Dovetail Jig: design feedback sought - Page 4 - Router Forums
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post #31 of 35 (permalink) Old 01-25-2020, 07:18 PM
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Uniformity of the fingers and blocks is critical. Why not mill a block of aluminum to the exact shape, drill the block, then slice off each finger. You're likely to get more uniform pieces that way, and you might be able to do it on a table saw if the aluminum is fairly soft.

I think there are several precision measurements involved that may not seem apparent at first. The angled fingers not only have to be exactly the same as the DT bit angle, but the inside edge must be a precise depth, same with both ends of each finger. They must line up precisely with the body of the jig so the bits depth of movement is just right.

If you can locate a woodworking store that has one of these jigs, I'd go and give it a good looking over. I think you might also download an instruction sheet for either commercial jig. I know the instructions for the Sommerfeld jig are quite explicit and will answer a number of questions for you. Most such instructions are on websites as pdfs to download. This will get you to pictures of the Sommerfeld jig: https://sommerfeldtools.com/sommerfeld-s-dovetail-jig I posted a picture showing the bar with the stops.

Youtube has two videos by Sommerfeld showing the jig in use. I think it will help. But to be honest, at $240, I think I'd rather just buy one.


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post #32 of 35 (permalink) Old 01-25-2020, 09:25 PM Thread Starter
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Originally Posted by DesertRatTom View Post
Uniformity of the fingers and blocks is critical. Why not mill a block of aluminum to the exact shape, drill the block, then slice off each finger. You're likely to get more uniform pieces that way, and you might be able to do it on a table saw if the aluminum is fairly soft.

I think there are several precision measurements involved that may not seem apparent at first. The angled fingers not only have to be exactly the same as the DT bit angle, but the inside edge must be a precise depth, same with both ends of each finger. They must line up precisely with the body of the jig so the bits depth of movement is just right.
My CNC router isn't going to do a big enough block of aluminum so that's out for me. Though, it has pretty good repeatability - I have confidence that I can cut 10 fingers and have them all come out very close - 5 mils or better.

I think you are referring to where the fingers line up with respect to the workpiece and determines the width of the pins. The "depth" of the finger (i.e. the width of the pins) can be adjusted by moving the platen as shown in the picture. That's how you tighten/loosen the joint. The LV jig has a similar adjustment. Also, you would use the adjustment to handle different backer thicknesses. You can see a line on the fingers that indicates the nominal position for the inside edge of the workpiece. In practice, I expect some amount of tweaking to be done to get the joint exactly tight. All the through DT jigs out there have some sort of way to adjust this and their instructions all talk about adjusting for a perfect fit. I'm thinking of putting ruler tape (measure tape?) on each side to allow visual adjustment. Would prefer some sort of screw adjust - thinking about how to do that.
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post #33 of 35 (permalink) Old 01-26-2020, 08:34 AM
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Phil, I still think a 3d printer would be the way to make the pins. Since they would be the most likely item to get nicked by a router and could be easily re printed as a set or individually. As far as precision they need to match each other as a set.

I watched a video where a guy made a cube 1"x 1"y 1"z in a file, then printed and measured the cube after printing. The cube had the x y and z axis printed on the cube, so when he measured the result...he then knew which axis needed adjustment.
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post #34 of 35 (permalink) Old 02-06-2020, 12:54 PM Thread Starter
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Design update. Family issues have slowed me down a bit and several funerals have eaten time (go to other people's funerals, otherwise they won't come to yours) but finally got some more time to work on it.

Here's the latest. Biggest change was to add screw adjusters to control moving the finger platen. While it adds a little cost ($10ish), I think it makes it easier to use. I also did a lot of spec work on HW and some test cuts for fit. Cleaned up my drawings, hopefully much clearer. Started on a bill of materials though it's not done until the fat lady sings. Cost of hardware looks to be about $25. Anyway some pictures. As was said before, I'm interested in your feedback and questions.

Next steps are build the base, platen and cutting test fingers with 1/4" mdf (saving the lexan for when I'm done with the tweaks). Still need to figure out the tension springs for the platen adjuster.
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post #35 of 35 (permalink) Old 02-06-2020, 06:15 PM
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Quote:
Originally Posted by DesertRatTom View Post
But to be honest, at $240, I think I'd rather just buy one.
I agree. I did. Super simple to use and comes with the correct router bits.

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