I found this site quite interesting:

https://www.cutter-shop.com/information/speed-and-feeds-calculator.html

There are others like it, of course. What struck me is that to have optimal chip load on our machines, it is difficult to use a 1/4" bit. It would appear we would be better served to drop down to 1/8" bits for everything as we can’t achieve a high enough feed rate to hit the optimal zone for two flute cutters.

While we can and do scale down the calculations to adjust for our machines, it doesn’t mean that the equation scales down really. Has anyone done deeper chip load calculations?

Also interesting to note that the site recommends the lowest RPM possiblel, which also helps reduce the required feed rate. But even at 10,000 RPM (bottom for the Makita), with a 2 flute 1/4" bit the recommended feed rate range is in the 5500 mm/s (220 ipm) to 6600 mm/s (260 ipm) range.

If you drop down to a 1/8" bit at 10K RPM then you get a range of 2032 mm/s (80 ipm) to 3048 mm/s (120ipm) for approximate optimal chip loading.

It appears a lot of us may be running our RPMs too fast for the feed rates of the machine and the size of the bits we are using. The site doesn’t mention depth of cut, but I think it’s fair to assume the fairly standard practice of 1 x cutting diameter, as you normally apply a reduction factor for deeper cuts from the starting calculation.

Has anyone else gone down the detailed calculation hole to get a sense of what the sweet spots might be using industry standard calculations on the Longmill? The challenge with the 1/8" bits is we can’t get enough length to cut through thicker material, like 1" BB.

Amana does have a OD 2 1/2" bit with a 7/8" cut height in a compression configuration: https://www.toolstoday.com/v-13354-46170-k.html so I’m wondering if that may not be the sweet spot (the insane almost US$60 price tag aside).

Thoughts?

-Jeff