Ali-Bronze

HI,

I'm getting a hot air engine base plate and flywheel cast by a (relatively) local firm. They've offered me what I believe to be a good price to do the base in Aluminium and the flywheel in ali-bronze. The latter is in order to get a decent weight into the flywheel.

I'd be grateful for advice on whether there are any particular diffficulties with machining and drilling the flywheel that you can envisage.

Grateful for all and any advice.

All the best.

Peter

Some useful notes on Machinability, here: **LINK**

https://www.pentaprecision.co.uk/services/bronze-machining/aluminium-bronze-machining

MichaelG.

Hi Peter I wouldn't make a flywheel out of aluminium/bronze as it is lighter than bronze or brass or even cast iron. I would think any of the other materials would be preferable especialy the machining difficulty.

David

The Link confirms what I have experienced in the distant past, I was given some aluminium/bronze to make some 2stroke cylinder head buttons that were threaded and finished in a tapered end to seal the gasses in.
In aluminium this tapered face would be pushed down into the combustion chamber with constant plug changes, the al/bronze held up to the job for a much longer period.

Emgee

Edited By Emgee on 26/02/2021 18:20:05

Peter

A few years ago I posted a similar question about Auminium Bronze and followed up with my experiences after doing the job.

Tuning and drilling was was not difficult but you knew in was hard. Remember it is a Bronze so any tool or drill has to have a minimal or no top rake. Tapping, 6BA, was a completely different matter. The tap would cut OK but on withdrawing the Aluminium Bronze would not release the tap. It was grossly unpleasent and frightening.

I agree with David about its suitability.

JA

The most appropriate material for such an engine's flywheel is cast-iron, but if a solid disc-type rather than finely-spoked, mild-steel would work well, be easy to machine and probably cheaper.

I made a manifold for the tank plumbing on a locomotive, using what someone later identified as probably aluminium-bronze. The external turning was not too bad, but it was a nightmare to drill and almost impossible to silver-solder.

I recently completed some motorcycle rear brake peddles in Aluminium Bronze. The choice of materiel was to allow the peddle to bend if the bike was dropped. Cast iron peddles tend to snap. Machining to turn or mill was OK. Drilling/tapping/reaming was a bitch. Like a lot of bronzes it can tend to snatch when drilling.

Should be ok in ali bronze. Heavy enough for a model flywheel and will allow those nice cast spokes. Just machine it at a bit slower speed than for other bronzes and to minimise drill grabbing, grind or stone a small flat on each cutting edge of the bit to give zero rake as you do for brass. To make tapping easier if needed, drill the tapping hole a bit oversize, a la Tubal Cain's suggestions in his Model Engineer's Handbook. If reaming, drill first to about 5 thou under final reaming size. It won't be as easy peasy as machining brass or even leaded bronze but completely do-able with suitable care.

Another alternative if you are getting the other bit cast in ali is get the flywheel cast in ali and turn up a steel rim that can be shrink fitted onto the machined down ali centre section. This will put a bit of weight at the outside diameter where it will do the most good.

Edited By Hopper on 27/02/2021 09:03:13

Machining to turn or mill was OK. Drilling/tapping/reaming was a bitch. Like a lot of bronzes it can tend to snatch when drilling.

Thanks, Chris. I have about 40 small holes to drill and some of those to tap. Nearly all less than 3mm, most more than 2mm. 5mm deep, max.

Any recommendations/tips for doing the job, please?

After my adventures tapping 6BA holes, there were only six, I thought about what I would do next time. The only thing I could come up with was to heat the item, lets say to about 180C, before releasing the tap. Time consuming to say the least. That is why I never want to see the material again.

By the way, I managed not to break any taps.

JA

Well thats given me something to think about. Other materials are possible, but it is the heavier material choice that came up in discussion. The original instructions merely suggest a zinc based alloy, but the foundry have little call for such and so proposed the bronze.

I'll let you know how I get on.

Many thanks.

I was tapping 1/4" x 26 tpi for grease nipples. Ended up grinding up the tap flutes to make the tap really sharp. This stopped the tap binding on withdrawal. A 5/8" reamer that had previously cut a bit oversize left a tight hole and bound up on withdrawal enough to release the Morse taper.

Go for brass for the flywheel ! Noel

Depends on what else they have available. Cast iron or brass would be fine too and both easier to machine. You are lucky these days to find a foundry that will give you the time of day on small jobs. Lucky to find a foundry at all most places today. Let us know how it works out for you.

Edited By Hopper on 28/02/2021 12:24:05

Edited By Hopper on 28/02/2021 12:24:34