Leigh Dovetail Question

[sroxberg]

I am cutting my tail boards. They are cut with a dovetail bit at 8 degrees.

I did not cut the first pass as deep as I would have hoped. Can I add a 64th to the depth of the router bit and take a 2nd pass on the first set of cuts, or do I have to cut them all too shallow.

I am talking about a 64th of an inch shallow so I'd like to add a 32nd of an inch to raise them proud of the pin board surface.

Is this possible or just plan to sand to scrape the corners.

[Superglide]

Proud is better than shallow. If I understand your question correctly.

[JGrout]

If you are talking about lowering the router bit to cut the pins deeper no you cannot do that the pins would be on two planes if you do this

[cputnam]

If you've not already cut the pin boards, and the fingers have not moved, I see no reason why could not deepen the cut by 1/32".

[JGrout]

cputnam said:

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If you've not already cut the pin boards, and the fingers have not moved, I see no reason why could not deepen the cut by 1/32".

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there are two distinct ways that a cut may be deepened

The first is to reset the pin guide on the jig further back to make the back of the pins deeper. This is what I believe Curt has referred to in his statement this adjustment is possible.

When the OP said he wanted to move the router bit and not the rail ( I believe) that changes the entire layout of the dovetail and is not possible without making large gaps around the fitted parts except for the last 1/32" one would have once the cutter was reset.

This is why I encourage allowing extra length on the initial parts to do setup work before trimming to final lengths. It prevents exactly what happened here from occurring, and wastes the least amount of material being scrap

[Joel H.]

JGrout said:

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This is why I encourage allowing extra length on the initial parts to do setup work before trimming to final lengths. It prevents exactly what happened here from occurring, and wastes the least amount of material being scrap

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+1

When I was learning to use the Leigh DT Jig, I did just what the OP did, and tried to lower the bit slightly. Just as Joe said, the fit was not close.

I have learned to mark the thickness of the pin board and lower the dovetail (or straight bit for that matter) to cover the line. Works perfectly with little excess (proud) wood. Sands down nicely.

Joel

[cputnam]

Joe, I need enlightenment. If I am cutting tail boards and discover the cut is too low/high, what is the problem with simply moving the bit down (jig to board reference) another 1/32 and then recutting all the tail sockets? This is a real question and not an argument.

[Joel H.]

I'm not Joe (but I'm Joel). This is one where a picture is definately worth a thousand words, but I'll give it a go.

Think of the DT bit's form, similar to a pyramid. If you make a cut with the top (narrow part) above the surface the width will be say 1/4". then if you move the bit down, the top cutting part will not be cutting because it's narrower than was already cut. And the pin will be the same width as the final cut - so there will be a gap. Maybe small but it'll be there.

Also the bottom of the DT bit may (because it's only a 32nd of an inch) make a wider cut the first time then the bit will make after lower it - showing a "Christmas Tree" cutting design.

Hope this helps and also hope someone with the capability puts pictures up.

Joel

[JGrout]

Part of the problem with your argument of doing the cuts then discovering the issue is that even Leigh strongly encourages testing joinery _before_ final cutting of even one joint.

dovetail jigs are fussy there are tons of adjustments that can be made and not making them in test pieces ( the extra length I allude to constantly) is a recipe for disappointment

I would encourage you to refer to pg 77 of the user guide; all the answers are there and in the following sections including drawings of what happens when you change the bit depth of cut.

They did such a thorough job of describing the issues that I defer to the manual in all cases where detailed information is needed.

HTH

Joe

[dav]

If I understand your question correctly, once you've cut the tails to a given depth (usually the pin board thickness plus about 1/32"), that's it. You can't go back and make the cuts deeper. I suggest you try it on some scraps in order to prove it to yourself.

On the other hand, if it were the pins, you could go back and cut them deeper.