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Carcase Cramping Jig...Part I

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woodbloke66

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Noodling around the other evening on this new fangled t'interweb thingie, I came across Keith Thompson from Ax demonstrating the quite expensive :-" MTR-18 jig, one feature of which is the ability to bolt a couple of bits of angle 'iron' to it and turn it into an assembly jig.
The next big project in the 'shop will be a new bookcase with 6mm sliding glass doors, so it's absolutely essential that the carcase goes together dead square. Normally, I'd check the diagonals which is the tried and tested way to check for squareness, but in this instance, it's not accurate enough to ensure the glass butts snugly against the verticals as you can see from the original bookcase; the gap has been a constant irritation :evil: for the last 35 years.

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This jig is based on that feature of the MTR-18 but at a significantly reduced cost...a length of pine, a couple of No.10 biscuits, some glue and a couple of 25mm screws.
Select a bit of dry pine about 90mm wide x 15mm thick (not crucial), plane it true and square all round and cut off a couple of chunks around 600mm long...again, not crucial. Cut and shoot in a mitre joint and add a couple of No.10 biscuits (or doms) for good measure; glue and cramp, leave to dry:

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Glue on a couple of bits of planed pine about 30 x 50mm onto each face; cramp in place and leave to set, making sure there's a mm or so proud to plane flush:

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Plane the excess off so that the it's flush and level; check for squareness:

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The next bit is important 'cos you need a really accurate way of measuring a large, right angled triangle and a 300mm square isn't big enough. However, if you have a Parf, MFT table or equivalent, the holes form a true and square matrix which is certainly good enough for this application. A 300mm square sits comfortably touching four dogs...

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...but when I place the jig on the table so that it's touching three dogs, you can now see the error:

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Plane off material from the appropriate ends of the jig, checking for squareness and flatness...

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...until it fits snugly against four dogs on the Parf table:

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Continued in Part 2 - Rob
 

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