7/8"x8tpi thread tap.

[smokey]

Hi Members.

I am new on this site and need some help, i have a Myford ML4 lathe that needs a new back plate machineing for a 3 jaw chuck, i have the blank casting but are having trouble locating a 7/8"x 8 tpi tap to mount it on the headstock.
Can anyone advise where i can get one from, any help would be most welcome.

Best Regards.

 

[CrewCab]

What part of the world are you in Smokey .............. if you are in the UK and anywhere near West Yorkshire RDG have plenty in stock, if your not local they do post out, including overseas.

Click Here and Scroll down a bit lot ;D


CC

 

[CrewCab]

Just a point .......... having thought about your original post I have a little dilemma .......... the Myford spindle thread is, and always has been AFAIK ........... 11/8" BSW ........... so why would you need a 7/8"x 8 tpi tap ???
Anyway, RDG do keep Taps and Dies to suit Myford spindle's if that helps.

CC

 

[vlmarshall]

Some of 'em are 7/8"-8... an odd thread, to me.

http://www.paichl.cz/paichl/knihy/hodiny/soustruhy/myford/page7.html

 

[Blogwitch]

The early 'all cast' lathes from Myford such as the ML2,3 and I think the 4, had a standard nose thread of 7/8 X 8 TPI. They later standardised on the 1 1/8" size.

It is NOT recommended you tap backplates out, but single point screwcut them instead. The back face and spigot plain lead in are just as important as the thread, if not more so, and the only way they can be guaranteed to be square and fit correctly is to single point cut from the back of the required chuck backing plate. Then after it is fitted to the lathe, the backplate has the front and edges trued up.

Even a few years ago the backplates were not available, as they were long out of date, and I had to make my own.

RDG 'Myford taps' are for cleaning out backplate threads or for finishing off nearly completed single point cut threads, so you get a 'perfect' profile, NOT for cutting new backplate threads in full.

Blogs

 

[smokey]

Hi Members.

Mank thanks for your replies they where most welcome. CrewCab your lathe must be a ML7, after the ML4 the headstock spindle was changed on the ML7 to 1.1/8", as far as i could see on the RDG website the taps ended at 3/4" and jumped to 1.1/8" for the later Myford.

Blogwitch, many thanks for the pointers, i think i will take your advice as this is a first for me at screw cutting, but i suppose you only have to do it once then you think what was i worried about.

 

[Tin Falcon]

smokey:
measuring an internal thread is difficult at best. What i have done in the past is to reproduce the lathe sindle thread as a gauge. Take your time and get the dimensions as precise as possible this includes the shoulder. then when you mount and machine the back plate you have a guage to check the dimensions with. I have a guage for my south bend and made one for my buddies little lathe. I also made one for the ball screw nuts on my little mill project.
Tin

 

[Blogwitch]

Smokey,

I think I got the pitch wrong in my last post, I am sure it is 7/8" x 9TPI @ 55 degree form (standard BSW size), but that is easily checked with a thread gauge. It is best just to double check, rather than taking my word for it, as it is a long time since I cut one.

As mentioned by Tin, your main problem will be when it comes to check the thread on your spindle if you are cutting it on the same lathe.

Normally you would turn and screwcut up a dummy exact copy of your spindle nose, and use that to check for fit.

It is much better if you can remove the spindle from your machine, a very easy process on the early Myfords because of the plain bearing head, and get the backplate machined on another lathe, and use your original spindle for checking the fit. While you are at it, if you are going to keep the machine for any length of time, get two or three backplates made up at the same time.

The early Myford ML2 that I rescued and rebuilt many years ago is still in daily use by a friend of mine, and the accuracy of it is as good as any modern machine, and can single point almost any reasonably sized thread, left or right handed, imperial and pseudo metric, because of the change gears setup on it.

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[smokey]

Hi Blogwitch.

The spindle nose is a whitworth thread of 8 TPI i checked this at the begining with the thread gauge. That was sound advice you gave, so i will be taking that road.
Once again many thanks for your and other members help.

Best Regards Theo.