Day 2: Starting work on the cylinder casting.
As mentioned previously, the cylinder casting is a little rough. The main circle is not quite round, and the top/bottom bosses are not square to it in any dimension! At least there is a bit of extra material in a couple of places that I was able to get it decent. There wasn't a good place to hold it in the vice, so I had to get a little creative to form my reference surfaces. At first, I tried to do a bunch of filing on the top boss, but I was doing a poor job keeping it square so I gave up and decided to just do it on the mill.
here is the cylinder casting (aluminum, the flywheels are bronze, everything else is Al):
I decided to start by trying to set the top 'boss' as a reference surface, since it was the squarest thing on the casting. I held it in the vice by the cylindrical part, squared it horizontally as best as I could (which was surprisingly difficult, the cylinders bowed up quite a bit!). You can see some of my filing marks in this picture.
I started by facing the top of the boss. I'll later shorten this quite a bit. The purpose of this boss is to be a coolant reservoir, so I'll need to remove the center of it.
Using the same endmill, I then went around the outside of the boss in an attempt to make it square. I'll have to spend some time cleaning up the casting/marks with a file/burr later, but since I wanted to use this for a reference surface this was necessary.
Next, I milled the hole in the casting as deep as I could with this endmill. This needs to make it down into the 'cylinder' part, since there is an area in the middle of the cylinder where the bore is larger to allow water to go around the cast-iron bore liner. The plans tell me to make it .825 "square", but also tell me to make it .750 in one of the other pictures. I opted instead to choose a .100 wall thickness and did my math off of that. I did this by plunge cutting with the above endmill (which I hadn't realized has a step in it!), then slowly going around the outside at greater and greater depths. Other than the 'step' from the endmill, this turned out fine, and I don't really mind the step in retrospect. If I have to come back with a longer endmill at one point, I might make the hole a little larger. You can also see the final height, I took quite a bit off to make sure that my mill reached deep enough.
Next, I set it up as vertically as I could to try to face the cylinder. I used the top of the boss I just cut as a reference surface and used a square to try to get it as straight as I could. I had a lot of material to take off, so I started with my carbide face mill then used my (newly ground for only the 2nd time!) HSS fly cutter. There is A LOT of material to take off here, roughly 3/8 on each side to hit dimension. I did this by measuring the boss, then using a depth mic + math to figure out how large each had to be. I think I ended up 2 thou under, which I'm happy with.
After I got both faces done, I moved to the bottom boss. This is simply to be the mounting area for the cylinder. Also, an interesting thing with this design, the cylinder sits 'low' and off center. It is measured off the bottom of this boss, so I chose to remove quite a bit of it. In retrospect, I sort of wish I'd flattened the bottom quite a bit more in order to get the cylinder more centered. I ended up taking off about 1/2" here! Check out the other pictures to see how tall this once was!. I started by face milling. I also went along the left/right sides to try to square those up, but I didn't have enough material to make it not so wonky. You can see in the pictures after this one that it isn't perfect.
I took it out of the vice to mark the center of the cylinder. You can see in this image how low that it has to be! Check out the front cover of the plans, this is actually a part of the design for some reason! Perhaps with the intent of increasing the water capacity?
It was at this point I realized I don't have a good way to measure the left/right of this, so I opted to use the top-boss for left/right, and used the bottom boss for the height. My scribe line and the DRO seemed to agree perfectly.
I put a deep center drill for the cylinder bore itself, then used the DRO to drill the head-mounting holes. At the moment, they are not tapped as I have yet to get the correct tap in the mail
I can always re-indicate for when I tap if necessary.
I used a piece of aluminum to protect the water reservoir , and popped it into my 4 jaw. I also used a parallel against the face of the 4 jaw, though I don't see where it was in this picture! I used the tailstock to press the part into the parallel, then tightened down the 4 jaw. I used the tailstock to confirm placement.
Then, came drilling! I started with a 1/4" bit, then 3/8", and finally 1/2", which is my largest drill bit smaller than the final dimension. I'm supposed to hit 1.000" for the liner, plus mill a center section to 1.300" for the water jacket, so I've got quite a bit of time left for my boring job!
I setup the largest boring bar I have that will fit into the hole currently, but I still haven't used it, so I don't have a tool ground! Looks like that is my next task! But alas, the dinner bell rang at this point, so the rest of this bore will have to wait until another day.
