What kind of bits to use with a die grinder spindle?

[doorknob]

I have seen several DIY routers, engravers, and the like that use a die grinder (such as the Harbor Freight #44141) as the spindle for their CNC machine. The Harbor Freight die grinder has a 1/4" collet that holds tools such as the following recommended accessories:

- abrasive cut-off discs and wheels
- wire brushes
- 1/4" shaft grinding wheels
- flap wheels
- wire wheel brushes
- rotary burrs

Out of that list, I'd guess that the most likely category to find usage in a CNC machine would be "rotary burrs".

That particular unit is rated at 25,000 rpm. The instruction manual for the die grinder warns against using tooling that is rated at less than 25,000 rpm due to safety concerns.

Harbor Freight sells a lot of interesting looking 1/4" shaft tools (for example, a number of different shapes of diamond-coated cutters), but they all seem to be rated for a maximum rpm of 20,000 or less.

Do people use some kind of motor speed control to reduce the rpms to a range where you can use that kind of tooling, or are there specific tools that come with 1/4" shafts that people use that are rated for 25,000 rpm or above? Do people use standard HSS or carbide milling cutters in these machines? Do they use adapters for small diameter drills? Router bits? Something else?

So, what tools or bits are people actually using with these spindles, for milling tasks, for engraving, and the like (and for what types of workpiece materials)?

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[ger21]

Router bits.