[Mooser]

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

[SCzEngrgGroup]

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.

[ger21]

If you are using Mach3, then there is a known issue with high FRO settings affecting motion, but it usually occurs at 150%-200%.

[AUSTINMACHINING]

If you are using Mach3, then there is a known issue with high FRO settings affecting motion, but it usually occurs at 150%-200%.

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 reboot

[jmosley]

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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