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Thread: Sliding Dovetail Frustration

  1. #1
    Join Date
    Oct 2013
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    Sliding Dovetail Frustration

    I'm working on a workbench from FWW plans and spent the weekend trying to learn how to make a tight-fitting sliding dovetail for the drawer dividers. It was mostly an exercise in frustration and I know there must be an easier way.

    My method is pretty basic - I made a simple jig for my handheld router to make the female dovetail, set the bit (a Freud Industrial 17/32" 7 degree) at 1/2" as measured with my Wixey digital gauge and cut the female dovetails.

    For the male dovetails, I moved to my Kreg router table and that's where the frustration really set in. I set the height of the bit again using the Wixey gauge and then spent hours (literally - probably 3-4 hours at least) fiddling with the fence, trying to find the "just right" setting that would give me a joint that fit cleanly. I eventually found a point where the joint was too tight and I could move the fence almost imperceptibly and suddenly the joint was sloppy and loose. Eventually, I settled on "too tight" and got out a sanding block to take the male dovetails down to where they would fit better.

    The end result was still some unacceptably poor joints, so I'm ready to re-do the joinery as needed if I can find a better process. I'm not opposed to getting a Freud 3/4" dovetail bit if that would make things any easier -- the stock for the male dovetails is 3/4" thick, so maybe a bigger bit would be more appropriate.

    Any suggestions would be appreciated!

  2. #2
    Marty, sliding dovetails are a very frustrating and fussy joint, there is a very small difference maybe (.010") between a joint that is way way to tight and one that is very sloppy. First, I would only cut a non tapered sliding dovetail that is only 2 - 4" wide, any more will result in great frustration.. Just as a caution, the joint will need some space for glue, it will swell, so even if you have the most perfect of fits, you will need to allow for room for the glue..

    I cut 180 degrees from the method you attempt, first cutting the female dovetail, then fitting ever so carefully the male dovetail 'pin' to the fit the just cut female dovetail on the router table. I use a sample piece of the exact cut off from the the pin board board is used to dial in the fit.

  3. #3
    Is it Philip Lowe’s bench you're building?

  4. #4
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    I have done sliding dovetails and like Robert, I cut the female dovetails first. Then I sneak up on the male dovetail "pins" to fit.

    Again, like Robert, I use an actual piece of scrap to test the fit on first.
    Ken

    So much to learn, so little time.....

  5. #5
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    @Dave - yep, that's the one - I've been "working" on it for almost a year, got sidetracked over the summer with a dozen other projects and finally getting back to it. I've watched his video multiple times and am trying to emulate his steps the best I can. I've got it all down perfect -- except for the part where he makes the joints actually fit...

    I did make the female dovetails first then spent hours trying to get the male "pins" to fit. And I certainly found that a .010" shift in the router table fence was the difference between too tight and too sloppy.

    It also seems like maybe my router table setup isn't quite square, as I noticed that on nearly every cut I made on the male "pins", when slid into the female dovetail, one end of the pin would show a little bit of a gap at the upper edge, while the other end was tight. So maybe I need to look into that a bit more.

    Thanks, Robert for the reminder about glue swelling the joints - I may need to make them just a tad looser than they currently are; I can already see myself in a full panic with half of the glue-swollen dovetails not fitting and the clock ticking as the glue sets up...

  6. #6
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    I've done some cabinet width sliding dovetails. The trick is to make the joint fit pretty loosely for at least half the width; that's the only way you will get the whole thing installed and even then I sometimes need a clamp to pull it the last few inches. I also cut the female half first and then the male. I can tell you that a change of 0.010" on the router table is huge! You need to be thinking about changes of 0.001 - 0.002". How? Feeler gages. With my homemade RT fence I clamp both ends, then pivot one end and make another cut, etc. until the male will just start into the female. Then I clamp a stop block behind the end that I pivot, loosen the fence clamp, and insert a feeler gage between the two and reclamp the fence. Make a single pass on one side of the male and check the fit. If it's still too tight, make a pass on the other side with the fence in the same position. Each cut removed 0.001". If it's still too tight, change to a 0.002" shim and repeat, or slide the stop block up tight to the fence and repeat with the 0.001" shim. Eventually you will get it so that it easily slides in half way. At that point you are ready to put it in permanently. When you do that, insert the male with NO glue and stop about 3" short. Then add glue to the lead or trailing section only, depending upon which end you want fixed, and pull it home.

    This process works well as long as the stock for the male half is absolutely flat and constant thickness, so be sure to check your stock carefully before even starting. It also helps to take a piece of sandpaper, file, or block plane to the two top edges of the male, leaving only the first and last couple of inches untouched. Just remove a little bit (1/64 - 1/32") along those two edges; it helps a lot. Similarly, it sometimes help to sand the two corner edges of the female. Good luck.

    If all that is too much of a pain, you could make a tapered female. That's easily done by skewing your guide jig about 1/64" and taking a second pass against the side in the direction you moved the jig.

    John

  7. #7
    Marty, that's a good project. I'll be interested to see yours when it is complete.

    Another thing you may find useful is the application of Tage Frid's "Dovetail Hammer." You probably have one if not more in your shop.

  8. #8
    it is not a joint that I have attempted yet but the one video I watched i thought the WW'er had a clever way to fine tune the fit. he used a solid strip along one side of the male dovetail that was held in place with double sided tape - that strip was what ran along the router table fence - he would then trial fit the DT, note where it was tight and then use a hand plane to take a fine shaving off the reference strip where needed and then ran it back through the router table - it looked like he could not only take a thousands off in a pass but also just where desired

  9. #9
    Join Date
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    My first though is check the fence, it has to both tall enough and rigid enough to support the shelves or cross members as you run the dovetails. Next issue is any adjustment is doubled, so they really are very minor. Perhaps you can clamp a block behind the fence to act as a stop. If you need to move back, place a piece of pAper between block and fence, clamp down the block, remove the paper, loosen fence....it moves back .004"! That's an .008" adjustment on fit. The bump by eye method rarely gives you predictable precision at the level required for these cuts. You need to develope a precise micro adjustment scheme on your fence. I use sticky note pads and stop blocks.

  10. #10
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    I get it close with the router then taper slightly taking very thin shavings with a shoulder plane until it will come close to sliding home. I don't try to glue the whole length, a dab at the front couple of inches seems to be fine and avoids possible cross grain expansion issues. Paper shims as suggested by Peter Quinn above are great for adjusting the taper on the machine, but a plane lets you sneak up on a fit a thousandth at a time without the danger of going too far.

  11. #11
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    I have repaired the occasional mishap with a slice of veneer. I shave it so that there is a very smooth transition.

    The key, in my opinion, to getting sliding dovetails down is to have everything jointed and flattened very accurately. Fine tuning by hand if you prefer to use machine is also helpful adding a moderate taper is helpful and also undercutting the female slot can be helpful.
    Bumbling forward into the unknown.

  12. #12
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    Quote Originally Posted by roger wiegand View Post
    I get it close with the router then taper slightly taking very thin shavings with a shoulder plane until it will come close to sliding home. I don't try to glue the whole length, a dab at the front couple of inches seems to be fine and avoids possible cross grain expansion issues. Paper shims as suggested by Peter Quinn above are great for adjusting the taper on the machine, but a plane lets you sneak up on a fit a thousandth at a time without the danger of going too far.
    Do you wind up with a step at the shoulder where the plane can't reach? Seems there would be no way to reach completely into the corner. Lee Valley has a dovetail plane for that exact purpose, I can't imagine spending $175 for the pleasure. I wonder if it might be possible to make a custom scratch stock to tune in the pins? Makes more sense to me than the hunt and peck approach I usually use! I usually fit tenons with a shoulder plane, wish they had a small affordable dovetail plane along the lines of a stanley 92 shoulder plane to accomplish the task with sliding pins.

  13. #13
    On many blades (the separation piece between drawers), only the front couple of inches is a sliding dovetail. The rest is a regular dado. [Note: The dado has to be the thinner, as thin as the "inside" of the dado portion, so you can slide it through the dovetail portion of the slot.]

    Another approach is to make a one sided dovetail. That is, the male piece is only cut on one side (the top). The female piece is cut to match, a flat cut on the bottom and a "dovetail" type cut on the top.

    But if you're going to go sliding dovetail all the way, make sure the back is loose, as John suggested. As you slide the blade in, it will get very tight.

    Also, one more suggestion. A lot of people fill the center of the blades with a piece of plywood so that the blade is a "dust shield," as it's called. I think this is a good idea, but the piece of plywood should be let into the bottom of the blade, instead of the top. The reason is that many people overload drawers. If the bottom of the blade is smooth, the drawer will still open without jamming. If the plywood is let into the top, you can get a jam of the overloaded stuff on the bottom of the blade.

    Mike
    Last edited by Mike Henderson; 11-17-2014 at 11:22 PM.
    Go into the world and do well. But more importantly, go into the world and do good.

  14. #14
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    I find a tenoning jig makes these things pretty easy.

    Garrett Cabinet tenoning.jpg . GH Wall Cabinet-pecan- (3).jpg

    As mentioned, I start a bit fat and sneak up on it.
    "A hen is only an egg's way of making another egg".


    – Samuel Butler

  15. #15
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    The tolerances for a good sliding dovetail are very tight, which is why I avoid using this joint along the entire width unless the joint is only a couple of inches deep.

    A few more points:
    - make sure both boards are absolutely flat. Even a small amount of cup in either board will make the joint very difficult to assemble (see anecdote below).
    - put glue only in the last inch or so of the female part. Glue in the rest or glue on the male part will create a huge amount of friction that will again make the joint very difficult to assemble.


    Anecdote: I once made a large cabinet out of pine for a vacation home. The house is on a remote island, and I didn't want to have to transport a bunch of tools out and back, so I designed it with joinery that would self-lock with a minimum of clamps - mainly dovetails, including sliding dovetails for the shelves. Well, of course the air on the island was a lot more humid than in my shop and inevitably all the boards cupped. I tried putting cauls to flatten the boards, but the sliding dovetails were still nearly impossible to assemble. Lacking proper tools, I ended up using a paperback book I had just finished (and hated) as a cushion block while I pounded them in place with a hand sledge hammer! The embossed image of horses on the cover was completely flattened, and ever since we refer to that series as the "tales of flat horses".

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