# 50,000 RPM Mill Spindle



## JimDawson (May 26, 2014)

I have been wanting a high speed spindle for my mill for light routing and engraving.  I did a project a while back that required that I use my friends router to get the spindle speed that I needed to run the really tiny end mills I was using.

So with a Micro Air Die Grinder from HF, I made it happen.  The HF grinder is about 5/8 diameter, so it fit nicely in an end mill holder, after a bit of lathe work on the end.

A little modification to a #30 taper tool holder.  I had to drill it 5/8 all the way through, and trim the end a bit.  I don't need the drawbar threads on my mill.  It got a little warm on the end while drilling, these tool holders are made of some pretty tough stuff.  I was only turning at 115 RPM.





The air grinder inserted in the tool holder.




Connecting the air line.

The grinder has a M6 threaded air fitting on the back.  This was supposed to provide the grip on the air line in the original configuration.  The air line blew off the first time I tried to run the thing, the collar had split so it was loose.  So much for Chinese engineering.  It worked out well for me, the M6 thread screwed nicely into polypropylene fitting I wanted to use.  I didn't even have to make an adapter, it just screws right on.  The polypropylene is soft enough that it formed the threads very nicely.




The air line goes down through the drawbar hole.  Note:  Don't turn the spindle on!!  There is an in-line oiler to the right of the regulator.

I need to install a 1/4 turn valve on the regulator as an On/Off switch.






A carbide V-cutter engraving bit installed.





The first test run in a scrap piece of acrylic.  Everything worked great!!  This is engraved from the back side, so you are looking through the acrylic.  To get the contrast in the picture, I'm holding a piece of paper behind it.

~50,000 RPM, 10 IPM, 0.006 deep, with soy based cutting fluid.

This is part of the labeling on my new mill control panel.  It will be side lit with LEDs.  I'll post that project when I get to it.


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## dave2176 (May 26, 2014)

That's pretty sweet.  I'll stick that in my box of future projects. 

Dave


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## Dave Smith (May 26, 2014)

Jim---I have about 10 of the HF small grinders for the high speeds of small cutters and drills---one question--did you turn the small drill speed adjuster to wide open when you mounted it inside the holder?--if so then do you have an external speed switch or do you just run it always at full speed?----I guess I never thought about mounting the unit inside of a collet or tool holder-----good idea-----Dave


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## JimDawson (May 26, 2014)

Dave Smith said:


> Jim---I have about 10 of the HF small grinders for the high speeds of small cutters and drills---one question--did you turn the small drill speed adjuster to wide open when you mounted it inside the holder?--if so then do you have an external speed switch or do you just run it always at full speed?----I guess I never thought about mounting the unit inside of a collet or tool holder-----good idea-----Dave




I turn the internal valve wide open and adjust the regulator to adjust the speed for now.  I may play with putting a flow control valve down stream of the regulator.  I need to also put a shut off valve before the regulator.


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## DMS (May 26, 2014)

I have a setup with the same little pencil grinder, except I mad a clamp that goes around the spindle collar, rather than through the spindle. I made mine for cutting PCBs (worked great). Haven't tried engraving anything yet though. That panel looks really clean.


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## JimDawson (May 26, 2014)

DMS said:


> I have a setup with the same little pencil grinder, except I mad a clamp that goes around the spindle collar, rather than through the spindle. I made mine for cutting PCBs (worked great). Haven't tried engraving anything yet though. That panel looks really clean.



Please post a picture or 2 of your setup.

I am going to make a mount that clamps onto the spindle also.  That one will be for a larger drive motor, probably a small router, or something similar.  I thought about building a system that would have the motor on top of the spindle and drive it with a shaft down through the drawbar hole.  Then I realized that it would have so much shaft whip that it would tear it's self apart.


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## george wilson (May 26, 2014)

I have planned some day to make a clamp that goes around the spindle housing and holds my 10,000 RPM Dumore die grinder(electric) on the other end. Since we have a home business of jewelry making,and I sometimes make brass master models using small end mills,such a rig would be helpful. And,you do not run the risk of automatically turning the milling spindle on!! I'm going to make it out of 1" thick aluminum plate. Or,I could use my sweet little polished aluminum Stanley 1/4 HP router,which goes twice as fast. And can also be regulated with a router speed control.(As can the Dumore).

I saw a little rig made out of a Dremel tool,connected to a small ball bearing spindle by a little belt,at a Cabin Fever show. I don't have that much faith in Dremels,though. Their puny plastic coupler breaks so very easily,I have quit using mine. I have never used it hard,and the silly plastic coupler breaks anyway. Plus,lack of much power at all. Must be a regular problem,because Lowe's sells the couplings.


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## JimDawson (May 26, 2014)

george wilson said:


> I have planned some day to make a clamp that goes around the spindle housing and holds my 10,000 RPM Dumore die grinder(electric) on the other end. Since we have a home business of jewelry making,and I sometimes make brass master models using small end mills,such a rig would be helpful. And,you do not run the risk of automatically turning the milling spindle on!! I'm going to make it out of 1" thick aluminum plate. Or,I could use my sweet little polished aluminum Stanley 1/4 HP router,which goes twice as fast. And can also be regulated with a router speed control.(As can the Dumore).
> 
> I saw a little rig made out of a Dremel tool,connected to a small ball bearing spindle by a little belt,at a Cabin Fever show. I don't have that much faith in Dremels,though. Their puny plastic coupler breaks so very easily,I have quit using mine. I have never used it hard,and the silly plastic coupler breaks anyway. Plus,lack of much power at all. Must be a regular problem,because Lowe's sells the couplings.




I agree about turning on the spindle accidentally, in my case I can pop the control console off of my VFD and put it in my tool box.  Just squeeze and pull, as long as I remember to do that!

I may build 2 brackets, one for my router so I can use 1/4 and 1/2 bits, and then another for a RotoZip so I can use 1/8 and 1/4 bits in it.  I think the router has enough power that I might have to use 2 inch thick aluminum for that bracket.

I think your Dumore would make a great tool to use that way.  A Dremel is just about useless for metalworking with the exception of light deburing and chewing out broken taps and ez-outs.  I have a little cordless that is kind of handy, but I don't use it that much.

Be sure and post pictures of your project when you get to it.


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## Dave Smith (May 27, 2014)

JimDawson said:


> I turn the internal valve wide open and adjust the regulator to adjust the speed for now. I may play with putting a flow control valve down stream of the regulator. I need to also put a shut off valve before the regulator.



Jim--it is best to put the speed control on the exhaust side of air motors so you still have full power at lower speeds--but I don't think there is any exhaust port that you could put a control on the tiny grinders--probably full speed is all a person needs to use on those and a shutoff ball valve---very cleaver idea of mounting in a holder--:thinking:---Dave


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## JimDawson (May 27, 2014)

Dave Smith said:


> Jim--it is best to put the speed control on the exhaust side of air motors so you still have full power at lower speeds--but I don't think there is any exhaust port that you could put a control on the tiny grinders--probably full speed is all a person needs to use on those and a shutoff ball valve---very cleaver idea of mounting in a holder--:thinking:---Dave




Dave I agree 100%, unfortunately this has a rear exhaust and without coming up with a coaxial air hose system, that will fit down the drawbar hole it would be impossible.  It may be possible to fabricate a coaxial airline that will fit.  I have only made one test cut with it so far, haven't really had time to play with it.  Later this week I'll have a bit more time to play.


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## KMoffett (May 28, 2014)

Just to throw in another approach with that kind if grinder...if you can lock your spindle.

Ken


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## Ebel440 (Jun 1, 2014)

I had to mill some very fine slots in aluminum and had the same idea of fitting the Hf grinder to a bt40 holder. Did you try to use it for anything besides engraving or possibly measure the run out on the grinders spindle? I may have to look into doing this. Thanks


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## JimDawson (Jun 1, 2014)

Ebel440 said:


> I had to mill some very fine slots in aluminum and had the same idea of fitting the Hf grinder to a bt40 holder. Did you try to use it for anything besides engraving or possibly measure the run out on the grinders spindle? I may have to look into doing this. Thanks



I haven't had a chance to play with it since I ran the first engraving test.  I haven't checked the run out yet, by eyeball it looked pretty good.

I have heard of others using this grinder for circuit board work, so it is probably up to some light milling.

For $24 (on sale) and a little time I would say it's worth checking out


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## countryguy (Jul 21, 2014)

*so simple I smacked my head!  LOL .: 50,000 RPM Mill Spindle*

Ken,  LUV it!   Duh-  So simple and it's perfect.  Awesome call!     Going to HF!  




KMoffett said:


> Just to throw in another approach with that kind if grinder...if you can lock your spindle.
> 
> Ken



- - - Updated - - -

Frigg'n AWESOME Stuff gang!  Going to HF tomorrow to grab the pen holder grinder and see what else they have.  Jim, D  thanks for always posting Pics!   Very kind of ya Sir.       And Kens post on his holder is just too easy to say no too.  I'm embarressed if I do not at least make that setup.    If I cannot, the wife can chuck the machine out so I'll come to bed again most weekends.  ;-)

- - - Updated - - -

I think this might be design to also put in a tension (spring) loaded setup as well??  Say 1/2" to 3/4" of V travel?   I saw some neat tricks w/ that type of capability. 
CG 




KMoffett said:


> Just to throw in another approach with that kind if grinder...if you can lock your spindle.
> 
> Ken


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## JimDawson (Sep 1, 2014)

I did a job today that gave me a chance to give the HF pencil grinder a real workout.  I was starting to get a bit of chatter towards the end of the run, so I suspect the spindle bearings might be getting a bit loose.  I don't think it was designed to run under a heavy load for 16 hours.  The in-line air oiler doesn't seem to work, so I stopped to squirt a bit of oil in the line every so often.  I will replace the regulator that I have on there now with a complete air service unit with filter and oiler.

I had to make 550 of these little guys out of 0.020, 260 brass.  The endmill is a HHS, 2 flute, 10* taper, with a 0.005 tip.  Because of the low power of the grinder, I found about 3.8 IPM was the best feed rate I could muster.  My 5 HP air compressor got a pretty good workout also, it ran about 50% of the time, about a 2 minute on, 2 minute off cycle.  I was running the grinder at about 70 PSI.  Power cost for air for the run was about $4.00



The 10x24 brass sheets (2 req) were double-side carpet taped to pieces of 3/4 inch MDF.  I used deck screws to screw that down to another piece of 3/4 inch MDF that was bolted to the T-slots with countersunk screws.  




16 hours later, it's on the last column of parts.  




I had a lot of time to work on cleaning up the shop while this was running.  Still not done with the shop, maybe tomorrow.

To see the guts of this take a look here  http://www.hobby-machinist.com/showthread.php?t=23186&p=205311&viewfull=1#post205311


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## Tim9 (Jan 27, 2021)

JimDawson said:


> I did a job today that gave me a chance to give the HF pencil grinder a real workout.  I was starting to get a bit of chatter towards the end of the run, so I suspect the spindle bearings might be getting a bit loose.  I don't think it was designed to run under a heavy load for 16 hours.  The in-line air oiler doesn't seem to work, so I stopped to squirt a bit of oil in the line every so often.  I will replace the regulator that I have on there now with a complete air service unit with filter and oiler.
> 
> I had to make 550 of these little guys out of 0.020, 260 brass.  The endmill is a HHS, 2 flute, 10* taper, with a 0.005 tip.  Because of the low power of the grinder, I found about 3.8 IPM was the best feed rate I could muster.  My 5 HP air compressor got a pretty good workout also, it ran about 50% of the time, about a 2 minute on, 2 minute off cycle.  I was running the grinder at about 70 PSI.  Power cost for air for the run was about $4.00
> View attachment 82941
> ...


That is awesome Jim. Really slick stuff there. And that is one tiny end mill.
 The slop in my old Millrite would snap that end mill in a New York second. But, I'm hoping that I can pull off a decent Pentograph engraver. Thats what I'm building right now. Bought the plans of the Pentograph from Joe Pie and am about 80% complete. And have my new die grinder like you have. So I'm hoping I can pull off some basic engraving. But, I know ( or think? ) before I even tried,  that my mill has way too much slop to pull off using a end mill that small. 
   Very cool stuff Jim.


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