hss or carbon steel?

[taycat]

going to need to make some backplates for southbend lathe i am getting.
i need some 1.5" x 8 taps carbon steel ones are approx £20 each and hss £60 each.
normally i would go straight for hss but cost is a lot here.
only going to be used 12 x max.
or will i get away with just getting second tap in hss as its a through hole and not get taper and plug taps?

cheers

 

[KemppiFrog]

Personally I would go for the 2nd HSS, though it might be cheaper to find someone who has the taps for a one ( or two) off?

 

[Pete.]

I would not try to tap a backplate thread. The only proper way is to cut it on a lathe IMO.

 

[Digger6135]

In making lathe back plates, they are usually screw cut in the lathe, though the thread needs to be accurate, it's not as important as the registar that locates the backplate onto the lathe spindle, see Doubleboosts making a collet chuck, he explains it well.

Digger6135

 

[taycat]

can only go down to 11tpi using my clarke lathe not sure what i can do on southbend as not coming till next week.

 

[Pete.]

It's a very common spindle thread size - Boxford, Denford, Southbend, Atlas plus many others use it. You should be able to find a cheap face plate for making backplates or complete chucks for sale on eBay.

EDIT: 6" faceplate for an Atlas would make a handy backplate http://r.ebay.com/djS8ys

 

[taycat]

boxford are whit and southbend are unc been told boxford ones go on couple of threads then jam.
will have to find out what atlas ones are.

 

[Pete.]

Ah, never knew it was Whitworth. Doubt the Atlas will be though, being a USA-built machine.