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10bulls
04-27-2005, 11:40 AM
I'm very new to lathe work and as a masochisitc challenge, I'm planning to turn some leaded bronze bushes to use as linear slides on silver steel printer rods. OD of bar I have is 1", printer rods are 12mm. My lathe is a 7x12 mini.

My plan of attack is going to be this...

1. Cut bronze round to bit larger than required length.
2. Face both ends in lathe to required length (easy so far)
3. Mount in 4 jaw chuck and dial in to get as central as I can.
4. Centre drill, then scribe a circle about 10mm dia around centre
5. Mark off about 6 points round this circle and drill 3mm holes on drill press for 'clearance?' channels
6. Return to 4 jaw chuck and dial in again
7. Tailstock drill center hole using progressive sizes...if 12mm drill hole is tight on the printer rod use that, otherwise stop at 11.5mm
8. If needed, use boring bar to get ID close to required
9. Lap to finish off with valve grinding paste (maybe).
10. Have beer

Phew! Does all this sound sensible? Anybody have any good pointers or tips?
(...other than just go buy some! :p)

Any advice gratefully received!

Many thanks
Andy

cncadmin
04-27-2005, 11:47 AM
Try a spad bit, that will rough out the hole, and than you can finish up boring it to your finished size.

10bulls
04-27-2005, 12:00 PM
I did that (22mm in aluminium) when making (anti-play?) bearing blocks for the ends of my lead screws. My head still hasn't stopped spinning from fumes of all the WD40 I sprayed on it in the process! ;)
I was hoping to do something a little bit more precise this time. These are for the Z axis of my router.
However I reserve the right to go into 'bodge' mode when it comes to it! :D

Mcgyver
04-27-2005, 12:02 PM
bunch o stuff to think about - this is a straight forward job that you may be making too complicated (although drilling some types of bronze can test your mettle)

easiest way is to hold the stock in the 3 jaw. Yes, the three does not hold things perfectly centred, but that’s irrelevant because we’re going to, without disturbing the work in the chuck, turn the od, drill out in progressive steps using the tailstock and finish with a boring bar. Finishing with the boring bar is very important - a drill is removes metal but does not produce either a round hole, a concentric hole, and accurately dimensioned hole or a straight hole. If the od is already at the dim you need, then either hold it in a collet or centre as described in the 4 jaw and then follow above finishing with the boring bar

By turning the od and id with single point tools at one set up you've ensured they are concentric and straight. finally, part off and then face to length - it doesn't matter that you've removed the stock for this step, you are only facing now so concentricity is not an issue

DO NOT use grinding lapping or any other kind of abrasive paste on bronze/brass etc. The abrasive particles become embedded in the bronze and instead of a bearing you’ve made a lap

One more thing, if you are working with cast bearing stick (not sure if its cast or forged), cut the od first as this stuff is full of stresses and will feel likes its trying to clamp down on the drill bit

I don't really follow what you were doing with the clearance holes - did i miss something?

10bulls
04-27-2005, 05:43 PM
Thanks heaps for all that good advice Mcgyver. You've save me heaps of time and headaches! Didn't think about the lap...I know it does that in aluminium...didn't think bronze was the same.

Sorry, I didn't explain the clearance holes well. I have seen bushings with grooves cut into the inner surface (parallel to the rod). I presume they are there to reduce the friction of the bushing on the rod whilst preserving a snug fit. I think I'll do without them and see how it goes.

Thanks again!