Different radius with different speeds?

While making this simple engraving I increased the feed speed and on the next pass the radius of the corners were bigger and the Z feed came out of the cut befor the end of the cut. (The second pass was just a cleaning pass) Why would the cut be different?

One answer i got was, the CAM settings has constant velocity mode. Could this be a cause? I will have to try another engraving set to exact stop and see if that might be the problem. I have read the user concepts and understand now what might be the problem. Carl

Yep,

Look at G61 as well as G64 P-Q-

G64 P- Q-
(Blend With Tolerance Mode) This enables the "naive cam detector" and enables blending with a tolerance. If you program G64 P0.05, you tell the planner that you want continuous feed, but at programmed corners you want it to slow down enough so that the tool path can stay within 0.05 user units of the programmed path. The exact amount of slowdown depends on the geometry of the programmed corner and the machine constraints, but the only thing the programmer needs to worry about is the tolerance. This gives the programmer complete control over the path following compromise. The blend tolerance can be changed throughout the program as necessary. Beware that a specification of G64 P0 has the same effect as G64 alone (above), which is necessary for backward compatibility for old G Code programs. See the G Code Chapter for more information on G64 P- Q-.
Blending without tolerance
The controlled point will touch each specified movement at at least one point. The machine will never move at such a speed that it cannot come to an exact stop at the end of the current movement (or next movement, if you pause when blending has already started). The distance from the end point of the move is as large as it needs to be to keep up the best contouring feed.

Rick G

Rick G wrote:

Yep,

Look at G61 as well as G64 P-Q-

G64 P- Q-
(Blend With Tolerance Mode) This enables the "naive cam detector" and enables blending with a tolerance. If you program G64 P0.05, you tell the planner that you want continuous feed, but at programmed corners you want it to slow down enough so that the tool path can stay within 0.05 user units of the programmed path. The exact amount of slowdown depends on the geometry of the programmed corner and the machine constraints, but the only thing the programmer needs to worry about is the tolerance. This gives the programmer complete control over the path following compromise. The blend tolerance can be changed throughout the program as necessary. Beware that a specification of G64 P0 has the same effect as G64 alone (above), which is necessary for backward compatibility for old G Code programs. See the G Code Chapter for more information on G64 P- Q-.
Blending without tolerance
The controlled point will touch each specified movement at at least one point. The machine will never move at such a speed that it cannot come to an exact stop at the end of the current movement (or next movement, if you pause when blending has already started). The distance from the end point of the move is as large as it needs to be to keep up the best contouring feed.

Rick G

Should I put the G64 P-Q- in the g code header?

I tried G61 in header and that worked correctly. I ran the engraving at 20 ipm and at 45 ipm. Both worked right. Will play with the G64. Now, would it help if I change the MAX_ACCELERATION rate? If so where and how. Thanks Carl

Look in your .ini file for

MAX_LINEAR_ACCEL = 20

under the axis you want to change.

However you will need to experiment with it, you could exceed the machine's ability to accelerate and stall / loose steps.

Try testing with some air cuts.

Rick G

Take a look here...

www.linuxcnc.org/docview/html/config_ini_config.html

Section 2.2.8


Rick G

Thank you Rick. I was looking for this info, just didn't know where to look. Carl