sb 9a spindle thread

[robert102653]

i was looking to make a backing plate for my 1947 9A, including the 1-1/2-8 spindle thread but as i was looking at taps i noticed that many have one, two, or several letters after the tap size and i have no idea what those letters mean. is there a certain thread form of tap i am looking for? i know there are many different ones. like whitworth, and british standard, and ase, and pipe tap, and acme, but what is the type i am looking for with the southbend 9A 1947 version? And no i cant single point it or at least i don't think i can. i would have nothing that big to hold the plate to tap it on the lathe so a hand tap is what i will use.If i can find the right one. thanks in advance for the help.

rob

 

[toolman87]

Rob
Check out ebay 1 1/2 8 back plate...might be an option there.
h.t.h. fred

 

[kitno455]

And no i cant single point it or at least i don't think i can.

You can. It is not that hard. Cast iron cuts well, its a low speed operation, and you have lots of clearance. It also happens to be the same pitch as the leadscrew, so you don't even need a thread dial.

allan

 

[gadget73]

it'll cut as long as you aren't using some terrible grade of cast that chews up bits.

You'd want SAE if you buy a tap. It'll be an expensive tap though.

 

[promacjoe]

You may spend $100 or more for a a used tap, That you may only use once, And may not give you satisfactory results. And You definitely do not want to try to hand tap the threads for a adapter plate. Single point them is the way to go. Everything has to be absolutely in alignment. The shoulder that seats against the shaft must be square with the threads. And you just can't do that reliably using the hand tap method. I have a tap, but the only thing I use it for is to clean up the threads by hand, No wrench. It is used to remove the burrs. Nothing more.

stay safe and have fun.

Joe.