Thread: Sourcing or converting a backplate for 1.5" 8TPI 55deg

Hi Chris,
1 1/2" x 8 TPI Is actually standard BSF. British Standard Fine. Taps and dies can be available.

Phil

Oops. Is that inch and five eights that you have written. If so, ignore everything I wrote.

Mr Bigot, if you have no joy, backplate blanks are available for your machining pleasure, eg: RDG Tools - Online Engineering Tools Blank Unfinished Cast Back Plates.
I don't think you can convert American to British because 55 is narrower than 60. The other way, maybe.

I'm not so sure its that simple Bryan. I'm thinking the 55 degree thread must be deeper than the 60 degree thread. I can't find any numbers on a 60 deg 8 TPI its not UNC thats 6 tpi, UNF is 12tpi.

Stuart

But 1 1/2 x 8 TPI is BSF

Phil

If it is a 60 degree thread then it will be an American standard 8 pitch thread.

Phil

Isn't BSF Whitworth 55 degree?

American standard what?

If the spindle is BSF then the thread grooves will be deeper than the crests on a UN series back plate.
As well as UNC, UNF, UNEF etc , remember that there were also UN inventions like the 8tpi series (and I think 16, 24, ...)
As you say, it's the wrong way around. the only way that you could use the backplate that you have would be to bore it out and sleeve it. You could then re-cut a 55 degree thread

Michael

Originally Posted by Stustoys

Isn't BSF Whitworth 55 degree?

American standard what?

Exactly that Stuart.
American standard 8 pitch.
All the screw diameters in the American Standard 8 Pitch have 8 TPI

PHIL

Originally Posted by Michael G

As you say, it's the wrong way around. the only way that you could use the backplate that you have would be to bore it out and sleeve it. You could then re-cut a 55 degree thread

If the major diameter is the same and the tpi are the same, wont the 55 degree thread have to be deeper? therefore a 55 deg could be cut into a 60 deg thread. not the other way around. I think. Would help if there were dimensions about.

Stuart

Originally Posted by Stustoys

If the major diameter is the same and the tpi are the same, wont the 55 degree thread have to be deeper? therefore a 55 deg could be cut into a 60 deg thread. not the other way around. I think. Would help if there were dimensions about.

Stuart

Hi Stuart
Correct
The general rule of thumb is
55 degrees is 0.64 x pitch
60 degrees is 0.61 x pitch
So 55 degrees is deeper.

Phil

Originally Posted by Steamwhisperer

.
American standard 8 pitch.
All the screw diameters in the American Standard 8 Pitch have 8 TPI

Hi Phil,
Ok I'm confused, threads often do that to me, so many different ones.
Isn't American standard UNC? Google is no help on "American standard 8 pitch"

Stuart

Hi Stuart
No, UNC is Unified National Coarse.
American Standard hails from the American Society of Mechanical Engineers. A.S.M.E.
Unified National is a derivative of this.

Phil

Just to add to the confusion. Whitworth is pre war. When the war came along, they ran out of steel so they made the bolt heads and nuts smaller and called it British Standard Whitworth
I will stop now lol

[QUOTE=unixbigot;1412366]I have a Mars "Great Scot" lathe with a 1-1/2" 8tpi spindle.



My 9" Hercus Craftsman has 1.5" x 8 tpi USS (Sellers Thread) 60 degree profile.

Col