Turning Acme Screw Ends Without a Lathe

[ger21]

I had tried using a grinding stone in a router to grind the end of my screws to mount bearings a few years ago, but it took waaaayyyy too long. This new method is much faster. After the first one, I was able to get them turned down in about 15 minutes each. Threading them took almost as long, as I didn't reduce the diameter enough for the threads, and it was tough going with the die in a cheap die holder. All you need is a drill with a 1/2" chuck, a file, and an angle grinder.

Here's what you do. Make a simple jig to hold two 1/2" ID (screw diameter) bearings. Ideally, you'll do this on a drill press so they line up pretty good. Slide the screw through, so it sticks out a little more than you need to turn down. Chuck the other end into the drill, and clamp the drill down, and clamp the jig down. If you don't clamp the drill, the screws will move in the bearings. One of the screws was very tight in the bearings, so I sanded it with some 220 grit paper until I could get the bearings on.

I just put a spring clamp on the drill to hold the trigger. (Just now realize there's a trigger lock. ) Then take the angle grinder, and rough grind the spinning screw, stopping frequently to check the diameter. I was using skate bearings, so I was able to grind until the threads were completely gone. Once you're done grinding, while still spinning, take a file to it. If you're somewhat careful while grinding, you should be able to get a very clean "turned down" section in a minute or so. Once you get it smooth, stop and measure frequently. When you get really close, start using the bearing instead of measuring. Work more toward the end, until the bearing starts, then carefully work your way up until the bearing slides all the way on. With a fine file (I just used some old ones I had), you can easily take off about .001-.002 at a time. Maybe even less. Be sure that you take off quite a bit more where the threads will go, which will make threading a lot easier.

This is easy, and works extremely well. Sorry the last pic is blurry, need a tripod.

Next machine I build will use 10mm angular contact bearings, so I'll only need to take off about .05. Should be simple.

I also tried using a belt sander instead of the grinder, and with a rough belt, it's almost as fast. But I didn't want to mess up my $220 belt sander. So if you don't have a grinder, you can also pull this off with a belt sander.

[Geof]

That is really good; just shows what imagination and innovation can do. And a steady hand on an angle grinder.

[CarveOne]

Originally Posted by Geof That is really good; just shows what imagination and innovation can do. And a steady hand on an angle grinder.

Another good excuse to build a 4th axis and angle grinder mounts for the Z axis.

CarveOne

[ger21]

The angle grinder did a pretty rough job, as you have to use it pretty vigorously to remove material quickly. The file is the key to the good finish.

[Geof]

Try using a flap wheel in the angle grinder if you have not already tried them. I find they remove metal as fast or faster than the solid discs and they are much easier to control.

[randyf1965]

Is there a bushing/bearing in the wooden box?

[ger21]

Originally Posted by randyf1965 Is there a bushing/bearing in the wooden box?

Two 1/2" ID bearings, One on each end. Like these. http://www.vxb.com/page/bearings/PROD/1-2inch/Kit7478

[martinw]

Dear ger21,

Brilliant. One thing, and I do wish to appear wimpy, but I would strongly advise anybody using a file on a rotating part to make sure that the broken file comes off the workpiece away from the operator, not towards them. It is probably second nature to experienced machinists, (amongst whom I am not numbered), but it will not be to many.

Broken file steel is horrendously sharp and jagged.

Best wishes,

Martin

[ger21]

Yes, make sure you stand to the side, and that the file is not pointing at any part of your body. Especially the arms, where you may not notice.