Corner Bridle Joint Cutting Issue

[David Prochniak]

I'm having an issue with cutting the tenons and open mortises on some window sashes that I'm throwing together for a chicken coop and hoping you guys can help. When using my tenoning jig on the table saw, the leading edge of the piece that I'm cutting appears to cut straight and vertical. However, as the blade exits the backside of the cuts, it seems to cut a little bit more off at the bottom left side of the joint. Hopefully the picture below shows what I'm trying to describe. The red line is the corner that gets removed from the backside of the cut after the wood exits the blade; the front side of the cut remains square.

398027

Does anyone have any ideas what might be causing this? It almost seems like the blade is flexing as I make the cut, however the problem happens regardless of the rate that I feed the material through, and no matter what blade I use. I can detect a slight wobble when spinning the blade by hand which appears to be due to some play the arbor and/or motor shaft. If wobble was the issue, wouldn't cutting slower then fix that since it would let the tooth that is farther out finish its cut?

[Gary Ragatz]

A slight tear-out? Might try a sacrificial push block.

[David Prochniak]

A slight tear-out? Might try a sacrificial push block.


I wouldn't say it's a tear-out, it appears that the blade is actually cutting deeper at the end of the cut. The sides are cleanly severed and you can see the circular tooth marks where the cut got deeper than intended.

[Jim Becker]

Have you carefully checked the saw blade alignment to whatever is guiding your tenoning jig? It could be the blade or it could be the tenoning jig that's slightly skewed...I'd guess on the latter first if your saw otherwise cuts normally for everything else.

[Peter Christensen]

Is the clamping face of the tenon jig parallel to the blade? It would skew things a little so that the last bit of blade cut that corner a touch. Clamp on a much wider piece of scrap for a test cut and see if it is worse.

Jim types a lot faster than I do And he likely didn't have to stop midway and let the dogs out.

[David Prochniak]

Thanks for the input guys. I did a quick initial alignment check of the tenoning jig, but it was pretty cold in the shop so I might have been careless; I will double check.

[Richard Coers]

How sharp is your blade? Is the runner of the tenoning jig snug in the miter gage slot? Might be getting a slight wiggle as you exit.

[Jim Becker]

Bottom line is that the jig/workpiece has to move exactly parallel to the whole blade cutting arc...with the workpiece perpendicular to the table.

[David Prochniak]

How sharp is your blade? Is the runner of the tenoning jig snug in the miter gage slot? Might be getting a slight wiggle as you exit.


Blade is brand new, and the runner is tight in the slot, that was the first thing I thought of as well. The issue seems to happen no matter what blade I'm using.

[Wayne Lomman]

Often happens when the cutting action applies sideways pressure to the saw blade. There will be a misalignment somewhere. If you need to get the job done so the chooks don't freeze, try a sacrificial piece at the back. This has to be chunky enough to cop the wobble and leave your work piece intact. This should get you out of trouble until you check alignment. Saw blade parallel to table slot? Cheers

[Jim Becker]

And for all of the non-"down under or nearby" folks...a chook is a chicken. :)

[Andrew Hughes]

And for all of the non-"down under or nearby" folks...a chook is a chicken. :)

If a chook is a chicken what’s a henway? :confused: :)

[glenn bradley]

Is it a thin kerf blade? I generally got very good performance with TK blades but, the saw and jigs had to be very well aligned. Something traveling an irregular path can push a TK blade a bit out of plane and it recovers as you exit the influencing material. the good news is that whether it is or isn't, setting up your saw and your accessories as true as possible leads to a more enjoyable shop time going forward.

[David Prochniak]

It is a thin kerf .091? Freud blade. I was thinking that if it was deflecting that feeding the wood at a slower rate would fix that issue, but like everyone else said, maybe the alignment is not quite right.

[Peter Christensen]

If a chook is a chicken what’s a henway? :confused: :)


Four to six pounds.:rolleyes:

[Jim Becker]

It is a thin kerf .091? Freud blade. I was thinking that if it was deflecting that feeding the wood at a slower rate would fix that issue, but like everyone else said, maybe the alignment is not quite right.

A thin kerf blade very much can deflect more on cuts like these...there's less metal than the ~.125" that a regular kerf blade has. But as you note, alignment remains my first suspicion, particularly due to the nature and repeatability of the issue.

[Andrew Hughes]

Four to six pounds.:rolleyes:

Excellent Peter you got the joke. :D

[Edwin Santos]

Perhaps try making two cuts to sneak up on your final dimension. First cut will remove most of the material, perhaps 1/16" short of final dimension. Second cut will just shave off enough to bring the tenon cheek to final size and clean up the distortion left from the first cut.
Since your jig apparently operates in the miter slot, you can use a spacer/shim to help with the two setups, which would be more consistent than adjusting it back and forth.

If you are still getting the distorted cut even when shaving off only a small amount of material, then I think you can at least rule out blade flex as the root cause.

If you have a bandsaw, you could do the first cut(s) there and use your tenon jig and table saw for the second clean-up cut.