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Repairing a broken vise

Why

One day, it was needed to crimp a 25mm2 copper cable into a lug. A vise was chosen to perform the operation. However, the force needed was a bit too high and prolonging the vise's handle with a steel pipe exerted too much force on the cast iron part and it cracked.

A logical approach was to throw it away and buy a new one. This was decided against due to several reasons. The vise was a birthday gift from a now-deceased grandma, there is no reason to throw out something that can be repaired even potentially, there was a lot of experience to be gained on this job (whether success or failure), and repairing things instead of throwing them out can serve as a political statement against the "culture" of throwaway consumer capitalism.


Cracked vise

Cracked vise

Cracked vise

Cracked vise

First repair - gluing

The first choice of repair strategy was epoxy. A layer of epoxy was deposited on the crack surface and the parts were clamped together.

It worked well enough for a very light duty. However the joint cracked when more force was exerted. So, back to the workshop.

Second attempt - bolting

It was decided to try to join the parts with screws. Holes were drilled to both parts, and best effort was done to make them matching. (This turned out to be less trivial than hoped for.)

An obstacle was encountered in the vise head; the hollow cast was shaped in a way that prevented good mating to the screw heads. An attempt was done to mill away parts of the cast iron to make flat surfaces friendly to the screw heads; the success was only partial.

A mishap occurred during the thread cutting; the tap broke in the hole. It was decided to just leave it there as there was no way to get it out without really really great hassle.

The result was not entirely optimal. The parts did not mate properly, due to wrong alignment of the holes between the parts. While the mechanical integrity was sufficient for light duty, the jaws were not parallel and the grip was not good. Still, good enough to hold together parts for brazing, or circuitboards during disassembly.


Drilling holes

Drilling holes

Drilling holes

Holes with thread and broken tap

Holes with thread and broken tap

Holes with thread and broken tap

Matching holes

Milled head positions

Milled head positions

Milled head positions

Bolted together

Bolted together, detail

Bolted together, screw head

Bolted together, screw head

Acme screw

Acme screw

Acme screw

Acme screw, being secured

Acme screw in place

Result of bolting the vise together

Third attempt - welding

After obtaining a stick welder, it was decided to reattempt the repair.

The bolted assembly was disassembled, the parts were clamped together.

A grooving electrode (OK21.03, 2.5 mm) was used to burn away some of the material in the vicinity of the weld, and to remove traces of oil and dirt remaining from cutting the threads. The electrode melts the metal with electric arc, and its coating burns with production of large amount of gases, which blow the molten metal away. It has to be held in a steep angle to the workpiece, so the melt is ejected to one side. The work is fast and quiet, compared to a grinder, the downside is a copious amount of smoke and lots of brown dust. A window nearby, or working outside, is suggested. Two electrodes were consumed for this operation. The groove itself could've been deeper; will be done if a rework is required.

The weld itself was performed with a cast-iron electrode (E-S716, 2.5mm), with iron-nickel core. Two electrodes were consumed; it turned out one would likely be enough, as due to the inexperience of the welder the weld had way too much of filler metal. These electrodes are awfully expensive, but apparently worth it.

The excess filler metal prevented the "stator" and "rotor" of the vise from mating correctly. An attempt was done to file the excess away. However it turned out that the filler metal is very hard, and part of the file was damaged. A grinding wheel on a power drill was therefore used, and after some sweat and cussing and noise the excess metal was removed and the parts mated together well. A millimeter or so of the original cast iron was removed at some places by accident, as the cast iron is MUCH softer than the weld.

(A nickel electrode could have been chosen instead of nickel-iron. The weld would then be easier to machine, however the electrodes were more expensive.)

The vise now appears to be performing like new. It is suggested to refrain from loading it heavily, as the weld is not entirely professional. Time will tell if the joint is sound.


Clamped for welding

Prepared with grooving electrode

Weld

Weld

Weld, ugly side

Weld, excess material ground off

Weld, excess material ground off

Weld, excess material ground off

Weld, excess material ground off

Weld, excess material ground off

Weld, excess material ground off

Weld, excess material ground off

Weld, excess material ground off

Finished repair

Finished repair

Finished repair

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