Circles are not cut round - loose pinion gears
 

Gerald,

I am having another problem. . . . . . . . It will not cut a round circle.

I have included both the cut file and the ArtCam file.

Nils,

Can you make a short video and post on youtube?

A picture is worth ..... blah, blah, blah,
But, a video with sound may solve your problems faster.

Most digital cameras have video. Not good quality, but one more tool for troubleshooting.

. . . . . Is the circle "squished" in a particular direction, like perhaps the X axis? What happens if you slow the feed rate way, way down, like 10x too slow?

I took these photos to see if they will show the bad cut. The wood is scrap and the lighting is not very good. The bottom of the photos are on the Y and the sides on X.

The first one is at 10 and the second a 5 acceleration.

You can see the machine jog at the two spots. But besides the jog spots the circles are not very round. I am using a 1/4" end mill. The bottom of the cut is very good. I sure have the Z and router set up good.

The outer circle is 2" Diameter and the inner is 1.5".

Nils did you clamp your work properly - I think you did.

think the motor is missing steps - if otherwise

I am myself not an expert.

RGDS
IRfan

IRfan,

Yes the piece is clamped well but thanks for the input.

Yes, that looks like missing steps, in the vertical dimension of those photos.

Interesting that it's pretty consistent, location wise. Were both of those pieces clamped in the same place on the table? If so, I'd start looking for a mechanical issue. If not, I'd look for an electrical or software issue.

Those wobbly circles are typical of a z-slide that is wobbling around inside its rollers. The eccentrics need to be tightened.

Gerald,

The Z slide is tight in the VWheels. I adjusted it the other day because the cuts were not smooth on horizontial. I just checked and they are tight.

What else can I check?

With the router switched off, and the stepper motors switched on, grab the router collet by hand and push/pull it with lots of force in various directions to see if there is any slop in rollers or the router bracket, etc.

Gerald,

I think I have discovered the problem and once fixed it will fix both of my problems.

I did go out and shake the Z and Y and things are tight but I also pushed and pulled on the gantry and moved with out the motor moving much. I took off the X motors and discovered my pinon gears were slipping and sliding. I used the wrong size set screw when I first drilled the pinon gears. I discovered this on the Y but I thought I would wait until there was a problem before switching them out. I used 10-32 when the manufacturer calls out 1/4-20.

Monday I will replace all the pinon set screws and see if I have a problem.

I will keep you posted and thanks to all for your suggestions.

The fact that your glitches happened close to the reversal of an axis' direction proved that there was mechanical slop:

I have replaced all the set screws on my pinons and cut another circle and it looks great. . . .

Thanks for everyone's suggestions and help.

Nils,
Did you end up using the 1/4-20 set screws in the end?

Drawing M2 30 110 T says the following about grub/set screws:

"Drill and tap 2 grub-screw holes at right-angles to each other. M5 or M6 [3/16" or 1/4" UNC]"

We make sure that the motor or gearbox shaft has two flat spots 90 degrees opposed, and then tighten the screws really tight (until the allen key bends) onto those flats.

Our original motors came with 2 flats and we were surprised to see that the higher torque geared motor only had one flat spot. So we grind another small flat in the geared motor shaft.

DO NOT TIGHTEN A GRUB/SET SCREW ONTO THE ROUND SHAFT OR INTO A NARROW KEYWAY. This disturbs the round surface of the shaft and effectively "rivets" the pinion to the shaft, making replacement of the pinions very difficult.

Replacing the set screws with 1/4-20 has fixed the problem with the cutting. Circles are round!

If I had to use grubscrews in inch sizes from McMaster-Carr, I would probably pick 98637A527: MIL Spec Alloy Steel Cup Point Set Screw Cadmium Pltd, 1/4"-28 Thrd, 1/4" Length, MS51964-64. They have a finer pitch and will grip tighter.

The 6mm metric screws we use have 25.4 threads per inch.

Nils,

So glad to hear it's fixed!:):):)

Please provide a few more details for some of us that are just getting started and will face these issues in (the) future.

When you say you replaced 10-32 set screws with 1/4-20 set screws, you mean you re-drilled and re-tapped the pinions. Is that correct?

Also, do you have the two flats at 90 degrees on the shaft as Gerald recommends? Also, do you have two set(grub) screws in each hole?

Regards,
John

Nils please post some pictures of the new cuts for comparison.

Yes, I drilled and tapped the 10-32 holes for 1/4-20. I only have one flat side on my shaft and I did not use two set screws but the set screws come with pre loctite material on them - I don't know what it is called but I don't think they will be coming out.

I think the circles look pretty round now. Also the bottom is very very smooth.

This did not fix the problem I have with the X shudder.

Now that is what a MM is capable off. Glad it is fixed :D

Hi Nils,

Did that K2 post help out with shudder? I spent some time cutting circles today. I had a similar problem in that I forgot to loctite my grubs screws and was making circles that looked like charlie brown was drawing! By the time I had everything tightened down, everything is starting to look good. I have to do some better measurements to make sure that the x/y scaling is right on but it gets better every day.

What's your feedrate on the circles you are cutting?

Greg