Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: Smokingman on October 08, 2013, 01:24:54 PM

Title: Constant Velocity problem with rotary 4th Axis
Post by: Smokingman on October 08, 2013, 01:24:54 PM: I've just added a 4th axis to my K2CNC and I'm having what seems to be a continuous velocity problem. The X,Y,and Z axis seem fine, but the A axis keeps stopping when it hits it's coordinate as if it's in exact stop mode. Has anyone seen this before?

The G-code is coming from RhinoCAM and includes an A-Axis coordinate every 11.25 degrees for some reason when cutting a test cylinder. MechSoft support says there is no way to change this behavior, and I would rather not have to edit the g-code by hand every time I make something.

Here's what it looks like:
Code: [Select]
G00 G49 G40.1 G17 G80 G50 G90 G20 (4th Axis Roughing) M6 T6 M03 S18000 G01 Y0.0000 Z1.2250 A0.000 F35. Y0.0000 Z1.1000 A0.000 Y0.0000 Z1.1000 A0.000 F360. Y0.0000 Z1.1000 A-11.250 Y0.0000 Z1.1000 A-22.500 Y0.0000 Z1.1000 A-33.750 Y0.0000 Z1.1000 A-45.000 Y0.0000 Z1.1000 A-56.250 Y0.0000 Z1.1000 A-67.500 Y0.0000 Z1.1000 A-78.750 Y0.0000 Z1.1000 A-90.000 .....
Every 11.25 degrees the rotary axis stops and restarts. Anyone know how to fix this in Mach3 without editing the g-code?

Thanks!
Title: Re: Constant Velocity problem with rotary 4th Axis
Post by: Fastest1 on October 08, 2013, 02:06:21 PM: Rotational soft limits?
Title: Re: Constant Velocity problem with rotary 4th Axis
Post by: Smokingman on October 08, 2013, 02:13:50 PM: Soft limits are off.
If I do this:
Code: [Select]
G01 Y0.0 Z1.1 F45 (cutter down) G01 Y0.0 A360.0 F300 (rotate A axis) G01 Y0.0 Z1.5 F45 (cutter up)
It cuts fine. But for some reason RhinoCAM wants to split a circle into 32 sections (11.25 degrees) and Mach3 is treating them like Exact Stops instead of Constant Velocity.
Title: Re: Constant Velocity problem with rotary 4th Axis
Post by: Fastest1 on October 08, 2013, 02:27:33 PM: Rotational soft limits is in the general config page not the home/limits. Sounds like a post processor issue. What little I know.
Title: Re: Constant Velocity problem with rotary 4th Axis
Post by: BR549 on October 09, 2013, 10:51:42 AM: What are you r settings in Gen Config/Toolpath/ Rotational . You have to link the rotational axis to the XYZ in order for Mach3 to be able to sync the feedrates. You may also have to include the Work diameter in the rotational axis to make the feedrates correct .

Main page / Settings / top RH side rotational diam /radius settings

Should have nothing to do with your CAM but I would look for a new CAM IF it could not resolve less than 11.5 deg per step in the A axis. (;-)

(;-) TP
Title: Re: Constant Velocity problem with rotary 4th Axis
Post by: simpson36 on November 05, 2013, 08:23:30 AM: You might investigate G93 to control feed rates for coordinated linear and rotary axis moves.
Title: Re: Constant Velocity problem with rotary 4th Axis
Post by: Bodini on November 05, 2013, 09:42:27 AM: Smokingman: I sent you an email.
Title: Re: Constant Velocity problem with rotary 4th Axis
Post by: Greolt on November 07, 2013, 06:00:13 PM: Some years ago I remember Art saying that CV does not really work with a rotary axis.

His suggestion at the time was try to set the acceleration of the rotary to as close as possible to the other axis.

When you have very different steps per unit settings, I don't know exactly what that means.

Never got any more info on this.

I set the G's to somewhat match and that worked for me. I get good CV on 4th axis work.

You might want to play around with that.

Greolt
Title: Re: Constant Velocity problem with rotary 4th Axis
Post by: Bodini on November 07, 2013, 06:02:41 PM: Agree with Greolt, and also want to mention that the slower the A turns and the higher the acceleration, the less noticeable the problem is.