The Talking Machine Forum — For All Antique Phonographs & Recordings

When my friend George Ovesrtall produced his diaphragms, by spinning them on his lathe, some heat was produced. I imagine this sort of toughened the material. Some gramophiles cold stamp their diaphragms. I wonder if annealing the finished article might be a good idea. The aluminium I have at present, which came from George's stock, I think is too soft and too thick. I did have a couple of original ones, years ago, but dampness had started to corrode the Aluminium to Aluminium Oxide. Pity. I did read, way back, that Duralium would be better than just plain Aluminium. Has anyone got an original Ginn or Davey diaphragm out of a soundbox, that can be weighed, and the thickness measured? If I could get some of the correct stuff, I would be happy to try to produce some. The real art in making the diaphragms was at the end, when the excess material had to be parted on the lathe as it was spinning round. George had a special shaped piece of ivory or similar material. Trying to cut the excess off with scissors is impossible, and makes a ragged edge. The edge of any diaphragm must be super smooth. I also read that some of you manage to flatten out, quite successfully, warped or bent diaphragms. Roger Thorne once told me that to test that a diaphragm was suitable, was to drop it from a height of several inches onto a thick china plate. If the diaphragm gave a clear ringing note, it was suitable, If it gave a dull note, then it was either too thick, or unsuitable. I have tried this and it seems to be true, unlikely as it sounds! I somtimes wonder if flattening old ones will make them "work weary" and not give the same results as a new one. As no-one I know has an original aluminium diaphragm from either Ginn or Davey, then I imagine we will never know how it would sound when assembled properly in a soundbox.

The original diaphragms I have measured seem to have a thickness of between 0.0035" and 0.0045". I think these were EMG and Astra from memory and, as you say, the alloy and condition/heat treatment is important. Paul Morris, who I think I am right in saying used to have (or perhaps borrowed ?) the Overstall tooling, made a very good batch a few years ago and the sound reproduction was first class. It would be interesting to ask him what the material specification and source was.

Hello Graham, I now have back from Paul,all the Diaphragm making equipment. Phil. Lewis lent all the tools several years back, and I went and collected it all last year. So, I am looking around for someone with a small lathe in our area, or otherwise, lend all the equipment to someone who will be able to make a few good diaphragms for us all to use.

Should you fail to find a suitable lathe I might be happy to try my hand but have absolutely no time until well into the autumn I am afraid. I think a project like that could be very time consuming if taken seriously and much experimentation would be necessary as so much knowledge has been lost. I have a small stock of various grades of aluminium alloy sheets here somewhere, having started to look into things some years ago. Might Paul have time to make some more I wonder ?

I have several original diaphragms and they do vary slightly, I suppose the making process, especially spinning would have varied the thickness slightly.
They do average out to 0.0049" or 0.0125 mm. The same thickness as a can of coke.
I'd love to see pictures of the Ovesrtall templates.

I have several original diaphragms and they do vary slightly, I suppose the making process, especially spinning would have varied the thickness slightly.
They do average out to 0.0049" or 0.0125 mm. The same thickness as a can of coke.
I'd love to see pictures of the Overstall templates.

Hello all, here are a couple of pictures of the Overstall diaphragm making equipment. It comprises of-Aluminium on a roll (2 thicknesses.) Two different configuration impression dies, made of brass. One brass clip-to hold the aluminium in place on the former. A piece of plate glass, which is used to make sure the aluminium, when crimped up by the brass clip, is made flat. A soft "forming" piece of material, which is pressed against the spinning diaphragm on the lathe to form the features, or rings. Two different thicknesses of felt, in small circles about 2inches square, to polish the formed diaphragm whilst it is still spinning on the lathe. Two horn spoons, which were used to make sure the aluminium on the lathe, whilst spinning, would take up the form of the pattern. There should be in this kit a parting piece, made of ebonite or suchlike, but now lost. so a Stanley knife blade is used to "part" the diaphragm, when ready.

Now, a close up of the brass formers. As can be seen, two designs are possible.

That has made my day. Thank you for the pictures. The clamp is the only thing I find clumsy .
It all looks very simple but I am sure it's not.
As for annealing, I always thought it softened the metal?
Anyone have any thoughts on using a coke can? After cutting one open it really looks like it might work.

chunny-A Coke can-well it might be suitable, but will it retain a "memory" if you are using the curved side?-and not stay flat enough. I am sure there are other things that have been tried as well. I did have a session at making varnished diaphragms once. Frank James showed me an Expert or EMG box with a diaphragm made of varnished silk! Anyone tried glass-the professionals used it in acoustic days for recording. Might be tricky in getting glass that thin, and to cutting it round though! I remember seeing the advert for "Bozon's end-cut tortoise shell diaphragms", many years ago, from a 1920s gramophone type magazine. and recently I have found someone with an Exhibition soundbox fitted with one. I have a friend with a small lathe. I will ask him if I can have a session on it, sometime in the not too distant future, and see if I can produce some useable diaphragms.