Advice For Making Leadscrew

When I splice screws together, I bore the internal out so it runs dead true with the OD. Usually have to use a steady rest to do this depending which lathe I do it in. Regardless, I ge this running within about .002 TIR max. Next, I turn the OD of the screw to fit the bore and give it a slip fit, about .0005-.0015" unless the OD of the screw is already established. When I pin the two, I generally put tow pins at 90 degrees from each other. Doing this will keep runout from end to end within about .005" TIR on two foot of screw. Of course this depends on how straight the lead screw is in the first place. I cut all of my own lead screws using my 9" SBL using a follower rest. Lot of work, but I like doing it.

Here's some pictures of one that I spliced a new section of lead screw in for my B & S surface grinder.

DSCN1244.JPG DSCN1245.JPG DSCN1246.JPG
 
Oops, I missed that the longitudinal lead screw is imperial. I agree with not using a press fit on the two sections. Aim for line to line fit and take what you get. A tight sliding fit would be ideal. Either a very light press or a very slight clearance fit would also be fine. .009" in 12" is a "precision" lead screw? The only saving grace there is that we do very little precision movement of the cross slide and the compound over longer distances, mostly just depth of cut and facing, so probably OK. There are other ways to get closer tolerance on those important cuts...
 
Here's a cross feed screw I made for another grinder I have in my shop.

DSCN1777.JPG DSCN1778.JPG DSCN1780.JPG DSCN1782.JPG
 
Lead screw done. I used a tight slip fit pressed together by hand ( though ended up needing some very light tapping for the last .100" or so) and pinned 90 degrees apart as suggested. When supported at the handle end and rotated there is no visible runnout, though I'm not sure how to measure it with what I have available. The pitch is so close to the original, combined with some wear in the nut, that I was able to test it out and it works smoothly with no tight spots through the rotation (I have a tap on order to I will make a proper nut when it arrives - it is possible some runnout will rear up with a properly fitted nut). I still need to make the imperial dial, which will be the first "serious" job for the Chinese rotary/dividing head so far - I just have find a nice sharp tool for the fine engraving, and find some time.

Thanks again for the help!
 
4gsr - What makes your 9" South Bend your lathe of choice for threading the lead screws?
 
Last edited:
Jester966 said:
4gsr - What makes your 9" South Bend your lathe of choice for threading the lead screws?
Click to expand...

It's my choice because it's the only lathe I have that has a good not so worn lead screw on it that I can count on being accurate enough to cut a precision lead screw on. I know that doesn't make a lot of sense, but I have checked the lead of a cut thread off this lathe against a digital readout and the sample piece checked out within a couple of thousandths in ten inches. If I cut a screw on my 13" Sheldon, which has a very worn lead screw, I get over .008" in ten inches. My newer 15" Sheldon I'm working on restoring has a newer unworn lead screw on it, plus a new set of half nuts on the lathe. Can't wait to set up and make a new lead screw on it for my 13" lathe! To replace the worn out screw on it.
I made a new cross feed screw and nut for this lathe back in 1979. To this day, the nut has only worn about .005", the screw still looks new!
 
You must log in or register to reply here.
Back
Top