I used to manufacture an aluminum valve that had a polished bore. I mounted a small permanently-lubricated ball-bearing assembly (sealed both sides) on a stiff rod and clamped that in the lathe turret, and clamped the valve body in the chuck. Spun the body and fed the bearing slowly into the bore using power feed and some pressure, and got a usable surface. I got the best finish when I had ground the bearing's outer race to a barrel shape, and polished that. Minimum bore size will be limited by the bearing OD, of course, and for smaller holes there are proper roller-burnishing tools available. They cost plenty, and only fit given sizes.
On a related subject I was making a cross slide stop for my Southbend lathe
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materials at hand where a salvaged chunk of cast iron (broken Record vice) and some string trimmer shafting. BTW - string trimmer shafting is high quality, precision machined carbon steel more or less equal to drill rod - NEVER THROW IT OUT and if you come accross some - grab it. I wanted a hole (actually two) drilled in the cast iron that would give a sliding, no shake fit for the shafting. I forget which number drill gave the loose fit but the next smaller size was a somewhat too tight fit - light press? I drilled the smaller size and then used a length of the shafting in this manner. I chucked it in the lathe and applied a vibrating engraver to the rotating shaft. Then I chucked the (now modified with vibrator warts) shaft in my drill press and jammed that through the undersized hole in the cast iron - rerady for disaster that never came. The result was a *perfect fit*. Pushing the shaft through the hole felt like pushing against a well tuned dashpot (and still does after several years of use).
A buddy, and my maching guru came by later that day for a rum and coke session. I dragged him down to the shop to show off my latest triumph. As soon as I said "no shake" he got that "total BS" look in his eye and grabbed the protuding shaft. Try as he might he could not detect *any* play! This guy had forgotten more about machining than I will *ever* learn. Essentially, I guess, I sort of 'burnished' that hole.
I can visualize you forcing the bearings into the hole and the outer race of the bearings picking up the same RPM from the hole as the two meet. So the relative positions of the bearing race and the hole remain constant throughout the push and withdrawal. Now, if my understanding of what you are doing is correct, then is there any particular advantage drawn from having the chuck rotating? The operation appears not unlike swaging a barrel.
The impression that I got was that the OD of the bearing was smaller than the ID of the bore, so it rolled around the bore as the workpiece rotated. (The "some pressure" would be pressure of the roller against the side wall of the bore, not axial pressure. Thus, it became a form of roller burnishing tool. Not as stiff as one with three rollers pressing into the bore at 120 degree spacing, but for a soft workpiece material, it should suffice.
Ned Simmons wrote in news: snipped-for-privacy@news.suscom-maine.net:
I stand corrected. I did a quick search and found the ones on page 3404. You would think that there would be more of a price difference between the two. I guess since 52100 is used for bearings, the quantities they are made in offsets the price for the extra precision.
I haven't visited the newsgroup in quite a while, and you have probably already finished your project but here is how I would do it.
I would use the same basic procedures that are used in making a custom rifle barrel. First drill the hole undersize, ream and polish for a good finish leaving the hole slightly undersize. Then silver solder a button (ball bearing) to the end of a rod that is smaller than the hole size. Using a good high pressure lubricant such a moly powder, or even anti-seize compound that contains a fair amount of copper I would push/pull the button through the barrel. Doing this with the hole about 0.005" undersize to start with should leave a good finish.
Clean the inside to remove the moly or copper with a good penetrating oil (such as Kroil) and very mild soft abrasive such as "J-B Bore Compound". This is what is used by some shooters to clean the moly and brass from their rifle barrels, without causing any extra wear. The J-B is a soft vegetable based abrasive and will not remove any steel.
Thanks, project still in progress....it seems that alot of these methods require making things a "normal" size...I gueass that's the key. If you wander out of "normal" you enter tha land of cutom tooling (cutum reamers....yikes).
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