Name this part! (square nut on a machine vise)

[rawbutter]

I need to find a replacement 1/2-13 nut for my machine vise. The one I have (original to the machine) has completely stripped. Unfortunately I also don't know the same for it, so I can't search for a replacement. If I search for square nuts or square retaining nuts or anything similar like that, I only get results for normal square nuts with maybe a few odd shapes for T-slots. Not helpful.

The nut is square, but it also has a round protrusion coming out of the bottom. That round part fits into a round hole in the bottom of the vise between the ways to keep it in place horizontally. (It's kept in place vertically by the two halves of the vise once assembled.)

Obviously I've checked the manual, but the manual lists the entire vise as one part. Useless. I've also looked at manuals for other vises, but I can't find one that uses the same kind of retaining nut.

I've attached some pictures for reference. The nut I need to replace looks like it's made of brass, which seems really stupid to me, but whatever.

[DocsMachine]

The same part in a lathe cross slide is called simply a leadscrew nut. They're made out of bronze, usually, or brass on cheaper parts, because those wear well (low coefficient of friction) on a steel or iron leadscrew.

The brass or bronze does wear faster, but it's cheaper/easier to replace the nut than the whole screw.

If you can't find a replacement, I can make you one.

Doc.

[rawbutter]

If you can't find a replacement, I can make you one.

Thanks, Doc. I might take you up on that. But if this nut is usually made from brass or bronze, I should be able to make it myself. I don't have a 4-jaw chuck, so I can't do the square part, but I found this leadscrew nut on eBay, and I think I can make something similar.



I'm assuming the fact that this one is round won't be a deal-breaker. It will be a little more tricky to get the vise reassembled since the lead screw might rotate, but once it's all together the lead screw itself will keep the nut from spinning.

I've got one more question, if you don't mind. The lead screw itself seems to have square threads, but a normal 1/2-13 nut will screw onto it. Can I just use a normal 1/2-13 tap to make my leadscrew nut, or is there a different tap I should buy for this?

[DocsMachine]

That's what's known as ACME thread, a blockier, sorta-triangular thread that can stand up to more force/pressure. A nut made with a standard 1/2-13 tap, if it fits, wil work, but will wear out and get sloppy in short order.

However, mot ACME threads like that are used for machinery- like lathe cross slides and the like. As such, an odd thread like 13 TPI would not cooperate well with a lathe dial, so a 1/2-13 ACME is rare. I'm not actually sure they even exist. Most you'll find are 1/2"-10.

Which means your options are to either single-point one (tricky, but by no means impossible) or just use the standard 60-degree tap, and just know the nut won't last terribly long.

There's several good videos online, including one by This Old Tony that explain how to do internal ACME. Be good practice to try.

Doc.

[WORR13]

they sell replacement leadscrew nuts for lathes. i know they sell em for south bend lathes on ebay, im unsure of the thread size though. looks very similar

[DocsMachine]

they sell replacement leadscrew nuts for lathes. i know they sell em for south bend lathes on ebay, im unsure of the thread size though. looks very similar

-Entirely possible, but they won't fit a 13 TPI thread. Remember that the thread pitch directly relates to how far the part moves per turn. An even number like 10 TPI will make the part move 1/10th of an inch per turn, or .100". (Taking .200" off the part on a lathe.)

13 TPI would move .077" or so, which I'm not sure you could actually make an understandable dial for, without adding in a bunch of gearing.

Doc.

[rawbutter]

The plot thickens.

All of Doc's talk about dials and things divisible by 10 reminded me that, duh, I have a metric machine. So, I took the whole lead screw to the hardware store again and discovered that it's not actually 1/2-13. It's M12x2.0. And they don't have metric nuts that coarse. They only have 1.25 and 1.75 thread.

Looks like I'm buying a new tap.

[DocsMachine]

The plot thickens.
Looks like I'm buying a new tap.

-I hate to say it, but if you can find one, I suspect that's going to be an expensive proposition. McMaster doesn't even have an M12x2.0 ACME (technically metric trapezoidal.) The closest they have is an M12x3.0, and that's $176.

You're going to have to find somebody with a metric lathe, or a good CNC lathe, to single-point it.

Doc.

[rawbutter]

I hate to say it, but if you can find one, I suspect that's going to be an expensive proposition. McMaster doesn't even have an M12x2.0 ACME (technically metric trapezoidal.) The closest they have is an M12x3.0, and that's $176.

You're going to have to find somebody with a metric lathe, or a good CNC lathe, to single-point it.

I'm worried about the same thing. If that's the route I have to go, I might as well buy a new vise. I should probably mention here that my machine is a Harbor Freight 3-in-1 lathe/mill combo thingy. Looks just like this one. I bought the whole thing for $500 on sale, so it doesn't make sense to spend $176 to fix one part of it when I can buy a whole vise for less than $100. Granted, the new vise won't be very good quality, but honestly it can't be worse than the one I already have.

On the other hand, I did find this tap/die combo on eBay for $20. That way I can try to make a new nut, and if it doesn't work with the lead screw I have, I can make a new lead screw as well with the die.

Is there any particular reason to single-point a new lead screw instead of using a die? My lathe can't do single-point threading, so my options are limited.

[DocsMachine]

On the other hand, I did find this tap/die combo on eBay for $20. That way I can try to make a new nut, and if it doesn't work with the lead screw I have, I can make a new lead screw as well with the die.

-If you're sure your leadscrew is, in fact, 12mm 2.0, it should work just fine. And for $30, I'd give it a try.

Is there any particular reason to single-point a new lead screw instead of using a die? My lathe can't do single-point threading, so my options are limited.

-Yes, It's very hard to get a die to thread straight down a shaft for any appreciable distance. If you start it even slightly crooked, it'll try and stay crooked, and get worse the longer it goes.

Single-pointing eliminates that as a worry. (Well, unless you lathe is really worn out.

Doc.

[rawbutter]

Time to finally update this thread.

I ended up buying the 12x2.0 tap/die combo on eBay to try and make this leadscrew nut myself. Sadly I couldn't find a piece of bronze bar stock for less than $40, so I decided to make a prototype out of aluminum first, just to see if it works well. If it does, then I'll invest in the better quality material and make a second one.

I almost ruined the part when one of my center drills broke while trying to drill straight down on the round section of the piece. The tip of the center drill even got jammed inside. But I turned it 45 degrees, tried again, and made it through. Turned out pretty well, if I do say so myself, and right on spec.

I've already got it installed in my vice, and I've done a few tests. Seems to hold up perfectly, so I'm one happy guy.