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I am trying to get a needle thumb screw for the Apollo. I have looked at
alot of my tiny bolts...the one that fits the Apollo is the size of the backplate
bolt on the Victrola 4 reproducer. I have no means of determining pitch
or diameter of this bolt. Would anybody know this?? Can make a thumb screw
if I can get a bolt!
Thanks Terry

I don’t have a No.4 to measure a screw from. Does anyone know if it is the same as a No.2? If so, I can measure one of those.

I have often wanted to say publicly that it would probably be worthwhile for phonograph collectors to own and know how to use a micrometer and thread pitch gage, (or at the very least, a good digital caliper).

Just a side note for future reference, (sorry for being so picky), a screw is only called a bolt if it is used with a nut.

These reproducers were made in Switzerland by Paillard. Therefore, metric thread. I would post a wanted ad in our UK-European trader. You may get lucky.

I've just removed one of the back screws from a HMV brass backed No.4
My understanding is that these use the same threads as the Victor ones, even though they were made in the UK at a time we were using different imperial thread systems
Anyway, by my measurements its a 1-64 UNC, which has a diameter of 0.073" and a thread pitch of 64tpi

If its actually a European thread, then its likely to be a 9BA which has a diameter of 0.075" and a thread pitch of about 66tpi (its not an exact number per inch)

For the small number of threads in a needle screw hole, either would probably fit.

It certainly is useful having some tools to measure these things, though my thread gauge only went down to 60tpi, so I compared it to a 1-64 tap.

This sort of size seems quite common for needle screws as several European soundboxes/reproducers I have identified as taking 9BA, but they could conceivably be 1-64 UNC.

I have so far made one replacement needle screw, but intend to make more

Hope that helps,
mrrgstuff

Just an idea, if it hasn't already been done:
Would someone be willing to make a chart of the known thread sizes of the various common screws/bolts used on the most often encountered machines - needle chuck knurled screws, bedplate screws, cabinet screws, reproducer screws, etc. - before all of this knowledge is lost to future collectors? I think it would be a very valuable tool to have, rather than having people re-tap holes to fit modern thread sizes.

Victor used UNF or UNC threads and these were also used by HMV in the UK I guess as all the early machines were imported it made sense if any repairs were needed , i guess Edison also used UNF UNC as the bolts which fix the gem base to the machine are exactly the same as the bolts that fit tone arms to motor boards in HMV portables

The Apollo screw will be metric so if a Victor screw fits it this is only serendipity as the pitch will be different

this is a good site for some comparisons

https://www.zytrax.com/tech/mech/threads.htm

soundgen wrote: Thu Mar 11, 2021 3:03 pm The Apollo screw will be metric so if a Victor screw fits it this is only serendipity as the pitch will be different

The BA thread is a metric thread very largely based on the Thury thread which originated in Switzerland.

In these very small sizes, small differences like 66tpi (BA) vs 64tpi (UNC) will not make much, if any difference when there are only a few mm of thread engaged with the threaded hole for the needle screw. Likewise being .002" undersized will make the fit slightly looser, but maybe not noticeably so.

Ideally of course we would find the exact period screw, and with larger threads, say ¼", it is possible and worthwhile differentiating between the thread profile of BSW vs UNC, but its not so practical (or so important) to do so in the very smallest sizes.

Curt A wrote: Thu Mar 11, 2021 2:49 pm Just an idea, if it hasn't already been done:
Would someone be willing to make a chart of the known thread sizes of the various common screws/bolts used on the most often encountered machines - needle chuck knurled screws, bedplate screws, cabinet screws, reproducer screws, etc. - before all of this knowledge is lost to future collectors? I think it would be a very valuable tool to have, rather than having people re-tap holes to fit modern thread sizes.

I think this is a good idea, though could become quite a task in itself . Of course its much easier if you have the screw as its always going to be possible to measure it, and the diameter and pitch will give a good indication of what it is. Digital calipers are cheap enough and so are thread gauges. Much harder is where you only have the threaded hole. Its a lot less practical to have a comprehensive sets of taps which you can try in a hole, and taps are not really gauges anyway, and will easily ruin a thread if forced into a threaded hole they don't actually fit. Having said that I would never rethread a hole with a modern thread size unless it was so damaged as to be unusable and unrepairable. I one did rethread a 2BA to M5, but I have learnt a lot since then!

The advantage in having a chart would be for missing screws...
We could start a thread where everyone with specific info could post what they know, then after awhile a chart could be made... Again, just an idea.

The screw from the Vic 4 backplate turns in and out perfectly
on the Apollo thumbscrew hole. i am going to assume
that it is a 1-64UNC No other screw removed from the Apollo or any other
reproducers I own will work! perhaps it was rethreaded before
I owned it! I would have thought that the thumbscrew on the
Vic 4 would have been the same but it definitely is slightly too
large. If I source a 1-64UNC screw I can silver solder a knurled nut
on!