Sliding Dovetail Frustration

[Marty Tippin]

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!

[Robert LaPlaca]

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.

[Dave Richards]

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

[Ken Fitzgerald]

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.

[Marty Tippin]

@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... :rolleyes:

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...

[John TenEyck]

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

[Dave Richards]

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.

[Erik Christensen]

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

[Peter Quinn]

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.

[roger wiegand]

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.

[Brian Holcombe]

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.

[Peter Quinn]

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.

[Mike Henderson]

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

[glenn bradley]

I find a tenoning jig makes these things pretty easy.

300463 . 300462

As mentioned, I start a bit fat and sneak up on it.

[Steve Baumgartner]

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".

[Dave Richards]

The sockets for the sliding dovetails in question are only 1-1/4 in. long. Not so long that there should be any worry about sliding the tails home.

Steve, your idea about not using sliding dovetails for the full length is good for things like shelves.

Marty, it's too bad you don't have a Router Boss at your disposal. Sliding dovetails are a walk in the park with it because you use essentially the same setup for cutting both the socket and the tail.

[John TenEyck]

The sockets for the sliding dovetails in question are only 1-1/4 in. long. Not so long that there should be any worry about sliding the tails home.

Steve, your idea about not using sliding dovetails for the full length is good for things like shelves.

Marty, it's too bad you don't have a Router Boss at your disposal. Sliding dovetails are a walk in the park with it because you use essentially the same setup for cutting both the socket and the tail.

1-1/4" long ! Why are we having this discussion?

John

[Marty Tippin]

1-1/4" long ! Why are we having this discussion?

We're having this discussion because I had difficulty making dovetails that fit well and was looking for help. I never said anything about how big they were.

I'm sure cutting a 1-1/4" dovetail is trivial to many of you, but always keep in mind there are folks like me who haven't climbed that learning curve yet.

[Pat Barry]

One thing to keep in mind on this is that it really isn't necessary to trim both sides of the male end. In fact, this basically doubles the amount of material being removed and because small adjustmnent are kinda difficult to make, it amplifies the setup issues. What I suggest therefore is that you cut the female socket first, then do what you did to get close by making equal cuts on both sides of the shelf (for example). The to sneak up on the final fit, pick one side of the shelf dovetail to trim on both ends of the board (top or bottom or left or right) and trim both ends on the same side. Then do your test fit and repeat as needed. Unless you need a perfectly centered dovetail this will be a much easier task. Also, a bit of sandpaper - 220 grit with a few light passes on the sharp corners and a small roundover on the leading edge will make things slip together with a lot less force.

[Dave Richards]

Of course doing what Pat suggests could have impacts on the size of the openings and the alignment of the surfaces of the kickers and runners so you'll have to watch out for that. If you have to take material off the long faces of the top drawer divider to get the surface to align with the top runners, that could impact the way the divider fits into the notch in the vertical partition. One change usually leads to others so take some time to think about the potential downstream effects.

If you aren't too far committed, it wouldn't be that big of a deal to omit the sliding dovetails and use a different joinery method on that bench.

[Brent Ring]

I am doing them on a media center project. 12" long. I have purposely left them ever so loose for gluing purposes. and I want to echo the cupped board statement. Mine are glueups and making sure they were flat was critical (Read - pounding them in and out) I try to limit the amount of time putting them together for dryfit and removing them. They are an awesome joint for strength, but a bear to get just right. One other thought is to cut of a few inches of the dovetail, and make the fronts look like butt joints. That will reduce the overall length without compromising strength.

[Dave Richards]

One other thought is to cut of a few inches of the dovetail, and make the fronts look like butt joints. That will reduce the overall length without compromising strength.

...except in the case of the dovetails in question since cutting off several inches would more than cut off the entire end of the piece. ;)

[roger wiegand]

The sockets for the sliding dovetails in question are only 1-1/4 in. long. Not so long that there should be any worry about sliding the tails home.



Mine range from 6" to 24" depending on the size of the cabinet in question. Shorter than that and I wouldn't refer to it as a sliding dovetail.

[John TenEyck]

We're having this discussion because I had difficulty making dovetails that fit well and was looking for help. I never said anything about how big they were.

I'm sure cutting a 1-1/4" dovetail is trivial to many of you, but always keep in mind there are folks like me who haven't climbed that learning curve yet.

Sorry, I apologize if I offended you. I don't consider a dovetail that short as a sliding dovetail although it technically probably is. It would have been helpful had you said how large or small the dovetail is. For one that short the answer I gave you doesn't apply; you don't want a loose fit at all, you want it to be hand snug from the get go. You should be able to push it in by hand and remove it with just a few light taps, but there should be no slop. But the approach is the same. Get it to just barely start, then shim your fence in increments of 0.001 - 0.002 inches, mill one side at a time and check the fit. If for some reason if ends up sloppy, glue a sheet of paper to one or both sides of the male. You can even remill after wards, if required. The comment that your fence needs to be dead flat is important, too, but for a dovetail that's only 1-1/4" that's probably not the source of your problems.

John

[Marty Tippin]

Thanks, John - I'll try your suggestions and let you know how it comes out.

@Dave Richards - I'm already pretty far into this, with female dovetails cut in the legs and rails. I do have a 3/4" dovetail bit on order and am going to experiment with it on some scrap using the suggestions that have been made and if I can "maybe" get some better fitting joints, I'll re-work the existing 17/32" dovetails with the 3/4" bit and try again. My logic with the 3/4" bit is that my drawer divider stock is 3/4" thick, so if I can get the fence adjusted to just barely touch the end of the stock, I should be pretty close. We'll see what happens.

[John TenEyck]

Marty, as has been mentioned a couple of times, your stock has to all the exact same thickness or you will get inconsistent results from piece to piece. I can't over state how important it is when a few thousandths makes all the difference from tight to loose.

John

[Marty Tippin]

Marty, as has been mentioned a couple of times, your stock has to all the exact same thickness or you will get inconsistent results from piece to piece. I can't over state how important it is when a few thousandths makes all the difference from tight to loose.

All my stock was milled at the same time to the same thickness, including the pieces I'm using to test fit with.

I suspect slight variations in how tightly I hold the piece against the router table fence and/or flex in the fence itself contributes to the variability. My router table is a Kreg, using their fence and I've never been very happy with it for general use, let alone for something like this where precision is needed.

And having to move the bit from the hand-held router (when cutting the females) to the table (for the males) introduces still more potential for error - though I'm using a Wixey digital depth gauge to set the bit height the same on each.

[Dave Richards]

Marty, what are the chances you could take the router out of the table and use it hand held? Then you wouldn't have to move the bit from one machine to another and you could leave the cutter height exactly the same.

[Marty Tippin]

Marty, what are the chances you could take the router out of the table and use it hand held? Then you wouldn't have to move the bit from one machine to another and you could leave the cutter height exactly the same.

Don't see how I could do that - still need an adjustable fence of some kind for cutting the male dovetails.

[Dave Richards]

I was only thinking about removing the router and the plate from the table for cutting the sockets. Return it to the table for the "male" parts. That would eliminate the need to move the cutter between routers.

[Marty Tippin]

Well, I can finally report some success!

I made a number of changes to my process and while I'm not sure exactly which one made the most difference, the end result is a set of snug-fitting dovetails that I think I can live with.

Some things I changed or found along the way:
* I added the Kreg "Micro-Adjuster" to my Kreg router table fence - it's a $18 gadget that doesn't have a lot of positive reviews but I was able to use it to make the kind of tiny adjustments to the fence position that are needed for fitting dovetails. Not really wowed by the micro-adjuster - it's sloppy and difficult to use - but it did get the job done.

* I carefully milled a pushblock out of hardwood and ensured that it was square on all sides. Previously, I had been using a chunk of 3/4" white pine 1x4 that may not have been perfectly square or parallel on the sides.

* I cut all the female dovetails that I could (all but 2 in this case) at the same time and with the same depth setting of the 3/4" dovetail bit. Originally, I made them in several different groups and I'm sure the depth was slightly different for all.

* I discovered that the plastic inserts in my Kreg router lift are a good .010" lower than the surface of the lift. When cutting the male dovetails in the new pieces, I used the router lift surface as the reference and tightly pressed the stock against my pushblock to keep it from slipping downward as it passed the bit. Ideally, I should have made some kind of clamp but my fingers worked well enough for this time around. Not sure what I'll do in the future to address the issue with the inserts; it's an issue that only crops up when routing smallish pieces (1-3/4" wide in this case) so maybe I can work around it.

I lost track of the number of test cuts that I made, but it was upwards of 40 to 50, I'm sure.

Thanks again to all who offered advice on this thread - there were some good tips that I'll definitely keep in mind on future projects!