just like you say ..

if deep then probably Screwcut . if very shallow( and left hand)..done by rapid withdrawal without lifting tool off work

Ronan,

Some years ago when helping a friend rebuild a vintage bike we came across the same problem. How to put the figure of "8" oil grooves inside a bronze bearing.

I think they would have done this on an hydraulic copy lathe of sorts.

We managed to replicate it quite well but it meant heavily modifiying a little Unimat lathe. We removed the leads screw so that the carriage could be push up and down by hand. We cut a piece of tin plate to wrap round the chuck, which was cut like a sine wave, so it acted like a cam, a piece of steel bar with a little roller bearing on the end was clamped to the sadddle to act as a follower. The top slide held an internal grooving tool. Slowly turning the lathe by hand with a little crank handle in the spindle, the saddle could be made to follow the cam and the cut gradually put on with the top slide. After the first half of the figure of 8 is cut the "cam" was moved around 180 deg and the second half cut.

Hope that makes some sense. Barry

Edited By Saxalby on 16/10/2013 00:43:07

Used to cut figure 8 grooves and similar inside bushes with a small chisel with rounded end. the bushes were bigger than usual model eng. ,about 1" to 2" dia. but could be done.

.

Ronan,

Quote: On BSA bantam fork bushes, i notice that they are a flat piece of material folded around a circular former

It was almost exactly 50 years ago that my Dad helped me refurbish the forks on my D1.

We very carefully measured the wear, then removed the bushes and re-fitted with a suitable shim on the outside of the bush. This closed-up the bore, and all was good !!

I think this was a trick they developed when he was working on Spitfires, out in India during WWII.

MichaelG.

The shape of the oil groove isn't critical so couldn't you cut a straight axial groove instead? You could do that in the same way as cutting a keyway with a suitably shaped tool.

Russell.

That’s astonishing, Bruce … in so many ways

Thanks for the link.

MichaelG.

Fascinating video Bruce – just shows how a bit if thought and some quick welding can solve a multitude of problems!

We did compete, but then we got civilised. Go back in 100 years and they'll be asking the same question.

Regards Ian.

Edited By Circlip on 27/12/2022 11:39:15

FWIW Steel backed shell, bearings, and bushes all start life as a huge roll of steel onto which the, for want of a better word, "white metal" bearing material has been bonded by immense pressure..

Having been sheared to the required size, the embryo bearing shell is wrapped, (pressed ) and broached.followed by the oil grooves being machined in, before the anti rotation tang is formed.

(Any swarf is collected, and recycled )

The suggestion to produce helical oil groove ( s ) by slowly withdrawing the tool as the chuck slowly rotates is the method that i would use. Preferably before final boring to finished size.

Ideally the groove stops short of the edge of the bearing, to retain oil.

The depth of the groove is probably not that vital., since in a non pressure fed bearing, the oil provides boundary lubrication, because the oil molecules are smaller than the depth of the groove, and distribute themselves along the groove.

On a pressure fed "white metal" steel backed bearing, the clearance between shaft and bearing will be about 1/1000 of the journal diameter. The clearance provides for an oil flow to act as a coolant to keep bearing temperatures where the bearing overlay material does not start separating into it's constituents.

In a less highly loaded, and non pressure fed bearing, the clearances may be a little less (Again, boundary lubrication ) to minimise the impact loads from irregular loading.

Where the bearing is a thick wall, bearing (Such as metalled in the rod or crankcase ) the clearances are likely to be closer, because of the lack of support provided by the steel backing..

Howard.

My firm used to make large quantities of bushes for aircraft with beautiful internal grooves down to 1/2" bore on CNC machines. The last time I wanted a groove, I used a dremel, the oil will flow even in a shallow groove.

A device for cutting grooves in bushes is nothing new. Please see page 455 (462 of the pdf file) here:

https://archive.org/download/ladesignconstru00perrgoog/ladesignconstru00perrgoog.pdf

Note that this book was first published in 1907.

Edit: turn over a couple of pages above and there is an idea for the person asking on another thread here about turning a crankshaft.

Edited By DC31k on 27/12/2022 20:15:56