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question on repairing the screwbox on a post vise.


Countryboy39067

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Has anyone used the pouring of Babbitt in the screwbox to form the threads? This is my grandfathers post vise so I don't want to damage it so I'm a little against brazing if there is another way. I've also concidered getting three nuts threaded on the screw and building a cage of sorts to hold them online and form a new screwbox that way. Any ideas will be appreciated.

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Pouring babbitt around the screw is a method or repair mentioned in Practical Blacksmithing, Richardson. You may want to ILL that book and read up on their suggestions.

If your grandfather gave you a car with a blown engine---would you refrain from replacing it?

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If your grandfather gave you a car with a blown engine---would you refrain from replacing it?



Great analogy!

Replace the engine...yes. But I would not braze a motor to the frame if another method is a available....no. What I mean is if there is a proper replacement part or a way to make it look original then that's the way I wanna go. Thanks for the reference ThomasPowers!!
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Multiple nuts would be hard to keep from jamming. How would you hold them in the box? You would need to keep them from rotating and moving lengthwise too.


I was thinking of completely replacing the screwbox buy doing this.
My idea was to equally space three nuts on allthread that's about 12-18 inches long. I would then weld barstock on the flat area of the nuts therefore lining them up and preventing them from twisting. Hence a six sided hex nut would have six pieces of barstock running full lenght from the first nut, attaching to the second nut and finally the third nut in unison.  Then I would forge a case , similiar to a pipe, to protect the threads from trash. Also in the process I'll forge wings in the cover to lock into the recesses in the rear jaw to keep it from turning when you loosen or tighten the vise. 
 
 
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Welding barstock to the flats sounds like a great way of getting the nuts in weird orientations!

I remember when I was welding a rod to a flat plate and had my finger on the top of the rod how much it moved all over the place while welding the other end.

The "wind sq rod and braze" technique has already been mentioned as out of bounds.

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I absolutely 100% guarantee that welding nuts together will jam due to shrinkage and distortion. Heck, welding on one nut is usually enough no prevent a bolt from going in. Don't ask me how I know! You can get Acme all thread and nuts from ENCO, MSC and others.

Actually, babbitt works very well for this kind of thing. A steel nut requires about 1 diameter of length to have full strength. Babbitt, at 1/4 the strength requires at least 4X diameter thread engagement for full strength. Split nut on a lathe is often babbitt and seems to follow the 4X rule.

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Often thought about how to forge a large nut for something like a fly press. Finally decided I could do it like a split nut. I'd machine one piece of threaded rod down so I had half screw (like a fuller), forge that into 2 pieces of bronze to make two halves. Then machine the outside and press it into a housing. In the case of a press I'd machine it with a shoulder and press it in from the bottom.

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I absolutely 100% guarantee that welding nuts together will jam due to shrinkage and distortion. Heck, welding on one nut is usually enough no prevent a bolt from going in. Don't ask me how I know! You can get Acme all thread and nuts from ENCO, MSC and others.

Actually, babbitt works very well for this kind of thing. A steel nut requires about 1 diameter of length to have full strength. Babbitt, at 1/4 the strength requires at least 4X diameter thread engagement for full strength. Split nut on a lathe is often babbitt and seems to follow the 4X rule.


I have to disagree with using babbitt to repair the treads in a vise box. They just won’t hold up to the abuse. Some vises boxes were made by forging material into a tube and threads were then brazed into it. Some later vises were made as cast with threads cut into the box. There is a proper way to repair a leg vise box. Dick Sargent posted a blueprint on the process but since the blueprints are not currently available I’ll tell you what it said.

I know this process works because I just repaired a vise using it.

If the threads are brazed into the box (you will know if you see brass between the threads and the tube) then remove them by putting the box in a forge and heating and pulling the threads out. Or, you could turn them out on a lathe. If the threads are cut or cast, you will have to turn them out in a lathe.

Then make new threads by wrapping stock (say 1/8 X1/8) around a good part of your screw. You really only need about 2 inches of thread. An OA torch works well for this. If you don’t have a lathe, you will need to size the stock to fit into the box.

Take the threads you made and put them in the box, add flux and brass and put it into a forge, either coal or propane. Bring it up to temperature and rotate to let gravity and capillary action do it thing. That is the way vises were made before there were screw cutting lathes.

Then start working the screw into the box to break up the flux. Use grinding compound to cut clearance for easy use.
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I have to disagree with using babbitt to repair the treads in a vise box. They just won’t hold up to the abuse. Some vises boxes were made by forging material into a tube and threads were then brazed into it. Some later vises were made as cast with threads cut into the box. There is a proper way to repair a leg vise box. Dick Sargent posted a blueprint on the process but since the blueprints are not currently available I’ll tell you what it said.

I know this process works because I just repaired a vise using it.

If the threads are brazed into the box (you will know if you see brass between the threads and the tube) then remove them by putting the box in a forge and heating and pulling the threads out. Or, you could turn them out on a lathe. If the threads are cut or cast, you will have to turn them out in a lathe.

Then make new threads by wrapping stock (say 1/8 X1/8) around a good part of your screw. You really only need about 2 inches of thread. An OA torch works well for this. If you don’t have a lathe, you will need to size the stock to fit into the box.

Take the threads you made and put them in the box, add flux and brass and put it into a forge, either coal or propane. Bring it up to temperature and rotate to let gravity and capillary action do it thing. That is the way vises were made before there were screw cutting lathes.

Then start working the screw into the box to break up the flux. Use grinding compound to cut clearance for easy use.

Thats what I was looking for!!! Thanks! Are you refering to the brass stock you can get at the hardware store or the brazing sticks you see at welding shops. Also what do you suggest would be the best flux for this application? Thanks again!!
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Working thru the calculations for screw force and the yield strength of babbitt, it does indeed look like babbitt would not be a good idea. Makes one wonder if the author ever actually did it.

Pretty interesting, putting 200 pounds on a 20" handle going through a 4 pitch thread yields a force of 50 tons! That's disregarding friction which is a big factor with the poor thrust bearing and all, but still! Checked my calculations three times.

Good post ciladog! Glad to see someone who has actually done it. Practice beats theory any day!

Apologies to dablacksmith too!

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From someone who has not done this. Back in the day, one could buy something called spelter. It was a brass powder or finely granulated brass, and it could be mixed with borax. Further, if the mixture were moistened, it could be brushed on the area to be brazed. You want a tight fit on the parts to be brazed, no daylight. The molten copper runs between the surfaces by capillary action. The iron must be at least at a cherry red. I was thinking of possibly getting a more uniform heat in a muffle, perhaps by using and heating a pipe.

Proprietary brazing rod is alloyed to melt at about 1600ºF, which makes it a known quantity and fairly easy to use. Other brass alloys may melt at higher temperatures.

Reference, James F.Hobart,"Soft Soldering, Hard Soldering and Brazing," Van Nostrand, 1912, 1919.

http://www.turleyforge.com Granddaddy of Blacksmith Schools

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That is correct Grant. Jack-out screw force is amazingly powerful. I have tested this many times on aircraft parts.

What's amazing to me is that the brass used to braze the screw into place can handle this force. I don't have any data with me at the moment to calculate tensil/yield strenght of brass, however counting the friction in the threads, the axial load, and torque applied, brass must have sufficient if not impressive numbers for the application at hand. It would be interesting to figure this out.

EDIT: I should clarify that screw force is amazing. I used the term "jack-out" because I do a lot of testing jacking out inserts from aluminum and titanium. I was thinking of a jack-out condition if the brass gave way resulting in pulling out of the threads.

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You're dealing with about six square inches of area in shear given 1-1/4 acme 5" long. At 5,000 PSI average yield for babbitt, that can only resist about 15 ton and your brass about 4 times that, or 60 ton. Yeah, it fits. Friction might rob 30% of your twisting force with a poor thrust bearing.

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Here are a few more tips for those who will actually try to re-thread a vise box.

The box I re-threaded was cast so I had to cut out the old threads on a lathe. You need to use a stead-rest when you cut the threads out. Chuck the box in the lathe as true as you can and put the stead-rest about an inch back from the end. It will be a bumpy ride at this point. Then cut the first ¼ inch of the box on the OD to true up the end. Then reposition the stead-rest and cut out the threads.

Leave the box in the lathe until you have made your threads so you can do some final sizing. The threads (on the screw) should just slide into the box with a few thousands clearance. If you need any force to insert them, you will most likely distort them when the screw isn’t supporting them.

Before you insert the threads for brazing, put the empty box in the forge and burn out any old grease and scale from the back. Grease vapor will contaminate your weld. You can clean the inside of the box using a brake cylinder hone, works very well. Use brake cleaner for a final cleaning.

To make the brazing power, I put a sheet to wax paper under my belt grinder and just collected dust from grinding up brazing rods. I added borax as flux and ground it up into a fine power. I added this mix to the box cold and then put it in the forge. You can add more brass as short lengths of rod once the box is up to heat by laying them across the threads. But if you try to add flux, you will most likely end up with brass on the threads.

When the brazing is finished let the box cool completely before you attempt threading in the screw (the metal contracts when it cools you know) and you don’t want it contracting around the screw. The first time you try to thread the screw it will seem like it just won’t go but it will. I sharpened the end of the thread on the screw to a chisel point with a cutoff wheel to cut the flux and excess brass as it threaded in, in a little then out (you know the drill) and use some muscle.

Use some valve grinding compound on the screw once you have the flux and brass cleaned out to cut a few thousands clearance and it will work like a new vise. Remember to wash out the grinding compound or you will be re-threading again in short order.

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Nice article! Ty for posting.

We rebuilt a couple that way with nuts and new thread. We put 2 nuts in a piece of tubing (one on each end) screw the thread in and welded the nuts. This doesn't happen all in one setting. We take our time to help that the heat doesn't get out of control and warp. Thus making a new box. On the tubing we put a wedge, similar to what the box had, so it would set in the eye of the vice and not spin. Obviously you have to cut the thread off the handle and attached the new one, getting that centered can be tricky. If it is off you risk racking your vise. And if the weld wasn't solid it will fail eventually.

Another thing we have done, depending if the box isnt shot,, is cut the thread off and flipped it. Sometimes the end is just worn, but the meat closer to the handle isn't used much since it sits in the eye.

This being said, 5" leg vises go for $75ish...we put all this work into em and they are still...$75 lol. I would probably not use your vise due to the emotional connection with it, and get another one until your ready to modify.

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Working thru the calculations for screw force and the yield strength of babbitt, it does indeed look like babbitt would not be a good idea. Makes one wonder if the author ever actually did it.

Pretty interesting, putting 200 pounds on a 20" handle going through a 4 pitch thread yields a force of 50 tons! That's disregarding friction which is a big factor with the poor thrust bearing and all, but still! Checked my calculations three times.

Good post ciladog! Glad to see someone who has actually done it. Practice beats theory any day!

Apologies to dablacksmith too!


Thank you Grant.

Most tasks we do are a process of orderly steps. The task, as a whole, can seem overwhelming or beyond one’s ability. But broken down into the steps, and we have already accomplished it.
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