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Mach4 and Constant velocity...
« on: September 05, 2018, 09:18:51 PM »
Hey Everybody,

New to this forum, hopefully i'm posting in the right place. I have searched extensively online and know that CV has been covered quite a lot. but i'm still not really finding what i'm looking for. So hopefully somebody can point me in the right direction...

because of the limits with the number of attachments, i have put my images into a zip folder.

I have a custom made machine. I have attached a pic of it.. pic #1...

The carraige is quite heavy. Originally i didnt have the motor currents set high enough on my boards so to avoid jumping i had set my acceleration down to like 25mm/s^2 which is very slow and i was getting massive rounding effects on constant velocity. see pic#2 for an example of these round cuts... this was cutting from the attached step and tap files produced in fusion360.

I since increased the current on the motors so now i have been able to set the acceleration to 400mm/s^2 and it doenst seem to be missing steps (still yet to put that to the test properly)...

anyway.. when set to CV, its still rounding corners quite badly. Attached is pic#3 showing the corner rounding as it goes to do the dive for that hole. I can set it to exact stop, but the machine runs horrible and jerky and i think it will probably destroy itself.. I believe in older versions of mach there may have been a way to set the allowed tolerance so it would maintained CV but if it was going to have to detour from the actual path by more than a specified distance then it would slow down? I cant see that option any more, some people have spoken about modifying machine.ini but its a bit vague as to what the settings in there do.

If anybody is able to help it would be greatly appreciated.

Re: Mach4 and Constant velocity...
« Reply #1 on: September 06, 2018, 08:26:31 AM »
Hi Ash,

I think what you're looking for is the CV Tuning Wizard. In Mach4, go to Wizard>Select Wizard>McCVTuningWizard and check it out. It allows you to set your maximum feedrate and choose a maximum angle for which CV will be applied. It also has a nice little writeup for you about CV in general. Hope this helps!

Newfangled Solutions Helpdesk: http://support.machsupport.com
YouTube Support Channel: https://www.youtube.com/c/MachSupportOfficial

Offline ger21

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Re: Mach4 and Constant velocity...
« Reply #2 on: September 06, 2018, 08:58:08 AM »
If the max accel you can get is 400mm/sec/sec, then your machine is very underpowered. To get good performance, you really would like the accel to be at least 1000-1500mm/sec/sec.

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Re: Mach4 and Constant velocity...
« Reply #3 on: September 07, 2018, 02:31:41 AM »
Thanks Bryanna. That wizard is exactly what i was looking for. Didn't realize there was functions in there to adjust settings :)

ger21, with the acceleration. at 400, it sounds to me like it suddenly is snatching hard when i press the jog buttons. But i'm really just basing it on how i feel about it. Do you know if there is there a good way to test what acceleration i can get away with?

Thank you both for your help! :)