Yesterday I finished fixing my thickness sander. The ball bearings made a big difference, it did not over heat at all. If I had been thinking straight when I made the thing I would have made a much larger drum, in which case it could spin slower for the same SFM and the bushes would have been fine, oh well live and learn!
Dimensions of the linings are 22mm high, 2.2mm thick. After thicknessing I planed one edge smooth with this great set up:
Then trimmed them to 22mm on the bandsaw, leaving me with a bunch of little spruce sticks to use for toothpicks or model airplanes maybe…
After that I started on the mortises for the ends of the linings where they meet the blocks. In the Cs I set them in about 10mm, and a depth of 20mm (my notes say 18mm, but I didn’t look at them till afterwards, haha, it doesn’t matter). The mortise follows roughly the tangent of the ribs, not too tight or it’ll be impossible to bend the linings to fit.
Next I start the mortise by chisel on the lines (may not be necessary):
Then down with the home made mortising chisel:
Because my mortising chisel is not quite 2.2mm wide I need to clean up the mortise a bit, a finger plane blade works alright for this, but someday I’ll either make a new mortising chisel, or a nice thin straight chisel.
The wall of the mortise where the lining will butt is angled away from the open end of the mortise, the lining will be cut to match and that assures a tight fit as you push in the lining.
Next the mortise inspector, inspects: “You call that a mortise?!”
I did some little tiny (2mm long) mortises at all the other blocks. The reason they are longer in the Cs is because the tension of the linings unbending pulls them away from the ribs, whereas the others unbend into the ribs, making the risk that they pull off much less likely.
Now I figured a great trick to bend and fit linings. No need to use any muscles, just get your wife to do it!
There’s not really a trick to bending linings, spruce is hard to bend, it tends to want to crack or compress, a little compression isn’t too bad, but cracking is not good. We only broke 2 out of 6 linings, one could be salvaged as a C, and the other was long enough to still use. That’s a bonus of not cutting them to length until they’ve been bent I guess. I mark the length of the linings and cut them with a chisel, with the ends beveled so it fits tight once dropped in the mortises. There’s a bit of finicking to get it right, they shouldn’t be too tight or too loose because then they’ll distort the ribs.
Fit and ready for glue:
The straps of poplar are to protect the ribs from the clamps, and are basically made the same way as the linings, and then covered with clear packing tape so they don’t get glued to the instrument. They are also reusable so find a storage place that you won’t forget about! Those really flexible clear plastic rulers from you school days also work great for this.
For clamps I have some 1” clamps with the T-bars cut off, and a bunch of reinforced clothes pins. Unfortunately I don’t have enough of either to glue the whole way around which I believe would be about 200 clamps on a cello. So I can do the two Cs at once, and then just one bout at a time, giving between one and two hours of drying time, it becomes a whole day affair. I’m trying to find a source for small clamps, hopefully under $1 each, but the ones that look good more than double in price when the shipping is tabulated. I saw some bent steel wire clamps once that are applied with a special pair of pliers, I’ll have to look into that some time.
Clamped up Cs:
Clamped up lower:
Oh and to check the fit on the bottom side of the lining I polished a piece of aluminum to use as a mirror. I have some real mirrors somewhere but couldn’t find them.
And there you have it, several pages of literature on a pretty simple subject, that won’t even be very visible when the whole thing is done.
Next time I’ll flatten this side of the assembly and trim the other side, before putting linings on there! The trimming should be pretty fancy if my idea works out.