Leigh D4 dovetail jig driving me nuts

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I've had this jig for a good 4 or so years and have primarily used it for 1/2 blind dovetails for drawers. Every time I use it, I spend a great deal of time getting it set up and in the past have finally "settled" for as good as I can get. I decided not to settle this time and have spent a great deal of time trying to get the jig to provide me with gap-free 1/2 blind joints. I get the part about adjustment up and down loosening or tightening the joint. The problems I am having are getting gaps on the *side* of some of the joints, and the bottom gaps when adjusting tightness not being even across the width of the board (only 3 1/4") despite the fact that the fingers are flat on the pin board and the spacer board and the tail board is uniform across the width of the spacer board. I've tried recentering the router bit (one of the reasons I bought template bases for my Bosch laminate trim router was so I could easily center the bushing), I've tried swapping jig fingers (now I've got a bit of springiness when tightening the finger jig because of having to remove the ends). I've tried rotating the router 180 degrees to rout the pins after routing the pins. Nothing seems to be helping much.
Next thought is lapping the router baseplate dead flat. I've been trying to hold it flat to the center, but am getting rocking. Would a 5 mil rock cause significant problems?
Any help would be appreciated. As a pre-emptive, the answer, "just chop them by hand" is not an answer I'm seeking -- I'm really trying to figure out why this machine is not working as advertised.
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Mark & Juanita wrote:
Just added a picture at abpww illustrating the problem.

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I'm not sure how much this matters, if at all, but I've watched the demo at many shows before I bought mine, and I remember the presenter saying that you need to push straight down on each finger as it is tightened. I don't remember if he said just what the significance of that act was, but I've always done it that way and have not had these type of problems. The guy who I bought mine from is Mark Hensley and he runs a shop and a school at his home in Florida. Maybe try sending him your pictures at .. .. .. snipped-for-privacy@markstoolschool.com .. .. .. and ask him for a response. If anyone is qualified to give an opinion, it would be Mark. I think he knows that jig better than the engineers who designed it.
Mark & Juanita wrote:

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"<<<__ Bøb __>>>" wrote:

Thanks. I'll try re-setting the fingers as you suggested and if that doesn't work, will contact Mr. Hensley.
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Mark & Juanita wrote:

No solution, but feel your pain.
As much as I like the jig, I continually fight with it when attempting to do a "production run" of drawer sides for dozens of drawers at a time.
I've pretty well accepted that there are simply too many parameters, from stock, to router, to jig, to obtain the kind of ideal CONSISTENCY in that situation, from first to last.
But, I do remember my "pre-jig" days, and the alternative was worse ...
On the current project I'm toying with going with the Multi-Router just to see if the "consistency", from first to last in a many part run, improves.
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Swingman wrote:

Thanks. It's helpful knowing that I'm not the only person who has been fighting this.

That pretty well describes the issue -- piece to piece consistency even after getting things set up as best as possible is an issue.

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Mark & Juanita wrote:

Is there any possibility of movement between stock/fingers?
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Morris Dovey wrote:

After I posted that, it occurred to me that movement of the bushing could produce a same/similar effect...
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Morris Dovey wrote:

That I'm pretty certain is not happening. The bushing is very solidly seated in the base plate. I was also seeing the same problem when using my 1613 for the router, so I think this cause can be eliminated.
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Morris Dovey wrote:

Morris,
I don't think so, I've got things clamped down pretty tight. I'll look at that a little closer, it may be that router torque is causing something I can't see, will have to look more carefully.
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Mark & Juanita wrote:

- the fingers are flat on the pin board and - the spacer board and the tail board is uniform across the width of the spacer board. - I've tried recentering the router bit (one of the reasons I bought template bases for my Bosch laminate trim router was so I could easily center the bushing), - I've tried swapping jig fingers (now I've got a bit of springiness when tightening the finger jig because of having to remove the ends). - I've tried rotating the router 180 degrees to rout the pins after routing the pins.

Mark:
As you've discovered - while having variable spacing fingers - there are several inherent problems with the Leigh DT Jig design - starting with those moveable fingers. To move them you have to have SOME slop in the hole in the finger - and some way of locking the fingers in postion where you want them. That's the first design flaw. ANY slop introduced error is DOUBLED because of the Flip The Fingers Over design of the jig.
The second design flaw is support for the router. You didn't mention if you have the accessory Front Support Bar. If you don't, you're supporting the weight of the router plus any downward force you're exerting on those adjustable then locked down fingers. And the longer the support bar is - the more it must resist flexing, bowing downwards under the weight of the router and the downward force you provide. You didn't mention if this is the 12" model, the 16 or 18" model or the 24" model.
Now to what YOU may be doing to cause the problem.
The Tails board appears in the photo to be cupped a little - which could explain some of the problem
The most common problem with using dovetail bits is that they want to pull themselves out of their holding collet. Since ALL of the DT Jigs that use Fingers require that the bit's shank diameter be small - 1/4" or 8mm diamter, the router's collet holding the bit doesn't have that much gripping surface area - even with the four slots collets. And if you've got gunk in the slots the collet can't close all the way.
The other common problem is setting the bit ALL the way down in the router. THAT can lead to a jack hammering affect as the bit cuts - sometimes pushing the bit up out of the collet - and even just a little height change can screw up the fit.
Then there's the router itself. I may be mistaken but I think you said you were using a Bosch - and I think it was the COLT - a small, fairly light weight trim type routers - with a relatively small base - and not a whole lot of weight - and thus not much inertia. While the lighter weight may be of benefit in terms of less weight on the ends of the jig's fingers, there's not much mass to resist "bouncing" as the bit begins cutting harder then softer grain. A full sized router may be part of a solution to your problem.
Have you checked to see if the GAP is on both sides of the joint and not just at the Show Face side? Rub a pencil lead on the faces of either the pins or the tales, put the joint together, take it apart and see where marks have been transfered to the sides of the tails. This might give you a clue as to what's happening.
Also, are you sneaking INTO each cut or going all the way in and then to the side and then back out? A "fronter board" can reduce or eliminate grain tear out.
Hope this gives you some more things to check out.
BTW - The AKEDA, by design, eliminates the Fingers Slop Problem AND the router support tilting problem.
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charlieb wrote:

Thanks, Charlie ... I think you hit the nail on the head with many of your points.
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charlieb wrote:
Charlie,
Thanks for your detailed and thoughtful response. I'll interpose some additional information.

I don't have a front support bar. Not sure if it was available for the D4 or not -- I'll need to check into that.

I've got the 24" model

That was a bit misleading. The cupping is due to the thin remaining stock after I cut the tails from the test stock. The tails tended to curl the off-cut. The original stock was square and flat.

At this point, the bit does not seem to be moving in the collet -- what I set it at depth-wise is where it stays.

You are correct, I am using the Colt router with a template base. In the past, I've used my Bosch 1613, but had issues with being able to center the bit in the template bushing. I saw the same issues with the side gap with the 1613 as I'm seeing with the Colt. However, depth adjustment was better. I think you may have something here as far as the bit bouncing.

Good suggestion, I'll try that with a solid test piece. I just tried it with the cut-off and am not seeing a mark all the way through, so the gap is all the way through.

Definitely sneaking into the cut, not trying to go in all the way at once, not seeing any tearout at this point.

Yep, this was very useful. It helps eliminate some things and points to other areas to investigate further.

I'm also going to look into this. I've wasted enough time already with the Leigh that if I were charging for my time, I could have bought another jig. This is definitely getting to the point of not being fun nor enjoyable. Hobbies aren't supposed to drive a person to the verge of profanity. :-(
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A couple of thoughts...
To check how much you have to lower the dovetail bit, pull the two boards apart as hard as you can, and use feeler gauges to measure the biggest gap. Lower the bit that much(*). I use a 1.5hp (yea, right) PC router with the fixed base, and I've calculated how many thou each tic on the ring represents so I can do this "accurately" (again, yeah right).
Beware of cupped boards.
I always do two corners at a time, one on each end of the jig. Not only is it faster, but it keeps the jig squarer to the boards. At least put a spacer on the other end, using one of your other milled boards.
Yes, your router base should be flat. Compare it to some reference flat, not to the jig. I got a cheap granite surface plate from Grizzly for this purpose.
Don't rotate the router when routing - hold it in a fixed orientation throughout. Consistency is more important than concentricity.
When I do through dovetails for batch jobs, I do all the tail boards first, then all the pin boards, and it doesn't matter which tail boards I match up with which pin boards - all the joints are the same. The D4 *can* make accurate joints, so keep working on it.
(*) If that's way too tight, next time do half the thickness, I lose track of when the adjustment doubles the results and when it doesn't.
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DJ Delorie wrote:

Yep, that's what I've been doing.

The Colt is a little more fussy setting depth, but I had the same issues with the 1613 EVS with the microadjust.

Will double-check, but I'm very fussy about getting both flat and square stock.

Have been putting a spacer on the other end to make sure

That seems to be the next action I need to take. I know for certain the router base on the Colt is not flat. I can't speak for the one on the 1613 when I used it last time.

After considering this, I think it is also necessary to rotate the router 180 degrees when doing pins vs. tails. When you look at where the router bushing contacts the jig, it seems that you want the same point contacting the jig for both pins and tails. To do that, the router needs to be rotated 180 degrees. Would you concur?

That's good to know. I'm still struggling with whether this is setup or technique.

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No, because you want to consistently register the center of the bushing against the same reference edge with the same offset. For example, if your bushing was 1/4" to the left (assuming that were possible), you want that offset to move the pins to the left *and* move the tails to the left. If you rotate the router, you end up with the pins moved to the left but the tails get moved to the right.
If the bushing has an in/out position error, you compensate for that when you position the D4 rack after flipping it.
This assumes that the largest error in the bushing is it's position relative to the router bit. Errors in the shape of the bushing, while nonzero, are likely far smaller than the position error.
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DJ Delorie wrote:

I agree with needing to offset the same amount from the reference edge. However, the reference edge changes when you flip the template. Here was the thought process:
Say the offset is as shown below: bush bit bush -->| |<-- offset ----| | | |------- | | | | /_\
When cutting the tails:
-->| |<-- offset relative to jig ----| | | |------- | | | | <---- this part of the bushing contacts the jig, /_\ The cut will be offset by the off-center here
| Cutting wood on this side
If I don't rotate the router 180 degrees when cutting the pins:
-->| |<-- This is the now offset relative to the jig ----| | | |------- | | | | /_\ | Cutting wood here This is the side that will contact the jig
| Now cutting wood on this side of the bit
It seems like the cut will now be greater for this offset on the pin side than on the tail side.
However, if I rotate the router 180 degrees: -->| |<-- This is the offset relative to the jig ----| | | |------- | | | | /_\ | Cutting wood here This is the side that will contact the jig
and the same offset from the bushing to the workpiece will be obtained.
It seems like I want the second condition to get the same offset. What am I missing?

From what I can tell right now, I agree, the biggest offset is in the router bit centering.
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Mark & Juanita wrote:

Hopefully the ASCII art turned out better for others than when I read the posting. If not, my apologies, let me know what I can clarify
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Mark & Juanita wrote:
OK, just posted a better sketch of what I'm trying to illustrate on abpww.

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USE constant width font. That helps. Martin
Mark & Juanita wrote:

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