No doubt someone with more competence on the matter will tell you more, but my experience shows that ali-ali pair does not work. There will be welding and galling pretty much at any power. However I think you can make one gear on aluminium and pair it harder or sofer material and you should be fine. Smaller gear is usually made out of stronger material.

There are may different grades of aluminium, fairly pure is not that strong and it's not nice to machine. Many more alloyed grades probably would offer success.

If you pair aluminium alloy with plastics, you ususally don't need any lubricant, which might be plus.

Pekka

I made an aluminium changewheel for my mini-lathe. It runs very happily with the standard nylon ones.

Neil

I repaired the small cog on my backgear on my Drummond Mseries over a year ago with T6 aluminium

It's done some pretty serious work over the period without any problems

Edited By Ady1 on 06/05/2012 00:11:06

Please be aware that as far as anodising goes, for maximum wear resistance "Hard Anodising" is normally specified as opposed to the normal decorative (coloured) anodising we see everywhere.

I have not seen it used for gears but I have used it for 16 mm static film guides with the film travelling through the guides at a very fast lick.(old engineering expression)

It has the drawback of increasing the component dimensions.

For example you can specify a thickness of up to 5-6 thou and this would result in a dimension growth of half this amount (i.e. 50% in and 50% out) and this would be taken into account at the design stage.

Also the finished coating is porous and non-conductive, in the dim distant past I have used it as an insulator on diode holders in Doppler Radar systems.

Most hard anodised components are subsequently sealed (closing the pores) and this sealer could be one of many things including lubricants, ptfe etc.

Whether or not Anodising companies nowadays are prepared to accept very small orders is debatable.

Clive,

There are other metals that can be anodised including Titanium and Zinc.

Len. P.

I don't see why aluminium wouldn't work, but one would have to choose the grade carefully. As far as I can see 7075 is about the same hardness as CZ120 brass, so should be ok, and machines well.

Ideally for a really hard and resistant finish one would use the Keronite process:

http://www.keronite.com/

But, as always, the problem would be actually getting it done.

Regards,

Andrew

All this talk of friction between the gears is confusing me. Perhaps I am missing something but as I understand it with correctly depthed cycloidal gears there is a rolling motion on the teeth and no rubbing so there can be very little friction. Any wear is caused by dirt? The only wheel with rubbing on the teeth should be the escape wheel.

In the 1720s John Harrison famously made a turret clock from oak with lignum vitae bearings and it is still running. I'm sure aluminium alloy should be more durable!

Russell.

Russell,

You are going into clock making ,good. The first thing you have to remember is FRICTION, friction, friction.

Forget all about the proper fits between gear wheels as given by calculating the PCDs etc fitting the gears is done by hand using a Geneva tool and make them a nice light fit. Back lash is never a problem. The pivots (shafts ) are a rattling good fit in their bearings . Remember clocks are very highly geared items. Ask yourself how many times will the thing beat in say 30 days and how many times the winding drum (or spring) will rotate in that time?

Aluminium can be intrinsically a very sticky metal, hard brasses used in clocks are not.

As a well known clock maker remarked “If it rattles it will run”.

Old John Harrison was a ‘downy old bird’. He knew the properties of lignum vitae. It is a very hard, dense and oily material. It was (and may be still is) used as part of the main of the thrust blocks which transfer the push of the propellers to the ships. Harrison’s lignum bearings make your aluminium seem like soft cheese and they are self lubricating.

Rdgs

Dick

I have a comercially made French three train wall clock from the 1930's that has aluminium plates and gear wheels along with the spring barrel as well.

The pinions are steel as per a normal brass wheeled clock, it still runs OK so obviously the use of aluminium is not as new as you might think.

Here's another one for you to think about. Have you decided to use cycloidal or involute teeth ?

I know of one local company (Sinclair Harding) that currently produces some remarkable clocks using involute gears, but there are also many people who will also tell you that they will never work in a clock.

Phil

Yes, quartz clocks and watches use involute gearing. This is because, with cycloidal gearing, you shouldn't let the pinion drive the wheel. The disadvantage though comes when you need small tooth counts on the pinions.

I agree about conservatism. Much of clockmaking practice has been derived from trial and error using what was available at the time. It still works well but could probably be improved using modern theory and technique.

Russell.