[Tristar500]

Hi All,

I'm going to share my experience here of building a quieter, better and longer lasting spindle for your home brewed CNC router/mill.

After a couple of weeks listening to the angry drone of the mounted Ryobi router for hours on end and then witnessing it’s torturous final demise. It finally whirred to a grinding halt after several hours cutting a mold from a block of MDF. (medium density fiberboard) I unceremoniously tossed the aforementioned unit into the trash as it spewed forth its “magic smoke” into the passing breeze. Ah, quiet at last!

I was faced with purchasing another noisy router or look for an alternative. A better router might have been an acceptable alternative and if so it would probably be a Porter Cable.

After careful consideration and upon looking at literally dozens of various types of motors from A/C 3 phase to DC brushed units I settled on a 3 HP DC servo motor I had sitting around the shop. I was able to salvage the motor and it's matching controller from a nearby scrapyard a year or so before. The unit is manufactured by Aerotech designated BM1400.

Here are a couple of pics showing the modifications. An additional bearing on the front end of the motor is essential if the spindle is going to last any length of time. I turned a bearing housing from a piece of 6061 T-6 aluminum on my lathe and drilled and taped a series of holes to fasten it to the front end of the motor cap.

The shaft of the motor had to be turned down and threads cut so it would accept the chuck. This is the tricky part. I turned to a nearby machine shop that specializes in aerospace quality work as I wasn’t completely comfortable doing this part of the job myself. Everything this spindle would machine in the future was only going to be as accurate as its placement on the motor shaft. I chose a ½ inch Rohm chuck made in Germany. Nice unit, I’m looking forward to using it.

I’m in the stages of mounting the unit on my home brewed gantry mill/router and sometimes plasma cutter. More pics as I progress.

[Tristar500]

another pic

[Tristar500]

Here's one on the machine

[Tristar500]

Here's a shot of the whole machine in progress. Tools everywhere!

[RotarySMP]

Nice job. Looks like that motor cost the original purchaser a fortune!

Are you mounting milling bits in a drill chuck?

[ynneb]

Welcome to the forum Tristar. I see you have made your first 4 posts in the one thread. Good effort. Great pictures too. This is just what we like.

So how much noise does it make?
How fast does it spin?
How hot does it get?
Does it do the job you want it to do?
Do you have electronic speed control?
Can you please post a mp3 file of its sound? ( Just kidding )

I have been thinking along the same lines as you about a less noisy spindle.

[marvinstov]

Me too. I want to know more.

Thanks,
Marv

[Boros]

Great job and nice work with the front bearing housing.

I've been thinking along the same lines for a while now as I have quite a few spare servo motors and drives sitting around.

The thing which concerns me is the max RPM.

Most servo motors are rated to around 6000 RPM max.
The armature starts to self destruct after this.

I don't think this would be fast enough for a small 2 flute cutter.

Most hight quallity/ priced spindles are induction squirrel cage rotors which allow for greatter RPM.

What is the max RPM of your spindle?

Thanx

Boros

[Al_The_Man]

Originally posted by Tristar500
Hi All,

.

I settled on a 3 HP DC servo motor I had sitting around the shop. I was able to salvage the motor and it's matching controller from a nearby scrapyard a year or so before. The unit is manufactured by Aerotech designated BM1400.

That is actually a DC brushless, its wound like a 3 ph motor, nice motor, no brushes to worry about, its top speed is rated at 6000rpm.
Al

[ESjaavik]

Should do very nice as a spindle motor. It keeps the speed dialled in. Does not slow down at all under load. Unless it goes in overload, when it will just shut down. Most drives will look after the motor so it does not overheat. And it's rated for continous use.

One warning though since you mentioned machining the shaft. Don't dismantle a BLDC (or stepper) motor! That will demagnetize it with loss of power as a result. Unless left to companies doing this kind of service of course, they have the right equipment.

[arvidb]

Thanks for sharing your project!

I've been thinking about using a 400-800 W servo motor for driving a spindle, with a belt drive coupling. A switchable 2:1/1:2 ratio and 4000 RPM motor should make a nice spindle drive for both aluminum and MDF cutting, I think?

Well, perhaps I should finish the machine itself first...

Arvid

[Al_The_Man]

Another trick you could use if this motor has the encoder option included as well as the commutation (and most have).
If you are not using the encoder you could (or get someone) to whip up a ratemeter circuit and you can read the actual rpm. you could probabally just use the marker pulse (one per rev). Also there are a lot of cheap off-the-shelf ratemeters.
Al

[ESjaavik]

I Googled that motor and found it has almost 10HP peak power (24Nm peak torque) !!
If your controller matches, it can probably rip the Z-axis mount straight off the gantry!
Maybe you should program your drive to not give full torque? :-)
I'm just mentioning this so you can consider gearing it up quite a bit. It will still give enough torque even when running the speed down low. It will give almost 8Nm continous torque. For a wood router using small bits you would need 20 000 RPM or so. But even with some loss in the belt drive you should still be able to create huge amounts of dust in a short time. The rated speed is 3000RPM, so calculate with that, above that you will be limited by the available voltage. The 320V DC recommended needs 225-230V AC line voltage.
And remember that you are dealing with lethal voltages and up to 18Amp! So make sure the cabling from the drive to motor are properly terminated and cannot be pinched or in other ways damaged. Make sure that safety ground is brought out to the motor frame. We need to see your next project too.

Gosh, I'd like to have a motor like that to play with. I'd hook it up to a 0.5 TPI ballscrew and use it to launch pumpkins over to Sweden!

[Tristar500]

Ok, here's the update.

first in answer to some questions. Max rate is 6000 RPM. This is more then enough for both routing and mill work. Most router bits are two flute so by using a 4, 6 flute tool the RPM can come down. Another consideration is feed rate. If you slow down the spindle you decrease the feed rate. Since this new spindle will be so much quieter I may run at slower feed rates but I'll be able to run it in the evenings while the wife and I are having diner and watching the tube. I'll no longer be getting "that look" from my wife as she asks "how much longer is that noise going to go on?"

[Tristar500]

Ok, now onto the bad news.
After a couple of hours tinkering with the servo amp and its many jumpers and a few phone calls to tech support I got the motor to spin. Well.. Sort of. It had a bit of a tight spot as I'd rotate the shaft around and was binding a bit. At first I figured it was just the new bearings needing to be run in but as I ran the motor a few times it got worse and worse.

I pulled the spindle from the machine and started the disassembly process. This is where the trouble started. I was unable to get the encoder off the shaft without destroying it. It was frozen on the shaft. It took a angle grinder and a small chisel to finally split the collar and remove it from the shaft.

Now on to find out what was binding. After complete disassembly it appears that the Kevlar filaments holding the magnets in place was a total tangled mess. How they got this way I have no idea. (this was the first time the motor had been disassembled to this point.

After a lot of careful cleaning I decided to move ahead and rewind the motor magnets with Kevlar tow. I just happened to have a nice spool of the stuff laying about so around and around I went. The photos show the motor rotor in my lathe but I did this primarily to hold the piece as I worked on it. A word of caution! If you take apart any motor with really strong rare earth magnets be advised they have a lot of strength and can really hurt you. If you were to attempt to place the rotor on your metal work table you will probably find it will pull itself and maybe your hand into the table with considerable force.

I put on a pair of gloves and wound the Kevlar around the shaft. Once done I mixed up some aerospace grade epoxy and wet out the Kevlar tow. After all was done I used a shop rag to pick up any excess resin and moved a 100 watt bulb close by to heat it for the night.

Well, I’m now looking for an encoder! That’s all for now. Here’s a few more pics.

Lawrence

[Tristar500]

Here we are winding Kevlar..

[Tristar500]

all done and epoxied up. Just have to wait for it to set up and find another encoder.

Lawrence

[Al_The_Man]

Yeah, I have never had much success with removing the on shaft type encoder, they seem to freeze on with age, also some use a loctite type compound when mounting.
Renco have through shaft encoders that have the Commutation tracks, RCM21 series. You will probably need access to a double beam scope to align the commutation tracks with the stator.
Al

[arvidb]

Many people have said that removing the rotor from the stator removes much of the magnetic strength from the magnets (since it breaks the magnetic circuit or something like that). But you seem to know what you're doing with this kevlar stuff. What's your comments on this?

Arvid

[Tristar500]

According to the company that makes the motor it shouldn't have any negative effects on the motor magnets. I know this is not the case with most stepper motors. I recently attended a seminar with Oriental (VEXTA) motor and they explained this in great detail.

One really cool thing I learned from them was that they completely assemble the motor in a demagnetized state and then it is put into a machine that magnetizes the core. Petty cool I thought.