I have 3 round windows to make, if I draw a 20" circle with a compass and do a test run with the router it wants to go close to an 1/8" above the line on the top and bottom making it oblong, the sides are right on. I made sure that the router is square, even made it out of square and no difference, checked the settings in mach3, kinda know what to look for. From center I can type in move in x and y the 10" and it hits the line perfectly. Anyone have/had issues like this
Thanks
Cutting a true circle
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RoutnAbout
- Vectric Wizard
- Posts: 2088
- Joined: Mon Sep 19, 2005 11:09 pm
- Model of CNC Machine: 24x18 Desktop
- Location: North Manchester, Indiana
Re: Cutting a true circle
hi woodworker48,
What kind of router are you using with mach3.
I've never used mach3, but I'm sure you can adjust your steps on each of your axis's
The best thing to make sure, to is to cut a circle and/or a square a known size.
Create your toolpath.
And then with digital calipers measure your actual distance.
The Mach3 users will have to jump in and help where to make those adjustments, if in fact that is where the problem is.
I've had to tweak my Z axis in like this on my shopbot.
What kind of router are you using with mach3.
I've never used mach3, but I'm sure you can adjust your steps on each of your axis's
The best thing to make sure, to is to cut a circle and/or a square a known size.
Create your toolpath.
And then with digital calipers measure your actual distance.
The Mach3 users will have to jump in and help where to make those adjustments, if in fact that is where the problem is.
I've had to tweak my Z axis in like this on my shopbot.
Re: Cutting a true circle
Hi Woodworker48,
Since you can manually move 10" in X and Y and it hits the line, the axes sound like they are calibrated (steps/inch). If they are not I seem to remember the Mach 3 help file describes how to do this and recommends working it out based on the stepper motor pulses per rev, steps / microsteps of your driver, pulley ratio, screw threads/inch etc, rather than cutting a piece and measuring. My motor is 200 pulses / rev, I have direct drive, my ball screw is 5mm / rev and my microstepper gives 1/8 steps. This maths ((200/5)*8) works out at 320 steps per mm which I type into Mach3.
Another thing to try is checking whether you are loosing steps during cutting. I am currently trying to track down glitching on one of my stepper motors which results in lost steps and offset cutting in one particular direction. Feel your stepper motors during cutting and see if they glitch.
Does the machine go back to 0,0 after the cut? Can you mark the machine or set up DTIs to check that it returns to exactly 0,0?
How about flex in the gantry? If you do a very shallow cut (0.5mm) does the same thing happen?
Also, I'm not sure where this will lead to, but since you can jog manually to 10" with no problem, but cutting to 10" gives an error, you could adjust the manual jog rate to be the same as the cut rate so both are like for like drive signals (just to see if that demonstrates that error). For example, I jog at 1500mm/minute but might cut at 300mm/minute.
Since you can manually move 10" in X and Y and it hits the line, the axes sound like they are calibrated (steps/inch). If they are not I seem to remember the Mach 3 help file describes how to do this and recommends working it out based on the stepper motor pulses per rev, steps / microsteps of your driver, pulley ratio, screw threads/inch etc, rather than cutting a piece and measuring. My motor is 200 pulses / rev, I have direct drive, my ball screw is 5mm / rev and my microstepper gives 1/8 steps. This maths ((200/5)*8) works out at 320 steps per mm which I type into Mach3.
Another thing to try is checking whether you are loosing steps during cutting. I am currently trying to track down glitching on one of my stepper motors which results in lost steps and offset cutting in one particular direction. Feel your stepper motors during cutting and see if they glitch.
Does the machine go back to 0,0 after the cut? Can you mark the machine or set up DTIs to check that it returns to exactly 0,0?
How about flex in the gantry? If you do a very shallow cut (0.5mm) does the same thing happen?
Also, I'm not sure where this will lead to, but since you can jog manually to 10" with no problem, but cutting to 10" gives an error, you could adjust the manual jog rate to be the same as the cut rate so both are like for like drive signals (just to see if that demonstrates that error). For example, I jog at 1500mm/minute but might cut at 300mm/minute.
Barry
Homemade 900x400mm, 25mm rails, 16mm ballscrews, 3Nm 33V, DIYCNC system3, 900W router
Homemade 900x400mm, 25mm rails, 16mm ballscrews, 3Nm 33V, DIYCNC system3, 900W router
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zeeway
- Vectric Wizard
- Posts: 3157
- Joined: Thu Feb 11, 2010 9:24 pm
- Model of CNC Machine: Self-built
- Location: SC, USA
Re: Cutting a true circle
If your machine has the x and y axes square to each other...and you can move 10 inches in the x or y from center, and hit your lines...here's what may be a long shot. In Mach3 check your Config/ General screen, in the second column. Is the Constant Velocity mode checked or Exact Stop? Make sure you have Exact Stop checked, and see if that helps.
Good luck.
Good luck.