Thread: Rotary Table CNCing
As I said I managed to machine to the inside of the offset to accept a needle thrust bearing and then realised that there would be no support at that end so I inserted a sintered bush and reamed to size on the outside a normal ball thrust could be used as there is more room.
There were several momenst during the whole thing where I thought I had taken on more than I could do with my limited skill set. I also ended up with several bearing revisions as the whole thing was designed from bad idea to bad idea, if I had to do it again I would just buy a Arc euro(John S) finished one!
Never one to be phased by my incompetence or lack of skills (just a learning curve right?) if I decide to fit a thrust bearing at the lower end of the worm spindle I reckon there are two options:
1/ mill 5.5mm of the bearing housing and fit a 10x18x5.5 ball thrust bearing, then bore out the table body to 20mm dia at the right depth for about 6 - 7mm. Assembly would be put the worm in, drop the thrust bearing over the spindle, push to one side so that the offset bearing can be inserted over the spindle and into the table body. See pic...
2/ manufacture a new offset bearing, 5mm shorter than the current one and bored out 8mm not 10mm. turn down the worm shaft to 8mm and use 8x15x5 hrust bearings each end. Or maybe reuse the existing offset bearing but line with a 8mm ID, 10mm OD oilite bearing. This won't require boring out of the table body.
Last edited by irving2008; 06-01-2010 at 06:25 PM.
Irving, your option 1 sounds very similar to my escapades only unforseen problem I had was that with the inner bearing fitted the offset wouldnt(couldnt) turn sufficently to engage the drive. I cured it by using a carbide burr in my drill press to make enough clearance for the bearing.
How did you do that? I've added a drawing to show how I propose to do it..
Irv, why add the thrust bearing inside the housing?
Would it not be easier to add a pair of deep groove ball bearings in your motor mount to take the thrust?
Or maybe reuse the existing offset bearing but line with a 8mm ID, 10mm OD oilite bearing. This won't require boring out of the table body.
The thrust bearings are for the worm drive so as to limit back lash. My reason to fit an internal one was that I wanted to rotate in both directions and so wanted no movement of the screw. If you are cutting gears I think you could get away only having the outside one as you could always go in the same direction.
Ok, heres my thoughts.... the left hand diagram shows an approach using two 10x18x5.5 thurst bearings and a miniature 10x15x4 bearing. the top bearing cap screws on to contol endfloat. The right hand version shows the same idea using two 10x26x8 deep groove bearings to give both axial and radial support.
In both cases there is a central piece that acts as a shaft extender that goes over the existing shaft and is locked to it using a grubscrew or two. The only issue with this design is cutting the threads which are 25 x 1.5 (LH diag) or 27 x 1.5 (RH diag) for the end cap. I don't have a way to do that right now and the tap and die is £50!
Just one comment, the inner thrust bearing is to take the thrust when the table rotates in reverse which was the reason I did it in the first place, otherwise in reverse the worm part will wear on the offset part and worm drives excert a lot of force and I foresore a lot of wear.
I agree Peter, but my thinking is by controlling the thrust externally the worm doesn't come into contact with the base of the offset part - its held off it by a few thou so that wear can't occur.
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