Circles are not cut round - loose pinion gears

sailfl · #1 Sun 21 December 2008, 06:02

Gerald,

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

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

Greg J · #2 Sun 21 December 2008, 06:34

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.

bradm · #3 Sun 21 December 2008, 07:14

. . . . . 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?

sailfl · #4 Sun 21 December 2008, 08:51

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".

javeria · #5 Sun 21 December 2008, 10:18

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

sailfl · #6 Sun 21 December 2008, 10:36

IRfan,

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

bradm · #7 Sun 21 December 2008, 11:13

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.

Gerald D · #8 Sun 21 December 2008, 12:43

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

sailfl · #9 Sun 21 December 2008, 12:52

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?

Gerald D · #10 Sun 21 December 2008, 13:02

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.

sailfl · #11 Sun 21 December 2008, 14:09

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.

Gerald D · #12 Sun 21 December 2008, 22:57

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

DSCN1134.jpg

DSCN1135.jpg

The reason that the glitch is not exactly at the point of reversal is because the rotation of the router bit puts a sideways cutting force at the bit which distorts the picture.

sailfl · #13 Mon 22 December 2008, 08:41

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.

domino11 · #14 Mon 22 December 2008, 10:04

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

Gerald D · #15 Mon 22 December 2008, 10:18

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.

sailfl · #16 Mon 22 December 2008, 10:27

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

Gerald D · #17 Mon 22 December 2008, 10:39

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.

jhiggins7 · #18 Mon 22 December 2008, 10:46

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

J.R. Hatcher · #19 Mon 22 December 2008, 12:28

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

sailfl · #20 Tue 23 December 2008, 06:09

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.

Kobus_Joubert · #21 Tue 23 December 2008, 21:29

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

bradyaero · #22 Sun 15 February 2009, 17:19

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