Hi, the first picture is the oak lampshade frame I am making. it requires a 39 degree angle with half-laps at the ends. I am using an Incra t-Square set to 39 degrees and a dado blade set to 1/8 deep on a 1/4 thick piece of wood.
You can see in picture #2 it isn’t cutting a clean half-lap, it has a curve to it. I have cut several, they all turn out like this. Can’t figure out how to do this. The outside blade of the Dewalt dado blade has alternating teeth, one has a steep angle, the next is nearly flat. If all the outside teeth were all angled I would get this but they aren’t. Seems the flat teeth would cut the line straight. Or, is the because I am approaching the blade at 39 degrees? Stuck. Thanks,
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I'm not sure you have your dado blade assembled correctly. A dado assembly should have 2 blades with raked teeth with chippers in between. You look like your outside blade is a chipper and it's almost rubbing against the chipper in front of it. That should never happen. If you would raise the blade and post another picture of the dado stack it would be easier to state with certainty.
+1 on the dado stack not correctly installed. Also, are the pieces securely fastened in the Incra Jig, or are they moving back as you cut the lap?
Stack assembly aside I often do delicate part joinery on a larger blank and then cut the part from that blank. I would not want to try a hold down on that small part over a spinning dado stack to add control to that cut.
If the dado must be cut from small stock a push block over a bit on the router table against a fence would be my preferred method.
It also seems to me the part is moving while being cut.
Try the same cut on a beefy piece of scrap. If it cuts clean, you'll know the answer.
Something in the system is shifting as you cut. The parts are either sliding on the miter gauge or riding up on the blades. Build a sled. You have a bunch of theses joints to do; it will be worth effort and safer too.
I really think the problem lies in the dado stack. That outside blade is way too close to the chipper beside it and can't cut any wood and has the effect of pushing the board up. I have the feeling the OP is relatively new to woodworking and simply did not stack the dado correctly it just doesn't look right.
All of the above is correct.
Even with the dado stack installed incorrectly, the cut should be straight.
If this is the method you're going to use, clamp the piece to the miter fence to make the cut.
A sled is safer for cutting small piecess like this
Dado blade setup aside, when you get that straightened out, you should spin your miter guide around to the opposite angle.
With a narrow piece and cutting against the grain as you are doing, you are flirting with a nasty event. Note the split end in the photo. In the other orientation the blade will want to pull it away from the stop, so clamp it or use a sandpaper covered fence for control.
The attached pic can be enlarged quite a bit. This is the stack, I don't see how it can be installed differently but...see note below
The wood is held down firmly with a large block, it isn't rising or sliding, that was my first thought.
Note: The dado set was made for a right hand arbor I think, the "This side out" label on the blade would cause the blade to be installed backward if this has any bearing.
I will set up the square on the other side of the blade and see if that helps. Thanks for all the comments. I do this to learn. :)
Your inside and outside blades need to be switched. The rake teeth should have there high points on the outside of the cut.
There also appears to be a significant gap on one side of the chipper and overlapping teeth on the other. One tooth looks like it is damaged but that could just be because of the low quality image. It definitely does not look right but the image is not sharp enough to say for sure what is causing it to appear so.
https://youtu.be/KPYXUe1q9yM
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yes, took me a sec to figure out that question. Forgot the wrenches were in the photo.
What is the direction of feed? Are the wrenches in the photo on the outfeed side?
I reversed my blades and learned something. I flipped the angle of my fence, feels safer. It now cuts as expected. The Stumpy Nubs Video was also worth a watch. Thanks for all the help.
I'm glad we could help
Excellent!