Spindle Rates / Feed Rates

[wojocad]

When I look at the stock tools in the PartWizard tool library, it looks like part diameter has nothing to do with spindle speed or feed rate. For example, a 1/16" diameter bit and a 1/2" diameter bit have the same machining numbers. If I want to add a larger diameter part to the library, where do I get reliable information for proper spindle and feed rates for various materials?

[Brady Watson]

Steven,
The tool library is a generic library included in PW, Insignia and ArtCAM. You will want to customize it to your needs and add whatever tools you work with to it.

Feedrates ultimately come down to chipload. There is a nice little chipload calculator in the control software under Tools. By using this calc, you can get fairly close to what your speeds will need to be for a given material. It is good for rough estimating, and I find that every tool varies a little on what speeds work best.

Pay no attention to the spindle speed and default feedrates in PW...You will manually set RPM on your spindle/router. If you want to know the real chipload that you machine is cutting, just pull some chips out of the kerf after it has cut, and put a digital micrometer on it. The thickness of the chip that comes off is your chipload. To increase chipload, increase move speed or lower RPM (or increase stepdown distance per pass). TO lighten the chipload, do just the opposite.

-Brady

[richards]

Brady,

I agree with what you wrote: "To increase chipload, increase move speed or lower RPM (or increase stepdown distance per pass). TO lighten the chipload, do just the opposite." except for the part about stepdown distance per pass. Unless the increased stepdown causes the router to slow down, the chipload will not change, since it is a function of feed speed and router/spindle rpm.

[Brady Watson]

OK ~ Just reiterating what it says in the Chipload Calculator in SB3:

If depth of cut = 2x diameter then reduce chip load by 25%.
If depth of cut = 3x diameter then reduce chip load by 50%.

While I haven't adhered to exact calculations, I will say that I have reduced chipload depending on how deep I was cutting per pass. The deeper you go, the more force is required for cutting at the same chipload...so maybe there is another factor that is left out of the calculation process, which should be included? Volume of chips?

-B