Re: [CAD_CAM_EDM_DRO] Cheap 56,000RPM milling upgrade (not a dremel :)

I'd try a cheap panel router with a small timing belt like 1/8" wide for low mass with a 2:1 pulley arrangement to another arbor and a set of high speed bearings. Be worth a try. Jon is exactly right, air motors are extremely inefficient. They are ok in a production environment where 50 hp screw compressors are running non stop and there is an ample and continual supply of air. Good comparison: I have a $300 1/2" air drill and $140 1/2" Milwaukee, both are new, The electric drill is at least 3 times more powerful. Manufacturers are generally conservative when specifying the air consumption as Hydraulic component manufacturers are aggressive in specifying load capacities. Take the area of a hydraulic piston and calculate the pressure limit of the system and it rarely adds up to the listed capacity. In short, they lie. A small turbine like this turning at 50k rpm is like having an airline wide open. Air is a very poor medium in which to transfer energy.

Ron

Jon Elson <elson@...> wrote:

Abby Katt wrote:

>Hi all,
>
>I found this great link while looking around, for about $150 you can
>basically get a air-powered mini die grinder and hold it in a collet on your
>mill with a special hollow drawbar for the air intake. This way you get
>56,000RPM milling for 2/16" (3MM) and smaller end-mills. But you'll need a
>beefy compressor... You need 28CFM to run it 100% duty cycle, but I think if
>you turned down the pressure you'd just get a little bit lower rate.
>
>

28 CFM? At roughly 90 PSI? That's about 8.75 Hp on a single-stage
compressor! How much power OUT do you get from this spindle?

For the cost of this device and a big compressor, you may be able to pick
up a high speed electric spindle and the gear to drive it. I have a 3/4 Hp
Rockwell/Precise spindle that will run to 54,000 RPM, using 950 Hz power.
AC Teck makes VFDs that will go to 1000 Hz. The later Rockwell/Precise
spindles
are TWO phase, however. So, you need a Scott Tee transformer or a special
VFD for it. I still have to work on that.

My guess is that these spindles actually have more torque that the air
grinder.

Jon



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