[intorqueo]

This is my first post here, so apologies if not correct.

In a nutshell: I'm getting crowned cuts when crosscutting a thick piece of hickory.

The details: I'm making a picture frame out of hickory, which is 2.25" thick and 3.25" wide. I'm making the miter cuts on a Delta Professional table saw (meticulously matinained and tuned), via a custom dedicated 45 degree miter sled. I've done this dozens of times, with many different wood types, and have achieved excellent results with this setup. What's changed is that now I'm using thicker stock. The resulting cut is perfect in every way except there is a crown (convex lobe) right in the middle of the cut (see attached image). This is completely baffling me. I've been using Freud commercial blades, 50T, 60T 80T and 90T, in both full and thin kerfs. I don't believe the issue is blade 'wobble', as the crown is perfectly centered within the cut. Blade 'wobble' generally causes off-centered and/or multiple lobes. I've tried increasing/decreasing the feed rate and various amounts of stock removal per cut, all with the exact same results. The crown/lobe is not considerable, only 0.5mm, but that's unacceptable for a mitered picture frame. Anyone ideas about how to tackle this would be greatly appreciated.

 

[intorqueo]

So you've tried 4 different blades with same results?

Yes. Full and thin kerf.

 

[intorqueo]

Have you tried cutting in two passes or tried skimming off a few thousandths to clean up the face? It's possible taking a full cut in thicker wood is causing some deflection that you wouldn't see when cutting thinner stock.

Is the miter slot perfectly aligned with the blade or is it off a thousandths or two?

Thanks for your reply. Yes, the miter sled is absolutely, perfectly aligned with the blade and the mitrer slots. The sled even uses both miter slots to reduce play. The sled also allows cuts on the left or right side, and both give the exact same crowning. Both are also exactly 45 degrees.
Two passes is never a good idea when making picture frames, but I understand your point. As a matter of fact I have tried two passes, with expected results; burning and an uneven surface.

 

[intorqueo]

The thickness of the wood is dragging against the blade and is being pulled in. Clamp each piece tightly to the sled rather than holding it by hand.

Thanks for your reply.

The thickness of the wood is dragging against the blade and is being pulled in. Clamp each piece tightly to the sled rather than holding it by hand.

 

[intorqueo]

Thanks for your reply. I seriously doubt that the wood is baing 'pulled' into the blade, for several reasons. 1) The blades I'm using are Teflon coated. 2) The blades don't get even slightly warm. 3) I have been using two very capable clamps to secure the workpiece to the miter sled. They don't budge a micron.

 

[intorqueo]

My 2 cents (if its worth that) is that when you are cutting the hickory its being pushed away from the blade during the cut...try clamping it to the fence really good.

Another suggestion to get rid of crown, is to use a belt sander or circular sander to sand off the crown. Use a light touch. Shooting board (as others have mentioned) would work too.

Another thought is that the hickory is not dry? And when you cut it, the middle is still wet and expands more than outside? Something akin to that?

Thanks for your reply. I already clamp the workpieces to the miter sled with two very capable clamps. It doesn't budge, towards or away from the blade. Also, the wood is thoroughly dry. It is, in fact, 4 layers of 3/4" glued together, grain opposing for stability.

 

[intorqueo]

Don't claim to be anything but a cabinet/trim/furniture shop owner for a little over half a century..... so this might be a a bit of a tough description(really BAD technical writer).

As a thinking excerszie.... look at a tapered leg rip on say a small hall table. Your choices are BS vs TS. Where we really want to concentrate our efforts is where the taper "runs out". After the cut,this fade out needs to be at a very accurate 90*.

The BS "wins" because of the blade's angle of attack to the cut. The TS loses because of flex,as it exists the cut. Simple experiment....

Hope you followed that poor explanation. So towards the OP, it's blade flex... plain and simple. Not sayin to cut your mitre's on a BS. AM saying, pay attention to this "angle" of engagement from the tooling's perspective. Same can be said for stationary sanders... a big disc,vs a vert,vs an edge sander. Each has nuances(sp).

Shooting boards are "cordless" and just plane(haha) cool.

Thanks for the reply. I'm not sure I understand your analogy; TS? BS? OP? The blade hits the workpiece at 45 degrees to the grain, every time. Clearly this is being caused by some sort of flex or deflection, but exactly how?