Anyway, the first one went well with no incident. I cut the blanks with a hacksaw and sanded them to size in the belt sander. Blued them up with a magic marker and marked the four holes followed by the centre and ends of the slot. Shipped the piece in the milling vice on thin parallels. Centre drilled the four holes and a line down the centre of the slot. Drilled the securing holes and put. 90° counter sink in the holes at one end. Drilled out the slot with one size down from 3/16” then shipped my new slot cutter and cut out the slot. Reversed the piece in the vice and counter sunk the the two holes in the other end. Removed the piece, demurred and filed each end of the slot square. Perfik. The second piece didn’t go so well. First mistake was countersinking the third hole on the wrong side before I cut out the slot. Caught myself and no worries as the screws locate on the countersink so did the other side. Phew. But the slot cutting didn’t go so well. Half way up the slot deviated. Something moved. Never did find out what. Any way it was only a bit and won’t cause a problem in use. I’ll make another later because I can see it.
Using plate 2 1/2 thou undersized does have an issue because top and bottom fixings are on opposite sides so the plate will not be parallel to the axis of the piston rod. I planned to make four shims from an aluminium cake can but when I measured the thickness it was 3 thou. I didn’t think that was too bad but then wondered if I used a Diet Coke can if it would be thinner. Measured one and bigger me it’s 2/ 1/2 thou!! I made the shins with a pair of scissors and placed them under the plates and drilled through the holes into a block of wood. Fitted the first one and everything spot on. The holes I’d drilled in the p/b support bracket we’re not in the correct place so I machine some brass 7BA studs indeed plugged the holes with a bit of Loctite to glue them in. Pet the plate on secured at the top and drilled the new holes in the support bracket and tapped them 7 BA. Fitted the two c/s screws and shins. The plate was way out. Not parallel to the axis of the piston rod. The p/b bracket must have bent when I machined it. Measurements showed I needed to remove 15 thou where the bottom screws go. 5 minutes with the file and it came out right. Me and p/b don’t get on!
As I’ve still not received my replacement 4 jaw chuck I decided to make a mandrel with a 5 BA thread on 1/4” of 1/4” mild steel round bar. Made the mandrel in the 3 jaw chuck and left it there and screwed the piston rod end of the crossheads on the mandrel and rounded off the top ends of the crossheads. Removed the crossheads and replace on the mandrel and turned the sliding face to thickness leaving a 3/16” boss which located in the slot in the slides.
Fitted one conrod onto crosshead and crankshaft. Big end of conrod fouls bedplate which was a puzzle as I’d Maxine’s it to the correct size. Out with the Dremel and relieved the sides. Will do it properly later. Rotated crank shaft and everything works but there are two tight spots. Removed bottled cap, marked the bearing surfaces with magic marker, refitted end cap, spun it up on a drill for a few seconds before removing end cap again and looking at the Wear pattern. It seems when I machined the sides of the big ends rather then leave a burr it left a slight bulge. Rant the 5/16” reamer through and cleared it. Still a very slight tight spot so ran it in for a bit either the drill. Disaster! I didn’t put the locknut on the crosshead bolt and it unscrewed itself, resulting in a bent threaded end of the piston rod and a ski jump shaped slide. Saved it, straightened the thread, it didn’t break, straightened the slide and reassembled, with locknut this time. It spins over nicely with no tight spots or play. Will do the other side shortly.
Two things I’ve noticed 1) on the drawing for the slides the dimensions are correct but but when you offer up the part to the drawing the drawing is about 1/4” too long and 2) the brass washer on the crosshead fouls the bracket at the bottom of the stroke. I’ll put them on the mandrel and reduce them to clear. They don’t look the part anyway and spoil the model especially the Cheesehead screws.
3) I’ve spent more time looking for nuts I’ve dropped than in actually making things. The position they are eventually found in defies Physics! Why the hell do Stuarts supply the exact amount required?!! I’m still live in hope that I’ll find that tiny grubscrew that goes in the eccentric.
It was 48°C in the shed today and after that bike ride I’m shattered.
Night all.
Jerry C.