feed rate vs override feed rate
With no real testing to actually see if it's true I SEEM to notice that there is a difference in surface finish (machine vibration) when using the feed rate override vs a programmed feed rate.
I'm doing some surfacing right now. 1/4" 2fl carb ballnose, 5000rpm and 15ipm, pretty fine step over (.010) and DOC. and I've been playing with some feedrates.
When I override the 15ipm feedrate to about 20ipm or so the machine has a more noticeable buzz (vibration) and the it shows in the finish.
If I program a 20ipm feedrate it seems smoother and leaves a slightly better finish.
I don't think this makes any sense what-so-ever from any program, mechanical or electrical standpoint and I've not really sat and compared apples and apples but that's what it seems like at first glance.
Anyone else notice?
M
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Re: feed rate vs override feed rate
You are correct - it makes absolutely no sense whatsoever. FRO is simply a multiplier applied to the commanded spindle speed before it is output to the hardware. It is nothing more than a mathematical calculation performed in the PC which cannot possibly affect surface finish or anything else.
The key phrase is: "it seems smoother". It may SEEM so, but it cannot possibly BE so.
Regards,
Ray L.
Re: feed rate vs override feed rate
If you are using Mach3, then there is a known issue with high FRO settings affecting motion, but it usually occurs at 150%-200%.
Gerry
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(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
I've noticed this also with mach, but I've also had the problem at programmed feed rates at random intervals. Only way I've fixed it is to rebootOriginally Posted by ger21
feed rate vs override feed rate
I've noticed that at certain feed rates my 770 will buzz much louder. If I change the feed rate up or down by 1% it will resolve this harmonic vibration pattern and the machine will quiet down. I think this has more to do with the vibration of the machine falling into a groove and less with the evenness of steps of the motors.
I'd imagine that this factor in machine sound could be visible in surface finish. I have never noticed it though. I suppose you could test but who knows how many ipm numbers would create these bad vibrations?
There is a funny hoax video about reading sound ( like wax recordings) from ancient ceramic vessels , decoding the ancient potters' conversations ..
Another part of the question is whether there is a difference in 9ipm at 100% feed and 12ipm at 75%. In path pilot they both appear to run at 9ipm. It might be an interesting test to record the sound of the steppers and compare the waveforms , or ask tormach how this is controlled in the background
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