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Thread: Patternmaking failure!
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8th March 2022, 12:50 PM #1Most Valued Member
- Join Date
- Aug 2015
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- 4,458
Patternmaking failure!
Vintage engine guys want to do a run of brake drums.
They spent a while on Sunday trying to cast Ally in the drum to make a pattern, but it didn't work out. Then they come to me yesterday asking for plywood to layer together to make a pattern.
So, I scrounge for plywood, then find some of Dad's old 8" x 3" pine. (Dad was a patternmaker)
Cut two squares, lop the corners off, mount onto a faceplate:
IMG_2689.jpgIMG_2690.jpg
and start to machine round. Wasn't easy to get the tool far enough out:
IMG_2691.jpgIMG_2692.jpg
so in the end I used a cheaper cutter half way out of the holder for roughing down:
IMG_2693.jpg
Then clean up with a sharper tool:
IMG_2694.jpg
(ground positive rake Aluminium cutting insert, small cuts).
Now, measuring shows this is a little small for the outside of the drum, because the drum has a lip at the back. So we can use it for the inside mould, right?
IMG_2695.jpg
Spend an hour tapering, radiusing the inside corners (fillets), replicating the inside core/negative shape...
until I realise I am being an idiot!
The sand mould needs to be that shape, not the pattern to make the mould!!!
IMG_2696.jpg
So, here is the brake drum, on top of a much larger bit of old timber (Jelutong), ready to chop the corners off, and bore a CAVITY into.
Might get lazy, and with a quick trip to a foundry with the drum, cast the cavity in Alloy instead, to machine out into the cavity pattern.
Attached Images
- IMG_2696.jpg (194.2 KB)
- IMG_2695.jpg (155.7 KB)
- IMG_2690.jpg (228.4 KB)
- IMG_2691.jpg (208.8 KB)
- IMG_2692.jpg (199.2 KB)
- IMG_2693.jpg (162.4 KB)
- IMG_2694.jpg (124.9 KB)
- IMG_2689.jpg (228.0 KB)
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