One-Pass, Half-Blind on a Leigh Dovetail Super 12 Jig

Just a stab in the dark but is it possible this happens if the router bit is not centered in the bushing?

Or is it that the joint is slightly loose and one board was offset from the other by a sliver?

-- Until you spread your wings, you'll have no idea how far you can walk.

looks to me like the Tails part wasn’t positioned properly – it seems like it was positioned a tad bit (the distance equal to the gap that you see) too much to the right… it should have been positioned slightly (the size of the gap) to the left – IF you cut the dovetails positioned as the pieces are viewd in the photo (otherwise the positioning is a bit more to the right)

-- When in doubt - There is no doubt - Go the safer route.

In the instructions it tells you to move enough fingers to cover the wood being cut and then center that group of fingers on the board. I forgot to center the fingers on the wood the first time and got a odd finger as you show the first time around.
Also, did you use one of the board widths from the chart? The single pass set up is dependent on board width. I have talked to a few guys who forgot that part with this specific cut on the Super Jigs.
You can get gaps if you turn the router while cutting the joints. That eliiptical bushing can change things if you don’t keep the router facing the same way. I found that it helped to mark the base on my side of the router so I can prevent rotating it while cutting the joints. We really should do this regardless of what jig is being used.

-- Tom Hintz, www.newwoodworker.com

Looks to me like your setup is a little off – you have a tiny, tiny pin on one end – your two end pins should be about the same thickness. Not sure that that’s the problem with the gap though. I just got one of these and can’t wait to give it a go. You’re already several steps ahead of me.

-- You can't get a hug from Facebook.

Thanks for the great feedback! I have a flat side on my router base, so I shouldn’t be turning it as I go. I was very careful about that. I don’t really care about the layout of the tails being centered on the board. I can handle that. This was just a scrap run on some poplar. I figure there are enough variables to tweak. I’ll save centering the tails for after I get the one-pass, half-blind dovetails. I made my test pieces directly from the directions, so the thickness should be correct. I can see that the bit might be slightly off center, but not the same amount as that gap. The Leigh bushing and 8mm router bit work with pretty tight tolerances. I’ll take all of your advice out to the shop with me and give it another go.

-- You can't control the wind, but you can trim your sails

Just a tip. I have a 12” leigh and have never contemplated using the one pass half blind method. I have found a much greater success by utilising the variable spaced method. Not only is it easier to set up but the finish is true to the traditional finish. One pass shows it was machine made and the round backs show. Set up and a period of practice, as with all jigs is necessary to get YOUR jig right. There will always be differences between individual jigs. Practice, practice and practice. This way you will master the learning curve.

-- I cut the damned thing twice and its still too short

I have had the same problem but havent had time to work on it to much but I belive the problem might have somthing to do with the top left stop spacer (what you rest the wood against) I dont think its adjustble but there might be some play in it. Thats the first thing I’m going to try

Thanks for the feedback guys. I was obviously going to try the variable spaced method next, but I thought I’d master what I mistakenly assumed would be the “easier” method. Good point about the round backs, but I cover that with the drawer face. Regardless, I’ll make up some test pieces of poplar and give the “hard” way a go. I’ll be making the drawers of the night stands dovetailed, and possibly remake the dresser drawers. That’s the first place everybody looks, regardless of whether they’re a woodworker. I’ve often said that Stickley doesn’t use dovetails, instead they use a lock joint.

Yeah, there’s no play in my offset guide, but interesting. I guess at worse, I could order another one and shave one down a tad.

-- You can't control the wind, but you can trim your sails

I had a similar problem with my Rockler d-tail jig. My bit was not centered in my router’s guide bushing. Repositioned and got perfect results.

Yeah, I just bought a centering pin. Hope that helps. I don’t remember a lot of adjustability with my bushing. I had to buy a special adapter for my Hitachi M12V. One of these days, I’m going to get a Porter Cable router which will simplify my life immensely.

-- You can't control the wind, but you can trim your sails

I’m guessing the router bushing guide is a big part of the problem. When you change bits from the dove tail to the straight bit you may be inadvertently moving the bushing guide to a different position relative to the bit’s shaft. If you can’t get the bushing guide “perfectly” centered try putting an index mark on the bushing guide so you can rotate it to the same location on the router relative to each bit. Also make sure your are making the cuts with the router held or approaching the dovetail guide the same way.
Lastly make sure the stop on the left side of the dovetail guide has been properly set up. See the book for instructions on that. The learning curve for the Leigh jig is steep but once you master it you will be cranking out dove tails like crazy. ....Just wait until you try making asymmetrical dove tails with it. It’s a brain twister but produces great results.
Good luck.

-- Les B, Oregon

[QUOTE]I can see that the bit might be slightly off center, but not the same amount as that gap. [/QUOTE]

The amount of bit offset is only half the amount of the gap. It is doubled what you turn the parts around to fit them toegether. So as you can see, it takes very little to cause a fit issue.

[QUOTE] When you change bits from the dove tail to the straight bit you may be inadvertently moving the bushing guide to a different position relative to the bit’s shaft. [/QUOTE]

There is no bit change going on with “single pass” half-blind dovetails. Everything is done with the dovetail bit.

Thanks, I will definitely follow your advice when I get to the two-step dovetails. Right now, I’m working on the one-pass dovetails, which doesn’t require changing bits, so the centering issue isn’t as critical.

-- You can't control the wind, but you can trim your sails