Replacing Knurled Thumb Screws


[Pete] bought himself an old South Bend lathe, but unfortunately some of the thumb screws were missing from this fine old machine. Originally, the lathe had knurled thumbscrews, and with a thumbscrew from Ace hardware the lathe itself was functional, but by no means looking its best. With a lathe you can make just about anything, so [Pete] decided he would make his own knurled thumbscrews and bring this lathe back to life.

Knurling is a diamond or linear pattern of indentations usually found on fancy metal knobs, flashlights, and other equipment that needs a good grip. While there are knurling tools for lathes, [Pete] decided to use his knurlmaster – a handheld device that looks like a pipe cutter – to cut a few knurls into a steel bar.

As for making this knurled bar into a proper thumbscrew, [Pete] shows us two methods: the first is tapping the knurled steel, putting in the right screw for the job, and securing the parts with Loctite. The second method involves cutting the threads on the lathe, an excellent example of how a lathe can make just about anything, even parts for itself.

32 thoughts on “Replacing Knurled Thumb Screws

    1. What the heck is a milling lathe? There are milling machines and lathes. If you are referring to those swiss-army-knife-like combo mill/lathes, I think most people would rather have separate machines.

      1. I’ll second that. Don’t waste your money on a combo machine. It’s not worth having a ‘combo’ machine because then each function is slightly (and annoyingly) crippled.

        I think I’d go for a lathe first, then a mill. The bigger, the better.

        1. Bearings? That’s the easy part..

          Look up plans for building a lathe from aluminum castings. I remember reading a tutorial that used the lathe to ‘machine itself’, machining the recesses for the bearing journals, then machining the journals once they were in place.

    1. This is a straight up misconception that has been passed down for so long people repeat it as a truth. It even occasionally pops up on machinist forums, where it is promptly shot down.

      Ask anybody who has used a lathe whether it can replicate itself and the answer will always be no. Even if you start including a ridiculous number of attachments (such as a milling conversion kit for the lathe), the answer is still no except for a very small toy machine.

      The series of books that show how to build a lathe “from castings” uses purchased precision ground stock as the ways and cheat in other similar ways.

      1. The article I was referring to (again, this was years ago – written by an old-timer) demonstrates how to scrape (yes, physically scrape with a cutting tool, by hand) the ways to ensure they’re flat and true. It can be done, if you’re industrious.

        There is another article somewhere in the ether written during WWI about construction of lathes using concrete so as to conserve materials for the war effort. At the time, production couldn’t keep up with demand for heavy machinery, so the concept was developed as a solution.

        Look up “Yeoman’s Lathe” if you want more information. Yeah, the design uses pre-fabbed stock for the ways, but it’s still an interesting design none the less.

  1. could a similar effect be made by threading the surface in both directions? it seems like a pretty easy method of making a grip texture, as long as the second threading doesnt wipe out the first.

    1. You’ll get a texture, but it won’t look very good. When you knurl material, you’re not removing much material at all, but rather mushing it around to raise the diamonds.

      Also, bearings don’t have to be the round balls you’re used to. Bearing bronze makes a great bearing, hence the name.

  2. When knurling you need the OD of the material you are knurling to be a multiple of the pitch of the knurl to get a nice knurl without the double lines you see in the photo above. He is very close to the right diameter, shaving a few thou off will make it look better. Also use fluid for knurling, cutting oil for cut knurls, lubricant for forming knurls.

    1. And he bought the screw at Ace to replace a screw that already replaced the original one.

      He must not have anything better to do than to make his tools not look like they’ve been cobbled together.

  3. I actually highly suggest watching ALL of mrpete222’s videos… he’s a (retired?) high school shop teacher and has a clear and practical-minded instruction style that I find very easy to understand.

    Makes me wish I took metalworking when I was in high school… a sadly lost program of study at most schools.

  4. I wouldn’t have known there where brass inserts under the set screws. The only knurling hand tool I ever used is dirty repair of engine valve guides. Now that I have a bench machine to insert new valve guides I don’t use the knurl type of rep repair. I suppose push comes to shove a sharp cold chisel or a center punch could be use to create knurl on an exterior surface Now I have another YouTube channel to check out further. Curses ;)

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