1-1/8 x 3tpi ACME tap???

[LD1]

Without measuring the screw, we really don't know if it is an 29deg acme, a 29deg brown & sharp, or a modified acme etc. We would need root, crest, angle, and thread depth measurements.

Yes you really need all that info IF and only IF there were options for a 3tpi for several threads.

That fact that there are none....makes pitch angle, root depth, crest, etc all irrelevant.

 

[LD1]

A 3 TPI screw seems quite course for a vise of that type. Normally, 3 tpi would be like a carpenter's bench vise. I wonder if someone broke the original screw and fed in that 3 tpi one???? Something isn't right.

https://taytools.com/products/copy-of-2-1-2-drill-press-vise

Agree it seems coarse.

But I don't think it was ever modified.

The handle is one piece. The cast anchor nut appears unmodified
If someone really did break the original they did a darn good job making this look original.

 

[etpm]

Is 3 TPI a common thread setting on lathes?

That is really coarse. I didn't consider that. I'm glad you pointed that out. Thank You. But if the OP has the right change gears it would be possible. Tomorrow I'm gonna take a look at one of my lathes to see if a 6TPI thread is listed and if I have a change gear to halve that. I may even have the gears for that lathe to quarter a 12 TPI thread. Since that particular lathe just has normal change gears for its quick change gearbox if I can cut 3 TPI threads on it the OP may be able to do the same thing. If the OP has an old lathe without a quick change gearbox it is probably more likely to be able to cut a 3 TPI thread if the lathe also has the complete compliment of change gears. I am so used to using my CNC equipment to cut unusual thread pitches I forgot about manual lathes with sometimes limited thread choices. Depending on the age mainly, lathes could have either a quick change gearbox, or if older just a bunch of gears. The quick change is of course mostly better because it will cut most or all standard pitches. But the older lathe with a full compliment of change gears will cut many non standard pitches as well. Doing prototype work only the lathe without the quick change gearbox might be better. Or a CNC lathe, which will cut any pitch within the lathe's capability of HP and RPM. Since I started machining nearly 50 years ago I have considerable experience with all 3 types mentioned, but have been spoiled by the easier to use options.
Eric

 

[LD1]

Yes I can cut 48 different thread pitches from 1.5tpi up to 92tpi on my monarch k16.

Problem is cutting such a large thread, in such a small bore...through a 3.5" deep piece.

Not impossible....but not an easy task because it requires such a small bore threading tool and it would have to stick out so far to get depth. A tap would be so much better.

And trying to chuck the odd shaped anchor block poses another challenge. Unless I made it out of two pieces and welded the "nut" part to the anchor block.

If I went to all that trouble....I'm thinking it would just be easier to get a stick of 5tpi ACME rod and a nut. Make a new handle/draw rod and make the new anchor block out of the ACME nut.

Dunno what I am gonna do yet....was hoping someone would help identify a tap.....then it would be a simple fix

 

[etpm]

Yeah, I think you are plain outa luck. For that thread you would need either a rougher and finisher tap or a tap with a rougher section. If you could even find that tap it would be expensive. Last year I had to tap a new bronze nut for a lathe cross slide. 3/4-10 acme thread. Brand new tap with a rougher section. It was very hard to run that tap through. I can only imagine tapping cast iron or steel with a 1 1/8-3 TPI acme would be very hard to do. Your idea of building your own part with the 5 TPI nut is probably your best option.
Eric

 

[lpakiz]

I worked on a couple of my vises and the screw was always 4 TPI, no matter the diameter.
3TPI will yield less clamping force with same torque, and there will be more friction in your larger OD screw.
I didn't even look for that coarse or that large a diameter of a nut, but when I found mine for 1/2-4, 5/8-4 and 3/4-4, my intent was to scavenge the internal threads from a new nut, then marry it to the old original holder. I got lucky and was able to modify the new nut/holder so it fit my needs.
I believe I just Googled 5/8-4 Acme and a bunch of vise nutsshowed up.

 

[rScotty]

Looking at your photos of the threaded rod.... and comparing the center with the ends makes me wonder if that rod itself is any good. If that rod is what did the stripping of the internal threads then the rod itself might have yielded along its long axis....particularly there in the center of the thread. Take a look at the center of the rod vs the ends. Does it look to you that the sides of the the threads are not only beat up, but are at different angles? I wonder if even with a new nut that rod would ever tighten and loosen the vise reliably.
I'd go with a new rod and some new nuts. Would surely work better.

rScotty

 

[LD1]

The rod is fine. Showing some wear and age....yes. but it's the nut that is stripped. The pics may not represent it clearly

 

[dstig1]

Yeah that is an odd one. I think your only decent option will be to make new with new Acme rod and coupler from McMaster, etc. If the nut is stripped out, even if you could find a tap, how will that help it? If the metal is worn away or torn out from being stripped, then you wouldn't have enough to reform into threads in any case. Plus it is cast, so the odds of fixing it seem low. If you have room in the vise, 1.25" Acme seems a lot more common and you could go with 4 or 5 tpi. Get a coupler nut to match, then machine up a piece of steel to match the rest of the existing nut/follower and weld them together.

And geez that thing looks massive!

 

[LD1]

Yeah that is an odd one. I think your only decent option will be to make new with new Acme rod and coupler from McMaster, etc. If the nut is stripped out, even if you could find a tap, how will that help it? If the metal is worn away or torn out from being stripped, then you wouldn't have enough to reform into threads in any case. Plus it is cast, so the odds of fixing it seem low. If you have room in the vise, 1.25" Acme seems a lot more common and you could go with 4 or 5 tpi. Get a coupler nut to match, then machine up a piece of steel to match the rest of the existing nut/follower and weld them together.

And geez that thing looks massive!

The idea of finding a tap would be to only have to rebuild the anchor nut. I could make it out of one solid piece of steel....or even make my own "rod coupling nut" and weld it to a dovetail base that I would make.

Going to a different thread.....not only do I still have to rebuild the anchor nut....but would also have to remake the threaded spindle/handle.

Even with its odd 3tpi.....the vise always worked great and as expected. It never did have the clamping force of the wilton bullet....but partly because the throat depth is so large. But but it had the ability to grab ahold of some larger odd parts that the bullet just wouldn't. I used this vise for years when I was a millwright punching a timeclock in a factory. Until it stripped. Factory got a new vise and canned this one. I took it with the intent of fixing it one day. So right now I have nothing invested. So even ~$60-$80 and some time to remake some parts its still a worthwhile investment.

Just cant bare the though of thowing it away.

The hole where the handle/spindle goes is only 1/1/8". So dont really wanna have to open that up to go 1-1/4. And I dont see them as being "more common". Maybe they are....but I can get 1-1/8 just as easy and its cheaper. Might be like 7/16 or 9/16 bolts. No they arent as common as 3/8, 1/2, or 5/8....but still just as easy to source and get