Shrinking Rims onto Hubs
Decided to get all scientific and calculate the expansion of the Rims.
At first I calculated the expansion on a temp change of 300°C at this point my boss started to get interested in what I was doing (usually a bad sign) but no, when I explained she said why not put it in the oven, a quick check and the oven would go up to 250°C then she floored me and suggested I put the hub in the freezer that would give at least a temp difference of 260°C, another quick calculation and that would give a size difference of at least 0.3mm (0.012”). As a rough rule of thumb for any of you Chaps who want to try this, temp difference of 250° will give an increase in size of about 3%.
I could have used high strength Loctite but hay where the fun in that
Elbows
I bought four 12” length of ground ¼” Ø mild steel bar I checked them for size with a mic and found that they were bang on size. I then put a ¼ drill down the ends of some brass bar to use has bending handles.
I then parted of 8 lengths of bar 70mm long keeping them all the same length as well as possible.
A quick search of my tool stash came up trumps with this little beauty, I don’t know where it came from but if I see a bit of discarded tool steel on my trips to the scrap yard or any were else I never pass it by.
As I like to work in metric a did a quick sketch of the elbow in mm with the sizes I wanted to work too.
I put a piece of bar in the drill chuck to act as a stop, so that I could zero the machine dials up so that when I’d got the first one done I wouldn’t have to do any more measuring. As I would be winding the tool up and down the grooves I worked off the dial zero for one end and a crayon mark at the other.
To bend the elbows I decided to use the method John had recommended, I set up my little gas torch in a retort stand, heated the elbow in the wasted area to cherry red and bent it roughly square round a short stub of ¼ bar held in the vice. As I was using mild steel I quenched them in water.
Now for the tricky bit getting them square:- Using a 1*2*3 block as a square and holding it up to a strong light I checked each elbow for square-ness, and kept tweaking them with the bending handles until they looked pretty good, I’ll have another go at getting them spot on when I’ve skimmed them to length when I start to assemble the engines.
Cylinder Blocks
I had a piece of Brass bar that was long enough to make all four cylinders from. The end of the bar was centre drilled and with a running centre a light skim was taken off the OD and checked for parallel it was within 0.05mm (good enough). Four pieces just over 1” long was parted off.
Using the back of the chuck as a stop each piece was faced off, the first one was then faced to length, the dials zeroed and the rest faced off to the same length so that they all came out the same.
A check with DTI showed that the chuck was holding them concentric to 0.02mm, as it’s the concentricity of the centre hole with the three cylinders that’s important this is more than good enough. They were then centre drilled roughed drilled 7/32 then letter D drill and finally a ¼” reamer put through with a carrier so that it finds its own centre and cuts dead to size, this gave a lovely sliding fit on the elbows.
Next job was to turn up a mandrel so that the cylinders could be clamped to the rotary table, this was carefully done to ensure a good fit in the cylinder.
That’s all for now I’ll finish off the mandrel and turn up the port blocks over the weekend.
