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Making the Pattern and getting it
Cast
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Updated pages are on the bottom menu item.
I decided to make the pattern from MDF, nice'n'cheap, god
it's manky stuff and not a patch on proper wood. Though MDF
doesnt warp, an 18 mm sheet left outside in my garage overnight
gains approx 20 thou; so I could have bought some 12mm and
added water;-)
I used 4 lamiantions of 18mm, which gives me 11 mm to machine
off the final casting. I cut the shapes out with a B&Q
router, I ground a 3° profile on several of the carbide
bits that came with it. I bought the router for £29
but with a bit more use it will burn out and I get my money
back. I managed to hold quite tight tolerances on the circles
I profiled with the router, when it was all glued together
it fitted quite well but a thin skim of filler was added/needed
to make the circular part perfect. The bosses for the bolts
were all slightly different, lot's of sanding/filling needed
on these, it would have been better to have cut them out of
a seperate uniform piece of wood and glue them on, so they
were all the same.
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Figure 1. Filled and partly sanded laminated
pattern, rib pattern was altered as the fully ribbed design
was time consuming. |
| The inside
ribs were cut into the botton lamination, and then extended
up into the second lamination with extra bit's of mdf, again
these should have been stuck in after wards. I forgot to mention
I made some changes to my planned pattern, I made a mistake
cutting one of the circles out, so I changed the whole thing
slightly, MISTAKE. I had to cut two loose pieces of MDF, these
fit where the starter and top bolt bosses are, they complete
the shape and makes it easy for the foundry; well I don't know
if this is true or not. As well as these two loose pieces I
decided to cut the flange down in two places as the wall at
these points was almost two inches thick;the thin wall might
make it difficult to hold in a 4 jaw to face the back as the
whole thing will distort...What an excuse to go and buy a mill;-) |
Figure 2. pattern as it was when it went
to the foundry, I will take some better pics when I get it back. |
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When the pattern was finished, well sort of finished it was
painted with spray filler, this is inert, thick and fairly
hard.
I sanded the spray filler down which got rid of any imperfections,
then I wacked another coat on and sanded that, notice the
word flat isn't being used. I didn't want water going near
it even though it was sealed, so I sanded it with 80 grit
and put a wet coat of filler on, the finish wasn't fantestic
but it's pretty smooth. I took it to White Eagle Foundry,
partly to see if it was OK and if the loose bits of MDF was
a workable idea, well he told me to come back in a few days
so I spose it's OK.
I will be altering the pattern so there is less machining,
possibly making use of a core. I have decided against a core
as a complete remake of the pattern would be needed to make
the most of the core. instead the pattern will have slightly
thicker walls to allow more clearance around the ring gear
and the top bolt bosses are gone, it will rely on an extra
two 10 mm bolt's inside the adapter. I have also altered the
edge, by the starter, to cover the original hole in the bellhousing.
I have removed a lot of the height of the pattern, before
I made the pattern a foundry gave me some figures for machining
allowance, they were quite riddiculous....
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