[Tristar500]

Thinking of using a 3 phase DC electric motor of the type used on model airplanes. I found one that turns 2700 RPM per volt and can run up to 18 Volts. That's 48600 RPM

http://www.hobbyking.com/hobbyking/s...idProduct=5146

This one is water cooled an only costs $30.00

I'm thinking of using it to machine really tiny stuff like jewelry and custom coins.

Any thoughts here?

[jeffrey001]

Hi

I think for the price, you really have nothing to loose.

But how you will mount your tool, if you build an adapter, you will have to use bearings that will support that RPM.

Jeff

[Tristar500]

I'm thinking of just building an adapter that will fit snug on the motor shaft and accept .125 micro end mills. Basically a tiny end mill holder.

It would be nice to fabricate a new bearing holder for the motor that would accommodate a couple of high end bearings.

[plasmator]

I saw a project where a guy used a hobby-type BLDC motor to drive a "Razor"-type scooter. To gear it down, he used a belt drive and it seemed to work pretty well.

Could you get an off-the shelf MT2 or MT3 spindle assembly (without motor) and do a 1:1 belt drive? That way, you could use a variety of toolholders and of course you'd get all the other benefits of belt drive as well.

[gfc62]

Here's one with a Taig spindle, smaller than MT2 but the same general idea.

http://www.cnczone.com/forums/showthread.php?t=104580

[Tristar500]

I wonder how well the belt drive holds up to those kind of speeds?

[rowbare]

Here is a thread which discusses using these motors to make a spindle: http://www.cnczone.com/forums/showthread.php?t=106904

Bearing selection is crucial to control runout and to deal with the speed.

bob

[mactec54]

Tristar500

That type of belt is a dumb idea for spindle use, they should be using a poly v belt, for your spindle drives

If you are just going to put a adapter on the shaft for your cutter, then support the end with a bearing, this will then take the side loads off the motor

[Tristar500]

I've ordered a motor. Went with a non water cooled unit and am going to essentially build my own can and bearing end holders. I'm thinking of using an tight fitting end mill holder or perhaps a collet extension in replace of the motors original shaft.

I ordered a motor that turns 80,000 rpm

[mactec54]

Tristar500

What motor did you get?
Your cutter mounting plan sounds like a simple way to do it,what are you going to drive it with

[underdog]

Depending on weight of the toolholder versus the size of the bearings you may want to think about balancing. At about 10K RPM toolholders start to have to be dynamically (while rotating) balanced. Otherwise the out of balance beats the bearings to pulp or throws the tool across the room.

Think of your tires. If they didn't balance them in a balancing machine what would it do to your car?

Not trying to be a wet blanket, but I would hate to get speared by a micro endmill during the, very promising, first test.

[Mike Everman]

I've ordered a motor. Went with a non water cooled unit and am going to essentially build my own can and bearing end holders. I'm thinking of using an tight fitting end mill holder or perhaps a collet extension in replace of the motors original shaft.

I ordered a motor that turns 80,000 rpm

Yeah, what motor is that? Sounds good. Using a collet extension is what I've been planning as the shaft for a spindle as well. There's a lower limit of size in extensions, which I think is ER-8.
Most distributors here in the states have english sized shafts, but I found a metric source at Somma Tool for ER-8 straight shank extensions. I haven't checked if they have precision balanced ones. the neat thing about that one is the shank is 8mm, so you could use 608 skate bearings.
The DIY turbojet guys have a lot of info on modifying these bearings for stupid high rpm's cheaply, by removing the cages and turning them into full compliment ceramic ball bearings. Though you might find some good ceramics at VXB.

[handlewanker]

Hi, your only problem would be balancing the motor pulley if'n you're going to mount it on a pulley set-up to drive the spindle similar as to what I think has been shown in a couple of posts back with the Taig set-up.

If you intend to direct drive the cutter with the collet holder attached to the spindle I think you'd get a dramatic drop in RPM, seeing as how the no load speed is probably 80K, but that would depend on the size of cutter and chip rate.

The use of that motor interests me as I built a small circuit board drill some years ago using a small 28 volt DC motor, but it didn't have enough guts to pull the skin off'n a rice pudding, and I had to peck the drill through just to keep the revs up, I might just see what's available down here in OZ.
Ian.

[eSilviu]

If you intend to direct drive the cutter with the collet holder attached to the spindle I think you'd get a dramatic drop in RPM, seeing as how the no load speed is probably 80K, but that would depend on the size of cutter and chip rate.

if the motor is like the one pictured in the first page of the thread, then it's a 3 phase motor. The controller will convert the DC voltage from power supply to a variable frequency 3 phase AC to drive the motor. So the controller know at any moment the speed of the motor. There are RC controllers with "governor" mode usually used in RC helicopters, that will drive the motor at constant RPM compensating the variable load.