another circles not quite round post

[twosoc]

I've got everything running smoothly again, all the cuts are neat and accurate for the most part, but small circles don't seem to come out well. I've tried the old rising and falling switch, but it doesn't seem to make a difference. I tried different speeds to see if it helped but it didn't. Large circles seem to be ok, but its possible that the wobble isn't as noticeable on a bigger circle, but small ones say 10mm across are oval and distorted.

They always join up, there are no gaps, but they're always disappointingly distorted. I'll try to get pics tomorrow to illustrate it and see if it sheds any light on it.
Any ideas anyone?
Cheer,s Tim.

[fnaranjob]

Sounds a lot like my problem, are you using servos or steppers?

[twosoc]

Hey, steppers, they came with the stages from here. I went for the lite version as I couldn't afford the pro version I replaced the flexible coupling that connects the stepper to the drive shaft for the x axis (or Y I can never remember which is which, I have it written on the keys now) It improved the cut not lining up, but not the circles, squares are a doddle, no problem there, just small circles go weird.

[fnaranjob]

Well my problem was servomotor tuning, but that's not an option for you, maybe compliance, do you have pictures to show the problem?, does it get better when you turn the speed down?, also try with lower acceleration

[twosoc]

hey, sorry for the delayed response. i'll try to get pictures, I've a feeling its the x axis somehow, I've had trouble with it since I got it. I seems to be that its shifting to the right which makes circles oval and stops engraving and cutting lines not match up ( I use low power settings to "engrave" line art onto a piece, so not true engraving)
I first hada problem with the flexible coupling joining the y motor to the shaft, I replaced it with an aftermarket part and it helped the y axis shift but now I have an x axis shift, which I can't seem to remedy via hardware.
I've tried different speeds but I'll try the acceleration to see if it is too slow. Maybe it cant keep up.

[twosoc]

Had a good play about with speeds etc, it does help at slower speeds but not much, and not consistently. I'm a little lost, I'll try to replace some mounts and tighten other bits, but its really just kicking the tires at this point.

[Rad Racer]

You may want to try adjusting the "circle speed" parameters in the system settings. The manual states that these settings can "greatly improve the circle cutting quality".

[twosoc]

any suggestions? Its been a long time since I looked at the original manual

[Rad Racer]

Start by enabling the feature and use the default settings.
If it makes a difference you can tweak the settings for better/best performance.

[Tech_Marco]

any suggestions? Its been a long time since I looked at the original manual

What kind of machine we're talking about here? Can you tell me the stepping motors and the driver you're using? What is resolution on the driver are you running? If you're using 1/8, try 1/16. But doing so may slow down the top speed of your machine as less torque from when higher resolution is used.

Also, check the DC power supply see if there is enough current for the motors. You may want to use a Digital Volt meter to check the voltage drop when motors are running. If it drop over 0.5V, chance is that the power supply is incapable to delivery enough current for the motor. The less voltage drop on the DC power supply while motors are running, the best of performance you will get.

If it still not fixing problem, may be you may try to switch a motor. When cutting a circle is not a circle (sometimes with crack), it is a symptom of missing steps. Two possibility; bad motor or bad driver.

Keep us update

Marco

[twosoc]

thanks for the tips Rad, I'll try it out.

Marco, its the steppers that came with the 400x600 stages you sell, and the motor drivers are the ones from the upgrade dsp kit as is the power supply, in fact everything is from you bar the chassis

I've got it to stop shifting at the moment by using either 1/16 or 1/32, I cant remember off the top of my head, I'll check when I go down to it.
So the shifting is greatly improved, squares and triangles are ok, its just small circles around 40- 10mm or smaller anything over 50mm is better, but it could be because there is a much bigger area you don't notice the error.

[Tech_Marco]

Check the Y axis coupling see if it got lose. If it did, it may cause distortion when doing round object cutting
Also, when you setup the belt, make sure you park the gantry all the way up or down (not left or right) so that weight balance issue on two side of Y didn't occur

Marco

[twosoc]

I've got a feeling its mechanical twisting when the gantry moves, I looked at an oval cut in 3mm mdf and I noticed that the edges on one side looked normal, with a bevel as you'd expect, but he other end also had a similar facing bevel, Kinda like /________/ Its maybe a bit exaggerated, I'll try to get a pic to illustrate it better, but it made me wonder if the gentry was shifting when both axis are moving.

I'm thinking of modifying it to have two rollers on the far end, not just one, whilst I'm fiddling I think I might modify the return roller too as it keeps throwing the belt.