Table Top Not Flat

[Chuck Keysor]

Hello Shopbot friends:

When recently cutting a V-carving, I noticed line widths that should have been even, were not. As carving proceeded in the increasing X axis direction, the lines got narrower when they should have stayed the same width.

Being in a rush, I put a shim under the low end of my plaque to raise it up about .030" and that made it so I could finish my V-carving. After that carving was done, I decided to re-flatten my table top using my 2 1/2" Amana planing bit.

The next time I did a V-carving, I noticed the same problem, and thought maybe my planing bit had slipped in the collet. So I flattened my table top again, and made sure the collet was tight. Well, the problem still exists, my table is still not flat.

I did some measuring of the area on my table top that I use the most, from (2,5) to (36, 30). Those readings are in the attachment. (I measured the gap using a set of "feeler" gauges. I didn't want to try and measure right on my table edges, lest I drop my feeler gauges onto the floor.)

The summary of what I found:
Moving along the line from (2,5) to (36,5), the table drops .010"
Moving along the line from (2,15) to (31,15), the table drops .036"
Moving along the line from (2,30) to (36,30), the table drops .049"

Any suggestions as to how I can fix this? I have no idea how this could happen,,,,,, as even if the rails were messed up, the gantry should have held a fixed distance from the table top.

Thank you, I hope this makes sense....... Chuck

[Chuck Keysor]

PS: In making my measurements, I installed a 60 degree V-bit into my spindle. I zeroed the bit at the edge of my table (1,30) and used that Z height (of the spindle) for all subsequent measurements.

I moved the bit to (2,30) then used feeler gauges to measure the gap between the tip of the V-bit and the table top. Then moved to (3,30), measured the gap, moved to (4,30) and so on............

[cowboy1296]

I get my wood planks from a furniture maker who finishes them by running them through a 50 inch wide drum sander. Even still my planks are not perfectly flat and i always plane them flat before starting a project or at least they are in tune with my table top. Now this does not address your table but just relating my experience. Before i started the process of planning i noticed a plaque that came out like you described.

[bobmoore]

Chuck it sounds like maybe your spoilboard or plenum is springing up in the corner where you zero it. The amana bit is pretty good quality so I wouldn't suspect the shank is slipping in the collet unless your collet is worn out.

[Chuck Keysor]

Thanks guys for the replies. As notes, my collet is pretty new, maybe 2 years old now, but to my embarrassment, it has low miles.... And the fact that I really tightened it down before flattening the second time pretty much eliminates the only thing that I can think would create such a problem.

The material I have been carving is manufactured material that is also very flat Vinyl Composite Tile. And I used to carve this material with good success (uniform line widths when doing small V-carved letters) on tiles that are 12" x 12".

My spoil board/plenum assembly is all glued together and is very solidly bolted to the steel frame members. Hmmmmmmmmmmm................ Chuck

[fredtoo]

Environmental conditions - temp or humidity variations?

Vertical play in "Z"?

Hmmmmmmmm.......

[bobmoore]

Chuck I have never seen a spoilboard warp anywhere close to .049" in the short time between dressing the spoilboard and running a part. It usually takes days or weeks in my experience. .049 in 34 inches might be visually detectable at slow speed. Try to slow your feed rate way down and just watch as it runs from 2,30 to 36,30.

[Burkhardt]

Clamp a dial indicator (http://www.harborfreight.com/1-inch-travel-machinists-dial-indicator-623.html) with a dowel rod as adapter into the collet (or attach to the z-plate) and scan the table surface manually (assuming it is smooth).
You will see right away if that is warped somewhere or when pushing the spindle if something is loose. Also useful for tramming the spindle with a swivel arm.

[Gary Campbell]

Chuck...
Your observations show a difference in height between movement under load (surfacing) and movement under no load (gap with feeler gauges)

This is most certainly a mechanical issue that you need to diagnose.

One related, but not often suspected issue is delamination of the bond between the spoilboard and substrate.

[myxpykalix]

THIS IS THE SOURCE OF YOUR PROBLEM.....rarry....

He is the official mascot of all the weird problems that magically appear on the shopbot....

[Chuck Keysor]

Thanks everyone,,,, here is a quick reply concerning the question of play in the Z axis. I often check for play in my X and Y axis, by pulling/pushing on the X car, and on the Y car, but I realized I had never done that on the Z/spindle.

So just now, I pulled/pushed on the X and Y cars, and could not perceive any movement. When I pulled up and down on the Z car, which is a bit more awkward, I was surprised to see movement (and expect I pushed harder on the X and Y cars). So I measured and found I was able to pull up .006" and down .014". How bad of a reading is that?

And a long time ago, when I first set up my machine, I had used my dial indicator on a trammel to square up my spindle. And while I don't recall the numbers, I did post them here and people told me they were good.

As to the spoil board delaminating, that may well be the case. I am pretty sure I used Tightbond glue and I put weights all over the top of the table. But who knows, that was maybe 7 or 8 years ago. I'll set up a cross beam with a dial indicator and see if I can detect any deflection over any areas of the table center.

Thanks,,,,,,,,,, later,,,,,,,,,, Chuck

[Joe Porter]

Chuck, I am just guessing here, but do you have a vacuum system? Could that be causing any pull down on the spoil board? ....joe

[Chuck Keysor]

Thanks Joe. I have a vacuum table, but no functional vacuum source......

I have gotten tied up, but hopefully tomorrow I will see if I can measure my table height, then add some big weights to the table, and see if the table deflects relative to my spindle height.

Chuck

[Michaelodunk]

I was having similar problems, I have one of the first PRS machines I added middle legs to to the rails and it helped a lot to fix the problem.

[EricSchimel]

I have (had) a 4 legged PRS that I upgraded to 6 because my extrusion had a bit of sag to it:

http://www.talkshopbot.com/forum/showthread.php?23249-X-Extrusion-sagging/page2

It should be noted though that the rails also sagged so that even though the table wasn't "flat" it was still flat relative to the spindle as I used the spindle to surface the table. I always use a vacuum table so when I suck a sheet of plywood down it conformed to the table surface.

If you're not vacuuming your stuff down and you do have some sag (and there's no play in your Z) perhaps your plywood is rising up a little when you cut it and you don't realize it?

If I were you I'd surface your table, zero off of it and check the disance in a few spots throughout the table. Write them down and see if they change signifigantly.

You do say you have play when you pull up, and push down your Z. If you're numbers are correct you've got a combined .02" difference. That'd be enough to screw up VCarving a lot. If you've got a sagging table too that might also compound the problem.

I'm no super expert, but this is what I'd do:

Pull off your Z motor and check the pinion. This might be a good time to get a new pinion gear, they are a wear item. Make sure it's tight to the shaft. I'd also see if there's any play in your motor gear box. After that I'd check the Z carriage for any play before you put the motor back in. Then, put the motor back in (assuming you have a good pinion, or with a new one) and make sure it's good and tight. Check it for play. It should be solved.

Then I'd go about shoring up your table, resurface and check everything again.

[Chuck Keysor]

Thanks Eric and Michael. My table does have 6 legs, all standard Shopbot issued iron frame and legs. Yes, I had been surprised, as I would have guessed I would have had the table flat relative to the spindle.

I got tied up making some other non-shopbot things, but now I will go back down into my basement and see if I can measure any deflection of the table relative to the spindle per suggestions by Gary late last week.

As to the Z slop, I'll have to investigate of course. But as a clue, the last V-carving I made turned out fine AFTER I had shimmed up the low end of the plaque, so that when I zeroed my Z-height at one end of the 12" wide board, Z was still zero at the other end of the board! It was a thick shim, something like .030" for just a 12" wide board!

Thanks, Chuck

[Michaelodunk]

I have one of the first prs machines. I was having the same problems. The first thing I did was put middle legs under the rails I now have 6 legs instead of 4. The other thing was to replace the clamping system that I had made. The mistake I made was to make it out of plywood. Plywood is not flat so I replaced it with MDF which you can surface which you can't do with plywood.

Mike

[Mayo]

Chuck, when you resurfaced did you remove material from the entire surface of the table top?
Or were there any areas which were still untouched by your resurfacing bit?
Does your Z have springs to assist it like mine does? At one point I had to increase tension on those springs to try and reduce some of the play in the Z but I don't think it ever eliminated it.

[Chuck Keysor]

Hello Gary C. I measured the deflection in my table top, at 5 locations.

I went to the middle of the y dimension, as logically, the deflection should be greatest there. And two of my test points, were right over the big angle iron that supports the table between pairs of legs. With my 60 x 144 table, that put my points of deflection measurement at: (4,30), (22,30), (40,30), (58,30) and (77,30).

I set the spindle with a 60 degree V-bit at each of the above listed points, then used C2 to zero the bit. And I checked it with a feeler gauge. Then, I climbed up on top of my machine's bed, and crouched down as close as I could to the spindle, and used feeler gauges to measure how far the table had sagged. (I weigh only 140lbs, and I am guessing my center of gravity was about 18" away from the tip of the V-bit.)

At (4,30) (over a leg cross support): Deflection = .003"
At (22,30): Deflection = .011"
At (40,30): Deflection = .007"
At (58,30): Deflection = .009"
At (77,30) (over a leg cross support): Deflection = .004"

As added notes: I have a three layer vacuum table top. The bottom two layers are single 5'x12'x 3/4" Medex (or equal brand, I forgot if the supplier had that exact brand or not). The top layer is made out of Ultralite, but that was not available in a single big sheet. So I actually cut up 4x8 sheets to get 6 equal sized panels, which I glued on top of plenum layer.

There is one small part of a joint where the top layer has slightly delaminated, as the height of that region of the table top is .015" low on either side of the joint, but for one inch on either side of the joint, the table height is exactly zero (relative to the (0,0) reference). But when I push on that area, I can't see any movement.

So, there is some deflection, but at least I can't see how that could account for the low areas that are low by as much as .080" relative to (0,0).

Does this suggest anything?

Thanks, Chuck (PS: I attempted to map out my entire table top, to show the patterns of where and how much, my table top is low. That was laborious, and a somewhat interpretive process, which is why it took me so long to reply to your question about deflection. I'll put those measurements in the next post.)

[Chuck Keysor]

Concerning my table top not being flat, I have attempted to map out the topology of my table top. I hope that by looking at my following notes, and then the figure with my measurements, that someone can figure out some pattern that may help to figure out why my table top is not very flat. (It is bad enough that it messes up V-carvings.)

I did not use my spindle for this measurement, as I don't know if the spindle itself is part of the problem or not. So I have two very good levels, one is 6 feet long, and the other is 8 feet long. I bought these when I had to assemble my Shopbot.

I started with the 8 foot level, with one end located on 0,0 and moved along the X axis. As the level spanned the distance from 0,0 to the 74,0 point and read level, and still read level when spanning from 74,0 to 146,0 this seemed acceptable to use, instead of the ideal 148" long level.

I used feeler gauges to establish how big the gap was between the bottom of the level and the top of the table. Looking at the figure, along the X axis, the table never went above zero, and never went lower than -.030" and I made my measurements in ranges, never trying to measure say .013". Anything between .020" and .015" I called .020". Anything between .015" and .010" I called .015".

Then I used the 6' level to measure dips in the table in the Y direction. In the attached image, you can see where I placed the 6' level: at x=0, x=24, x=49, x=77, x=98 and x=145

The readings shown going in the Y direction are relative to the height at (0,0). So if you look at (49,30) the shown reading of 50, means that relative to (0,0) the table is low by .050"

All of the numbers (except for the 5 deflection figures) that are not on the outside edges of the table, are the depth of the table below 0 shown in thousandths of an inch.

I had hoped to color code this to make bands of equal height more obvious, and possibly aiding in someone figuring out what may be wrong. But I gave up as this was beginning to look imponderably complicated........ Thank you, Chuckhttp://www.talkshopbot.com/forum/attachment.php?attachmentid=29710&stc=1

[Chuck Keysor]

Hello Mayo. Yes, I did surface the entire table top, with the exception of the far end part of my table shown in the figure, where I didn't want to cut down deep enough to clean up that area.

I do have Z springs. I have to work on evaluating where the Z-slop is coming from. My total Z play as noted above, was .020". I haven't ever disassembled my Z assembly. Hopefully it is straight forward.

Thanks, Chuck

[Mayo]

I'm wondering if your Y car assembly is sagging when the spindle is near the center of the table.

The section of the table that was not surfaced - is that lower than the rest of the table?

[Chuck Keysor]

Hello Mayo. The center line going from (0,30) to (146,30) is lower than any other region of the table. Yet IF it were just a matter of the gantry sagging when at Y=30, the dip would be the same at X=24 as it is at x=77. And it should actually be the same down the entire center of the table.

That type of inconsistency, was leading me to think Gary Campbell's suggestion of possible delamination may be coming into play. But because the deflection readings I got were so much smaller than the out of flatness readings I was getting, I tended to not see a connection.

Yes, that far end I didn't map is lower than the rest of the table.

Now, back to head scratching, even if my gantry sags in the middle, that does not account for the initial problem, of noting that the tip of a V-bit when zero'd at (0,30), would have a gap of .030" by simply moving to (14,30). That error messes up my V-carvings big time, requiring me to put shims under my work piece.

Maybe I should make a map of the table top, using the tip of a v-bit mounted in the spindle and measuring the gap between the bit tip and the table top. One would hope that gap would read zero everywhere, but of course it won't. And maybe that set of readings would be more confusing as it would combine the effects of the non-flat table with the sagging of the gantry........ Maybe I'll have to try that, and hope something becomes evident.

Thanks, Chuck

[Chuck Keysor]

Hello Shopbot friends: I have now mapped the gap between the tip of a V-bit and the table top, using feeler gauges to measure the gaps. I measured to the nearest multiple of .005 and all of these new measurements are shown in red, in thousandths of an inch. The tip of the V-bit was zeroed at the lower left corner of my table, the usual 0,0 point.

The previously measured gaps between the table top and level are shown in black.

Both sets of readings correlate in a rough sense even though they are usually not very close. I would have expected that the measured gap would be smaller along the 0,30 to 146,30 axis, due to sagging of the gantry, but that appears to be true only sometimes......

Worst, I still have no idea what would account for my table being so far out of flat. Does anyone have any suggestions? Thank you, Chuck

http://www.talkshopbot.com/forum/attachment.php?attachmentid=29713&stc=1

[EricSchimel]

I'm guessing here, but I think you've got two issues:

You say you can lift up and down on your Z axis with the motors engaged. That shouldn't happen. You need to fix that, get some new pinions, tighten your motors, whatever it takes.

It also sounds like your table might be delaminating. At this point you've expended a ton of time and effort, you might want to consider just replacing the entire table. If it's old and moving around too much you'll never fix it. The fact that you have a whole section that didn't even get machined when you surfaced leads me to believe that there a lot of badness going on there.

I did the same thing with my old table, it was delaminating and I was trying to reglue it time and time again. Best thing I ever did was replace everything.

[Chuck Keysor]

Hello Eric:

1) As to replacing the entire table, I assume you are talking about the top/sacrificial layer and the plenum layer.
2) I looked down into the Z column/housing and tried to see what was moving when I pulled up or down (with the motor energized of course). I was hoping to see the pinion slipping on the motor shaft,,,,,, But the only time I got anything to move, the motor shaft also moved. There was no slippage between the rack and the pinion, or between the pinion and the motor shaft that I could see. I simply pushed so much that I over-came the static torque of the stepper motor's rotor. I don't have a fish scale, or anything like that that I could give a calibrated measurement as to how hard I had to pull and push, but it was significant, maybe 40 pounds???? I was up over the top of the spindle so I could look down into the Z housing. Does this suggest anything?
3) For what it is worth, here is a photo of what I was looking at. Thanks, Chuck

http://www.talkshopbot.com/forum/attachment.php?attachmentid=29714&stc=1

[EricSchimel]

You mentioned earlier that you had measurable play in your Z axis... The best way I know of to check that is with one of these:

https://www.amazon.com/Indicator-Magnetic-Point-Precision-Inspection/dp/B002YPHT76/ref=sr_1_1?ie=UTF8&qid=1487215462&sr=8-1&keywords=dial+indicator

You set it up and pull up and down on your Z (you can also check your X and Y this way) to see how much free play you have.

And yes, as for replacing the table I was suggesting taking everything off and building it all fresh, after you've sorted any mechanical problems you may have...

[Chuck Keysor]

Thanks Eric.......... My brain is often too slow. In measuring the pinion lash, it seemed strange for me to simply be pushing down on the Z housing, without some reference level of force.... Then I recalled having read the Shopbot application note on measuring gear lash. So I re-read it just a bit ago, and it said to apply a force of 25 pounds, roughly equal to 2 1/2 gallons of water. So I got a bucket, put it on my bathroom scale, and filled it up to the 25 pound point. I set up the Z-height indicator which you see in the picture, then I carefully placed the 25 pound bucket on the top of the Z housing. The Z housing moved down .009" as shown.

Now of course I couldn't watch the motor shaft,,,,,,,,,, it may be that all that motion came from the motor shaft moving, and maybe it did not. I can only HOPE that the 25 pound force was specified as it would not over-come the static torque of the energized stepper motor. http://www.talkshopbot.com/forum/attachment.php?attachmentid=29715&stc=1

And lastly, the Shopbot article didn't say what a good number would be. Is .009" terrible, OK, or great?????? Anybody out there able to share their knowledge?

Thanks again, Chuck

[jerry_stanek]

Do you run your vacuum when you surface your top? When you check your top is the vacuum running

[EricSchimel]

Putting weight on the top of the Z only establishes that your motor is strong. What you need to do is put that gauge the Z like you have it and pull up and down. The amount it moves is the amount of freeplay you have vertically. I don't know if there's a published spec for freeplay, but .0095 is a lot. That'd mess up a 3D varving, or Vcarve real fast. Your Z might be vibrating up and down as you mill, or the material might be pushing the Z up when it plunges. Bottom line is that you need to tighten up that Z. Again, new pinions, tightening the motor, whatever it takes. You might also want to check to make sure your spindle shaft isn't moving int he spindle itself. There are bearings in there that possibly could be worn.

I don't know too much about the PRT's but I do know that the gantry seems more prone than a PRS to bouncing. Check to make sure all of your bolts are tightned up real good. I'd bet there's an assembly guide or a tuneup guide you can go through to make sure all's good. Years of vibration can loosen bolts.

AFTER you've fixed the Z and confirm that it's really tight (it won't be 100% perfect, but it should be much less sloppy than .0095) surface your ENTIRE table. Go as deep as you need to go to surface the whole thing. Drive around and measure again like you did. If you've got an old table that you think is delaminating, just get rid of it and start over.

[Chuck Keysor]

Hello Jerry. I don't have an operational vacuum source,,,,,,,, but thanks for your comment. Chuck

[Chuck Keysor]

Thanks Ed:

I think my brain was broken when I stood over my machine's Z housing and only put the weight on top, as I thought I would need a giant helium balloon to pull UP on the Z housing. It dawned on me this morning that I could hook up a pulley to the ceiling to reverse the direction of my spindle loading.

That is an interesting thought on the spindle bearings. I hadn't even thought of that. I'll have to cogitate on that, as having the spindle attached to everything else may make it a bit confusing as to isolating where the play comes from.... But first I'll hook up the pulley, and get back with measurements later this afternoon.

Thanks again, Chuck

[EricSchimel]

You don't need a pulley... Just set your calipers up like you had them and lift up and down on your Z.

[Chuck Keysor]

Hello Eric, I just got back home... The point for the pulley, is to be able to apply a known force. When pushing by hand, I pushed hard enough on the spindle that I could move it maybe an inch.... but I may have been pushing with 60 pounds. From what I read in the Shopbot back-lash measuring guide, they said to use 25 pounds. If I push by hand, I can only guess at what force I am applying............ Chuck

[Chuck Keysor]

Hello Ed:

++++++++++++++++++++++++++++++++++++++++++++++
Downward lash with gantry sag:
I realized that when I first measured the lash in the downward direction with the 25 pound bucket on top of the spindle mounting plate, that the spindle was in the middle of the gantry so that I was getting gantry deflection mixed into my measurements. So I re-measured the downward lash with the bucket on top of the spindle mounting plate, with the spindle in the middle of the gantry three times, (of course resetting the height gauge each time). I got these three readings: .005", .006" and .006".

++++++++++++++++++++++++++++++++++++++++++++++
Downward lash with minimized gantry sag:
Then I rolled the Z car over to the far right, where the gantry sag would be the least and put the 25 pound bucket on top of the spindle mounting plate three more times and I got the following three readings: .003", .002", and .003" So these are the readings I would say I have for the lash in the downward direction. (I pushed hard by hand, and was able to get a reading of over one inch! So pushing by hand could give any reading.)

++++++++++++++++++++++++++++++++++++++++++++++
Upward lash with minimized gantry sag:
I measured the upward lash, using the 25 pound weight, and two pulleys, so the force applied to the spindle, would be straight up. I measured the lash three times, and got three readings: .003", .003", and .003".

++++++++++++++++++++++++++++++++++++++++++++++
Rack and pinion lash or stepper motor slippage?
Thinking more, I watched down inside the spindle mounting housing to watch the rack, pinion and motor shaft, as pictured earlier. Pushing lightly, trying to simulate the 25 pound load, I still did not see anything move independently of the motor shaft. And when I would go to push the digital height gauge back to re-engage the collet (for both the upwards and downwards deflection tests), the collet was every time, either back at .000" or once, at .001" and so I feel confident in saying that the measured deflection of my spindle was due to the motor shaft moving as I was beginning to overcome the static holding torque limit of the motor. The motor, as soon as the 25 pound bucket was removed, was able to put the spindle back up where it belonged!

It seems to me that IF there would have been mechanical slippage between the rack and the pinion, (IE slop/play), the spindle would not have returned to the exact same zero reference point from pulling the spindle up, or pushing it down. But because there is effectively no lash in the pinion/rack assembly, the spindle returns to its static/rest position when momentarily pushed either up or down with a 25 pound force.

+++++++++++++++++++++++++++++++++++++++++++++
Gantry Play:
I experimented with putting the 25 pound bucket on the middle of the gantry and found I had .001" to .002" of deflection.

++++++++++++++++++++++++++++++++++++++++++++
Summary: I still have no idea why my table is so uneven. I'll rebuild it on the hope it has delaminated. And I'll order a new pinion, just in case. I suppose Shopbot is the only place to purchase one?

Any other thoughts? Thank you again to all who have commented so far. Chuck

PS: I also have a feeling I have gone "too far into the weeds" on this, but if anyone's brain, including my own, can figure this out, it seems as though lots of details would be required.

[EricSchimel]

You're closer but you're testing for too many variables at once. There are helper springs that lift the Z axis and essentially make it weigh nothing...

Do this: Power your machine on. Zero out your caliper and put it between the table in a fixed spot (doesn't matter where) and push up and press down on the Z with your finger. Maybe with 5 lbs of force. See if the reading changes. If your Pinion or gear box is warn you'll see movement here. Fix this before moving on to any other problem.



Next if you suspect that your motor is weak you can do that bucket test but I doubt that's the problem. They usually either work or they don't.

Dropping weight on the gantry or pulling up on it aren't typical forces it sees in cutting... Especially it you're saying a v bit has Z issues. There's hardly any forces here.

You'd be better served by tightening up all the bolts you can find around that gantry.

Next check for poor data. Get a dial indicator and put it on the top on your Z and zero it. Jog around. Does it change position? It shouldn't.

Next take the file you had the problem with. Run it again with that dial indicator and the job air cutting. When the job is over it should return either to Z zero or whatever you had it set to do at the end of the file. Watch is as it goes along to so you can see if it's at the Z height it's suppose to be.

If all if this checks out you've now eliminated a loose Z, a wobbly gantry and a data problem. The last variable you have is your table. Post some pictures of it for us. I suspect it might be the culprit.

At this point I'd surface every square inch of it and try again. Or replace the table.

Moral of the story is one variable at a time. Pinions are wear items. Start there.

[EricSchimel]

Addendum:

You should also check your X rails and make sure they're perfectly level. Also, make sure they're leve not only along X, but to each other along Y.

Lastly, make sure your gantry isn't racking really badly and lifting off of the tracks...

[Chuck Keysor]

Thanks Eric. I have printed out your directions and will bring them into the shop. Thanks, Chuck

[Mayo]

Chuck there is a local source for pinions - I'll see if I can find the receipt from when I got replacements.

[Chuck Keysor]

Thanks Mayo!

Eric, I started on your list of things to check, but got bogged down. The 5 pound lash test showed .001" when pushed down, and when pushed up.

In checking the bolt tightness, I was shocked! Two smaller bolts were just snug. The others were around 10 to 20 ft-lbs. I tightened all of the larger bolts to 60 ft-lbs, and there is a series of smaller bolts, where the head is hidden inside struts, and they slip when tightened significantly. But all the big bolts tightened up well. The bad news was that when I was all tightened up, my carriage was no longer square when I pulled it up against the stops. I did multiple cycles of loosening all the big corner bolts, which made the car totally floppy, drawing the car up against the stops, and re-torqueing in a gradual sequence. Yet every time, I was no longer perfectly square against the stops. So that is where I am stuck now as I used to pull up perfectly square against my stop blocks....... And today I have to do other work........

Thanks, Chuck

[EricSchimel]

I've never owned a PRT, but I know the PRS pulling up against the stop blocks is just part of the start up procedure. Just pull it tight to the blocks with the machine off, hold it there and power on. The motors will hold it square.

[EricSchimel]

Also, you might want to grab a tube of red Locktite and fix those bolts in place.

[Chuck Keysor]

Hello Eric..... I finally made it out to buy some red Loctite, and on Tuesday I removed each X car gantry bolt, one by one, applied Loctite to each thread and nut, and then torqued appropriately. (Except for the bolts that have a loose flat threaded plate hidden inside of the extruded cross pieces so I could only apply Loctite to the bolts.... Very challenging to re-install those bolts, when the threaded plates can slip and slide all over without any way to see them......)

And on Tuesday evening I made a magnetic base for my dial indicator. I can continue on with your list on Wednesday afternoon.

Thanks for the advise on pulling the X-car into square, and then powering up the Bot. I was so hypnotized by my long-time routine of checking the squareness of my gantry with the power off, I just would not have thought outside of my box.

Mayo,,,,,, any word on the local source for pinions?

Thanks, Chuck

[Mayo]

Chuck, I got pinions from Motion Industries Inc. 786 Church Rd, Elgin IL 60123
I brought them one of mine so it would be easier to order.
Looking at the 5 year old receipt, it may be time for me to get them again!
They didn't have mine in stock so they shipped direct to me from Boston Gear.

[Chuck Keysor]

Thanks Mayo! I go by Motion Industries once a month when I go to a local auction gallery. Chuck

[Chuck Keysor]

Hello Eric. I have done some testing results. First, I set up my digital height gauge and the dial indicator, both as shown. I used the MZ command to change Z, and see if the dial indicator and height gauge matched the Bot display.
With the height gauge measuring at the collet: Start at Z=0", MZ .5 -> .498", MZ.75 -> .747", MZ1.00 -> .995", MZ.75 -> .749", MZ.5 -> .501, MZ.25 -> .249", MZ0 -> .002", MZ1 -> .994", MZ0 -> .001", MZ1 -> .993" (IE: entered move z .5, measured .498") I don't know if these readings are acceptable or not. Thanks, Chuck
http://www.talkshopbot.com/forum/attachment.php?attachmentid=29749&stc=1http://www.talkshopbot.com/forum/attachment.php?attachmentid=29750&stc=1http://www.talkshopbot.com/forum/attachment.php?attachmentid=29751&stc=1
With the dial indicator reading on the top of the Z/spindle mounting plate: Start at Z=0", MZ.005 -> .005", MZ.010 -> .009", MZ.050 -> .049", MZ.1 -> .100", MZ.010 -> .011", MZ.005 -> .007", MZ0 -> .002"

[Chuck Keysor]

Hello Eric. With the dial indicator touching on the little bracket, as shown in picture 2 of the previous post, I jogged the spindle all over the table, at Z = 0". I kept the spindle moving around for about 20 minutes. The start of this movement is shown in the attached picture. At the start, z= .000" and at the end of 20 minutes, z was still at .000". But it was interesting, though probably not significant, that the entire time the gantry was moving, the needle on the dial indicator vibrated, almost to the point of being a blur, between the values of +.0005" and -.0005", always centered on zero for the average reading.

Then I ran the last actual file I had run, where I had to shim up one end of the plaque to get a good V-carving. This was a small file, that only took 10 minutes to run. I ran it as an "air cut". At the start of the test, the dial indicator on top of the spindle attachment plate (shown in middle picture of previous post) was at .000" By the end of the short test, the dial indicator read .002" when the SB3 screen showed it was back at the start value.

Does any of this suggest anything?????? Thanks, Chuckhttp://www.talkshopbot.com/forum/attachment.php?attachmentid=29752&stc=1

[Chuck Keysor]

Hello Eric. Here are some pictures of my table. What other pictures would you like to see? (My camera's macro/close focus doesn't seem to work.)

My bottom two layers are single big sheets of 3/4" Medex (or equal), screwed to the steel frame, with the plenum glued on to the bottom layer with Tite-bond glue. The sacrificial layer is Ultralight, glued on to the plenum with Tite-bond. The inside of the plenum was sealed with shellac, and the outside edges were sealed with shellac, and then painted. I couldn't find any visible evidence of delamination by looking at the edges, except for a short glue gap, of maybe 1" (it's too late to go back down and check), but it is painted over, so it has not moved since I built the table.

I will try to figure out how to get the Z pinion out, so I can buy a new one at the local source Mayo provided...... I have never had to take apart the Z car, and it didn't look obvious when I looked at it.

Sorry this has taken me so long....... I have been working on making a strange table for somebody, just using regular tools. I greatly appreciate your input!!!! Thanks, Chuckhttp://www.talkshopbot.com/forum/attachment.php?attachmentid=29753&stc=1http://www.talkshopbot.com/forum/attachment.php?attachmentid=29754&stc=1http://www.talkshopbot.com/forum/attachment.php?attachmentid=29755&stc=1

[EricSchimel]

Ok, here's where I THINK you're at:

You said that after you ran that file that your dial indicator read .002 instead of 0 like the shopbot display said for Z. You also said that if you push up, and pull down on your Z you can get it to move .001" in either direction. That's where I believe the difference is coming from. Did you tigthten your motor to the gear rack? Did you replace your pinion?

After you sort that check that your long X rails are prefectly level the long way, and too each other. This will probably require you getting your hands on at least a 6' good quality level. If they aren't level you'll have to adjust the feet on your machine to get them level.

Do that first.... THEN:

Zero off of table and surface your entire table. Surface deep enough so that every single square inch of the table is machined so that you can gaurantee that the table is flat. Then try your job again.

[Chuck Keysor]

Hello Eric. All the measurements I supplied were made with the old Z pinion, and without having tightened the Z motor (to tighten on the PRT requires disassembly of the Z car, which I didn't want to do,,,, I just wanted to measure one thing at a time).

I have a 6 foot and 8 foot level, which I bought for my Shopbot assembly, and have never used them for anything else. I measured everything (with a digital angle gage on top of the level for double checking) this morning, and will post pictures later. But everything checked in X and Y, from rail to rail and on the table, at many places was level.

I just got done removing the spindle and taking out the Z pinion. At that point, I checked the tightness of the Allen head bolts holding the Z motor, and they both snugged up without too much effort, but they were not actually loose.
I will be going off to the business Mayo told me about shortly to get, or order a new Z pinion. The old one does show some wear, which I think is clear in the photo.

Thanks, Chuckhttp://www.talkshopbot.com/forum/attachment.php?attachmentid=29757&stc=1http://www.talkshopbot.com/forum/attachment.php?attachmentid=29758&stc=1http://www.talkshopbot.com/forum/attachment.php?attachmentid=29759&stc=1

[Chuck Keysor]

http://www.talkshopbot.com/forum/attachment.php?attachmentid=29760&stc=1http://www.talkshopbot.com/forum/attachment.php?attachmentid=29761&stc=1http://www.talkshopbot.com/forum/attachment.php?attachmentid=29762&stc=1http://www.talkshopbot.com/forum/attachment.php?attachmentid=29763&stc=1Here are some of the photos of measuring. I measured the X car, the X rails, the table in X, Y and at odd angles. I measured all over, in increments of one foot, and everything was level. So on the big level, measuring over the scale of feet, everything was amazingly level. So I got something right! Thanks, Chuck

[bill.young]

A couple of things to keep in mind:

*) If you're getting that tiny bit of variation I wouldn't chase it any more... 0.002" is 1/2 the thickness of a piece of paper. I can't imagine that you would ever see that little bit of variation in anything you'll ever do.

*) ShopBots, and any other tool that uses stepper motors, move in fixed "steps" that vary in size based on the unit values. They will stop on the closest step to the command that you gave it, which may not be exactly the distance you commanded it to go. So you may see tiny variations between where you sent the tool and where it stops.

Bill

[Chuck Keysor]

Thanks Bill. I don't think I have ever had a message from a super moderator before....... I am honored! Chuck

[Chuck Keysor]

Hello Eric, and anyone else following this thread.....

I went to the local gear supply store, (Motion Industries) with my pinion in hand. It is marked "Browning EN-6415". They couldn't find "Browning EN-6415" in their catalogs.

So the salesman pulled out some gages, and fit them to the teeth of my pinion, and said he wasn't sure of the fit. So he asked me if I could come back with the rack. Since they are closed on Saturday and Sunday, I'll go back on Monday with my rack.

Is that normal? Is there any chance this gear isn't something ordinary that I just can't buy locally? Do I have to worry about the fact that his gage didn't fit in snugly to my pinion's teeth?

Thanks again, Chuck

[Knothead]

I don't know Chuck, but from a moral support standpoint, I would hope to he** that's not the case. Pardon me. I would really get concerned when he asked me to bring the rack in. Who wants to remove that? I thought one of the many, many pluses of ShopBot was that they keep their machines as proprietary free as is reasonably possible so the consumer has options, esp. on the fairly common mechanical parts.

I realize the whole ShopBot business model has changed since I bought mine in 2001, but I'd like to think their manufacturing model has remained true to it's original intent and concept. I don't think Ted and Sallye and all the others have changed. Keeping my fingers crossed this is a mis-fire. Good luck, man. Let us know.

[Kyle Stapleton]

Can't you just buy new ones from Shopbot?

[Chuck Keysor]

Hello Kyle. Yes, I could order from Shopbot. I was hoping to save a couple of bucks, and ideally pick the part up on Friday or Monday.

Knothead, not speaking for Shopbot of course, but in my past life as a electronics design engineer, it is pretty easy to start off using as many standard parts as possible, but then upon testing, something is found that can be improved, you talk to the salesman, and they say, gee, it won't cost much to make this change, and before you know it, you have a new custom part.

Now, not being a mechanical engineer, I was wondering if gears are fairly standard, in many regards, such that if my salesman's gage didn't fit nicely, that it really shouldn't be a concern. The salesman didn't seem to be really very alert or on the ball............ not that I like to pass judgement, but he didn't inspire my confidence.

Thanks, Chuck

[EricSchimel]

Is getting an ill fitting gear worth saving a few bucks? They aren't that expensive from ShopBot, I'd order them directly from them. That way you get a guaranteed good fit.

[Chuck Keysor]

Hello Shopbot friends: I checked out one of my two X pinions, and found it to be slightly worn, but much nicer looking than my Z pinion. But I decided to go ahead and buy three new pinions from Shopbot.

So I called Shopbot to order three new pinions, (they are all the same part number, EN6418), and I asked to talk to technical support about my flatness issue. No techs were available, so I went on-line and filled out the request for tech support. Hopefully someone can call me back this afternoon. I'll post what I find out.

Thanks, Chuck

[Chuck Keysor]

I have ordered 4 new pinions, which will come in maybe 4 business days. I will replace all of my pinions and then I'll resurface my spoilboard.

So the changes made since the previous re-surfacing will be re-torqueing/loc-titing my gantry bolts and replacing all the pinions. That will probably happen next week.......... I'll post at that time, thanks, Chuck

[Chuck Keysor]

Hello Shopbot friends,,,, I have installed 3 of my 4 new pinions, even though only one, on the Z car assembly was fairly worn. In cleaning out all the gunk inside the Z housing, the rack looked good. But on both sides of the Z rail, where it engages the V-rollers, there was significant "mushrooming". This was worse than any other mushrooming than I have had on the rest of my machine. The mushrooming is on all 4 areas where the V-rollers engage the Z rail, but it is worst on the lower end (near the collet) of the Z mounting plate. The worn areas are all 5" long.

I'll of course carefully dress the mushroomed areas with a file, and make those areas match the undamaged/worn parts of the z-rails. But my question is, is this suggestive of anything being mis-adjusted that I should watch for upon reassembling? Does it suggest anything else? (Sorry, the macro function on my camera is pretty bad....)

Thank you again, Chuckhttp://www.talkshopbot.com/forum/attachment.php?attachmentid=29812&stc=1http://www.talkshopbot.com/forum/attachment.php?attachmentid=29813&stc=1http://www.talkshopbot.com/forum/attachment.php?attachmentid=29814&stc=1

[Mayo]

I have never taken my Z assembly apart - so I can only offer general advice which may not pertain to your situation.
In looking at the photos though, one could surmise that the lower V-rollers may have been adjusted too tight against your mushroomed steel. Or the other possibility is they were adjusted properly and the upper V-rollers were too loose. I don't know if Shopbot has a torque recommendation for those or if it's just a "make them snug" kind of thing. I don't even know if a torque wrench would work in this situation but if it could, it would assure an even tightness on all adjustable V-rollers.

[Joe Porter]

http://www.motionusa.com.s3-website-us-east-1.amazonaws.com/bishop/Dual_Vee_Components_and_Linear_Guides.pdf Chuck, see if this helps. If yours is like my BT 32 Dual Vee Wheels, one side is mounted solid and the other side is adjustable. Maybe this will help you with the proper adjustment...joe

[Chuck Keysor]

Thanks Mayo and Joe:

Mayo, all 4 "double V" rollers have eccentric bushings, so each can be independently adjusted to get proper roller/track engagement. When I disassembled my Z plate, I removed only the two "double V" rollers on the right side, so I assumed when I reassembled everything, I'd just have to adjust the two parts I had removed.......... Wrong........ After reassembling, no mater what I did on the right side "double V" rollers could make , one of the "double V" rollers on the left side engage its V-track. So I wound up having to adjust the eccentric bushings on all 4 "double V" rollers. But based on the information Joe supplied, I probably had over-tightened the lower "double V" rollers 8 years ago when I re-assembled my Bot.

Joe, thank you VERY much for the interesting document on the Bishop Wisecarver "Double V" rollers. I had never even realized that the rollers could be used not only like in Shopbot's designs to ride on a single rail, but that they can also ride inside a 90 degree track..... cool. But MOST significantly was information they provided near the end, about adjusting the eccentrics. They said the adjustment should be made so that each "Double V" roller can me turned by hand/just slipping. Without any documentation, I had adjusted just to the point where I could NOT turn any of the 4 rollers by hand. And I very carefully snuck up on that adjustment, so I know it is not smashed down super tight. But knowing they should be able to barely slip is important, and I'll have to go back and fix that. THANKS AGAIN Joe!!!!!!, great information!!!

But that is as far as I got, as I had something to make (still not done) that doesn't use my Shopbot. But I'll have to go through and re-establish that my spindle is perpendicular to my table, which in the past was very tedious, requiring inserting thin brash shims, rechecking, reshimming,,,,,, And since I had to adjust all 4 "Double V" rollers, I have certainly thrown my spindle out of whack in at least one dimension.

And with my wavy table top, I'll have to lay a piece of plate glass on top of the table, and hope that rides out all the dips and waves of my table top, in the way that works out for my correct alignment......

On one hand, I'm sorry I'm so slow at getting this done, as I have needed to use my Bot one time. But having this new info from Joe will allow me to fix my over-tightening before I get into the spindle alignment.

Thanks again, Chuck

[Joe Porter]

Glad to be of help...joe

[dmidkiff]

Chuck, In later years shopbot Z had more than 4 v-rollers with eccentric bushings. I think they used 8. You might consider drilling and installing more rollers. Or maybe contact shobbot for updated Z.
Just a thought because I was never able to adjust those eccentric bushings with any confidence.

[Chuck Keysor]

Thanks Dmidkiff. I didn't know they had made such a change, but it makes sense as a way to beef things up. I'll have to entertain this after I see what happens after I re-align my spindle. Thanks again, Chuck

[dmidkiff]

Hope you get things working right soon.