Cut quality issue is it hardware or software?

[Cncal]

I have a homebuilt 2x4 that uses Avid Rack and Pinion drive on x and y. The y is a gantry with two drives. I use Linux CNC PlasmaC for control. I am getting a consistent alignment issue that I am not sure if it is hardware or software. I re-squared the gantry by attaching a pen to the Z and plotting 4 points. I then connected the points and all angles are spot on. I also re-tightened the rack drives and all other nuts/bolts. This is a new machine and these are the first cuts.

I cut about 5 of these shapes using the LInuxcnc shape library and they all have the same result. The lead in at the bottom middle is the start point. The cut looks good all the way around until it apepars to be missing steps and the final lead out doesn't align. So the bottom looks weird.

I exaggerated the lead in and out and cut this square to better show the issue.

I tried to reduce from 120 ipm to 60 thinking the speed was causing the issue but no luck.

Any thoughts would be appreciated.

Al

[robertspark]

acceleration? (Try lowering it)

something slipping (pinion? pulley?)

[adbuch]

Hi Al,
It appears to me that you might have some backlash in the Y axis direction - assuming your part is oriented with Y up/down direction in the photo. Another possibility is that you may be losing steps, or your sheet of material is moving while you are cutting. Perhaps post some photos of your machine so we can take a look at your hardware.
David

[Rodw]

Its possibly backlash from the spring loaded pinion.
Here is some feedback about them
https://forum.linuxcnc.org/30-cnc-machi ... ve?start=0
It has to be some mechanical issue.

[Cncal]

acceleration? (Try lowering it)

My current MAX_ACCELERATION is set to 20, but I will lower it a few times and run some test.

Thank you.

[Cncal]

Hi Al,
It appears to me that you might have some backlash in the Y axis direction - assuming your part is oriented with Y up/down direction in the photo. Another possibility is that you may be losing steps, or your sheet of material is moving while you are cutting. Perhaps post some photos of your machine so we can take a look at your hardware.
David

I can get more photos, but I had two already on me so they are below. It shows the test parts in relation to the axis. The machine is currently on my manual plasma table, but is clamped level for testing. Also I have a single clamp holding the work piece down. I will try pulling all the drives off and tightening the gear and belt setup.

Thanks for the help.

[acourtjester]

Any place you have a gear or pulley on a shaft or motor you should file a flat (or drill a dimple in the shaft) where the setscrew contacts the shaft. The motor shafts are hardened and they can slip as the setscrew cannot hold tight enough. Do not think this is the case here but with straight slats you can get a wiggle. your direction in this case would not have that, as your slats are parallel to the problem.

[adbuch]

I would be interested to see some more detailed photos of your Y-axis motor drive assembly. From your photo, it looks like the 4 holes in the Avid plate are quite a bit larger than your fasteners (bolts or screws) securing the stepper motor to the plate. Is there any chance for some slight movement here? Also would like to see some photos from the other side to see exactly how you have the motor assembly attached to your gantry bracket.

I have a similar CNCRP/Avid setup on both of my cnc routers.
David

[Cncal]

Success. I pulled the two Y axis drives and re-tightened everything and tried a cut. The result was the same. I then took apart the x axis and re-tightened and aligned everything. In doing this I had to re-adjust the Z axis also. I then ran a first test. After pierce the tip actually touched the slag on the top of the metal and tripped the break away switch. So I raised the pierce height a bit to run the test. This produced a much better alignment as you can see below. I am not 100% sure what fixed it, but the result is much better. Now I need to re-run all my squaring test to see where I am at.

adbunch: Here is a close up of the drive removed as you requested. This is the hardware that came with the unit. I went ahead and re-tightened all 3 drives to be safe.

[acourtjester]

You may look into putting a adjusting bolt to push the motor to tighten the belt and have a locking nut so it gives you added holding power so the motor will not slip over time.

[adbuch]

I have the Avid Pro Series rack and pinion drives on my machines. These incorporate a cam-lock mechanism to keep the motor from moving on the plate should the motor retaining screws come loose.
David

[adbuch]

Apparently the Avid Standard Series rack and pinion drives do not include this feature - so I would definitely agree this would be something worth adding to keep the motors from moving.
David

[Rodw]

Can you use a lock nut there at the bottom?

[Cncal]

Great ideas. I currently have them all locktight in place. I think I can add the cam lock feature or a simple bolt to push on the motor for tension. Thanks everyone.

[adbuch]

When I put mine together, they also recommend blue loctite for the setscrews that retain the pulleys to the stepper motor shaft. Glad to hear you've got it cutting smoothly again. Your cut looks good - nice and smooth.
David