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ID A vise screw, and help making an Acme Nut

M.B. Naegle

Diamond
Joined
Feb 7, 2011
Location
Conroe, TX USA
This old vise screw's been floating around the shop for awhile. It's nothing special and looks like it could have come off of any number of machine shop bench vises from the turn of the century, but has somewhat of an odd thread at a 1" OD, 3 1/2 TPI Acme. So for one I'm curious if anyone know what It might have gone to based on the odd thread in case it could be more useful for someone else in it's original intended capacity? No makers marks that I can find but I'm going to give it a dip in the chemical rust removal in case it has something hidden.
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Secondly, one of my back burner maybe/someday projects is making a custom bench vise, and this screw could be very helpful for that project if I can find a nut to fit it. Given the odd TPI, I think making one would be my only solution, so does anyone have any tips for single-point ID threading an acme nut? My 16" Hendey has the 3 1/2 TPI gearing, and I gather I'll need to custom grind a boring bar bit to the right profile.

I'm still mulling it over and if making a nut is going to be too much hassle I can always cut off the cross-bar and hub and splice that into some off-the-shelf acme with an easier to find nut, or just cut to the chase and modify and existing vise (where's the fun in that....).
 

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I'd definitely cut a new male thread as well, the rust etc on that screw willchew a nut up in no time.
To save time hassle and $$, I'd look at buying ''off the shelf compnents'' and grafting them to the application, before I machined anything.
 
It might be interesting to see the screw after a dip in sodium carbonate and a battery charger to remove the rust. I have seen some surprisingly good results and the rust on this part does not look terrible... well bad maybe but not terrible.

That is a coarse enough thread that matching a single-tooth cutter to the spaces between the threads by eye might not be too tough. My round dial does have a 3.5 pitch setting. The thread fit would not have to be "perfect" to make a perfectly good nut. Do you think the screw is hardened?

Denis
 
I'd definitely cut a new male thread as well, the rust etc on that screw willchew a nut up in no time.
To save time hassle and $$, I'd look at buying ''off the shelf compnents'' and grafting them to the application, before I machined anything.
100% agree for all the reasons you stated.

Unless it belongs to a rare museum piece I doubt that rusty oddball screw is worth the effort.
 
Curious what the width of the profile is. I know you said it's "Acme", but I ain't that "schooled", but I have a bunch of acme style carbide cutters laying around, and possibly a boring bar to fit.... 😎
 
Curious what the width of the profile is. I know you said it's "Acme", but I ain't that "schooled", but I have a bunch of acme style carbide cutters laying around, and possibly a boring bar to fit.... 😎
That's the kind of stuff a good machinist never throws out.... Way too hard/expensive to replace later. I've got a few myself. Also Acme inserts are easy to modify into specialty grooving tools if you have extra.
 
Pretty easy to make a male or female acmy thread
Not IMHO 1'' x 3 1/2 TPI Nuts, with a minor dia of <> .715, and a projection of cutter AT LEAST 0.290 from the bar, you are fast running out of room for an internal threading tool shank with any stiffness.
 
Fix the nut on the compound and set up the boring bar held in chuck and outboard end in live (or dead) center? Seems like the bar ought to be pretty stable that way and at 1" sturdy enough. I would also think part of the groove could be cut using a less-than-full-profile cutter and by using the compound set parallel to the bar successive cuts could be made of partial profile thus reducing pressure on the bar, if needed. (I will qualify these comments saying I have not actually done this, but I do not see why it would not work.) For even better rigidity, make a fixture for the nut to mount directly to cross slide. The nut could still be moved parallel to the bar using a guide bar, DTI, and loosening fixing bolts.

Denis
 
How do you get 3.5? The parts I build are labeled as 2 tpi, the late gearboxes are set to 2 tpi, and this is how they measure, which seems to be similar to yours? Unless the camera angle is making yours appear different... :cool:
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I'm sure M.B. knows his stuff and I have seen odd pitches like this used over the years. Here in oilfield country, we have a rotary shouldered connection called Hughes H-90, it is 3-1/2-threads per inch with 90° flank angle. I'm sure it is not a fluke.
 
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
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Quality vises do have a modified square thread.......just angled enough to proved clearance for a cutter or roller........a quality vise will also have a hardened screw and use a free graphitic ductile iron nut ..............this detail is what makes Chinese vises crap.......the first heavy loading the crap screw distorts in the crap nut and jams up......(actually one of many things that makes Chinese vises crap)
 
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.

The width at the Od will be narrow and at the root the width will be wider from wear. A catalog nut will work but may have more end-way play than a new thread fit. End slop likey won't be a problem for the likes of a vise. A little tricky turning a nonstandard Acme, I think the best way is to use the male part for a thread gauge, with seeing about .002 open at each side of your tool bit.

If never making a special/odd thread I think it is a good idea draw the thread and put in the dimension comparable to the grade specs of a standard thread of near the same size.
 
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