There are a couple of pairs of holes needed in the cab roof. One pair is for the cab ventilator unit, and the other is for the prop that will hold open the cab roof so you can more easily work the controls. To drill these, I used the outside printed form to hold the part level on the mill. The clamps are actually pressing on the very edge of the roof, rather than the form itself. This is probably not the most secure setup, but it was plenty good for holding it in place while drilling the holes where all the force is directed downward.
Next, I made the cab edge pieces. These go along the base roof line of the cab to help stiffen it. Not sure they correlate to anything on the prototype. It might represent the gutter above the windows, but it’s hard to tell based on the few pictures I can find.
These pieces were (previously) cut out from the same 1/16” sheet steel as the roof. I double-sticky taped them together, trimmed them to size, and then drilled a couple of holes for some #1 screws for holding the part during soldering, and one 3/32” hole for the pin that the cab roof will hinge on.
Now, to make the corresponding holes in the roof I had initially thought I’d hold it using the inside and outside forms like this, then drill the holes through the top of the form. However, this setup was just a bit too squirrely. The top edge of the roof was not straight with the x-axis. There was about 30 thou of difference between one end of the roof and the other. And when the part you’re holding on is only 3/16” wide, that’s a pretty big error. That didn’t make me happy. With a little more investigation, it seems that the top edge of the roof would twist oddly when I tightened the mill vise. I believe that the bends in the roof didn't match the form close enough and varying the pressure on the C-clamps or the vise caused the top edge to move quite a lot. So this setup was clearly a no-go.
I had worried that might be the case, so I’d had the foresight to drill the screw holes in the edge pieces to tapping size (as opposed to through size). This way I could use the edge pieces as a guide for drilling the roof. I used my corded drill for this since it has a much higher RMP than my battery drill. This worked quite well.
Then I made a pair of roof hinge pins from stainless steel round bar.
After tapping the screw holes in the roof, and opening out the holes in the edge pieces to #1 through size, I was able to assemble it and see how it looked. The pins are set right by where they want to go.
I disassembled everything and gave it a good cleaning. Then applied some flux and little pieces of solder along the joint:
Then proceeded to heat it up from the underside with the torch.
This went much faster than silver soldering, but the solder doesn’t wick nearly as well. I used a pointy solder stick to move the solder around quite a bit. The long joint worked out quite well. But the stainless steel pins didn’t solder at all.
I cleaned it up and re-soldered the pins in place. It seemed to work fine the second time around. Wonder if it’s because I used stainless for the pins? Anyway, got it to work eventually. Kozo says to make them a press fit or to use Loctite to hold them on. But I’m not sure Loctite would make it through the powder coating oven. I know that soft soder will survive because I’ve done that before!
All in all, it came out pretty well.
Next up will be the ventilator for the top of the cab.
Kim
