7x16 Mini Lathe [page 9]
Tuesday, Apr 25 2017
The tap follower I’m making will be used on both the lathe and the mill. I put this pate on the lathe series of web pages becuase it is being made on the lathe.
I scribbled a design to meet my needs — mainly that it must be able to fit in my mill which can support tool sizes up to 10 mm in diameter. I picked 8mm because I have a decent tap and die for 8 mm x 1.25 threads. The body will be made from 1/2" (12.7 mm) 12L14 steel because I have some of that, too.
I first turned down some O-1 tool steel to 4 mm with a 6 mm boss to make the retracting pin portion of the tap follower. This will fit in the body with the spring pushing against the boss. My target is for about 25 mm of pin travel. I put a 60° taper (approx) on the end of the pin. That is 1/3rd of the device.
The second 1/3rd is the shaft that will be used to hold the follower in either a collet or a chuck. I turned some 11/32" tool steel down to 8 mm and used a die to make the needed 8 mm x 1.25 threads. This shaft will screw into the body and capture the spring against the moveable pin. That’s the plan, anyway.
Before calling it a day I heat treated the pin to harden it and then brought it up to about 400° F for the desired temper. Don’t know if hardening this part is strictly necessary, but I don’t think it will hurt.
Tomorrow, time permitting, I’ll make the body.
Wednesday, Apr 27 2017
I put some 1/2" 12L14 in the lathe and drilled a 4 mm hole a little more than 50 mm deep. The picture shows me checking that the pin fit the hole. I pulled the stock out enough to cut off the 50+ mm piece that I wanted. The cut off piece was flipped and mounted to drill a 6 mm hole about 44 mm deep. A check fit of the wide end of the pin was a no-go. Too tight. I changed to a 6.5 mm drill bit. Much better. Finally I drilled and tapped the end for about 8 mm worth of M8 x 1.25 threads.
My spring collection isn’t what it used to be. I found a spring that will work at least temporarily. I’d prefer a spring with a bit more tension. The one I found will have to do until I find/buy a better spring. When I find one I like I’ll probably loctite the end into the body.