Hi everyone...longtime lurker, you know the story.
Anyway, finally found a Prentiss Vise. I've been looking for quite a while. Pretty damned good shape, except missing one jaw, and all four jaw bolts are broken flush! I know. Anyway, since many on here have gone before me, I was looking for advice on how best to proceed (with an easy-out I'm guessing.)
This is a Prentiss 96. Sorry to repost this same question but this thread has a lot more action than where I originally posted (
here)
Thanks in advance for any help/advice you can provide.
Hello, SierraGold,
Do you have argon-arc (TIG, heli-arc) welding capability, or have a friend who does?
If so, I'll suggest using my preferred technique for removing broken bolts/screws.
Pick out an unplated steel washer, of an i.d. size which matches the broken bolt. (If all you can get, these days, are plated washers, heat them red and let cool, then wire-brush/sand bright)
Carefully weld the washer to the broken bolt, using 316 stainless filler rod, which will alloy well with almost any grade of steel one might find in a bolt or screw.
When that weld has cooled, pick out an unplated steel nut of any suitable size, and weld it to the washer. The welding heat will have loosened the 'stuck' threads, and a good weld will allow for as much torque to be applied with a wrench as may be needed, but do let it fully cool before wrenching. Sometimes, the fastener will not unscrew out of the part easily, even after all that, so twisting it back and forth just a little whilst applying a good penetrating-oil will help to free it up, and preserve the threads in the tapped hole. Some 'very stuck' or rusted broken fasteners will require to be 'wiggled' thusly quite a bit before they actually come free, taking larger and larger partial turns as the oil works in.
'Clean up' the tapped hole with a tap, but if you're not familiar with this work, take care to get a 'best quality' American made 'commercial ground' thread tap, as the cheap cut thread taps sold by automotive and cheap hardware suppliers will often cut over size, leaving a needlessly 'sloppy' tapped hole. "Cut thread' taps are intended for 'blacksmith' or 'fabrication' grade work, and *must never* be used on tools or machinery. I'd recommend the 'Reiff & Nestor' make of taps, particularly, but any of the good standard American makes are acceptable, and the 'commercial ground' grade is dimensionally adequate.
I've used this method literally dozens of times, over the years, and it has always worked well, the only caveat being that the broken end of the bolt must be clean, to get a sound, uncontaminated weld.
If the part with the broken bolt is too large/heavy to go into the blass-blast cabinet, removing any traces of oil or grease with a mix of acetone and methylethylketone. and removing rust, to bright metal, with a little mounted wire-brush in a high-speed die grinder should leave the part clean enough for a good weld.
Using an easy-out is gambling with the part. If you feel you really must try that technique, use the 'tapered square' variety, in the Plomb/Proto/P&C make, or the 'straight spline type sold by Snap-on. Be ever so careful to drill the broken bolt in its exact centre and have the drilled hole small enough that you don't risk drilling into the thread.
(the all-too-common 'professional automotive mechanic' mistake involves drilling the fastener at an angle, just enough to get out into the threads, and then breaking a 'very hard' cheap oriental easy-out flush with the broken fastener. This mistake 'locks' the broken fastener into the part, making the task of removing it 'significantly more difficult'.)
Oh, and just for info, your Prentiss 96 is listed in old catalogues as 6" jaw, 10" opening, and 155 lbs. weight.
(edit) There is one of the gentlemen here who is making up very high quality replacement vise jaws, and should be able to make up a set for your vise, using the existing old one as a 'sample part'......look back in the postings here for reference.
cheers
Carla