Brushless DC CNC Spindle

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Brushless DC CNC Spindle

Postby bdring » Wed Sep 14, 2011 1:06 am

Over the summer I slowly collected parts for this guy. It appears to work pretty well, but still needs a little work and a lot of testing.

http://www.buildlog.net/blog/2011/09/ne ... r-spindle/


IMG_0698.JPG


Hold 2/3 HP in the palm of your hand.
IMAG0075.jpg
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Re: Brushless DC CNC Spindle

Postby r691175002 » Wed Sep 14, 2011 3:20 am

Looks like a pretty good idea. I really feel like plastic is the wrong material for this though. Even a few thou of deflection can turn a two flute 1/16" endmill into a one flute endmill.
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Re: Brushless DC CNC Spindle

Postby tylerv » Wed Sep 14, 2011 4:26 am

That looks pretty good. Any chance you'll be selling kits for the plastic parts once you're satisfied with the testing?

I plan on building a CNC router with MakerSlide once I get my laser finished.... :)
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Re: Brushless DC CNC Spindle

Postby bdring » Wed Sep 14, 2011 12:18 pm

The plastic is extremely stiff. It is 1/2" thick UHMW. The shaft will bend far earlier than the plastic.
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Re: Brushless DC CNC Spindle

Postby J45on » Wed Sep 14, 2011 8:39 pm

:shock: Me like , it sure beats the dremel in my router.
I am also thinking that motor would be fun on my push bike :lol:
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Stiff Enough?

Postby bdring » Wed Sep 14, 2011 10:19 pm

I challenge anyone else to park a car on their spindle. This a much less stiff HPDE version. Second picture is after car.

Honda Civic

car.JPG

after_car.JPG
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Re: Brushless DC CNC Spindle

Postby r691175002 » Wed Sep 14, 2011 11:48 pm

Point taken :lol:
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Re: Brushless DC CNC Spindle

Postby macona » Thu Sep 15, 2011 3:21 am

The bearing setup is wrong and will not be effective. It will be the equivalent of having one bearing. Standard bearings are not intended for axial loads. They can take a bit but you can't preload them like you need to for this application.

Though the use of a ER collet chuck is a good start.

The angular contact bearings need to be used in a minimum of a pair. They also need to be preloaded. Preload is determined on several variables including running speed and load. For something like a PCB router you can get away with a lighter preload than say a milling spindle. Heres the thing though. You can get bearing sets that come with the inner races ground to set the bearings to a specific preload. They will have a suffix of something like DUL (Duplex, Universal install, Light Preload). If you can't get the bearings you need in a preloaded set then you will have to set the preload though spacers where the spacer between the inner races on the spindle is a few tenths of a thousandth shorter than the spacer that separated the outer races. The parts can not be made on a lathe. The must be ground.

Spindle design is not easy, but there are materials out there to help. Timken/Fafnir has a section in one of their books that covers the basic designs of spindles. You can download it here: http://www.timken.com/en-us/products/Do ... -09-29.pdf

Starting on page 137 is cross sections of various basic designs. Most vertical milling machines Use a duplex of spindle bearings at the bottom and a single radial ball bearing neat the top of the spindle housing.

Good bearings are not cheap, though you can find NOS bearings on ebay for a fraction of their new cost. I had to replace the bearings in my surface grinder at about $150 a pop, times 4...

I may have a small set of preloaded AC bearings that may work for you. What is the OD of the collet chuck?

There are water cooled chinese made spindles on ebay that are pretty cheap. Look like a real good deal for the price. Though you will need a VFD to drive them.
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Re: Brushless DC CNC Spindle

Postby r691175002 » Thu Sep 15, 2011 4:27 am

You can also get the Chinese spindles from Keling:
http://www.kelinginc.net/CNCSpindleandController.html

I'm very likely to pick one up since my mill only goes to 2500RPM which is painful on composites and small aluminium endmills.

Tearing up aluminium at 60K RPM would be awesome. The math claims that kelings 100W spindle could push a 1/8" endmill through aluminium at 200IPM which is beyond insane.
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Re: Brushless DC CNC Spindle

Postby macona » Thu Sep 15, 2011 7:06 am

Yeah, those are the same spindles. Probably all come out of the same factory. Figuring a 1/8" Carbide, 3 flute end mill at around 800 sfm you will be limited to about 25000 rpm at 42 inches per minute pulling about 1/8th HP for a .050 DOC.

Once you do get your spindle going you will need some sort of coolant otherwise you will break bits in aluminum. Its no fun. I use Bijur SprayMist units on both my cnc lathe and mill. It is different than the generic coolant sprayers that use a venturi to suck coolant from the resoivoir. The Bijur units pressurize the coolant and uses low pressure air which mixes with the coolant in the nozzle. This creates a micro drop spray where you get a lot less airborne mist. Better for you and your equipment. I just added a second nozzle to my mill off the same unit. One on each side of the spindle. I was having issues where the work would eclipse the spray and chips would weld to the bit almost instantly. Broke a few $25 end mills this way.
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