The “What Spindle Speed?” tab shows you the calculated spindle speed for a given drill bit size. For example, if I was drilling a 10mm hole, I’d need to set the spindle for 2426 rpm for aluminium, or 291 rpm for stainless steel.

” A quick question – Drill speed. You touched on it briefly in one of the sessions, but is there an optimum speed for different metals? If so, how is it determined? “

The “What Diameter?” tab shows you the calculated drill sizes for a given spindle speed. For example, at 1000rpm, you could drill a 24mm hole in aluminium, but only a 3mm hole in stainless steel.

Its a super juicy question, so I just built this simple calculator in a Google Sheet. Its totally unlocked, so you don’t need a Google account to view it. Of course anyone can “edit” it, so I’d prefer you “Make a copy” if you already have a Google account:

I teach people how to build custom motorcycles by helping them build skills and confidence with my coaching, articles and training videos. I provide better technical information for custom motorcycle builders. And I shorten the learning curve getting you there.

The chart in the last tab is just a visual depiction of the formula. You could pick a material and a hole size, and estimate the spindle speed by reading it off the graph. The calculator in the first tab does this very accurately.

At the simplest level (its more technical in a manufacturing environment), it has to do with the metal itself, so its a “material property”.