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Author Topic: Rotary machining on a lathe feed rates  (Read 507 times)

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Rotary machining on a lathe feed rates
« on: September 18, 2018, 04:11:16 PM »
I have converted my lathe so that the spindle can be run as a 'C' axis rotary.  It works well when I cut threads but I have to use fedd rates of 12000 to get the z and C drive to turn at the appropriate speed.  I'm okay with that.

Vectric's Aspire has added rotary capabilities and I would like to use that.  I have modified their post processor to convert the A axis to C , the z axis to x, the x axis to z and doubled the x(z) values to compensate for diameter mode over radius.  So far so good.  

If I cut a circle on the stock surface there is coordinated movement and all works well.  Hypothetically 3d machining at an angle should work but there is a separate case that wont.  If I cut a square on the stock surface, one of the two axis is going to move drastically faster or slower than the other since there is no coordinated movement and the tool path has only on feed rate.  

I thought I would ask all of you seasoned CNC'ers  what alternatives I have/should consider.  I haven't asked Vectric yet if I can modify the post processor for one axis only movement feed rates.

Changing feed per revolution didn't solve the problem.  But that might be that I don't fully understand it.

TIA

RT

Offline ger21

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Re: Rotary machining on a lathe feed rates
« Reply #1 on: September 18, 2018, 04:43:53 PM »
Aspire 9.5 can now use G93 Inverse Time mode, which will get your feedrates correct if you use it.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Rotary machining on a lathe feed rates
« Reply #2 on: September 18, 2018, 04:47:34 PM »
Can you point me to where that setting is set, option, toolpath?

Offline ger21

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Re: Rotary machining on a lathe feed rates
« Reply #3 on: September 18, 2018, 05:54:54 PM »
I think you need to edit the post processor.
See the 44:40 mark of this video.
https://www.youtube.com/watch?time_continue=6&v=-y-lOOMHbZw
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Rotary machining on a lathe feed rates
« Reply #4 on: September 18, 2018, 07:15:39 PM »
Ger21, thanks for that. 

I have modified the post processor to now output what I think is correct code for g93.  I have attached a test Aspire file and the resultant gcode file.  It merely consists of a circle and square.  While the tool path is correct the circle takes 8 minutes to run and the square 12 seconds.  The square seems to run both the z and c axis at appropriates speeds, obviously the circle does not.  Anyone have thoughts as to what is wrong with the code or the setup?

TIA

RT

Offline ger21

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Re: Rotary machining on a lathe feed rates
« Reply #5 on: September 18, 2018, 07:48:30 PM »
Quote
I have modified their post processor.............................the z axis to x, the x axis to z


I'm confused about the type of machine, and why you have it set up the way you do?

Normally, in Aspire, the X or Y would move in and out from the headstock, and the other (Y or X) would be perpendicular to that axis. The Z axis would be a milling spindle moving up and down.
Basically a mill with a rotary axis.

It sounds like you are doing something very different? But I don't know if that's the problem or not.



Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Rotary machining on a lathe feed rates
« Reply #6 on: September 18, 2018, 07:58:27 PM »
It is a lathe not a mill.  With lathes the set up uses the same right hand rule for setup but with a view from the headstock rather than the mill spindle.  Z moves to and away from the spindle, x in and out like a mill.  Few have a y axis.  Rotary can be a,b, or c.  Mach4/fanuc lathe only supports c as a rotary with incremental moves.

RT
Re: Rotary machining on a lathe feed rates
« Reply #7 on: September 26, 2018, 12:46:47 PM »
Attached is an Aspire post processor for rotary on Mach4 lathe.  File extension of txt added for upload. See comments for axis changes.

HTH

RT