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<\/a><\/p>\nPictured here are most of the parts for the swinging saw assembly and the two clamping fingers. These almost go together as-is.<\/p>\n
Back frame rail temporarily slipped together. Drive motors mount to the two projections, and the clamp actuator is (mostly) integral to the frame itself.<\/p>\n Here’s the front frame assembly in the “glob on as much brazing alloy as you possibly can” stage of fabrication. I heat up all the requisite areas of the metal and liberally distribute and wet the surface of the aluminum at the tabs with the zinc-aluminum braze.<\/p>\n The interior fillets on this piece are some of the best joints I’ve done so far. I was able to properly fill these joints because of…<\/p>\n …my +1 Frayed-Aircraft-Cable-And-Chunk-Of-Copper-Tubing Brush of Oxide Breaking!<\/p>\n Instead of ordering $9 stainless steel pencil brushes from McMaster, I chopped one up out of some stainless steel aircraft cable and the nearest small tubing I could find. In retrospect, making the handle out of copper, a highly heat-conductive material, was probably a bad move.<\/p>\n The long and thin pseudobristles allowed me to get the brush into narrow corners where my stainless steel toothbrushes could never hope to go.<\/p>\n The stage after globbing is sanding the proverbial daylights out of the part. Using a large and wide belt sander helps establish a new flat surface that somewhat resembles the old. This actually makes the whole part look really nice<\/em>, almost like it was meant to look like that!<\/p>\n Here’s the backside in the globbing stage.<\/p>\n … and everything put together. Well, kind of squished together for the shot, that is. It looks great, but how well will it perform…<\/p>\n T-nuts installed into the thicker frame components. The waterjet cuts accurate enough such that these things either press in with thumb pressure, or, in the worst case, require a tap from a rubber mallet.<\/p>\n Mocking up the rear actuator. The bottom plate hole pattern mounts a Banebots 20:1 28mm gearmotor.<\/p>\n I bored, drilled and tapped one of the Surplus Center sprockets to fit the 1\/2″ ACME leadscrew. The screw itself has two flats to let the set screws grip properly, and an end-threaded hole to act as a physical stop for the clamp.<\/p>\n I ran into a foreseen-but-ignored problem when making the output shaft for the saw actuator. 11 tooth #25 sprockets have a hub that is barely over 0.5″ diameter. The output shaft of a drill gearbox is typically 12mm, or 0.472″. I already sized the output bearings for 12mm.<\/p>\n So that means there’s no way to actually attach the sprocket to the shaft. Too little thickness to set screw or cross-pin, at least that I was comfortable with. While I could have turned the drill shaft down, this required either changing bearings in the actuator body or making some kind of adapting sleeve. I thought the 11 tooth D-bore motor sprocket (from a scooter motor<\/a>) that I found would save the day, but alas, it was 10mm.<\/p>\n Naturally, I take the solution that would allow me to abuse machine tools: Make the sprocket hub bigger<\/em>.<\/p>\n Uh oh.<\/p>\n I turned a steel ring that was fitted over the existing sprocket hub. This increased its diameter to around 1″.<\/p>\n Then I welded<\/em> the ring to the sprocket on the exposed end. While all this was fixtured on the lathe chuck, of course. The sensitive machine surfaces were covered with a welding blanket first.<\/p>\n I could have done this on a less expensive or important fixture, but the steel ring bore was a hair too big to align properly without wobble. I used the machine spindle to correct the wobble, and decided to just weld it right there while everything was still squeezed together.<\/p>\n Mmm… porosity. After depositing the weld, I turned the surfaces clean.<\/p>\n You can tell I didn’t focus very hard on cleaning the sprocket surfaces beforehand. Oh well – this isn’t going into space.<\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n