Dynamo screw threads

[bikerboy]

Does anybody know the thread sizes that an E3L dynamo uses particulary the little countersunk screws that hold the field coils in?

[duTch]

 Call Andrew (Beezamacc on here) at priory magnetos.

 I would expect Tyne field coil owes tho be BSF, as is the drive-sprocket nut, and the others to be BA*

[JulianS]

The pole shoe screws are 5/16 x 22 tpi BSF.

The 3 countersunk screws in the end plate at drive end are 5BA.

The armature thread is 3/8 x 20 tpi BSF for sprocket retaining nut.

[trevinoz]

The through bolts are 2BA, the screws which attach the brush plate are 6BA, the earth screw is 5BA.

[coater87]

 So the single screw in the end of the tin brush cover is what size?

 The lucas part number is 200,902 for this cover, and the cover is called "one piece end cover".

 I dont think I have ever owned a screw for that end cover, it was held on with black electrical tape when I got it.

 Lee

[beezermacc]

2BA x 1/2"

[coater87]

2BA x 1/2"

 Thank you very much, I could have guessed at that until the cows came home and still wouldnt have gotten it.

 Lee

[duTch]

 

So the single screw in the end of the tin brush cover is what size?

 The lucas part number is 200,902 for this cover, and the cover is called "one piece end cover".

 I dont think I have ever owned a screw for that end cover, it was held on with black electrical tape when I got it.

 Lee

 Not to do Bezzamacc out of a highly lucrative international transaction, but fairly sure Birmingham Triumph unit points covers  are 2BA, so you may be able to procure one of them locally, fairly easily

[coater87]

 I was just going to cut my own.

 Then I looked up the thread form and TPI for BA screws......what were those people thinking?

 Lee

[Black Sheep]

"they were probably the most "scientific" design of screw, starting with 0BA at 6.0mm diameter and 1.0mm pitch and progressing in a geometric sequence where each larger number was 0.9 times the pitch of the last size"
Thus quotes Wikipedia.

[Rex]

  Then I looked up the thread form and TPI for BA screws......what were those people thinking?
 Lee

BA is/was an extremely good thread system. Although it's been fashionable for years for the Great Unwashed to laugh at something they have little knowledge of, it worked well in it's time, and gave a range which extended from small enough for watchmakers to universal in the electrical/electronic industries and all in-between.
 What they were thinking was, "this is a good thread system for small industrial threads and fixings and will endure for centuries" and they'd be right.

[groily]

Spot on Rex. It is a good series and well thought out, although the tpi, major and minor diameters do seem 'funny' at first glance, and 47.5° is not exactly an angle you'd ever guess at.
Screws of the various sizes/head forms and all the tackle to make them is easily available in the UK at least. BA Bolts is one good source, and that old favourite Tracy Tools has all the necessary in HSS and carbon steel, boxed sets included. 
Hex bar in stainless, mild, brass in the right, or very close to right, sizes for nuts and for the heads of bolts and setscrews is also out there.
(Not really threads to be cutting on a lathe - but it's not hard to turn stock to the right major diameters and use tailstock mounted dies to get pretty decent results.)

[bikerboy]

Thank you everyboody for your replies but now the real teaser

What size are the tiny self tapping screws that screw to the terminals on the face plate 

[coater87]

 OK you two,

 Being an American I can safely say you two have drunk too much of the Cool-Aid.

 A good engineers can take something complicated and make it simple.

 He does not take something simple like a screw thread and make it complex.

 47.5 degree included angle, 31.36 threads per inch, and a .185 OD for a threaded screw form sounds to me like a paper tiger, some engineer developed this using nothing but a math calculation. Someone should have kicked his ass right then and there.

 Lee

[beezermacc]

The self-tapping screws are no.4 x 1/4". No.4 is about 2.9mm. You're better off using no.6 which is 3.5mm as the no.4 holes are usually stripped. Next question?!