Thread: Convex curves left on face of mitre cuts

I'll take a guess and say that the blade isn't parallel to the mitre slot. the back tip of the blade must be closer to the mitre slot than the front tips. so when you cut, it starts cutting nicely enough, but as you push further in the timber which is stuck between the fence stop and blade starts pushing the blade away from the fence stop creating the convex. if you do a test run and just cut a piece without pushing the timber all the way past the sawblade, just enough so the trailing edge is cut and then back the timber out, it should leave burning marks on the leading edge and fade away to nothing as it gets closer to the trailing edge.

if the blade was out of parallel the other way, slot closer to the front tips. it would drag the timber off the end stop as you cut and give the burning marks mostly on the offcut side.

I made a picture because im not entirely clear where the convex is. this is looking at the side if a 19mm thick board with the top edge being convex.
convex2.jpg

Thanks Kuffy,

To explain i added a pic plus a photo of the setup. It is the actual face of the mitre cut that is bulging (in the centre of the face)

I've triple checked the squareness, absolutely spot on. took pains to make sure, and the problem didn't happen at all with some earlier boxes in softer timber.

seeing you have a sled and its all locked down, Have you tried running the timber thru twice?
Let the saw take the bulge off (and maybe the burn marks as well).

I thought possibly you were referring to it being convex in the manner you have illustrated, but i thought "nah, it couldnt be, freeken impossible!!"

when you cut the pieces, do you push the timber all the way through past the back of the saw? or just enough to cut the piece and then pull it backwards? if you go all the way, there is small possibility that you are cutting 2 facets over the face, once at the start of the blade and again at the end of the blade.

how sharp is the blade? if you have broken teeth or very dull teeth on it at all, i would say this is your problem. due for a sharpen or new blade.

Great, two excellent ideas there guys. I'll try running it twice Fly, and Kuffy, I only go through using the first slice of the blade. the material is only 11mm x 60mm i figured that was enough.

will get the blade sharpened though. that well might be a cause of some flex as it hits the real meat of the timber. I'll drop it in to Central Saws when I pick up the blade they are modifying to flat for box cutting. Excited about doing a variation of Ed Stiles box joint jig when we get back from Qld in May.

Box is assembled for now, some extra sanding to get the mitres perfect, ah, feels good to stand back and look at it taking shape. Now onto that nice bit of Huon pine for the lid

Might be worth having a read through this thread on blade problems https://www.woodworkforums.com/f153/table-cutting-advice-193310

Yes, did read that Treecycle, fascinating.

I'm going to do a bit more experimenting when I get my new 1/8th blade. things like test cuts at different angles, clamping both pieces etc till I get to the bottom of it.

In the meantime, my first box, ran the mitre key right along the box to double as shelf.

Nice one. You should put it in the Box Making forum.

Nice box Bob ! I know it doesn't solve your issue, but have you considered making a bevel shooting board ? Generally gives cleaner edges than a TS.


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