I popped into Chronos today and bought (amongst other things) a part-finished 4 1/4" backplate for a Myford ML7. I intended to machine it tonight but I cannot get it to fully engage on the spindle; the boss goes on about 1/2 way along the register of the spindle then stops. I used engineer's blue on the register diameter and it's not transferring, so I know that it must be sticking on the threads; I've confirmed this by fitting the backplate on backwards and it does not fully engage all the threads before it gets stuck. I've measured the ID of the backplate threads and found they measure 1.043"; I know the correct dimensions for an external Whitworth thread, but cannot find any reference to the clearance or the minor diameter for an internal Whitworth thread. Can anyone help with what this dimension should be? I was planning to bore through the backplate if the clearance was too small, but I don't know if the thread has been cut to the correct depth; perhaps somebody has a 1 1/8" x 12TPI tap they wouldn't mind loaning out (for beer tokens?) to clean this thread up. Martin
- posted
18 years ago