leadscrew babbit bearing alternative?

If it was me..and I wasnt going for authenticity, Id turn down the end of the screw, thread the last .375, and fabricate a thrustbearing mount, then put a smidge of preload on the screw using a nut on the end. Wont take much of a thrust bearing. Probably get away with a tapered roller bearing, though Id rather use a double angular contact bearing assembly. But thats just me. You could turn the screw, and stick in an oillite bronze bushing with a flip top oiler and do the job just fine.

Shrug, thinking about it..I think Id probably do the oilite bronze bearing, simply because of the cost and time making a thrust bearing housing. It wouldnt work any better than the bronze bearing.

Gunner

"What do you call someone in possesion of all the facts? Paranoid.-William Burroughs

jim rozen jim snipped-for-privacy@newsguy.com

I think you could use a modern bb-thrust bearing setup as a ready-made convenience, which I think was the original idea.

I think you could use either babbit pour or solid bronze insert. If you need adjustment, it could be done by scraping/shimming where the bearing housing attaches to the bed. In some of the old old lathes the feed rod (or combo feedrod/leadscrew) spun directly on the cast iron housing ID. This simple iron-on-iron shafting is found on many secondary bearings on older machinery (as well as machine tools). Frank Morrison

Chuckle..most every manufacturer uses a bronze bearing in a block simply dowel pinned to far right end of the lathe. So how hard could it be?

The reason I was thinking about the preloaded thrust bearing, is because Ive seen a number of older lathes with a bit of end play in the lead screw, largely due to wear of the collars inside the QC gearbox. A simple preload arraingment would pull that out of the equation, and be adjustable for further wear. Basicly, pulling the lead screw to the far right and holding it there. If one used a double angular contact bearing and put a nut on BOTH sides of the bearing block, it would remove any longitutnal strain on the aging QC gear box collars and hold the lead screw rigidly with no endplay. Adjusted with allowed endplay in the QC gearbox, the lead screw would still be held solidly on the far right end. Several lathes already have a similar arraingement, IRRC my Clausing/Colchester does, as well as the Cadillac line made in Taiwan. And of course many if not most CNC mills/lathes do that with ballscrews under tension, but for other reasons, mostly involving fast direction changes of heavy tables.

Gunner

"Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote!" -- Ben Franklin

Granted. I think SB clung to the historical methods simply "because that's how we always did it" and this may be one reason they went under. But I can imagine that they had it 'right' with their design for manufacturability as they say, pouring babbit in probably produced an acceptable bearing for less time spend in the factory. Angular contact ball bearings are way expensive how about as you say a simple tapered roller bearing setup. The biggest impediment to that would be the lead screw bracket has a fairly small diameter boss that actually holds the babbit - it's not much larger around than the leadscrew itself. One would have to fabricate some kind of housing to hold the bearings, it would be easiest to make this out of aluminum, from scratch, rather than trying to retrofit the iron casting.

The lead screw would be tighter, that's for sure. If one did this, it would be a nice idea to replace the halfnuts in the machine as well, to eliminate that source of slop.

Jim

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Right, like the Barnes that was topical here a week or so ago. Both ends of both lead screws run right on the iron castings of the bed.

I think one reason why modern lathes don't do this is not because of the bearing characteristics of steel on cast iron (which actually seems pretty good for this application at least) but rather the fact that quick change gearboxes tend to present the output shaft somewhat ouboard of the front bed surface.

From a manufacturing standpoint it's easier to bolt on the feedscrew stuff than to machine it in place.

Also any attempts at re-working the bed surfaces on lathes invariably involve changing the relative separation between the halfnut axis and the leadscrew axis. In more than one plane!

I would not want to have to attempt a re-scrape job on one of those barnes lathes.

Jim

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Not suprising, but this was not obvious to me. Is this a bonafide procedure or just another crafty machinists trick? While contemplating the tail end position I checked my books and low and behold not one reference to positioning the gear box or lead screw. I'm in trouble since I have the QC in pieces on the bench. Any tips, do I really lock the nuts and tighten up the QC housing adjusters too?

So you take I-70 to I-35 to Kansas HWY....

Thanks! C

Thanks Gunner, great ideas.

I am not familiar with the oilite bronze bearing process other than my guess of removing the babbit, or make some room, press the bronze and machine/ream to fit the shaft,,, or fabricate a new housing.

I hope I'm close.