So I started off today by drilling the exhaust hole in the side of the cylinder, it's drilled 2.5mm and will be tapped M3

Then it was time to drill the angled holes to connect the valve to each end of the cylinder. The plans call for them to be drilled at 25 degrees, and not having a tilting vice or a sine-bar setup, I used the next best thing that I did have, a set of angled parallels ( I don't know why they are called parallels as there is only one of each angle )
However the biggest angle is only 10 degrees, so here was my (not-very-pretty) solution, use 3 angled parallels stacked (10, 9 and 6 degrees) (A sine bar setup or tilting vice is definitely on the to-do list)

However crude it looks, it worked. I guess in Elmers engines there is a lot of "wiggle room" on the absolute accuracy of work.
My next great idea was to spot the face with an endmill before drilling, so as to give a level (relative to the drillbit) surface for the bit. However, because of my scaling down the dimensions, I needed to use a 1.5mm or smaller endmill. Not having a 1.5mm endmill I changed chucks and used a 1mm carbide endmill. I know that normally you shouldn't use a drill chuck to grip endmills, but my ER32 chuck wont grip a 1mm shaft.

It all ended up being irrelevent anyway as I was unable to down-feed slowly enough and the endmill just snapped off. So I then did what I should've done 1st, and used a centre drill to spot the face.
and then drilled through with a 1.3mm bit

After repeating on the other end (without the snapping of a 1mm endmill) then it was over to the lathe, and the 4jaw.
Using a wobbler-pin-thingy in the centre drilled centre hole I had drilled in the mill, I centred the bore (or where the bore should be)

I'd been waiting for this for a while and it happened today, things went a little wrong.
If you noted on the above Pic, I used some scrap ali pieces to protect the jaws from marking the cylinder, however I had not paid attention to them and I didn't realise that they were so rough and a little tapered. This had the effect of pulling the cylinder out of square with the jaws.
I didn't realise this until I had drilled the bore 10mm (eventually to be 12mm) and then faced the end off. That's what gave me the clue that something wasn't right, instead of taking 0.1-0.2mm off, I took off nearly 0.5mm.
I should have stopped before taking off so much, but my zeal ate me up.
I then realised that if I was to carry on then everything would be well off, so I took the ali shims off and reclamped without them, and re-centred the drilled bore, re-faced the end, and then set about opening up the bore with a boring bar.

I opened it up to 11.8mm and then used a reamer to bring to final size 12mm.

Hopefully the cylinder is not too short now.
At this point it was feeding time at this zoo so I finished there. Next up will be turning the flanges on both ends, then it will be back onto the mill to shape the outside of the bits between the flanges.
A little off topic, but as I was about to leave the workshop I thought I'd show a little habit I've got into in the workshop

This highly advanced, and may I say, Patent applied for, device is a hanging impliment for my workshop overalls. After reading many horror stories about wearing jewellery around machines I have been determined to form the habit of exchanging my wedding ring for my overalls as soon as I enter the workshop. It's now a habit, a good habit I think.
(thus endith today's lesson)
Tim