Repairing Prentiss vise

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pwint14

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Hi all,

This is my first post. I am a glutton for punishment who gets joy out of repairing tools. So, I bought an old Prentiss Bulldog vise that has seen better days. There is a crack in the slide of about 4” and part of the casting is missing on the fixed jaw side.

There is a lot of good information online about brazing the crack in the slide. I’m also wondering if it would be possible to build up the missing casting with bronze brazing. Alternatively, I was thinking that the broken casting could be machined/milled to accept a piece of mild steel that would be brazed into place. Curious what folks think about these options?

The catch is I am interested in learning machinist skills but I don’t have a shop or any tools to accomplish these repairs. I was wondering if there was anyone in Chicagoland or within a reasonable drive who is capable of doing the repairs to the vise and whom I could learn from (of course, I would pay for the worn but also would like to learn at the same time).

Thanks,
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Hi and welcome.

That one looks rough, before you start working on it I’d suggest defining what your expectations are.

If you want to use it like the previous owner I’d honestly suggest finding a better starting point. Most repairs are likely not going to be as strong as the original cast iron.

I’ll let others suggest repair techniques but unless this is a family heirloom it might be best left as is. Does it clamp securely now? I’ve used some pretty crummy looking tools that worked fine.

John
 
Thanks, John. I am mostly a weekend warrior so I did consider simply stop drilling the crack, sinking a machine screw into the side to pull the crack together, and using it as is. I thought I’d ask here about going further to learn and if it would extend the useful life of the vise. But it isn’t a family heirloom. I would just feel bad if I broke it worse when I had an opportunity to strengthen it at the outset.
 
I would braze the crack in the back, after drilling a hole to prevent it from continuing. I don't think I would work on the missing piece.
I would sandblast that, and see how it works. If it works fine figure out what you want to do. It will never be a valuable piece. It can be a workhorse.
Make sure the nut is in good condition before continuing.
 
What the guys have already said.

From past experience I’ve learned that while you could learn something from this, ultimately this vise was abused beyond its capacity and it’s not worth the huge amount of effort only to still be marginal. For every apparent problem there is atleast 1 or 2 not apparent. Like I’m sure the slide is bent. In order to do that kind of damage to the body and slide it had to be fully open then they beat on whatever was in the vise. You don’t straighten a slide easily, if at all. I’ll bet there is other internal damage like to the screw and nut. One of my most valuable lessons in restoring old iron is evaluating the total damage and when to cut bait and move on. It would take a lot equipment just to repair that vise that is more related to welding than machining.
 
Not to be argumentative, but my take is a bit different. I lost track of how many bench vises I've owned when I got to 300, and I've worked on some really beat up vises just to make them functional...including a fair number of Prentiss brand vises. With that as a background, I'll say I think that vise can be made to work just fine. No, it won't be like new, but if it isn't used for really heavy work, should be serviceable.

The damaged part at the back of the body was almost certainly caused by someone using it like an anvil, not from someone beating on something in the jaws. Beating on something in the jaws normally causes the static jaw support (ledge) to crack because that's where the force is directed. The other thing is, if you look at the shape of the crack, the center of the casting protrudes farther back so it wasn't caused by the slide pushing upwards in the casting...it would have chipped out the center as much as the other areas.

As far as the slide goes, I doubt it's bent. Ductile iron and cast iron cracks rather than bends in most cases. I have seen a lot of cracked slides and no bent slides. The crack in the center top of the slide is very common on Prentiss vises...they were a bit thin there. Often people use the slide as a hammering surface, and they crack. It looks like a big hunk of metal, but it's really just a hollow U, so it tricks folks. I like to TIG weld them with Inconel filler rod, but TIG brazing with silicon bronze or aluminum bronze works nicely as well. Traditional brazing is fine and stick welding with nickel rods also works.

I usually stop drill the crack, put a clamp or two on the slide to keep it in place, then tack weld on the very back and then lay down beads to fill the crack.

My technique for TIG welding cast iron and ductile iron came from a true master welder and machinist, but I have never seen it posted anywhere. Use a carbide wheel to V out the crack and get it to clean, white metal. Don't use a grinding wheel as that can leave behind grit from the wheel that doesn't play well with TIG welding. Once you've got it clean, run a low amperage arc across the crack without adding filler. As soon as you do this you will see black soot coming out. That soot is carbon. Use a stainless brush to remove the soot and repeat the process a couple of times until the soot stops. At that point run a bead of Inconel rod just trying to get it to stick, without worrying about perfect coverage. Once you've got a bead down, just overlap the first bead by about 50% on either side and keep doing that until you've filled in the crack.

The one thing about Inconel and nickel stick rods is that they leave a very hard bead so if you don't want to spend a lot of time grinding, don't put down too much extra.

I have a website dedicated to bench vises that some might find interesting....articles about repairs, restoration. I don't sell anything there, it's not a commercial site, just info and pictures: www.mivise.com
 
Detroit isn’t far from Chicago ;)
 
G-ManBart said:
I'd be happy to help him with it!
Click to expand...
Thanks so much to you and everyone else for your input. I’ll have to see when I could make the drive to Detroit but we have been wanting to visit! I am just glad that there are options for keeping it going (understanding the expectations need to be reasonable).
 
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