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Scale gearbox (or how I leaned to love aluminium)

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Steve Crow15/07/2021 19:14:51
283 forum posts
166 photos

This is a housing for a 1/12 scale Hewland gearbox to mate with an engine I'm making.


This is my first attempt at machining aluminium. I've drilled and tapped it in the past but that's it.

I really disliked the stuff and thought it was the Devil's metal but I wanted to keep this light as it's hanging off the rear of the engine so I bit the bullet (billet?).

It all went so much better than expected and I got a great finish.


I've rubbed down flat external areas but all curved and internal bits are straight from the lathe. It tapped nicely as well with a drop of WD40 which was just as well as I had 33 hole to do, nearly all M1.2.


It was made from a scrap of 1/12" x 5/8" bar 30mm long. It weighed 52g originally but it is 10.6g now.

I've just got to make a few more parts then I can drop in my differential.



Steve Crow15/07/2021 19:48:35
283 forum posts
166 photos

"It was made from a scrap of 1/12" x 5/8" bar 30mm long. It weighed 52g originally but it is 10.6g now."

Sorry, that should read 1 1/2".

Bob Mc15/07/2021 21:03:55
190 forum posts
17 photos

Thats a lovely piece of machining Steve, would be interesting to know how you held it in the lathe... also is the differential a bought in item it looks very well made..


Jon Lawes15/07/2021 21:07:47
635 forum posts

What a lovely bit of engineering! Now my next question is, can we see the rest of it!

Bill Pudney15/07/2021 23:10:29
559 forum posts
24 photos

Really nice work!!

The machinability of Aluminium is almost completely dependent on the grade and the temper. For instance pure aluminium in its' annealed state machines horribly, whereas some of the higher grades machine beautifully in the harder tempers. Where I used to work we did a comparison of machinability, the results could be summarised more or less as.........

Anything bought in a hardware shop is unlikely to machine well

Any Al Alloy grade 6061, 2011, 2024, 7075 machines well at temper T6 and better

Any Al Alloy grade 6061, 2011, 2024, 7075 machines poorly at T0

The preferred material was 6061 T651, it was cheap and available

For higher strength applications 7075 T651 was appropriate

It should be noted that the temper of the material is extremely important.

"T0" indicates that the material is annealed

"T6" indicates that the material has been tempered, the trailing "--51" indicates that the material has been stress relieved, stress relieving is a good thing.

In all cases a coolant should be used, WD40 is o.k., but kerosene (paraffin) is better. Really sharp cutters are recommended.

I understand that these material and temper specs may not mean much in the UK. They are internationally recognised though, so maybe a google search for Al Alloy equivalents may help

hope this helps



Martin Connelly16/07/2021 08:21:58
1844 forum posts
195 photos

I was making a couple of spacers on Tuesday. Nothing clever, just needed to have an M10 thread in the centre and be made of aluminium/aluminium alloy. I had a couple of slugs that had come out of the middle of Rotabroach cutters so drilled, tapped and faced one end. Put them on a piece of M10 stud machined faces together and held that to turn the outside down to the required diameter. One piece machined ok and the other machined beautifully. Dull finish on one and polished finish on the other. This was with them both being machined in one setup so no difference in any parameter apart from the material. A perfect example of what Bill is pointing out. I think one slug was from a piece of plate and the other from some bar stock.

Martin C

JasonB16/07/2021 09:07:36
21284 forum posts
2416 photos
1 articles

6082 (HE30) and 2014 (HE15) are the ones that are the closest to Bill's codes and easily available in the UK.

Nice job on the gearbox, it's also good stuff to carve crankcases from.

Edited By JasonB on 16/07/2021 09:08:51

Edited By JasonB on 16/07/2021 09:57:47

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