tap drill/bore for 2-1/4"-8 tpi thread
Re: tap drill/bore for 2-1/4"-8 tpi thread
I have made a few backing plates for my lathe, which is 63mmx 8 TPI.. I bought the lathe new, and it came with a couple chucks, which had factory backing plates. I entirely cheat, and just measure the ID of the factory ones, and bore to that. My lathe has a shoulder on the spindle, and I am careful to bore the area that fits the spindle quite close, within .002", and I make a good square bearing area on the back of the backing plate to bear on the face on the spindle. Then I cut the threads to depth. Long ago I made an extension for the nose of my lathe, thinking it would help me with something I was doing, however it did not. I threaded it until the factory backing plates would just screw onto it, so I have this laying around. Now when I make a backing plate, I just thread it until the false front fits it, knowing that if it fits the false front it will fit the spindle, I have never had a problem, and chucks center well. I have done this for a Collet chuck, a 10" 3 jaw and a 12" 4 jaw. I bought this lathe as my first lathe, and mostly to have a valid reason not to watch television, which I never was fond of. If you have one that fits, and you can turn a stub with threads that just fit it, it will make your life easier some day.