly see the second pass is a rougher cut and does not follow the pattern of the first cut. That indicates something is loose or worn (or both) . Check your Pinions. Check Spring tension.(Springs holding drive motors to the rack) Check your Router-to-mount is secure and the mount to Z Axis is secure. Tramming can't hurt. (Do a search on "Tramming" the router.) Checking for "play" in your axes is probably going to fix 90% of what you have going on there.

Best of luck. And with that new Basketball coach, too. I understand UT (Tenn) just got Rick Barnes. Good coach. Stupid move on UT(Tex) 's part.

[steve_g]

FWIW… If your issue involves missing steps, cutting in foam likely won’t replicate that part of the problem, sending you down the wrong rabbit hole!
SG

[TNWALKINGHORSE]

Thanks Mogul and thanks Dave and everyone else who responded. I really do appreciate all your help. I am now going to take a drink of water...lol. I will go ahead and check pinions, spring tension etc. I just need to find a few hours and sit down and do it. I really need to cut wood, so HDU won't solve anything anyway. Thanks again and I will report my findings. :-)

[TNWALKINGHORSE]

Ok, I took off the 20 tooth pinion on the "X" Axis to inspect further. By the looks of these pictures can you tell if this is a good or bad pinion. Not sure what to look for. Thanks again!



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[Joe Porter]

From the looks of the pinion, I would take the table off and give the rack a real good cleaning and do a careful inspection. The pinion looks damaged, not just worn. That could mean damage to the rack also. Have you tried shaking the table while the power is on but stationary? The X motor has about 65lbs of holding power so there should be no movement...hope this helps...joe

[TNWALKINGHORSE]

When I try shaking the table back and forth with the power on, I just hear a click, but just a hair thickness of movement.

[Brady Watson]

Pinion is wiped. Order a set of 3. One for each axis, although Z is probably OK.

The racks MUST be greased. Axle grease is fine. There are other options as well. A little dab every 6" & machine worked in with pinion + wiped with cloth is where you need to be.

The little 'tick' you hear is 'normal'. Most likely in the motor gearbox itself. SG-3.6 motors do this when new. No biggie.

-B

[simon]

Are you certain that you have held the work down properly?
Just saying cos it really looks to me like the work is moving around.
The cuts are all over the place.
This is not just a case of missed steps, this is random movement.
Simon

[Joe Porter]

I would also suggest reading up on how to check and adjust the spring tension on the motors. I think your X motor is like my Buddy in that it the motor shaft is horizontal and has a single pivot bolt that allows the motor to be drawn into the rack by the spring. Make sure that there is enough looseness to allow the motor to swing, but no extra looseness. The motor shaft wants to be at right angles to the rack and not wobbly. It is good that you got a ShopBot, especially a bench top (forerunner of the Buddy), they are built like tanks and are very repairable and put right, and then you will have a really good machine that will last forever....joe

[Brady Watson]

The spring should be 3.5 turns from just opening up. This will be different for the table on the Benchtop. Emulate the tension on the Y car (which is the Benchtop's X; Y on BT32/48 IIRC).

The Benchtop tools can chew up the gears if the Z bar isn't aligned parallel to the rails. The gear rack can become disengaged from the motor/pinion if the horizontal V-roller bearings are not properly adjusted.

Nothing to mountain climb over, but the machine could probably use a keen eye and a tune up.

-B

[TNWALKINGHORSE]

I also might be onto something else. The router measure a little out of level and was not square to table. The previous owner used PVC pipe as a spacer to hold the router securely in the holder. When I removed the router, I found this:http://www.talkshopbot.com/forum/attachment.php?attachmentid=24678&stc=1

I placed the small piece behind the larger and re-tightened. Now it was square to the table. I repeated the cut and no more steps. Also, the router that came with the Shopbot was a Makita RF1101. Does shopbot or another 3rd party make a holder for this router, so that I do not have to use that PVC pipe? Thanks!

P.s. Also going to order pinions. Would that also quiet down the noise when moving that axis?

[bleeth]

If you are hung up on continuing with a makita router then you can always design and mill your own mounting rig. Nice exercise in learning to mill aluminum.
SB's standard is porter cable.
The more square, level, plumb, and properly adjusted, as well as good pinions installed, the smoother it will run.

[Brady Watson]

P.s. Also going to order pinions. Would that also quiet down the noise when moving that axis?

Porter Cable is all that came from SB. Others have used the Makita because it was the quietest at the time. You're on your own to figure out mounting it. I am sure you could adapt something or fab something since you now have a CNC. Let's not forget that we have access to more information than anytime in history: Google search "Makita CNC Mount" (https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=makita%20cnc%20mount)

Fresh pinions will quiet it down some, but with a lot less vibration that can be transferred to the cut. Experiment with different speeds. For the heck of it, change the MS in SB3 to say 1 inches per second for the XY. Then using keypad mode (k or SK) move the tool around. Sounds like a diesel doesn't it? Now change the MS in SB3 to 2 inches per second. Repeat. Smoother, isn't it? This is called mid-band resonance. All steppers do this at some speed.

Those are like 1998 stepper motor driver technology running there...and they are 1/4 stepping. If you want to eliminate most of that horrid noise & be on par with a current BT tool, you'll want to do a 4G upgrade. It takes 15 minutes. Plug & play. You need a good computer. You'll get 2.5 times better step resolution and some faster speeds with this upgrade. It's exactly where you want the tool to be - you just don't know it yet.

-B

[MogulTx]

What kind of noise are you hearing in that axis? Is it a herky-jerky spasmic kind of thing? A grinding sound? What are you hearing? It should sound fairly smooth and rhythmic... should not sound rough or aggressive....

[TNWALKINGHORSE]

What kind of noise are you hearing in that axis? Is it a herky-jerky spasmic kind of thing? A grinding sound? What are you hearing? It should sound fairly smooth and rhythmic... should not sound rough or aggressive....

I just did another cut. The "Y" axis will stutter/hesitate and pause during start and stop movement. The noise is more of a grinding noise. however, the the X and z axis is very smooth.

[Brady Watson]

Sounds like a beat driver. Turn control box off & wait for a FULL 5 min. Then unplug the Y from the box. Plug it into the A spot. Open up SB3 & run the VI command. Change channel 4 to be Y instead of A. See if the noise goes away.

-B

[MogulTx]

Try what Brady Said. Swap your Y for your A driver. Jog and run the A driver and Y axis stepper and see if you get better results. If it is still problematic, you have one of two things going on ( AFAIK) - and they are: (1) bad wire / connector/connection or (2) a bad stepper motor. If you do, and things are cleared up, you are looking at one of three things (1) Bad zener diode on the Y driver (2) bad wire on Y axis (3) a bad Stepper motor.

Do this level of sleuthing and it should lead you fairly directly to your solution....

[TNWALKINGHORSE]

UPDATE: So my A port is already being used by the "X" port (I believe), since the original X had a blown port. So I swapped the "X" (A) and "Y" port and the noise is following the port, not the axis. So I guess I have a bad driver. I guess this is why I am getting bad cuts. I just received 10 driver chips from China with the same part number. So I guess it is soldering time? If this doesn't work, then I guess it's 4G time. Would the diode be bad if the chip is blown or not necessarily?

[MogulTx]

TN

I think the "chips" you are talking about must be the Zener diodes. Make note of the location ( end to end) of the colored bands on the diode before uninstalling. Solder the new one in in the same direction as the old. It is a directional voltage blocking device... so surely there is a need to maintain directionality to it....

Now: You say the noise is following the port not the axis, so that eliminates your steppers and your control cables.... so yes... you are down to driver and diodes, AFAIK. It should be a ten minute fix. While you have the board out, you may as well get your original X corrected, too.

Sometimes blown diodes occur because someone rolled the motors manually while they are engaged in their rack. This drives the stepper motor, which allows it to create electricity and send it back the wrong direction. This can blow the diode. It is possible to blow the old drivers this way, too. Hopefully it will just be a diode issue. ( Or two!)

Best of luck. Report back when you have installed the new diodes and let us know if you have cured your problem!!

Monty

[TNWALKINGHORSE]

Few more questions...I will start with the diodes....easier...., if that's what it may be...which diodes are they? Also, there are 2 stepper motor drivers per channel. So a port is bad (noisy)...would it be the driver closest to the edge of the board or the one towards the middle? P.S. I received 10 new 39555SBT chips in the mail today.


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Thanks! -Matt

[donek]

I just replaced the chips on a y-axis yesterday. I bought sockets with the chips though so it's easy to swap them out after repairing. After soldering I found a bad trace which may have been the culprit. It wasn't blown, but seemed to be tearing off the board at the pin.

I find desoldering to be the biggest challenge. I've used desoldering wick and a suction bulb. Neither does an adequate job. The only thing that ever works for me is to hold a blow gun against the board on the chip side, melt the solder and then hit it with a blast of air. Maybe somebody else has a better solution.

[TNWALKINGHORSE]

I just replaced the chips on a y-axis yesterday. I bought sockets with the chips though so it's easy to swap them out after repairing. After soldering I found a bad trace which may have been the culprit. It wasn't blown, but seemed to be tearing off the board at the pin.

I find desoldering to be the biggest challenge. I've used desoldering wick and a suction bulb. Neither does an adequate job. The only thing that ever works for me is to hold a blow gun against the board on the chip side, melt the solder and then hit it with a blast of air. Maybe somebody else has a better solution.

....So did you wind replacing both driver chips for each channel or just 1. I am not sure if 2 blow per channel or just one?

[MogulTx]

TN

See the close up pic that shows your X2 driver output area (diodes)? See the browned spot on the board by that one diode? Replace that Diode.


I replaced mine one at a time. ( I can't recall if I later went ahead and replaced both for each driver output section. Since they are so cheap, it would make sense, but if you replace one and it works... it CAN fall under the old adage of "if it ain't broke (anymore), then don't "fix" it... you have to make that choice. But I would start with the obvious and move toward the less obvious solutions. You have the diodes, so start with the worst looking and go from there.)

Monty

[MogulTx]

Sorry. That may be your Y ...

And there is a little discoloration in the traces just up from it. That may be dust/dirt.... don't know. You will have to look close. And look from the underside to see if it shows through as being heated.

And I do not assume that it is chipsets. I believe it is diodes ( the structures closest to the output plugs where you attach you WAGO connectors.) I COULD be wrong, but checking it out is nearly cost free and they are NOT difficult to de-solder or re-solder.

[donek]

I did both. If you have the board up and running, I'd put a finger on them and see which one is running hot. That's likely the one that is giving you trouble.