How to determine actual feedrate

[swallace84]

Howdy,
Hope y'all are well. I'm working on a project that has several small circles to cut out. About .3" each. In vcarve pro, even if I tell it that I want it to move at 300 ipm, I'm sure that since the cuts are so small, the machine doesn't have time to get all the way up to 300 ipm. Am I thinking correctly so far? If that's the case, is there some way I can determine the actual feedrate that the machine is cutting during all those circles? The DRO on wincnc doesn't show a live actual feedrate, but it does show the live actual coordinates. I'm asking because I'm getting burning in this 1/8" melamine and I suspect that my feeds and speeds are accurate if the machine was moving at the speed that I'm telling it too-- but that it is burning because the actual feedrate is much slower. Thanks for any ideas.

[gtgmarine]

Not sure I understand the focus on feedrate here.
If I was pocketing a bunch of .3" circles I would use a .25" endmill. Seems most of the machining time will be in cutting those holes and not in spindle movement... but I have no idea what your design looks like so I could be way off.

[DVE2000]

If you want a bit more understanding of the actual feedrates, you can figure some things out from looking at the acceleration. In WINCNC.INI the axisspec lines have an "f" value. For an imperial unit machine, that would be in inches per minute per second or ipm/s. So for example, if the f value was 300, it would take an entire second to get to 300ipm. If it was 600, it would take .5s to get to 300ipm. If it's at 1000, you're looking at .3s. The calculation is: final ipm / acceleration. I currently have mine at 700 for xy for feeds. That would allow me to get to 300ipm in .43s. For rapids, I have my "a" value (rapid acceleration) at 2000. That allows me to get to 800ipm in .4s. If I recall correctly, I experimented briefly with 5000, which is .16s to 800ipm. But I don't want to start snapping belts or have other mechanical issues. You can always experiment with increasing the f value until you start snapping bits.

If the bit is sharp and you're burning the wood, you may need to decrease your spindle rpm.

[swallace84]

Not sure I understand the focus on feedrate here.
If I was pocketing a bunch of .3" circles I would use a .25" endmill. Seems most of the machining time will be in cutting those holes and not in spindle movement... but I have no idea what your design looks like so I could be way off.

Sorry, I didn't clarify enough. The holes are not regular shapes-- there's some tight radii in there so I'm using a 3/16" bit. I thought it might be related to the melamine layer, so I got rid of just that thin layer and that was smoke free. The issue was with me cutting at a depth of .1" into the hardboard part of the laminated melamine material.

[swallace84]

If you want a bit more understanding of the actual feedrates, you can figure some things out from looking at the acceleration. In WINCNC.INI the axisspec lines have an "f" value. For an imperial unit machine, that would be in inches per minute per second or ipm/s. So for example, if the f value was 300, it would take an entire second to get to 300ipm. If it was 600, it would take .5s to get to 300ipm. If it's at 1000, you're looking at .3s. The calculation is: final ipm / acceleration. I currently have mine at 700 for xy for feeds. That would allow me to get to 300ipm in .43s. For rapids, I have my "a" value (rapid acceleration) at 2000. That allows me to get to 800ipm in .4s. If I recall correctly, I experimented briefly with 5000, which is .16s to 800ipm. But I don't want to start snapping belts or have other mechanical issues. You can always experiment with increasing the f value until you start snapping bits.

If the bit is sharp and you're burning the wood, you may need to decrease your spindle rpm.

Many thanks. I'll have to do a deeper dive on this during the weekend. I did decrease my spindle speed down to 7000 and used gwizard to make sure that my chipload recommended by the bit manufacturer stayed the same. I feel like that led to a very slight decrease in the smoke, but still enough that I didn't like it. I used a 1/8" compression bit and that seemed to help too. I'm cutting a voronoi pattern and I preferred the way that the holes looked when cut with a 3/16" bit (which is what I was using) than with a 1/8" bit. In future I should probably just modify the voronoi vectors so that they keep that look of being cut with a 3/16" bit but when using a 1/8" bit.

I wish there was some app where I could film the machine in use and it could tell me actual feedrates.

Many thanks again.

[DVE2000]

I think you should try use just an upcut bit. If you get chipout or fuzziness at the top, you can use a downcut bit just for the melamine first.