Why Brass??

I'm considering making my first clock. As a result, I wondered "why brass"?? Back in the days of yore there wouldn't have been too much choice, so the use of brass was fairly obvious, but these days, at least I would question it.

Why not a hard grade of aluminium alloy for instance, for instance 7075 T6, it machines beautifully, doesn't corrode much more, if any more than brass, and is fairly readily available, finally, it doesn't need a second set of cutting tools, at least for me.

Are there any reasons apart from convention? Convention and appearance are very subjective in my book and therefore are not valid reasons!

cheers

Bill

One significant difference comparing brass to aluminum for clocks would be the difference in coefficient of thermal expansion. For brass this coefficient can vary from 17.8 to 19.4 x 10 ^^-6 metre per metre K, and for aluminum it can vary from 21 to 24 x 10 ^^-6 metre per metre K. Not a huge difference but with wide ambient temperature swings it could affect wheel pitch diameters on large wheels, and centre to centre distances in plates, quite significantly.

Just for interest Invar 36 is one metal which can be obtained at some metal suppliers to aviation and has a very low coeff of thermal expansion of about 1.5 x 10^^-6 metre / metre K. However it is expensive and far more difficult to work with than brass or aluminum. It machines similar to stainless steel. No real need to use it in clocks unless you are chasing the last microsecond per decade of timing accuracy. It would however be handy for pendulum rods as it will be stable in length all year anywhere in the world, more so than most any other metal.

Running steel arbours directly in aluminum would not work well either, there would likely be high friction and wear. However aluminum plates could easily be bushed with bronze or brass bushings to reduce friction and wear.

Just food for thought, my $0.02 worth. Your mileage may vary. The above offered as a metals discussion only, I'm not a clock builder. JD

I have a 1930's French wall clock that has an all aluminium movement, I have often wondered why it was not more common as well.

Phil

Brass is prettier

Hmmm, interesting. I wondered about the temperature change scenario. Surely if the wheels and frames were made from the same material, then the relative clearances between the active faces of the wheels would stay the same?? That is the wheels would expand at the same rate that the frames expand, so the clearances would stay the same. In any event the difference between the expansion of a 65mm CZ120 brass wheel and a 7075 al.alloy wheel is something like 0.008mm, with the al.alloy wheel expanding more, obviously. Up here in South Australia the temperature rarely drops below 10 degrees C, and hardly ever goes over 50 degrees C, so I used a temp range of 40 degrees.

My suggestion of aluminium was/is because that's my preference and what I'm most familiar with. Also considered were Titanium (!!), free cutting steel and Invar but Invar was very soon discounted on the grounds of cost and availability. Titanium would be really interesting as with the right tools it cuts well and doesn't corrode. However again cost and availabilty were against it. My concerns with steel were that it corrodes, so would have to been treated in some way and it would always look like something out of a shipyard. Not that there's anything wrong with that, I spent some of my best years involved with shipyards, but not on the mantlepiece!!

Neill, "brass is prettier" doesn't count!!

cheers

Bill

Carbon Fibre perhaps, for that modern look? ...or an aluminium/brass alloy, if there is such a thing.

Ed.

Titanium TiAl6V4 cuts very well with usual tooling as long as these are sharp.

Surface finish is like a ground one, with satine touch on it. It is far easier to get beautiful finish on titanium than on carbon steel BDMS type. Threads made of titanium are working smoothly, and their surface is a spotless one.

Due to rather poor thermal conductivity deep cuts are not advisable if good cooling is not available. Overheated turnings can catch fire.

Turnings can be burned, they produce brilliant white light. My wife is a customer for these. Whenever I turn titanium, she will collect all of them, make some kind of bundle, set it alight and observe how white flame is travelling along wires.

Martin

I don't know but that shouldn't stop me having an opinion on the internet.

Wheels of brass, pinions of steel. I think an important aspect to consider is the interaction of the two different materials. My suspicion is that steel/brass is lower friction and more wear resistant than aluminium/steel and my trivial reading of tables of coefficient of friction support my cognitive dissidence. Standard practice for most clocks (that are open it the air) is not to lubricate the steel/brass interface - I think this is because the oil captures abrasive dust and increases wear.

Not to say components shouldn't be made of aluminum though. I think Burgess Clock B uses duraluminium for the big wheels and there isn't a better mechanical timekeeper. Not sure about pinions. Invar is used for the suspension spring and was tricky to work - I'd guess it isn't easy to use for pinions or wheels.

I think steel is difficult to beat largely because of its heat treat characteristics.

Edited By jaCK Hobson on 24/03/2018 09:34:19

How about anodising the plates/wheels after making, would increase hardness of bearing faces in the holes and you could have it any colour you like (As you can probably tell I have never made a clock)

John

Edit: Typo

Edited By Journeyman on 24/03/2018 09:33:51

I know nothing as well! But those clever clockmakers don't use any old brass that happens to be lying in the gutter:

• CZ108 for general purpose metal work. (Easy to bend and form)
• CZ101 for bells
• CZ106 for parts made by spinning
• CZ120 for the works - free-cutting

Brass is my favourite metal. Although not the strongest Brass is a good all rounder for many jobs in my workshop. I find it biddable; it cuts more easily than steel and is harder than aluminium. It can be plated, soldered and brazed. It provides a reasonable bearing against steel. Copper, Tin, Gold and Pewter are all too soft. Cast iron too brittle. Wrought iron full of fibre and takes a poor finish. Pure iron is soft and corrodes easily. Magnesium might catch fire when you turn it. Bronze is expensive and harder to work. Silver would be good but it's expensive.

Another advantage is that Brass is attractive; it takes a good finish and resists corrosion. When it does corrode it does so gracefully. Steel rusts badly, brass develops patina.

Modern clocks are different. My wristwatch contains no brass at all. It's made of stainless steel, several different plastics, titanium, copper, lithium, quartz, and artificial gemstones. No reason why you shouldn't go that way if you fancy a change.

Dave

Of course you could do away with metal entirely and 3D print your clock *** LINK *** as seen in Thingiverse.

John

There is no reason why you should not use aluminium for the frames if you use miniature stainless steel ball bearings for the pivots. The thermal expansion question is a red herring. The wheels in a clock should have enough clearance to accommodate that. Stainless steel should be OK for the wheels but is much harder to machine to a fine finish.

Russell

Many years ago I worked for a radio valve manufacturer and an aluminium/brass alloy was often used in the forming of the glass envelope of the valves as it had the same coefficient of expansion. I have no idea what the alloy proportions were but it had definite grey tinge, nothing like traditional brass colours. I still have a piece somewhere and even after 50+ years there is no discoloration or patina showing.

Apologies for wandering off topic.

Phil

If all frames and wheels are made in the same material (whatever that material might be) I agree you do not need to worry about thermal expansion coefficient of them. If frames and wheels differ in material it is worth thinking about.

For pendulum rods a screw adjuster as found on many clocks using a pendulum would probably do fine. An invar pendulum rod would be interesting to try though.

Jeff Invar pendulum rods are common on regulators. The one on mine actually expands as the weather gets colder and contracts as it warms up. I have been told that I should have put in a butchers fridge for a couple of days, then leave it at room temperature for a couple of days.

Roy

I designed a sextant once, and came in for a lot of stick from yottie types about not including temperature compensation. As a sextant measures angles, it matters not one iota what the sextant is made from, so long as it's all the same material. However, as the yotties were technically incompetent and there was no expensive temperature compensation, the yotties went off and bought ready made ones with knobs they wanted. Paid hundreds, possibly thousands for their ignorance. Fine by me. OK, do feel mildly disgruntled still, but it won't change how easy it is to part a fool from their money.

Regards

Richard.

And did any of those yotties actually know how to use one? And then do the calculations correctly using Navigational Tables?

My experience using a sextant was that they're difficult to read properly on a cliff top - hat's off to anyone who can do it on a bouncing boat. I spent most of an afternoon struggling with the maths (basic calculator and tables only) and couldn't get better than 60 nautical miles of my actual position, even though I already knew exactly where I was. Stood next to an ordnance survey trig point!

Not really sure what went wrong. Misjudging the altitude coupled with misreading the verniers and botching the stopwatch perhaps. It was a clear day and, as far as I know, the sextant and clock were both OK.

A friend belonged to yacht club. Seemed to consist of two types: chaps dressed stylishly in nautique discussing their Decca Navigator in the bar, and grubby types who'd actually been on the water this year. Back then I imagined myself being one of the old salts, a true British Blue. Now I know I'd much rather be indoors wearing a smart blazer covered in brass buttons carrying an anchor motif...

Dave

As a retired sextant user, plastic ones were rubish aluminium one were better but the brass ones were the favourite. Why because they are heavier easier to hold steady on a moving ship. Not tried on on a yacht it's all electronic now days.

There's nothing more conservative than clockmaking - clocks continue to use non optimum tooth forms despite quite a lot of evidence that involute gears work better. Brass is used for wheels because it always has been. Actually I think highly polished brass wheels in an open clock look ugly - boring colour and all the reflections mean you can't see what is happening.

I think thermal expansion is irrelevant - as said above there's so much play between clock gears that it will have no effect I think. Obviously thermal expansion of the pendulum is critical, which is why most clocks with any pretension to accuracy uses invar, or something like carbon fibre or fused quartz rod, or have temperature compensation.

Clock B has dural wheels and steel lantern pinions with the pins on small ball races. By the look of the photos even the escapement wheel is dural - but with a grasshopper escapement there isn't the same wear issue.

Aluminium would be a nice choice for wheels I think - either dural or one of the other free-machining types. Or aluminium bronze?

I've often thought that it's odd that clock wheels have symmetrical teeth - it's not as if they go in reverse is it? There's probably a better tooth form if you remove that constraint.

Maybe temperature compensation of a sextant is needed because of differential expansion when you move it from a warm(ish) cabin to a cold deck?