Feed rate different on Z axis

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15 Feb 2017 14:51 #87998 by bobhare
I want the feed rate on the Z axis to be different than that on the X and Y. That is, on the miller i want the plunge rate to be lower than the mill rate.
The F code allows me to set feed rate but i can't see how to set it differently for each axis. Some of the moves are co-ordinated in that it moves from x1y1z1 to x2y2z2 so i can't just change the F value between each Z movement.
I'm sure it's simple but it alludes me.

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15 Feb 2017 15:38 #88000 by Todd Zuercher
If you have a coordinated move of 1 unit length in each of 3 axis. It is not possible to have one of those 3 axis move at a different rate than the other 2, without breaking up that move into at least 2 moves. If one axis must move slower (or faster) than the others then the 3 axis will not reach their endpoints at the same time. So for the move to be coordinated (and be a straight line), all 3 axis must be restricted to the maximum speed of the slowest axis.

Ok, back to your problem. Is your problem that you need to restrict the maximum feed rate of your Z axis, because of physical machine/motor capabilities, or that you want to restrict the speed for machining reasions (machine can go faster but for this part I need it to go slow)?

If it is because of the physical limitations of your Z-axis, then the MAX_VELOCITY setting for [AXIS_2] in your ini file will limit the max feedrate for Z, and in a coordinated move using Z Linuxcnc will automatically restrict the feed-rate of all axis to within their achievable capabilities. Just remember when making adjustments to these settings in the ini file, that they are in units/second (inches, mm,...) and not the units/min you normally use in your G-code Fxxx settings. (so don't forget to divide by 60)

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15 Feb 2017 18:59 #88009 by bobhare
Thanks for the quick reply.
Plunge rates, movement in Z, are normally about half the movements in X and Y and this is for cutter/machining reasons. The machine feed rate limits on all three axes are well above what is required so the issue is the second of those you point out.

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15 Feb 2017 19:23 #88010 by Todd Zuercher
For that you are stuck with specifying the feed rate on the lines of code requiring different feeds. As far as I know Linuxcnc doesn't have this. I have used some controls that do allow for specifying different feeds for Z, and X-Y moves, But I think they may have also be limited to 2-2.5-D code as well.

If you are using CAM to generate your code, there are usually settings that will do this for you. (Set a different rate for plunging moves and milling moves.)

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