bronzes?

Leaded bronze. In fact, sae 660 would be best for your situation. If you are using a steel shaft. But it would be best if you could figure a way to provide at least a little lube. Perhaps some MdS grease. One thing that the 660 bronze will do is allow small particles to imbed completely. These particles then end up under the surface. 660 will not allow much imbedding compared to babbit, which is excellent in this regard. The phosphor bronze will not allow the particles to completely imbed. This leads to having the bearing surface become abrasive. You can also use sintered bronze. This bronze is filled with

Peter,

Depends on a lot of things. linear or axial motion, type of contact material, operating temp, side loads, etc, etc, etc,

Mark

If you're talking about leaded phosphor bronze as opposed to phosphor bronze, the difference is night and day. Leaded is the best material there is to machine, bar none. Without the lead, it becomes somewhat ugly. Needless to say, the leaded phosphor bronze would make a far better bearing than would phosphor bronze.

Harold

Have you thought of using a glass filled PTFE bushing instead of the bronze? They stand up to unlubricated operations pretty well.

Tom

Actually, I think UHMW Polyethylene would be a better choice than PTFE. While PTFE does have a lower coefficient of friction, it is fairly soft and therefore does not wear well (low abrasion resistance). UHMW Polyethylene, on the other hand, has a coefficient of friction close to that of PTFE, but is much harder and more durable; UHMW Polyethylene will outperform PTFE in abrasion resistance by a ratio of 30 to 1. UHMW Polyethylene is also considerably less expensive than PTFE.

- Michael

Good point about the price. Glass filled PTFE is expensive. I've found that the glass filled stuff is pretty good,as it stands up to higher temperatures than the UHMW PE. the PE is also better if the bushing gets wet as PTFE absorbs moisture and swells a lot more than PE.

Tom

Any comment on how appropriate UHMW would be for a cross feed nut bushing in a lathe? I have a 12" clausing for which I'm going to be turning a new cross feed screw (the old one has sharp! acme threads in the center (like you could literally cut yourself)). I'm guessing that if the screw is that worn, that probably I'll be doing a nut as well. It had occurred to me that boring out the old nut and sleeving with UHMW or delrin might be a good idea.

Comments?

Adam Smith Midland, ON

occurred

Personally, I wouldn't use anything less than a good (leaded) bronze. I'd be concerned with the materials ability to accept loads, such as when roughing, or when knurling. Should you end up using anything else, it would be interesting to hear how it turned out, although the real test would take years.

Harold

Adam, Uhmw will cold flow under pressure. It really is too soft for the cross slide nut. Delrin would be better. But bronze would be the best. ERS

Actually I'm pretty sure that a new bronze nut would be quite a bit easier to do. My reason for going with the low friction sleeve would have more to do with achieving a bit of a force fit on the screw, reducing backlash. If I become convinced that UHMW < bronze I'll go bronze. Quality is the only motivation here, not ease of task, or lower cost.

Thanks for your comment,

Adam Smith Midland, ON

Ok, that clinches it. Bronze it is.

Cold flow and deflection under load were my concerns.

Thanks,

Adam Smith Midland, ON

Have you priced a new nut and screw?

It would be easier to answer your question if you'd not mix and confuse your terminology. What are you proposing: making a bushing (to support the cross feed lead screw) or making a nut (to translate the rotation motion of the cross feed lead screw into linear motion for the cross slide)?

If you're asking about the nut, then I would not make that from UHMW, as it must unyieldingly -- and accurately -- resist the horizontal load vector of any cutting operations performed on the cross slide.

- Michael

Unavailable the last time I checked, but that was a while back. I'll probably have another go before I get too far launched on building them.

You can split the bronze nut. Then, tap a hole that runs parallel to the nut axis. Counter drill this hole to where the split is. Then, tightening a screw will pull the nut together and achieve a tighter fit on the thread. ERS

Which Clausing is it? I've bought the leadscrew and nut for my

But I've also just gone through buying a particular gear (the one which loses teeth if the threading hits an immovable stop) again. The price for the latest batch is about twice what it used to be. It looks the same, but they are having to go to new people to do the casting (and presumably the machining), so the cost has gone up correspondingly. (Now about $179.00 for the dual gear used between the tumbler gears and the sliding gear for 4:1 reduction.) Time to try to repair the old gears before this happens *again*. Back when it was about $79.00, it was a bit more acceptable to a hobbist. :-) I've got the tooth form milling cutters, so I should be able to re-cut after either brazing to build up where the material was lost, or to turn off all the teeth, put on a turned rim, and cut a full set of new teeth.

Enjoy, DoN.

What?! Now tell that to all the guys that say parts are still available for old american iron.

I've been thinking about this problem of losing gear teeth when something jams. I'm thinking that there should be a sacrificial element in the gear train, such as a shear pin or a shear key. Or maybe a slip clutch.

I posted this to the Atlas mill Yahoo group and got a link to a slip clutch from Small Parts. It was $52, but the real problem was/is knowing how much torque you need to transmit without slipping. If you bought one, fitted it, and it slipped even under normal operations, that would be annoying.

You need to know the torque needed with a shear pin/key, too. Even if I wanted to experiment, I don't want to risk gear teeth finding out.

What one needs to be able to do is measure the torque while doing a normal operation. One way I can think of is to drive the feed screw with a separate motor and measure the reaction force on it. I'd like it to be easier than that.

If you knew the torque you needed, you could do destructive bench testing on various shear pins/keys to determine what would work.

I just bought Al A's Jet 1024 and after hearing how hard it is to get gears for it, I'm even more interested in protecting to gear train.

Anybody ever do this? Bob

Sometimes factory replacement parts are not..however work arounds are readily available. Shrug...

Gunner

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