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ptjw7uk
05-10-2009, 09:14 AM
Hi All,
Had one of those jobs this week which I was beginning to wish I had never started.
All I wanted to do was put some thrust bearings in my rotating table, so searching through the forum I found the Sir john method of adding thrust bearings.
So after taking various measurements I soon realised that my rotab was nowt like the one Sir John had featured also none of the thrust bearings I had found had a 14mm bore. Nearest I found were needle bearings with a bore I also bought 2 small bearings with bore to accommodate side play.
So the fun began machined the shaft to diameter threaded the end 12mm x 1.0, recessed the offset part to accept the new bearing and then realised that there would not be enough meat on the outboard end to accept a bearing!
Second thoughts why not a sintered bush Ok look on fleabay and the nearest was 14mm od with 6mm bore, when these came inserted into outboard end and then thought this should be simple in the 4 jaw chuck.
After several attempts to get the offset part to run true I removed it to discover that I was in imminent danger of damaging the part as the outer edge due to the offset was quite thin, another rethink( all this thinking gave me a headache)
So I set the fixed steady up with the work between centres until it was running true removed the tailstock and the part moved with it, as the lateral force was not now present. So as an expedient I wired the thing to the face plate and machine the bore and reamed it.
So my question for today is how are you supposed to do this as the inner end needs the centre to line up on and I can say that I have never seen this carried out as normally one end would be in a chuck.
Any ideas!.

Peter

small.planes
05-10-2009, 03:20 PM
Peter,
after reading that about 5 times Im still confused :confused: Whats the actual question?
Is it how do you hold things on a face plate?

a link to the SJ thread might make things clearer....

Dave

ptjw7uk
05-10-2009, 04:22 PM
Sorry for any confusion, I'm confused myself.
The real question is is there a way of holding something against the centre in the face plate that will keep the object in place. A driving dog only supplies the turning force and supplies no actual holding force. I managed by use of wire but I feel that there must be something better suited.
If I had an er40 chuck I would have used that as the diameter was 24mm and my er32 only goes to 20mm.
If that is not clearer I may do a drawing.

The sj thread is http://bbs.homeshopmachinist.net/showthread.php?t=18787&highlight=thrust+bearing

Peter

small.planes
05-10-2009, 04:29 PM
Ah-ha, I think I understand now...
How about a strap clamp with a hole in it? so you can bore /drill through the strap, and the strap is bolted to the faceplate either side of the part you are wanting to push onto the point of the center.
Or most of the clamping methods used on a mill table ought to work.
I am assuming you have the center in the middle a the back? or is it that you have centered the workpiece on the faceplate and now cannot keep it there?

A Keats angle plate might also work.

Dave

DR
05-10-2009, 05:15 PM
I believe what the OP needs is called a center driver. It's similar to a wood lathe spur drive.

The main difference is the center drivers usually have more drive pins. The pins are spring loaded in some fashion to drive pieces that are not flat on the end.

BTW, I'm not 100% sure center driver is the correct name. I am sure that they typically cost more than the usual hobby lathe. I bought a used one with #4 Morse taper for $80, as I recall the list was over $1000. (And, I've only used it once in twenty years.)

Also, they obviously won't work on hardened material, the spurs can't dig in.

JCHannum
05-10-2009, 05:26 PM
I am still unclear as to the problem. It sounds like a job for an angle plate.

Back in the good old days, rawhide was frequently used to lash a part to the faceplate for turning when nothing else would work. It sounds like you used wire instead. There are no hard and fast rules beyond common sense and safety concerns when it comes to making a setup. If it works, it is the right way to do it.

japcas
05-10-2009, 06:05 PM
Peter, that's why they call it turning between centers. You stand a very good chance of eating the part and wrecking the steady if the part you wired up to the center comes off. You need to figure out some where to turn a reference on your part while running between centers. Then put the 4 jaw chuck on and indicate your reference mark in, run the other end on the steady you already set up, and then do the machine work on the end of the part.

TGTool
05-10-2009, 06:17 PM
I've seen photos of rawhide use as well. I would think these days that modest diameter nylon cord might be a useful substitute so you could use the elasticity to advantage. And of course always cutting toward the headstock.

NickH
05-10-2009, 06:17 PM
There's a really old trick to do this, use wet hide strips to bind the drive dog to the face plate, allow to dry, the hide will shrink & tighten,
Regards,
Nick

jdunmyer
05-10-2009, 07:32 PM
This is one place where a threaded spindle nose is better than a tapered spindle. You use rawhide lacing as described above, but unscrew the faceplate a couple of turns before lacing it up. Then, tighten the faceplate and it'll draw the lacing tight.

That's how the old-timey books show to do it.

ptjw7uk
05-11-2009, 02:26 AM
I think the keats plate is the way to go or make some right angle adaptors.

The reason I was doing the between centres bit was to line up the bore and keep it aligned then once tyhe fixed steady was in place I could remove the tailstock centre and then drill and ream.

Its all academic now as its all running now but must look for a keats fixture or maybe make one although with the price of metal probably cheaper to buy chinese.

Thanks to all who answered.

Peter

JCHannum
05-11-2009, 07:09 AM
Don't forget solder and Lock-Tite either. They can both be used for fixturing, soft solder the odd shaped or small part to another piece and desolder to remove when finished.

Lock-Tite can be used to hold something in a bore for ID work, heat of about 400*F will remove. Heat in a well ventilated area and don't breathe the fumes.