When sawboards go bad

[John Rumm]

So I cut a length off a full sheet of 3/4" MDF. Being too large to feed through my table saw I used my long sawboard[1]. Normally I am just breaking down a big sheet so I can machine it further, but this time was actually cutting to finished size.

When I checked the cut part in the middle, I thought "that's odd, its

2-3mm too wide". Then I checked both ends, and they were spot on. So a bit of further investigation showed that the trusty sawboard had a very slight bend along its length! Not sure if its always been there, or for some reason it had warped.

Anyway, to fix it I clamped it to the factory edge of the MDF sheet, and used a router with a fence to trim the face part of the board parallel to the edge of the MDF sheet - vutting just deep enough to take the face edge flush to the top of the board. Then I re-cut the board edge with the circular saw to make it match the now slightly shifted (and straight!) fence on the board. So it works ok again now...

[1]

[newshound]

Weird! Mine (4 foot and 8 foot) are both two bits of 9 mm ply, I would be surprised if they distorted that way. A very elegant fix though, I will try to file that away mentally. Will check my boards when they come back from loan too.

[John Rumm]

This was one made from 6mm ply, so perhaps that's part of it. Come to think of it, I did wax it the other day...

[Stuart Noble]

I suppose one should invest in plastic but it's so damned expensive. I suppose narrow strips might get chucked by fabricators.

[Adrian Caspersz]

For some reason my circular saw has has a bit of an occasional startout wobble and taken some material out of the start and end of my aging thin MDF sawboard.

It's a mm or so, so me using either end to match measured points on the workpiece doesn't work out that well for accuracy. I now prefer to align further down the sawboard against straight drawn pencil lines, where this sawboard damage hasn't happened.

[Jon Fairbairn]

This has happened with my MDF one. I noticed when I cut some strips of ply off the long edge of a full sheet. I suspect that when used on a full sheet, because it can only be clamped at the ends, pushing the saw against the guide bends it a little. After a few goes this bend sets in. I had hoped that switching to ply for the sawboard would solve this, but your experience suggests not.

[John Rumm]

Well mine was bent in the other direction - bowed against the direction of push...

I think 6mm base board, and 9 or 12mm ply fence is probably a better combination.

[newshound]

Certainly a bit easier to use with a thicker fence. I had spare 9 mm when I made mine. You lose a bit of cut depth with a 9 mm base board, but not a problem if you are mainly cutting sheet up to 18 mm. With 9 and 9 or 9 and 12 it is easier to screw and glue to make a very robust board.