Repair Existing or Fabricate New Leadscrew?

Machine Shop
#1

I have an old Craftsman drill press vise I inherited from my grandfather years ago. There isn’t anything special about it other than its sentimental value. Under other circumstances I’d just trash it.

The leadscrew binds pretty badly during parts of its rotation - it is surely bent a little. I can fully open and close the vise but it takes more effort than it should.

My question: Is there a practical way to straighten the screw, and barring that, would it be terribly difficult to make a replacement?

The threads are a sharp V but I haven’t measured pitch or removed the screw to match it to a die for confirmation.

Thanks!

Edit: Screw is about 1/2” diameter and 7 inches long.

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#2

old tractor implements use to have long threaded rods for adjustments and they were always getting bent. We would drill a hole in two pieces of angle iron and clamp them to a board then thread nuts on each end tighten and heat with torch being careful that you only put enough torque on the rod to pull the bent out and not stretch it.

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Another option if you have a really flat surface would be to heat it and roll it until it was straight

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#3

This is a brilliant idea. Thanks for sharing it. My parents used to own a farm and we had several tractors. Never heard of this but it is a very helpful idea.

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#4

I’d advise against heating it. Since you dont know the exact material, IE if its hardenend or not. If you heat it up, the likelyhood of bending it again is greater.

Your best bet is to remove it & roll it on a flat surface. You can bend it back by bending it between 3 points in a press. The key is you need to be very gingerly about it. Just a little bit at a time, patience is a virtue on this one.

If you have to remake it, it shouldn’t be too hard. Just single point the threads on the lathe. If you haven’t done it before I will gladly give you a hand.

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#5

If you can get three bolt that will thread onto it, use to to support ends, third at point you want press down. I’ve used multi layers of thick leather to protect threads - it cuts into the leather but the threads are spared.

#6

Do you mean support the ends with nuts and put the high spot toward the ceiling, then whack with a hammer?

It’s a mild bend. I wonder if I could do this in a vise, with the bend toward one of the faces…?

Might have to shave down one of the faces of the middle but to allow a little over travel to account for a bit of springback.

#7

Nuts on end to support it on whatever to protect threads. At high point, use third nut as point to press down, again, to protect threads. The ends need to be raised a little bit, 3/8" or so, this is because you’ll need to bend it threaded bar slightly past a “Straight line” so that you go past the yield point of the metal, otherwise it will it spring back. Concept is same with leather if you can’t find the nuts.

You may be able to since they a V and not acme thread.

But agree with Tim, don’t heat, you’ll make them soft, they’ll stretch and bend easier.

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#8

Here’s what I’m looking at. Something between 1/64 and 1/32 of deflection spread across nearly entire length.

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#9

Nuts would work. I was thinking more along the line of using wood as those 3 points.

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#10

Just a SWAG: you’d need to deflect in at least 150% of that gap to get it to yield. But do it progressively: 125%, 150%

Looking at the shape: you could support it the end parts that aren’t threaded on pieces of metal, then just use something like leather to protect the threads where you press down.

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#11

Looking at the original photo, reinsert the screw and press it there, there’s plenty of room underneath and you could immediately check if it is straight enough and free enough to be acceptable.

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#12

I doubt that it is bent. The handle is not bent and it would take considerable force to bend the screw. Just oil the threads some more, use a wire brush to get the crud out of it .
Oil the screw where it attaches to the jaw remove that little screw and put some oil in it. The vice looks like it is made of good metal. It can be tilted to drill an angled hole .Well worth saving

#13

See a few posts up with the photo

#14

Yes that’s bent. 1/2- 13 thread probably .

#15

This is a leadscrew, not a bolt; even then 13 threads per inch (TPI) would be pretty high in this design (0.077 travel per revolution)

Assuming the thumb is 1" wide (bad assumption, but lets us make an estimate), that lead screw would be a 5/8" diameter and about 9 TPI for about 0.11 lead travel per rev. which puts it in the territory of the finer lead screws in that size range.

#16

I guess I’m seeing things… it looks like the middle is thinner than the ends.

#17

I suspect there is a little of that. But in the middle you are seeing the thread pretty much straight on, and can see the minor diameter. Towards the end, the camera view is at an angle, and the minor diameter is obscured. This give a visual impression that it is thicker at the ends. I’m fairly confident that if you try to roll this on a flat surface, it clearly does not roll evenly, if at all.

#18

It’s bent. No doubt about it.

Good guesses on the size y’all but a 1/2-13 nut screws on just fine. @TORQUE was right on that.

So I put a nut in each end and one in the middle. I put the whole thing in my vise with the end nuts shimmed about 1/8” and the bend facing the jaw. I got down on it but it didn’t budge. It’s a decent size vise but it’s just not enough. I’m gonna have to use a press to do this.

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#19

I have a similar vice , tilting base , removable jaws .
I looked at it closely, with tired old eyes and a magnifying glass
The screw could be made from a piece of threaded rod.
The end cap,that the handle slides thru looks like a separate piece that threads on.
The handle may have end caps that press on but I’m not sure. One end of the handle may be a cap that presses on. How much would a piece of stainless steel threaded rod cost. That’s the part that rusts the most.
I may test my vice handle to see if the cap comes off .

#20

The handle and the threaded bit are clearly separate pieces but I can’t tell if they’re threaded together or if the shaft is pressed into the handle.