Bronze bushing

Hello

I'm needing to make bronze bushing for the brake camshafts on my Austin Seven project. For those not familiar, the bush carries the stem of the shaft through the brake backplate from the brake actuating cam itself to the operating lever.

The bushing needs to be about 26mm long, 13-ish mm O/D for a push fit in the back plate with a bore of 11mm.

I've got the stock set up in the lathe with a 10.5mm drill in the tailstock drill chuck. (The plan is to reamer to 11mm when the axle is attached to the chassis).

However, the drill is making painfully slow headway and repeatedly snatching in the bore.

I think this is because I haven't 'backed-off' or blunted the lips on the drill (didn't want to spoil a drill!). Would that be the likely cause of the problem?

As always many thanks in advance for a view/advice.

Martyn

Hi Martyn

Yes. Seems to me you know what the problem is, I always use "backed-off" or blunted drills on brass/bronze.

Thor

I would use a four jaw independent chuck for a thin walled bush, and bore it to finished size. You need a couple of thou clearance when in use in the car, no reaming needed.

I believe the brake cam bushes are usually self lubricating Oilite.

If the bushes were Oilite, the drill would not have any difficulty, it drills very easily.

My point was that in an Austin Seven the bushes were usally Oilite, so the OP might want to consider his choice of material, or maybe I have misconstrued Old Mart's post. Either way Oilite might be a better/easier route for both machining and operation.

Edited By Colin Wilks on 25/10/2019 19:41:59

Edited By Colin Wilks on 25/10/2019 19:42:35

Martyn,

You might want to consider that the originals were undoubtedly to Imperial measurements, not metric, so 1" x 7/16" IDx 1/2" OD? Nearest I can find to these dimensions is:

Oilite bearing

John

Edited By John Hinkley on 25/10/2019 19:49:57

Confess I coughed when I saw metric measurements! I hesitate to put this link up as the whole point is to make it yourself. I have no connection with the company, other than as a customer.

**LINK**

Many thanks everyone.

Yes...they were Oilite originally. I bought the Oilite replacements from the site Colin mentions of whom I am also a satisfied customer. But on this occasion the bushes were a mile too big. I baulked at making a tapered mandrel to hold them to try to turn them down largely because I'm not good with tapers. Hence I decided to make new ones.

Yes also...they were Imperial originally, but I always work in metric because I find it 100(!) times easier and logical.

Finally, the 'Oilite' bushes I got from the supplier had a lubrication hole halfway along! Struck me as a bit odd as there's no provision on the back plate for an oil/grease nipple and my understanding was Oilite bearings were permanently pre-lubricated?

Thanks again and a tres bonne weekend from la belle France!

Martyn

Oilite bushed are usually over size and need to be pressed in which will make the bore the correct size

Yes, in theory, Jason. But this is an old car, and will have been messed with by several past owners, many of whom had no knowledge, no tools and no money. So everything (yes everything) may be way off 'standard'.

Tim

Quite aware of that Tim, Used to have a 1928 Swallow.

Really depends what "miles too big" is. 2-3 thou would be about right for a standard 1/2" bush but they may supply oversize to go into a resized hole much like the oversize A7 king pins etc to take into account what previous owners have been upto. But would not have expected an undersize hole.

Can't remember what I did but know I made several bearings and bushes with smaller than standard bore to take into account wear on the parts or them needing a skim to get back to a decent surface. Similar with larger OD where the bush had worn the hole.

Edited By JasonB on 26/10/2019 18:44:05

Please do not machine the bores of Oilite bushes, because that will burnish the material, losing the porosity that is its primary characteristic.

Use gun-metal or buy an Oilite bush already to the correct bore. If you are going for metric, you can also buy thin-walled steel bushes with a PTFE lining, but I think these are made only in millimetre sizes.

An Oilite bush is vey likely to have an oil-hole. I don't know if they do come already soaked in oil, but that oil won't last forever!

Oilite is OK to machine with sharp tools like a CCGT insert or sharp HSS, it's reaming that smears the metal and mucks them up.

generally full of oil as you can see it ooze out as they are pressed in.

Ah, OK Jason, thank you for that advice.

Sharpness being the key to success here, presumably.

I'd taken my original point either from a model-engineering text-book or a stockist's catalogue. I still don't think I'd risk it if I could avoid it.