Cast iron bearing bushing?

[RainbowsParticipant @rainbows]

Now for something unrelated to that big lathe I keep spamming about.

I want to make a bearing that screws into its housing (22×1.5 thread) for a tapered shaft. It would have crenalations on the part facing towards but I messed up solidworks somehow so pretend those are there to help screw it in.

What materials are suitable for making this? Phosphor bronce seems the standard bearing material but is relatively expensive. I considered that cast iron stock is significantly cheaper and lathe spindles, assuming they are adequately oiled, seem to use cast iron housings for bearings with success.

[RainbowsParticipant @rainbows]

[Ady1Participant @ady1]

Cast Iron is good

Don't forget that babbit was used on 100 ton locomotives so it's no-bad

[JasonBModerator @jasonb]

From your other posts it seems you will be cutting both threads with taps and dies, it will be very difficult to get the accuracy and concentricity that will be needed to keep the bearing lined up in the tapped hole.

Also without some form of locking nut the bearing will be able to move in teh threaded hole as you will be unlikely to get 100% thread engagement. Also whats to stop it unscrewing?

Hollow cast bearing bronze will be a bit cheaper than solid but still same problems as above, though at about 1" dia and 1" long cost difference won't be worth worrying about.

[Paul LousickParticipant @paullousick59116]

 

My old 1950's Southbend lathe has cast iron bushes and is still running with no play in the spindle. Just has to be well lubricated.

The model of your bush is very thin at the end of the taper and looks like the thread almost breaks thru.

A thread is not good for maintaining concentricity.   Can you reduce the length of the thread and add a locating boss (slightly bigger than the thread OD) for locating the bush on centre ? Similar system used on a lathe spindle for locating a chuck or face plate.

A source of cheap cast iron is old sash window weights obtained from house building re-cycle outlets and scrap metal merchants for a few dollars each. Some are crap and no good but some are good cast iron after you remove the outer skin.

Paul.

Edited By Paul Lousick on 19/05/2016 09:13:32

[RainbowsParticipant @rainbows]

I was wondering if it need a locking nut or the thrust from the shaft working on the taper would keep in locked in place. Lock nut is the plan though. I thought by machining the thread relief to leave a dead flat face that might be enough to locate it but I will add in a locating boss in too.

And yeah after I cut the thread in the model I realized there's less than a mm of material at the end. Will have to make the taper shallower (just gotta hope I don't make a morse taper by accident).

Will keep a look out for sash weights on my travels. Don't think I have ever seen any before but on the other hand I was never looking. In the meantime 6" of 25mm cast iron is £5 from macc models (compared to £15 for Phos Bronze 😛 ).

[not done it yetParticipant @notdoneityet]

I'm not a metallurgist, but would think there are different 'grades' of CI – dependent on microstructure. Some cast iron items just use the cheapest material possible. Like dumbbells. Possibly scrap flywheels from old stationary engines might be different (not saying good, necessarily).

[Gordon WParticipant @gordonw]

For a job like this I would buy a bit of bar. Sash weights and similar might well be good stuff, but often have holes and inclusions. Often made with the left-over iron at the end of a pour.

[Ady1Participant @ady1]

A good source of decent quality cast iron is brake discs which would be buttons at a scrappie

[RainbowsParticipant @rainbows]

If only I had a cupola furnace to melt then into round bar

[JasonBModerator @jasonb]

Can't see how you would get the part shown out of a brake disc?

And with a suitable bit of CI costing £1.30 is it really worth inverting the time and effort into a bit of unknown scrap metal, for a job like this I would buy material of known parentage.

[John FieldingParticipant @johnfielding34086]

Good quality chill-cast iron is an excellent bearing surface and it is a relatively inexpensive material. The reason I and Doug Hewson advocate its use is that good CI has a lot of graphite within it and this is in itself and excellent lubricant when the oil supply is marginal. As someone already mentioned, many lathes ran the spindles in the CI without fancy bronze or babbit linings and they just go on and on if you remember a drop of oil occasionally.

As far as sash weights go, forget them. They are made from pig-iron, the lowest form of cast iron and they are really horrible to machine and contain all sorts of other muck in them. If you just want mass then thay are fine but for anything else I would not consider them. Chill cast continuously poured CI round bar is cheap, you can also get spun cast hollow tubes but these are harder to find. When making things like piston rings about 95% of the CI solid bar ends up in the lathe swarf tray as scrap! So in these cases hollow tube is less wasteful, depends on the diameter mostly.

Modern continuous cast iron round bar has an excellent surface if the foundry workers get it right. Some 35mm diameter bar I bought last week is almost good enough without skimming the outer surface, but the surface finish can vary a lot between batches. The spun cast variety is also much harder and longer wearing than normal cast round bar, but it machines beautifully with a carbide tool, just like chalk but the dust isn't as nice!

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