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Incra Double Dovetail Project #3: Cutting double dovetails and making a few mistakes

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Blog entry by SPHinTampa posted 1047 days ago 3161 reads 3 times favorited 2 comments Add to Favorites Watch
« Part 2: Cutting the side joints Part 3 of Incra Double Dovetail Project series Part 4: Cutting the Pins »

At the end of the last blog, I had glued up the trim to the tail sections of the R/L pieces:

I used my oscillating belt sander to sand the ends flush

Flush ends give me a flat surface for the next step

In my previous blog, I mentioned that you need a zero clearance insert to avoid having the bit pull the workpiece down. I forgot to mention the need to ensure that you hold the workpiece against the fence, particularly when you pull the sled back thru the bit (the climb cut) as it pulls the workpiece to the side. The result is a slightly out of square cut as you can see below. A little homemade wood putty (sanding dust and glue) will fix.

I then use a marking gauge to cut the trim back to 3/32” off the joint. Why 3/32”? Because almost all the incra double templates are designed to leave this much of a trim piece – the template book has the trim thickness listed.

Cross cut to the marked line on the Radial Arm Saw.

Next step is to cut a rabbit. First of all, bury the bit in the fence to zero it out.

Then move one of the measurement gauges to sit under the marking line. In the picture, the top ruler shows where the measuring gauge sat originally (11” inches and change). The lower gauge has been moved to 10” even so I can easily sneak up on the 7/32” rabbit cut. Why 7/32”, again rabbit depth is specified in template guide.

I then cut the rabbit with a very light scoring cut to start with (1/32”) and then cut the rabbit in 3 more cuts, advancing to 10 7/32”.

And this is what you get.

Now it is time for the big event. Time to cut the double dovetails.

First of all, clamp the tail sections to your right angle fixture and make sure there is no play in the movement. I forgot to mention previously but I will point out two important things now. First mark your pieces so that you are always putting the same edges against the fence. Even though I am sure that my centering was perfect, even a slight variation, coupled by cutting from the wrong edge, will leave gaps in your joints. Secondly, use a backer board (cut to same width as your work pieces) to avoid blow out. The book shows that you can cut two pieces at a time, which I am doing here. However, if I was working on a super fine project, I think I would cut each board individually. I find that the piece sandwiched between the backer and the front pieces always wants to move on me during cuts.

Other really important thing is to always perform a scoring cut and use 3-4 small cuts on the outside pin cuts. I am cutting 20C to start with. As you can see, I start far away from 20C, cutting 1/32” on my first pass and then advancing to 20C in 3-4 cuts. Similarly for the last cut, I will advance past the last cut, perform a scoring cut and then back into the cut slowly. In theory, give bit rotating into the piece, you don’t need to do this … my experience is that it is less wear and tear on bit and seems to give me better results.

Second pass after scoring cut.

Now you just have to advance the cutter to each individual cut. Pushing thru and pulling back smoothly (wax the table top) and make sure you keep the piece pushed laterally against the fence for the climb cut.

These look great when they are done.

Life sucks when the trim blows out.

When you cut the trim piece, you might be tempted to make it 4” and try to squeeze you end cuts out of a smaller piece of wood. Don’t do it. Make at least 2-3 extra trim pieces because you may need to fix a mistake or two (or in my case 3). I chiseled out the trim

And recut the entire sequence from rabbiting onward.

Next blog … cutting the other ends … way faster now.

-- Shawn, I ask in order to learn



2 comments so far

View ratchet's profile

ratchet

1285 posts in 2414 days


#1 posted 1047 days ago

This project is going to look great!
Makes me wonder if using a fronter and a backer board might help stop the trim piece from chipping out. Also , I’ve noticed that wooden screw clamps seem to work better at holding the material for me than quick clamps.
Please keep going.

View Kindlingmaker's profile

Kindlingmaker

2654 posts in 2153 days


#2 posted 1047 days ago

I found your “how I did it” really cool. Thanks!

-- Never board, always knotty, lots of growth rings

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