- Joined
- Sep 25, 2014
- Messages
- 1,115
I am making a lead screw (not for a machine tool) and struggling. The target size is 0.750, the blank is about 19" long and material 316SS - then 15" of 3/4-10 thread. I started with 1" bar (being what I had on hand) and when simply cutting with only the chuck and tailstock for support, found the vibration excessive for any decent cut. So I took it down to 0.77" by advancing 5" at a time out of the chuck (still with tailstock support) - getting it roughed out was pretty quick.
Now I'm trying to get it down to finish size and finding it "not so easily done":
- if I use carbide (positive rake inserts), I can take a pretty small cut (few thou) - the ends are the same size, but the center is 0.003" larger. Not a big surprise that the work deflects.
- if I use a HSS tool ("Diamond" holder), then I can hone it up real keen - but with a small cut the tool edge has started to turn by the time I get to the other end - so it starts to cut a little larger by the time I get to the chuck.
- I tried to set up the follower rest. I have never used the follower rest on this lathe. I used a cobbled together one on my other lathe when Acme threading - pretty dodgey but got the job done. The follower rest looks pretty straight foreward, not a lot of moving parts. I chose to put the support pad on the new cut (since the shaft was slightly barrel shaped) - the just cut surface would be the reference. I cut about 1" long to size from the tailstock end, set the pad about 3/4" behind the tool. All seemed to be good. Then it started to set up a wave - feeding back to the support pad (with nearly 0.005" variation in diameter).
- I can go back to my carbide inserts, get the ends right and tweak the cross slide as I'm feeding - then finish to size with a file. That seems rather defeatist!
- Threading will probably be okay, I'll just use the rest on the last few passes. I'll put the rest infront of the tool, and since the reference surface (the top of the thread) is not changing all should be good (which is what I thought when sizing the bar!).
Anyone have tips / pointers on using a follower rest?
Now I'm trying to get it down to finish size and finding it "not so easily done":
- if I use carbide (positive rake inserts), I can take a pretty small cut (few thou) - the ends are the same size, but the center is 0.003" larger. Not a big surprise that the work deflects.
- if I use a HSS tool ("Diamond" holder), then I can hone it up real keen - but with a small cut the tool edge has started to turn by the time I get to the other end - so it starts to cut a little larger by the time I get to the chuck.
- I tried to set up the follower rest. I have never used the follower rest on this lathe. I used a cobbled together one on my other lathe when Acme threading - pretty dodgey but got the job done. The follower rest looks pretty straight foreward, not a lot of moving parts. I chose to put the support pad on the new cut (since the shaft was slightly barrel shaped) - the just cut surface would be the reference. I cut about 1" long to size from the tailstock end, set the pad about 3/4" behind the tool. All seemed to be good. Then it started to set up a wave - feeding back to the support pad (with nearly 0.005" variation in diameter).
- I can go back to my carbide inserts, get the ends right and tweak the cross slide as I'm feeding - then finish to size with a file. That seems rather defeatist!
- Threading will probably be okay, I'll just use the rest on the last few passes. I'll put the rest infront of the tool, and since the reference surface (the top of the thread) is not changing all should be good (which is what I thought when sizing the bar!).
Anyone have tips / pointers on using a follower rest?
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