On 6/1/25 00:26, jrmitchellj wrote:
On my Jet Mill (Bridgeport clone) I have been noticing that the X & Y axises may start moving before the tool in the Z axis is clear of the part. I am running the 2.9 master. I noticed that the post processor I am using puts G64 PQ in the preamble of the NC files. I have not found an explanation for that in the documents.
I believe IIRC if the P&Q are not defined, that establishes the default lookahead for the trajectory planner. And the defaults I have found are a bit generous, starting xy motions before z is fully retracted & breaking 1/4" tools. That is explained in the docs if you have them installed.
It has been part of linuxcnc for several years. You may be able to address that with an editor, by assigning the P&Q to be very small or zero, or if using a CAM to generate the gcode by increasing the Z clearance move in the CAM. IIRC its the minimum speed to turn a 90 degree corner, with 0 being a complete stop.
I just logged into my go704 & grepped my nc_files and found I have set "g64 P .001" which IIRC is the time, so it does not completely stop but only allows a 1 millisecond lookahead. If your post processor is emitting that, you can probably find a config setting that will define the P&Q it emits. Enough to get z cleared b4 any major XY motion starts.
I write my own gcode, usually in nano, never got into production CAM toys. But using linuxcnc looping stuff quite heavily as a hobby. Neither am I a machinist, but a CET keeping TV stations on the air for the last 60 years. And my short term memory is getting a bit hazy at 90 yo. Hopefully this is helpful. And welcome to the list.
Has anyone else encountered this issue?
--J. Ray Mitchell Jr. jrmitche...@gmail.com "Much of the social history of the Western world, over the past three decades, has been a history of replacing what worked with what sounded good." -- Thomas Sowell
One of our better comments. Thank you.
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