Slowly but surely another few bits have been made. Bearings, another flywheel, screws for conrod to crank disc, and after much aggro the two crank disc's. I decided in my wisdom to turn the crank disc and part of to size on the Cowells lathe. This went reasonably well.
I then mounted them on the new 2 3/4 inch rotary table on Cowells Mill to drill the crankshaft hole and the hole for the connecting rod screw. Again this went relatively well. I made a couple of hold down clamps which did their job, and used edge finder in conjunction with DRO's to drill the two holes required.
Small 2 3/4" Rotary table shown below. Quite impressed with it. Very little backlash
Unfortunately I had not thought too far ahead and was now left with the problem of holding the disk to mill the two side of the disk away. and also the issue of centralising the disk under the drill. The centre of the rotary table has a 5.4mm diameter bore so I turned a spindle between centres to fit the bore and then reduced one end down and used die to put unc 3x48 thread on it, to match that on connecting rod screw. I screwed the disk on to the thread and inserted it in the bore. Because I had left the remainder of the centre drilled hole in the shaft I was then able to put same centre drill in chuck and zeroise the DRO. Partially clamped the disk and aligned the crank shaft hole with the Y axis and the threaded hole. So far so good.. I had put a piece of thin MDF under the disk to be a sacrificial base and then used one of the clamps to hold the disk. Thinking erroneously that this would be enough to hold it to mill a piece of soft brass. No such luck, as soon as the cutter had radiused the end by the crankshaft screw it all moved.
Back to the drawing board, this time I still used the threaded shaft I had made, but used a sacrificial plate of 1/8" aluminium bar, drilled to take the bar, and also drilled and tapped M4 for a screw through the centre of the crankdisk.. This whole assembly was then bolted to the rotary table.
If you look at the left hand side of the disk you will see the butchered radius from the first attempt. This was a lot more successful and picture below shows the milled crankdisk.
The second was a lot easier than the first but trying to keep track of the DRO readings as the item was rotated through 180 was a tad difficult.
The end result is show below with the connecting rod and screw.
All the bits so far.
All need now is two crankshafts, two pistons and two cylinders, and lots and lots of good luck.
Any comments or thoughts, good or bad gratefully received.
In fact just remembered an issue I had doing the screwdriver slots in the two screws. I had some new small 2 1/4" diameter slitting saw blades with a 5/8" hole. So made an arbor to fit 3/8" collet in the Cowells Mill.
The blades really appeared to struggle to cut the slot in the silver steel rod I had used for the screw. It was really singing and occasionally producing sparks ( not good in home office
). It took a long time to produce two piddling little slots. The blades are marked E.S.C. HSS 045. What might (am) I doing wrong.
Colin
