The structural surface of the garage roof is made from 18mm OSB sheets. The rafters run from front to back and the OSB will run side to side. All edges of the OSB should be fixed so as to keep the roof flat. This is done by having the short edges start and stop on rafters and the long edge being tongue and grooved (t&g) into the next sheet. When we got prices for commercially made t&g we were shocked that it was 50% more than plain boards (£18 vs. £12). This is over £180 for the garage alone! The same thing will be done on the main house and would cost £600 extra!
Something had to be done, so in our usual style we decided to DIY… Investigating tools gave us three options :- locked mitre, finger and comb joints. But I could not decide which would be best in OSB so I decided to try all three!
We made sample joints using the cutters and are waiting for the glue to set… We will destructivly test the joints to determine which is best, but after the comb joint is the easyest to make. You can see examples of the joints below in order.
And here are pictures of the cutters
