[ticica]

I got some precision duplex bearings on eBay and thought of trying to build my own spindle, following the footsteps of Jroque (thread: http://www.cnczone.com/forums/showth...?t=7004&page=7).
I want it to take R8 collets and to allow for automatic tool changes (such as Hoss's ATC in thread: http://www.cnczone.com/forums/showth...=43651&page=11).
I attached a drawing of what I came up with. Any suggestins are welcome.
My primary concerns are:
1. The thermal expansion and how to accomodate for it.
2. How to make a drawbar mechanism for ATC. I would prefer to use an electric motor based system, as I have no experience with pneumatics...
3. Is there anything terribly wrong in this design?



Thanks in advance for reviews and comments.

Ivan

[ozzie34231]

Yes, you are correct, thermal expansion will be a problem with your design.
Most designs I've seen don't lock on the upper bearings, only the lower.

[ticica]

Yes, you are correct, thermal expansion will be a problem with your design.
Most designs I've seen don't lock on the upper bearings, only the lower.

I thought I did not lock the upper bearings (since I have that spring washer). But it seems that the washer will only help with shaft contraction, not expansion relative to the housing. I guess I need to put a spring washer between the top cap and and the outer races as well. Or, if I only anticipate the shaft to get warmer with respect to housing, I can maybe get rid of the washer at the bottom.

I have updated the drawing.

However, I think I will still have to very accuratelly machine the shaft with respect to the housing, so I might put the old washer back in and have them both. Really, I don't know what I am doing Any help appreciated.

Ivan

[Riceburner98]

I thought the only pre-loaded bearings were supposed to be on the lower end of the spindle, the top end should be just a good-quality standard bearing for side support, with a "slip" fit around the shaft to allow for expansion. I recently rebuilt my Taig spindle with new bearings, but the inner race appears to have been way too tight on the shaft and they're already toast. I would really like to build one of these myself.. Is there nobody that could use their superior machining skills to offer a spindle like this to us cheap guys? I can grasp the concept in my head, but my skills definitely don't allow me to do this type of precision machining.. As far as an electric actuator, I bought a high-power fairly short-stroke linear actuator from Surplus Center that would possibly work with a lever. It runs on 120vAC, so you'd need to control it by a relay, but it supposedly puts out a few hundred pounds of "pull"... Never tested it beyond just powering it up and watching it move. Personally I like the air piston method, I've got a fairly short piston with a 3" bore that will easily lift my 200lb butt off the ground.. Cheap on eBay too. Pnuematics are pretty easy, just treat the hoses like electric wires, and the electric solenoid valve like an on/off relay. Simple, and they pack a lot of power.

[WillyK]

From your drawing I can't find any bearings supporting axial forces.
Please have me excused if I'm "blind".
Best regards Willy

ps
If "duplex" means angular contact (SKF terminology), you should be covered.

Single row high-precision angular contact ball bearing :

[ticica]

From your drawing I can't find any bearings supporting axial forces.
Please have me excused if I'm "blind".
Best regards Willy

ps
If "duplex" means angular contact (SKF terminology), you should be covered.

Single row high-precision angular contact ball bearing :

Yes, they are Angular Contact bearings. Both pairs.

I figured that the top bearing set needs to float. I think I will either leave them be in the slip-fit (in which case why not just use a regular single radial load bearing?). Or I will add two preload washers for the outer races (one on top, one bellow the bottom).

I am not really convinced that the washers would actually do anything to make the whole thing axially more stiff. Also, I am not sure whether I will be able to make this so that both washers come in contact with their corresponding races at the same time when tightening the top cap.

Ivan

[WillyK]

I do agree, for all purposes the spindle axis is axially stiff, so preloading both
bearings will not add stiffness, only unnessecary complexity.
Plain radial bearing at upper end - taking belt radial load - will be both simpler and cheaper.
Good look with your project, which I will follow.
Willy