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ID A vise screw, and help making an Acme Nut

QT; Chinese vises crap:

My Dads friend was selling China vises then a customer came to tell that the top jaw broke right of and almost landed on his foot. The friend was afraid to sell another one,
 
The screw's a bit cleaner now. Here's a better picture. It's almost 4 tpi, but not quite. Probably closer to 3.75. None of my pitch gages match it.

Crest of the threads measures about .125, and the valley measures about .135
View attachment 435751
"None of my pitch gages match it."
I dug out my pitch gages and tried to measure them, but even my 3-1/2 doesn't appear to match perfectly, FWIW...

...is there such thing a a "Metric Acme"?
 
The screw's a bit cleaner now. Here's a better picture. It's almost 4 tpi, but not quite. Probably closer to 3.75. None of my pitch gages match it.

Crest of the threads measures about .125, and the valley measures about .135
View attachment 435751
Is the shiny screw the result of a wire brush (likely) or electrolysis? I can see no reason that screw will not serve well.

Making an appropriate nut may be challenging if the TPI is something weird. Interestingly the pitch seems not too far from 7mm which I have never heard of for a vice screw.


Maybe a friend who has thread milling capability would save you the trouble for a cold 12 pack. IIRC you have 3-D print capability. So you could measure as closely as possible, draw up, and print a plastic nut to prove the design and then get it milled out of cast iron or steel. If you prepped the nut by pre-drilling it, it would not take long to mill it.

Denis
 
The original screw may have been made on a lathe that was worn out. The other, those threads may have been die cut instead of single pointed. Don't recall how far back thread milling was done. I would think thread milling started in the early 1920's, just a WAG. Definitly could be some lead error in that thread from manufacturing. I've seen it!
 
The original screw may have been made on a lathe that was worn out. The other, those threads may have been die cut instead of single pointed. Don't recall how far back thread milling was done. I would think thread milling started in the early 1920's, just a WAG. Definitly could be some lead error in that thread from manufacturing. I've seen it!
Any error in the lead of that screw could be pretty easily checked in the mill. If you just set the screw up on the table and then put a dial indicator in the spindle of the mill and using your digital read out then march on down and check every fourth thread crest or something like that to see how close it seems to repeat. Even if there were some error over 10 inches let’s say, since you’re only engaging 3, 4, or five threads in the nut at any one time, some modest lead error really wouldn’t matter too much.

The above does make a case for trying to print up a test nut in plastic, though, just to make sure that, in fact, it will screw fairly freely on down the length of the screw. And it wouldn’t be hard to then test just how tight a tolerance you’d be able to get away with. All that would be good to know prior to committing to iron/steel.

Denis
 
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Most of these older screws are made where they centralize on the OD and ID's and have lots of linear slop designed into them. Guessing around .030" to .050" linear slop IMO.
 
Is the shiny screw the result of a wire brush (likely) or electrolysis? .....
Dipped in "Rust 911" (economy version of Evap-o-rust) then a polish with a soft bristle wire wheel. The screw is used and has some wear in the center and a few gall marks along the threads, but I think it still has a lot of life left.... provided I can match a nut to it.
 
Measure across 10, 20 or 30 threads from the same feature to the same feature, perhaps the edge if a thread, then divide by that member. That should get right-on knowing the pitch.
....
Doing this method, It looks like it's consistently 7 threads per 2 inches, checked along a 12" length and at a few different points along the diameter, so 3.5 TPI should be right.
 
I made a vise nut once by molding a pattern with my hands out of warm wax, to fit the dovetail in the vise body, and squeezed into the threads. I dipped the dovetail in more molten wax to fatten it up a bit so I could file it to a drive fit in the body. Unscrewed the wax nut from the screw, and screwed it on and off a few times, hoping to wear it enough so that casting shrink would not make it too tight.

I would like to say I cast it in bronze, but aluminum was the flavor of that day. I had to work on the female thread with a hooked scraper I use for such things to open it up so it would run freely...but it worked.
 
I have a vise I saved from the refinery ..... left out in the weather ......the screw has sections rusted out from the salt air ......a new screw is over $200 ,which is a bit rich ,IMHO.............a screw from a gate valve is the same pitch and dia ,but different form........it fits OK ,but is not hardened ..
 
Here is another way to make the nut. Weld your blank up out of whatever pieces will make the shape, but with a tube for the nut portion, ID just a little bigger than the screw O.D.

Coil a wire or piece of slender keystock to fit nicely in the trough of the male thread. Fit it into the tube, check to be sure the screw still passes, and braze it in. Thread forms/flanks of course will not match, but it will work. It is a vise, not an airplane landing-gear actuator.
 
I'm still trying to figure out the manufacturer based on the spindle shape, handle ball ends, and the fact it was held in place with a set collar (the set screw hole is a giveaway). The set collar largely eliminates some brands entirely, but leaves quite a few as a possibility.

With that said, there are some completely incorrect statements being made here. Vintage, quality vises didn't used hardened screws (they still don't), and they generally didn't use Acme threads, or modified Acme threads. They used square threads, but often weren't standard threads at all. Not long ago I was asked to make a new screw for a Parker 975 vise. The screw was something like 1.10", 3TPI, and definitely square threads. That's not one you're going to find in a book. They simply came up with a screw size that would handle the load, and a TPI that had the vise open quickly enough and made whatever tooling they needed to produce that combination. After a hundred years of wear they may no longer look like square threads, but that's how they started out.
 








 
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