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F for feedrate
« on: September 04, 2010, 01:56:49 PM »
Hi,

Confused: F commands; do they set an overall tool feedrate which is interpolated from the velocities of all axes, or can each axis have it's own F value applied to it? Somebody asked me earlier and I realised I didn't know.

Rich B

Offline Hood

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Re: F for feedrate
« Reply #1 on: September 04, 2010, 03:09:12 PM »
My understanding ::D
The F word will apply the feedrate for the line of code it is used on and all subsequent lines after that until it is changed. If an axis is not capable of moving at the commanded feedrate  it will move at its maximum and if any other axis is moving at the same time they too will move at the slow axis max.
Hood
Re: F for feedrate
« Reply #2 on: September 04, 2010, 03:20:49 PM »
Thanks, Hood.

So I could set a feed rate for a particular axis; it would apply to all other axes as well, if those axes are mentioned in any G01 lines after the F command. So effectively I can't change just one axis' speed using F. So I need to set those by altering max speed in config/motor tuning.

Is there any way of altering the max speed of an axis 'on the fly', ie from Gcode as it runs? write and call a macro?

Richard B

Offline Hood

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Re: F for feedrate
« Reply #3 on: September 04, 2010, 04:05:07 PM »
Ok maybe this will explain things better.
If you are at X0Y0 and you command a move of G1 X10 Y1 F10 the two axis will move at a feedrate of 10 on a diagonal line, obviously tye Y axis does not have so far to travel as the X so the speed of that axis will be a lot slower than the X but the actual tool will move at a feedrate of 10.

Hood
Re: F for feedrate
« Reply #4 on: September 04, 2010, 06:07:14 PM »
Yep, thanks again Hood, that's clear Just wondering if it's possible to alter the speed of just 1 axis on the fly...

Richard B
Re: F for feedrate
« Reply #5 on: September 04, 2010, 06:51:40 PM »
The short answer is no.

The long answer is that the feedate for each axis on a given mutli-axis move is the propotional amount needed for each axis to complete the move AND satisfy the programmed feed rate.  If you change the feed (speed) of only one of the axes, the you would change the path of the motion.....if that makes sense.
Bill (the Cat) Shubert
Re: F for feedrate
« Reply #6 on: September 05, 2010, 11:21:45 AM »
I understand it as the feed rate is of the TOOL across the WORK (the axis speeds are calculated to give the correct tool feed rate in the desired direction)
Altering the feedrate of 1 axis (in anything other than a move perpendicular to an axis) would alter the tool direction.

ATB
Deker
You can "chop it off" but can't "chop it on"
Re: F for feedrate
« Reply #7 on: September 05, 2010, 03:23:55 PM »
Thanks all,

I think I got the idea!

Rich B