:big: :big: Thanks Robert - I'll take that as a huge compliment ;D - I never knew "terrible" and "passionate" were synonyms :big:. You're thirty days plus ahead of me then... I need to quit as well, but I'm scared of what will happen to my boss and assistant...........
Today's bit; I had a good shop session, so lots of photos...
I started work on the piston. Earlier in the build, I left the bore of the cylinder just a tad under the 16mm I wanted. That was on purpose; I have some 16mm round brass bar to make the piston from, but it needs a bit of skimming, so will end up under 16mm. I chucked the brass bar up in the collet chuck on the lathe, and faced it and then parted it down part-way on 5mm length:
Starting with a partial parting cut might seem silly, but there's a reason for it. If you look closely at the above photo, you'll see the burrs raised on both sides of the parting cut. If I left this for last, that would leave a ridge on the piston that I'd have to remove in some or other fashion - and there's no easy or accurate way.
A little later, and I'd used a small file to put chamfers on both sides of the piston, a free-hand oil groove with a triangular needle file, then turned it to final size and drilled it 2mm through the center:
After finishing the parting cut, I ended up with this:
The face shown is on the parted-off side; I still need to practice parting a lot more to get better finishes. The pronounced countersink on the hole was added manually; on both sides of the piston; these are needed for later steps.
Next I started on the forks. Drilled a 1.6mm hole through some 6mm thick square brass:
Then I mounted the slitting saw on the mill and used my height gauge to pick up the top of the block and set the slitting saw to height:
I just used my 0.5mm slitting saw to slit through for the fork bodies deep enough to later cut them off. Then added my 1mm slitting saw to the arbour to start cutting the forks - using the height gauge again - this left a 1.5mm wide slot; which I just slit to depth on the line I'd marked:
I then moved the mill quill down by 1mm, and slit again - leaving a 2.5mm wide slot, and then moved down and repeated:
If you look carefully, you'll see there's two stilling saws ganged together; a 1mm and a 0.5mm one. I really need to buy more slitting saws :big:
The block was then flipped in the vise and clamped down with a generous bit of cardboard to prevent things moving, and then the two forks slit off from the parent stock:
I then drilled the backs of the workpieces 1.6mm to tap M2 later:
After tapping and then some free-hand filing to round over the ends, the forks were done:
I needed some bolts to hold the cam to the base. Any old 3mm screw would have done, but I rather made my own. Here's some 5mm hex brass turned down and threaded with the tailstock die holder:
After some more machining, I had these:
The cylinder block needed some holes plugged - just two bits of 2mm brazing rod plugged in with high-strength retaining compound:
Ugly, innit ? ;D
Some more 2mm brazing rod followed to make the connecting rod; threaded both ends M2 to fit the forks and lock nuts. The piston have to be soldered on in the middle:
I used some aluminium drinks-can plate to clamp down the connecting rod with the piston in place. The plate keeps the piston on the correct height and prevents the vise from marring the connecting rod. Any solder that leaks through won't stick to the aluminium plate either:
Some soft-solder flux was brushed on before assembly, then I soldered the lot together with some electronics solder. I just used a small plumber's blow-torch to heat things up. It looks horrible here, but worked quite well:
Remember the chamfers I mentioned on the piston earlier on? - This is where they came into play; I made the hole in the piston a relatively tight fit to the connecting rod, but they had to be soldered together, and with the hole being tight the solder would not flow through. The chamfers provide the necessary area for the solder to make a reasonable secure joint.
Next I cleaned up some 6mm silver steel rod and drilled it through and reamed to 4mm, and parted off two rings 2.4mm thick:
Some brass followed, a tad under 4mm OD for a smooth running fit in the silver steel above, and parted off at 2.5mm lengths:
Makes for some OK bearings:
A quick trial-fit in the cam, and I could see how much to adjust the forks in the connecting rod:
All assembled together:
Please excuse all the oily marks and so on; when I assemble something for the first time, I use a LOT of oil. As can be seen from the photo, I''d also filed down and smoothed over the plugs on the air passages to blend in to the main shaft
There was a couple of tight spots on the cam with things all assembled; that was easily taken care of with some light filing and emery paper.
Things turned over fairly smoothly after that by hand, but wouldn't give me the easy flick with multiple rotations... and I was NOT happy; I'd built this engine so far to be EASY to run!
It was supposed to spin like a top...
At this point Thor threw a hammer at me noggin, and connected... HARD... ; Well, DUHHH - I've not yet drilled the main bearing column for an air supply or exhaust... - There is nowhere for the cylinder to suck or vent... So obviously it would not run well :big:- It needs a bit of breathing :big: