Marilyn over at the She Works Wood blog mentioned recently that she’d picked up a miterbox that needed a little TLC. I volunteered to lend a hand, so let’s get this knocked out.
Marilyn and already scrubbed the grease and dirt off, and disassembled it. Bless you, that made my life much easier.
There are two broken parts I needed to repair. One of the stands has a mounting tab broken off, and there is also a crack through the main part of the miterbox where the wood platform is supposed to attach. You can see the broken foot in the picture, the crack in the main part is hard to see (and harder to photograph) until it’s cleaned up.
First things first, let’s get rid of the antique paint and rust. My weapon of choice for this sort of thing is a bead blast cabinet.
Cleaning this part, the main casting, was the most time consuming part of the whole job. This is cast iron, and fairly porous. The paint and rust is down in the pores and would have preferred to stay there. Me and the glass beads had other ideas. Now that it’s clean you can clearly see the crack in the base.
Cleaning the rest of the parts was the same exciting operation, with one exception. The two posts that hold the saw need to be a nice, slop-free, smooth fit into the uprights. They look like they were chromed or perhaps nickel plated originally. I didn’t want to bead blast that area, but I wanted to make sure it was smooth and clean. I used some white lightening rouge and a spiran-sewn buff to polish off any burrs and discoloration. I didn’t overdo it because I didn’t want to mess up the fit.
Then I masked off the polished part and bead blasted the rest.
Masked & ready for blasting:
After everything is clean it’s time for repairs. I really, really (really) prefer to work on clean parts. Here is the crack in the main casting. I opened it up with an abrasive cutoff wheel. The crack goes right through the attachment hole.
Then I TIG welded it using Silicon Bronze rod. Some people call this Heli-Brazing. Cast iron can be welded, but it can be fussy too. Silicon Bronze rod is very strong, at least as strong as the original cast iron, and should make a good solid repair.
Here is the repair after grinding. There are a couple of tiny pits in the bronze, but they match the pits in the cast iron. I’ve heard cast parts described as “structures made of sand, inclusions and gas pockets joined together with molten metal”.
I welded both sides, and also welded the edge of the mounting screw hole.
Last step, fixing the foot.
This actually isn’t too bad. The way the break happened the foot still sits level, so I just need to graft on a new tab. Usually I layout the repair part, grind it to shape and weld it on. Since it was so small in this case I decided to weld on a larger piece and then finish it to size.
I used a piece of hot rolled steel about 1″ square.
It looks klunky for the moment, but it will work out well in the end. Welding on a tiny part can be problematic, if it shifts just a bit in welding (and it will) then it won’t look right. I ran a bead of Silicon Bronze across the top, flowing it into the joint. Then I welded the sides, and across the joint on the bottom.
I ground away the bulk of the bead so it would match the transition on the other feet. Then I flipped it over and painted the bottom of the repair with Dykem layout fluid. I clamped the good foot to the repair, scribed the shape onto the repair and used a transfer punch to mark the location of the mounting hole.
Which show just what needs to be removed to make this foot match the other three.
A little quality time with the disc grinder and we have a fixed foot. Note that the original foot next to it is a tad shorter than the one I scribed from, there is a lot of variability in castings.
That was fun. I like tools. Now I want a miter box…