Thread: Diy Brushless Spindle
Far better than mine...wow has it been that long since I last looked at this....been too busy spending money on RC helis.
Bought a small boring bar and today in lunch bored the inside of the bearing holder out. Tomorrow will face off (parting tool not big enough) the part to the correct dims. Then just need enough Bellville washers to fill a 12mm gap...that offer of some washers still on Mark? ;)
Last bit is the cap then fit it all together...will take pics later!
Looks like it's coming along!
I've had a shake up here as well, lots of my toys are still in boxes. Was laid off, found a job, moved from California to Michigan (~2300 miles!), bought a house... phew, that makes me tired all over again thinking about it!
Here are some pics of my copycat spindle design, I think I'm in the same spot of the build as you are Neil.
I'm using a Turnigy G110 motor, two 8x22x7 angular contact bearings, 4 belleville washers, and an er11 collet with 8mm shank. I'm mostly going to use this spindle for light work: plastics, engraving, PCB cutting, etc.
I'm a little concerned the bearings will heat up, any thoughts on this?
Also, did you re-install the e-clip ring onto the new shaft?
Looking good, I couldn't get the holding nuts in the housing as the PCD of them is too close to the 22mm centre hole. I'm going to have a real session on it this weekend as for once I'm in Hereford and not got anything planned (although if it continues to be sunny like predicted I'll be out up the field with my RC helicopters ) and as June will be a write off as I'm out every weekend
I think the bearings will get warm, what speed are you going to be running it at? blackburn mark or Jonathan will be the ones to ask as they use theirs! If it gets too hot I'll use the router it to cut a water cooling jacket for it
I'm not going to bother turning a groove for the circlip as I reckon that the grub screw (I'll drill a small recess in the shaft) will hold it as well as some locktite :)
Looknig forward to seeing pics of the finished spindle!
The outer rings of the angular contact bearings are fully constrained by the housing and axial force from the Belleville washers, however neither of the inner rings are attached to the shaft, so the two angular contact bearings are effectively acting as just a standard radial bearing with zero clearance. Currently when the shaft is subjected to an axial force it would move, except for the grubscrew and bearings in the motor - so it is those standard bearings in the motor that are actually resisting the axial force which defeats the object of using angular contact bearings.
You need to somehow fix the inner ring of the angular contact bearings to the shaft - best way is probably to machine a fine thread on the shaft and use a locknut (rather like on ballscrew mounts). You then have both bearings facing the other way round and place the Belleville washers between the nut and bearings and use the nut to apply a known preload by measuring the compression distance of the springs. This is how I've done it on a ballscrew... same principle applies. The problem is the shaft will be hard to machine so someone will suggest you simply locktight the lower bearing to the shaft, but that's rather crude.
The preload required must be greater than the maximum axial cutting force and greater than the minimum load specified by the following formula:
This avoids sliding friction within the bearing which will lead to excessive power dissipation and thus heat build-up. However equally you don't want to use more preload than necessary as clearly that will also cause the bearing to heat more. You could machine slots into the housing with a parting tool to make fins so the greater surface area increases heat dissipation. Even better, make a channel in the housing (or mount) and pump water through it.
Isn't the spindle up pressing up against the inner race of the lower bearing? So wouldn't this mean that any axial load is applied to the inner race of the lower bearing and the Bellville washers would transmit the load to the upper bearing?
Thanks for the replies...
How about if I add a shaft coupling to the stop with a couple of belleville washers? Then using the collet head pressed up against the lower bearing inner race and the shaft coupling, you would get your axial constraint.
I would also load the angular contact bearing in the same orientation (both loaded with "upward" force). This would make the bearings strong in plunge operations, but weaker in operations where the bit is moving up out of the work piece. Would this be a problem though? Most operations are pressing into (down) the work piece.
Maybe if I machine 2 steel collars 8mm ID and 10mm OD and secure them with grub screws (locktited in of course!!) one above the top bearing and one below the bottom then that would stop the movement? Would the grub screws be strong enough?
I'll do a drawing later as on the mobile...
Last edited by Jonathan; 23-05-2012 at 06:24 PM. Reason: Fixed the 'quote' tags.
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