I am making dovetail joints in walnut bookcases. I tried a homemade jig that didn’t work well so now I am cutting the tails with a dovetail router bit and sawing the pins by hand. I have the inevitable (for me) gaps in the joints and I want to fill them by shimming with slivers of walnut. My biggest problem is knowing when to cut the shims and insert them. Obviously I can only do this when the joints are glued up but then the squeeze out glue covers the gaps and I don’t know what to fill. If I wait till the glue dries it is almost impossible to insert a shim. Since I often read about plugging up dovetail gaps I know it must be a workable technique but how do I do it?
Edited 5/9/2007 10:56 pm ET by jrogerh
Replies
This reply forces me to admit publicly to having gaps in my dovetails, something I have always denied.
I use hide glue for all my assembly, but I don't think the process of filing the gaps would change if you use PVA glues.
I apply very little glue to my dovetails, and only on the pin board. When the joint is driven home, what squeeze out there is, is mostly on the inside. After the glue has cured and before the joints are planed flush, I'll go around and fit in the slivers of wood to fill the gaps; I saw these sliver with a very sharp wedge shape, which helps insert them. Sometimes, I have to clean out a little glue with a razor blade, before I can insert the slivers.
Rob Millard
http://www.americanfederalperiod.com
Sounds like a good idea for controlling squeeze out. Maybe I tend to glop too much glue hoping it will fill the spaces. (Never works).
No problem- it can happen to any body at any time no matter what they say. The trick is knowing when and how to fix them. You are on the right track with cutting or chiselling the wedge shapes: I always have these on hand as a by -product of the fact that I saw the tails and remove the waste with bandsaw.If these wedges are too wide (hopefully!) they are easily split with a chisel.
So the thing to do is to tackle any voids as soon as possible after removing clamps- i.e before that glue bridging or disguising the gaps gets fully hard. Obviously the glue between close fitting faces of the joint will have dried before this, making the joint strong enough for clamps to be released. When you do the initial planing to level the joint any gaps will be evident- it is this step which shows any gaps up.Then you can just hammer those wedges in with some fresh glue.
The pictures show some rough joins with pine timber- easy to have bits breaking off when you assemble . In the example the area has been levelled prior to any "doctoring", and still has to be smooth planed and sanded (when it will look a whole lot better)
Thanks for the pix. I suppose I could mark the location of the gaps during the dry assembly and then try to clean out the glue immediately after the final glue up.
Edited 5/10/2007 3:00 pm ET by jrogerh
I've always done it like Tage Frid did. Get your widest back-saw and cut shim stock the same width as it's kerf. Wait till the glue dries, then use that saw to relieve the gap, put a little glue on one end of the shim, and insert.
Tage Frid also had another method of filling gaps in dovetails. He visited my woodworking class at the University or Wisconsin-Madison. As part of his time there he demonstrated how he cut dovetails. After assembling the joint he began looking around the room. The professor asked what he was looking for. Mr. Frid replied, "A dovetail hammer." This had us all stumped. Then, with a big smile, he grabbed a claw hammer off the tool wall and began to whack the ends of the pins to close up the gaps.
The work of a master.
Got all of his books years ago when they first came out. Guy was, and still is, unmatched, IMHO.
"Bishoped" dovetails...
During the dry fit, I mark with a pencil to indicate which joint needs a shim. I then prepare a variety of shims. During the glue up it is easy to tap a shim into a joint that already has glue applied. Don't worry if your shim sits proud of the other surfaces, when the glue dries planing will bring down the shim along with the tails and pins. After finishing I defy anyone to find the shimmed joint.
Edited 5/11/2007 2:29 pm ET by fatboy
This is the approach I am taking. Marking the gaps before glue up. I have kept all my thin cut-offs so I think I will have a good supply of shims.
Hi,
I read your message and all of the responses. You got some great ones. For the most part, I use the Tage Frid method with the "dovetail hammer" that someone wrote to you about. It works fine. Sometimes I shim if the hole is large enough.
BUT I just saw an article on the Fine Woodworking Website, entitled:
"A Quick Fix for Checks, Gaps, and Tearout".
It is about mixing shellac, sawdust and possibly coloring to make stuff to fill holes and gaps. Wouldn't this work for dovetails?
I suppose it would work, but it still seems like too much trouble. The dovetail hammer (ball peen) works fast and easy .
Have fun.
Mel
Measure your output in smiles per board foot.
I have tried the sawdust/shellac mixture as a wood filler. It didn't seem to look any better than the commercial woodfillers. The hammer method seems worth trying.
Mel,I'm a big fan of shellac. But I have never found the advice about using sawdust and shellac as a wood filler worth much. The "repair" is not as good as commercial fillers and looks just as bland. Sawdust does not mimic wood grain, it just makes a featureless paste. I think hot hide glue and sawdust is better, but not by much.Rich
J,
I had perfected my DT-making with machines (a woodrat, usually) so there were no gaps. However, since starting to hand cut all my joints (to get the skilll, not for WW religious reasons) my inexperience has seen a few gaps re-appear.
If the gaps are worse than what can be filled with a bit of veneer (of the same species as the piece) I would cut the joint again. Otherwise the veneer is pushed into the gap whilst the glue is still wet, with an appropriate orientation of its grain. Once pushed in as far as it'll go, I snap it off flush. Any remaining sticky-out bit will be chiselled off when the glue dries.
This not only fills the gap but sticks the DT - I reckon it is about strong as a properly fitting DT, both mechanically (a tight fit) and via the glue (bound to both surfaces, albeit via the veneer).
If the other DTs are tight, even a biggish gap can be filled in this way by using a double thickness of the veneer. The trick is to get a tight fit.
For gaps that are too narrow for venneer (typically less than 0.6mm, I use hard wax to fill. I use Liberon hard wax sticks that come in 24 shades, always choosing a colour that is one or two shades darker than the wood of which the DT is made.
A thin metal artist's palette knife heated in the flame from an alcohol or meths lamp (no soot) gives enough heat to melt a small chunk of the hard wax placed over the gap. It gets sucked into the gap when it melts and the palette knife smooths it flush. Any residue is just polished off with a dab of Liberon dewaxer, when the wax has dried.
Wax filling gives no strength to the joint, so most of the other DTs have to be good.
Lataxe
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