Prototype Taper Jig Using Microjig Dovetail Clamps

5397 Views 7 Replies 4 Participants Last post by bfblack, Dec 6, 2019

bfblack

Discussion Starter · Dec 2, 2019

Since I first learned about the Microjig dovetail clamps (microjig.com), I have wanted to make a jig using the clamps. One might call this a solution looking for a problem. I decided to re-purpose an existing shop built taper jig to use the dovetail clamps. The prototype resulting from this exercise is shown in the attached photo. The thin black wedge shaped strip is the off cut from the first taper cut. The jig runs in the miter slot (as opposed to adjacent to the rip fence). The runner is intentionally undersized on the width. This allows the user to push the jig against the right edge of the miter channel while making the cut but pull the jig against the left edge of miter slot while returning the jig to the original position. This idea came from the internet but I do not recall where. In my estimation, the Microjig clamps work better at holding the stock in place than do toggle clamps that I had on the original jig. Also, I thing standing to the side of the saw blade is safer than standing behind the saw blade.

Based on my experience with the prototype, I am ready to proceed to the real jig. A drawing is shown on the attachment. (Note that the dovetail slots in the long direction are not shown as running the entire length. This is because of my inability to easily get SketchUp to do what I want. In this case, it is quicker to make the cuts on my router table than to make the drawing.)

There are some issues that I would like input from the community. The material I used for the prototype was good quality 3/4" baltic birch plywood. Unfortunately, cutting a kerf(s) in one side of plywood makes it "bendable plywood". Even though the plywood may have been perfectly flat in the beginning, the finished product is no longer flat. My thought is to try 3/4" MDF as it does not have a layered structure as does plywood. Rather than buy a full sheet of MDF, I am soliciting input from the community. Ideas would be appreciated.

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Cherryville Chuck

· #2 · Dec 2, 2019

The critical part is the 3 stops. They take care of all the pressure being put on the piece being cut. I don't think you require a lot of down pressure to hold it. But the clamps do keep your hands well away from the blade. I would be concerned about the clamps ripping through the surface of the mdf. This is where the toggles would be better as you could use flat head machine screws and bolt them down from under the sheet if you countersunk the heads in.

You could add another thin sheet of ply under the one you have if the flex is a problem but unless it's causing issues with keeping the cut vertical I don't know if I'd bother. As you said, you were in search of a problem that you could apply a solution so maybe you went into it with preconceived ideas of what you wanted it to be. Now ask yourself what it needs to be because maybe you've already succeeded. By the way, that's a nice jig.

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PhilBa

· #3 · Dec 3, 2019

I've seen those clamps, too, and were interested in trying them.

I don't think MDF will make any difference. Adding another sheet on the bottom will help but may make the base too thick. Maybe 1/2" would work ok. Certainly clamping the workpiece down will add rigidity.

I use toggle clamps on my taper jig. They sit on a second piece of 3/4" BB and cantilever far enough over to be out of the way.

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Ola C

· #4 · Dec 4, 2019 (Edited)

I wouldn't go for MDF and I think microjig recommend to not use MDF?

Other than that, using the dovetail clamps (or regular rail clamps in routed t-slots) is in my opinion superior to other hold down methods in most cases. Quick to slide to new position, easy to change height, quick to move from jig to jig, easy to control the pressure, can be used in thin jigs since the force is taken up in the clamp itself, whereas a toggle clamp is pretty much the opposite to all of the above.

I use rail clamps (dovetail clamps where not invented by the time I started using this concept) in almost all my jigs since a few years back. I haven't had problem with the plywood bending but I might have been lucky. I would point out though that it's very seldom I rout the tracks from side to side going through the entire width/length when it comes to thin jigs. I often keep one side full thickness, without tracks, for rigidity. In your taper jig, if you slide in the clamps from the same side as the workpiece is, you could have full thickness plywood without cuts on a large part of the surface, left of the clamps in your pic.

My table saw sled was my first "rail clamp in jig" build some 8 years ago, the routed tracks have survived well and it's really great! I can clamp any item of any size almost anywhere I want and it's done in seconds. I can also clamp additional jigs to the sled, like in sample pic attached where I cut drawer pulls to length using both a stop and a jig to hold the pull, both jig and stop attached easily with rail clamps.

See pinterest or yotube link for more examples where I use rail clamps in jigs.

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bfblack

Discussion Starter · #5 · Dec 4, 2019

Ola C: Nice looking cross cut sled! I like your ability to insert your hold down clamps from the top side of the sled. I asked Microjig about an inverted dovetail bit so that the dovetail bit could be used similarly but they do not offer that router bit.

I completely agree with your comments on the superiority of the rail and dovetail clamps over toggle clamps. I have used toggle clamps and mounted them exactly as Cherryville Chuck suggested. The toggle clamps are then typically mounted to a moveable fence. My experience was that the upward force applied to the closed toggle clamp would lift the fence up off the base of the jig. The attached photo is of a router table jig for safely holding small pieces. The darker wood under the two toggle clamps is being edge routed. When the clamps are activated, the fence lifts off the base. While that might not be critical in this application, I personally feel more comfortable when jigs don't move because of clamping action.

I was not aware that Microjig recommended against MDF as a jig material. Thanks for that information.

I think the reason you did not notice any bowing of your jig is because of heavy duty front and back portions of your sled. I put dovetail slots in a 10"x36" piece of 3/4" baltic birch plywood and got a bow of 3/32" in the middle of the 36" dimension. I found this unacceptable. See photo.

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Ola C

· #6 · Dec 4, 2019

bfblack said:
Ola C: Nice looking cross cut sled! I like your ability to insert your hold down clamps from the top side of the sled. I asked Microjig about an inverted dovetail bit so that the dovetail bit could be used similarly but they do not offer that router bit.

Thanks! I like it very much.

You don't need an inverted dovetail bit to be able to insert the clamps from above. Just rout a wider track with a straight bit, same length as the clamp head is long and minium same width as the widest part of the dovetail clamp, you see the wide portions where I insert my clamps….but I might have misunderstood what you meant?

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bfblack

Discussion Starter · #7 · Dec 6, 2019

Ola C said:
Thanks! I like it very much.

You don't need an inverted dovetail bit to be able to insert the clamps from above. Just rout a wider track with a straight bit, same length as the clamp head is long and minium same width as the widest part of the dovetail clamp, you see the wide portions where I insert my clamps….but I might have misunderstood what you meant?

I understand your suggestion on how to widen the narrow part of the dovetail. I made this cut in a sample piece and it works fine.

I had a different cut in mind as shown below. Obviously the inverted dovetail cut would have to be a stopped cut. My motivation was that you would have more material to keep the clamp from pulling out of the dovetail slot. Discussions with Microjig convinced me that was not a problem.

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bfblack

Discussion Starter · #8 · Dec 6, 2019

I went against conventional wisdom and rebuilt my taper jig using 3/4" MDF as the base. Routing MDF is certainly easier than plywood because it is a softer material. The MDF jig is certainly flatter than the one using baltic birch plywood. I think the MDF jig will be more than adequate for my hobby shop. After all, how many table legs am I going to taper. In a production shop environment, MDF might not be adequate.

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Prototype Taper Jig Using Microjig Dovetail Clamps

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