Amberola 30/50/75 Crank thread pitch?

[Governor Flyball]

The later Amberolas have a ¼" thread crank. I was planning to make a crank for an Amberola 50 cannot find information on the thread pitch.

I know it is not a 20, 26 or 28 threads per inch for my taps do not fit the crank thread hole. It looks like a ¼-24. Or is it a ¼-22?

Can anyone confirm? Thanks!

[rgordon939]

Why not just but a crank?

[Governor Flyball]

I have never tried butting a crank before. But I am willing to try.

[Governor Flyball]

Seriously, up here in Canada, the cost of an Amberola 50 crank sells for more than I paid for the machine.
I have been repairing machines for over 50 years and can easily make a accurate replacement in a couple of hours.

[JerryVan]

I don't have one handy to measure, but ¼-24 makes sense. While it's not a common thread pitch these days, it was somewhat popular in Edison's time. If you can't find a ¼-24 die, then a 14-24 may be easier to get and still do the job.

[Governor Flyball]

Thanks. Peering down the crank hole and comparing it with the 20, 26 and 28 tpi taps I have on hand, 24 seems the most logical choice. I just a few moments ago purchased a Chinese ¼-24 die on EBay for $8.99 US including shipping.

20 tpi is National Coarse and 28 is National Fine. The 26 tpi dies I have arei labeled BSF which is British Standard Fine. 24 tpi is called UNS or Unified Standard.

I have spent the past searching for old taps a dies for fixing older machines. I found Edison apparently used 5-40 screws for fastening the gear cover on an Edison Standard which have been obsolete for many years. I found taps and dies for many older obsolete fasteners for both British and American machinery and have made screws and nuts as required. I would be interested if anyone had data on early talking machine screw data.

Screw standardization remained a big problem during WWII and purportedly resulted in the death of audio pioneer Alan Blumlein. He was leading the EMI team on radar R&D and flew on a test flight in I believe a Lancaster bomber which was fitted with the wrong cylinder head fasteners. The maintenance staff torqued the incorrectly the wrong nuts down and the aircraft crashed shortly after takeoff and all crew and passengers died. This and other tragic mistakes after the war led to a cooperation between US and UK with the introduction of the Unified Threads.

Another example of the earlier craziness is British 2BA vs US 10-32 screws. Outwardly they look identical: same diameter and similar thread pitch. However 10-32 is 32 threads per inch and 2BA is 31.6 threads per inch. A 2BA thread almost fits a 10-32 screw except it is a bit tight.

This raises the question of HMV vs Victor machines: did the UK variants uses British or American fasteners?

[MarkELynch]

LYO

[mrrgstuff]

Another example of the earlier craziness is British 2BA vs US 10-32 screws. Outwardly they look identical: same diameter and similar thread pitch. However 10-32 is 32 threads per inch and 2BA is 31.6 threads per inch. A 2BA thread almost fits a 10-32 screw except it is a bit tight.

This raises the question of HMV vs Victor machines: did the UK variants uses British or American fasteners?

In my limited experience which has mainly been with British/European soundboxes, the BA size has actually proved to be the most used. They aren't a convenient TPI though, and with the very small sizes it is often very difficult to determine the correct thread.

A case in point was when I recently made a (temporary) needle screw for a HMV 5A soundbox. I am sure I read on this forum somewhere that HMV used American threads. A 1-64 looked like it should have fitted, but didn't. A 1-72 to the naked eye looks the same but did fit. Of course that is no guarantee it left the factory like that. The hole could have been retapped, but in this case I think not