Hi all
I've lurked here for quite a while, posted very rarely and am something of a newbie to metal-working. I've completed one project - Alpha to NER's articles in EiM and have embarked on my second, John Bertinat's Marcher from ME. While most things seem reasonably clear from the articles on Marcher and Borderer, I've got a couple of questions relating to the steam passages and port faces on the cylinder block.
First - The plans appear to show 2 parallel drillings at each end of each cylinder to each inlet port. However no drill size is specified AFAICS. From the drawing it looks about 1/16 inch but does anyone know if that's correct.
Second - the steam ports. Bertinat suggests cutting all 3 at once with a specially made gang-milling tool. That looks a great idea except that making the cutter is beyond me. The inlet ports are specified as
3/64 x 3/16. 3/64 inch is slightly more than 1mm so I wondered if I could cut them with a 1mm slot drill instead. The snag AFAICS is that the ends of the ports would be radiused rather than square thus losing a small amount of area. Is this going to be a problem? Otherwise is there another solution that doesn't involve making tools? I can see that I could make 2 cutters, 1 for the inlet and one for the exhaust. I might manage that I suppose, though I've not tried hardening and tempering SS before.Any advice would be appreciated on these or any other aspects of building this engine.
Cheers
Guy