Nearly there now
I need to remove the cut outs in the crank web. I marked the positions on the web and then used the Keats fixture to hold the crankshaft on the milling machine and roughed out the shape using an end mill and some XY hand cranking...
...before finishing off the curve with the boring head
The next job was to hack out the crankcase profile. First, I squared it up in the dividing head.
The aim was to cut the waste away to leave the mounting flanges. A miscalculation combined with sitting the wrong side of the job resulted in making the first cut too deep.
OK I can always re-make it, but tomorrow, or next week or maybe next year. A bit of sober reflection after I'd calmed down suggested it might be worth breaking out the "putting on tool"
I "tinned" both the patch and the job and put a bit of hand pressure on while it cooled
I'll see what it looks like when it's finished. So, carrying on, I cut the rounded base first by facetting in the X direction and then rotating the job under the cutter to get the circular profile
I then used my height gauge to find the correct angle to mill the sloping shoulder between the upper crank case and the mounting flange
and then milled that
before repeating the process for the other side. I also needed to put a radius on the joint between the crankcase and the crankshaft housing
If you look carefully you can see where the patch is - rather more in the photo than in real life actually but I know it's there. It was at this point that I decided to re-make the upper crankcase. As well as the position of the carb inlet in relation to the inlet port, there were some surface finish issues that weren't going to come out and I wasn't happy with the flair on the exhaust ports and decided to do without them. I used the same method as before except that I used a 2mm endmill, rather than slitting saw and file, to split the clamp.
I've recently managed to procure some metric Myford collets to supplement my Imperial ones. The carb body is made from 6mm FC steel which I was surprised to find in my store. This needs drilling through 3.5mm before opening out one side to 5mm. I used a 1/8" stub drill to get a good start before drilling through and then turning around in the collet to drill the 5mm hole.
The needle jet and body fit into holes milled across the carb body
The needle jet and body them selves are simple brass turning jobs. The needle valve has a knurled brass knob.
The carb was assembled using solder paint. I used the needle to ensure that the 2 parts were correctly aligned
I wafted a gentle flame over the job to melt the solder - even so it probably got hotter than it needed to
The whole thing assembled
There's roughness in the stroke - investigation showed that the con rod is interfering with the bottom of the cylinder. The contra-piston is not, I suspect, tight enough, there is some evidence at the compression screw of leakage. I'll try Ramon's heating method to expand the contra piston or make another. A bit of fettling to do yet.