Frustrated with the Bot

[gary_k]

I have a 2007 PRSalpha 120-60-8, 4hp spindle, version 3.6.44 with Artcam pro 2009 sp2a build 183 and windows 7. I believe the machine has less than 200 hours of usage.

The issue I have is when I move the X car from zero left corner with the key pad or running a file with an air cut, approximately the first 36-inches of travel is a little noisy, with chatter and vibration (hard to explain). Then in the center part of the machine the X car runs smooth all you hear are the motors (Model ASM98AA-T7.2) like it should be and then the noise starts back up again for approximately the last 18 inches at the opposite end. I have been dealing with this issue for the past few weeks and have tried several things.
- Rail spacing is correct (77.812’’ outside to outside).
- Replaced all pinions, old ones did not show much wear.
- While the motors were removed, the car moved freely with no binding or noise very smooth.
- Cleaned racks and all new grease.
- With the bot powered up, I can move the car .005’’ in each X direction with little effort and it makes a clicking noise. I tried to tighten the pinion into the rack on both ends and it did not make any difference.
- All bolts, screws, set screws are tight.
- I ran Gary Campbell’s Program (Tuning up the PRS Gantry). It is perfectly square.
- I checked all the wiring from the motors to the controllers, it all seems to be fine.
- The Bot is in a climate-controlled environment. Most of my work is 3D using a 1/8 ball nose.

Still noisy I am not sure what to do next. Has anyone ever adjusted the backlash in the motors?

Thanks for any assistance you may be able to offer.

[donek]

If the noise is changing as the motors travel down the rails, something about the rails is changing along the length. Usually noise is a result of backlash between the pinion and the rack. Have you checked the backlash in different locations along the rails? It sounds to me like the pinions are tight against the racks in the middle of the table, but not on either end.

[Brady Watson]

Still noisy I am not sure what to do next. Has anyone ever adjusted the backlash in the motors?

1) Turn up the radio and stop worrying.

2) You cannot adjust backlash on the motors.

The noise you describe is typical of straight geared steppers. There may be very minor inconsistencies between pinion to rack engagement and preload from one side to the other. You can try to turn off the control box, drop one x motor and clock it slightly one way or the other to change this slight difference, but I doubt it will make the sound go away.

Have you put a dial indicator on the gantry and actually measured .005, or is it just a guess? Is this affecting your cut quality or is it just an annoyance? My tool does the exact same thing...but I am not going to buy all new motors because of it. There are a lot of different areas that could introduce the noise from one area of the table to another - and it is important to realize that the gear rack alone is only rated to like .003 to .007" per foot linear accuracy. I don't the exact spec off hand, but these numbers are typical for this type of rack. You only get tighter numbers by going to ground rack, and that can get pricey.

There are some things you can do to tighten up your machine and tune it for doing very highly detailed 'micro' 3D work - but keep in mind that a rack & pinion machine is not the best tool for this type of work. This is where a Desktop tool would walk all over a PRS, which is designed for larger (and coarser) cutting tasks. Although, I have cut many micro reliefs on my machine with 1/64" ball tools with great results, considering my tool is 5X16'.

-B

[garyc]

Gary...
X-2 to Brady's comments. What you may be seeing is some combination of:

1) A change in thickness of the VHB (between the rack and rail block) caused by more use in one area than another. This is pretty typical in the 0 to 36 area of both X & Y. Especially when cutting 3D files that raster thousands of trips primarily in one direction.

2) A slight increase in lash of the motors reduction gears, also due to use.

Does this noise occur when doing single or 2 axis moves? (you mention only X) Has this affected cutting? How did you first notice it?

To diagnose I would do the following:
Use a dial indicator at numerous places along the Y both the X axis motors and write the backlash numbers down on each motor tested. I would expect around .010 +/- on a seasoned machine. This lash is the accumulation of tolerances in the motor bearings, the gear train and the rack to pinion clearace. Your numbers will tell if it changes thruout the axes motion.

The attached PDF will show some common ways to setup the dial indicator.

[gary_k]

I noticed the noise and vibrations during my maintenance check up. The Y and Z axis are quiet and very smooth. Not sure how long it has been going on; I don’t notice it when cutting and the dust collector is running. As far as my cutting quality, my last job I cut had several bowtie inlays using Ash and Walnut with a perfect fit.

Gary – as you suggested, I checked the play with a dial indicator. Starting with the x axis at the 0 corner on the left side, the measurements are as follows:

Front dimensions -.008 /+.006
Back dimensions -.006 /+.009

Moving the x car to the center:

Front dimensions -.007/+.008
Back dimensions -.011 /+.006

Moving the x car to the right end:

Front dimensions -.011 /+.009
Back dimensions -.011 /+.006

I then checked the Y axis on both ends are the same:
-.004 / +.006

The Z axis is .008 in both directions.

I put the indicator on a ½” bit and I got .017 in both X directions and .016 in both Y directions.

After I installed the new pinions, using the key pad starting the X car at 0 corner and moving to the opposite end, I have the noise and you can feel a high frequency vibration in the table and the legs but when the X car returns, you can still hear a noise but the vibration is gone.

While I was trying to diagnose the problem earlier, I took both X motors out and set them on the beam and ran them. When I ran them in 1 direction they wer both quiet but when I ran them in the opposite direction, the #2 motor on the front of the machine was extremely noisey – almost like a blender full of marbles.

I really appreciate everyone’s insight – you have been very helpful. My next step may be to get larger speakers for my stereo!

Thanks, Gary

[garyc]

Gary...
You may have a bearing going bad in the motor that is noisy. Turn the stereo down every now and then to check!

[Joe Porter]

I had a noisy X motor on my Buddy. It sounded like the gears were grinding in a transmission. After some consultation on the forum, I replaced the driver for that motor and all was well. You might swap drivers with your motors and see if that cures it. joe