lignum vitie bearings

I am building a small ic open crank engine.The bearings for the cam shaft should be oilite bushes but I am having difficulty in finding the right size.I have read that machining a oilite bush would seal its pores and make it useless so i was wondering if lignum bearings would be any use as plain bronze bearings would be difficult to oil once fitted.I cut to size lignum for bearings for an agricultural engineer who uses these bearings in large food mixers and would like the opinion of members on this issue of useing them in this situation .The shaft is .250" and outside of the oilite is .313".

Frank

Try it and see!

I agree with Clive, what is there to lose? Lignum is used as self lubricating bearings in ship prop shafts I believe so it may do the job here. Is there no way to get oil to a plain bearing at all? And if not arc eurotrade do bearings down to well below that shaft size.

You can in fact machine oilite bearings, there are articles on the recommendations for doing this if you google.

Yes you can run the risk of burnishishing the pores but if you stick to guide lines this means fine point boring to size ( not reaming ) with a very sharp small boring tool running at a surface speed ( from memory ) of around 150-200 metres/min.

Reamers will burnish the pores

I'm not sure if machining (if done with sharp tool etc) does actually negate the Oilite properties but if you are only machining the OD it matters not a jot!

Once the bush is pressed into a bore the external pores are blocked anyway.

Maybe I misinterpreted Clive, but Lignum Vitae is wood, so turning a such thin walled bush might be good fun. Anyway, if oiling is difficult to access, how were you going to lubricate a Lignum bearing?

Ian P

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Lignum vitae is 'self lubricating'

The nearest 'engineered' equivalents might be PTFE or igus drylin

MichaelG.

It's not really self lubricating, it's really tough and hard but also flexible to shock loading and resistant to sea water which lubricates the bearing in a sternshaft

Organic bronze kind of thing

Would still need a lubricant to perform at its best

The bearing longevity in a food mixer would be helped by any goo from the food product instead of sea water, plus it washes out easily, no issues with the bearing and water and cleaning water lubricates that point too

Edited By Ady1 on 02/03/2018 09:05:57

+1 for Ian's comments - As a woodturner, the idea of eaving only 0.031" walls in an LV bearing would be a real challenge IMHO. You'd need no short grain at all in your piece of LV.

I'd either make the hole for the bearing bigger in which case you'll find oilite might fit after all or opt for a lube-less bearing material that's easier to turn thin like PTFE.

Jon

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Hence my use of quotation marks around the term

Those with an interest can find what further detail they need.

John Harrison used it in his clocks because, for that purpose, it needed no applied lubricant..

MichaelG.

Edited By Michael Gilligan on 02/03/2018 09:01:07

The only trouble is that Lignum Vitae bearing are self lubricating when they are in water. I look after a water Turbine at a local museum, and if the Lignum Vitae bearing drys out it siezes to the shaft. I then have to undo the adjusting screws, and give the 4 wooden blocks a whack with a hammer, do the adjusting screws up and get some water into the turbine. Once its up and running again, the bearings can be tightened a little. Takes about 10 minutes, but had me worried the first time.

22 years ago, when we first propposed setting up the museum, the turbine was stuck, not knowing anything about it we decided to strip it and rebuild it, there were some other problems, so just as well.

The bearing is mounted in the thing with 4 legs at the base of the ladder. the bearing is in the form of 4 x 2" x 4" x 6" blocks.

Ian S C

Edited By Ian S C on 02/03/2018 09:12:16

The fit and forget stuff that springs to mind for me is vesconite

Edited By Ady1 on 02/03/2018 09:19:37

A food mixer bearing doing low hundreds of RPM could be very different from a miniature engine that might be doing tens of thousands.

Your wall will only be 1/32" or about 0,8mm thick. Lignum probably doesn't conduct heat well. Where's it gonna go?

Try lignum by all means, but I'd consider machining the oilite with a sharp tool, as some have suggested.

Frank, Simply Bearings carry Oilite bushes .25" x .375" in various lengths see *** LINK ***  shouldn't be too difficult to turn down the OD.

John

Edit: Typo

Edited By Journeyman on 02/03/2018 09:48:14

I would have made the walls thicker if I used it but with the information received I will look to getting a bush near to size and machine to fit.Thanks for all the help.

Frank

Until Frank returns to this thread it pointless speculating and suggesting possible solutions to a shaft bearing that is difficult to lubricate.

It's a 1/4" diameter shaft so modifying a standard 1/4" bore oilite bush should not be a problem.

Its an IC engine so temperatures could be relatively high, also as its a camshaft the bearing needs to be non deformable to ensure tappet clearances are maintained so PTFE is far from ideal.

IGUS have a wide range of materials and even wider range of technical documents but I doubt they would recommend one of their polymer bushes for a camshaft in an IC engine.

Ian P

deleted

Edited By Hopper on 02/03/2018 11:21:36

Here are Oilite's recommendations for machining their bushes:

oilite.com/Best-Machining-Practices

Neil

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Likewise Ian

My point was not that these plastics would be suitable for the engine, but that they are reasonably equivalent to Lignum vitae.

MichaelG.

If IPM, for the feed rate, means inches per minute, I reckon someone needs to proof read before putting things on the internet!

Two to six thou per minute does seem a little conservative
I suspect they meant .002" to .006" per revolution!