by

In:In the Shop

Comments Off on Dovetail Joinery: Part 6- Fitting and Finishing the Joint

Coming down the home stretch now (finally).  The pins should be cut, the waste removed, and the baseline chiseled square as discussed in Part 5.  You probably have something that looks like this…

Test fitting the joint

Test fitting the joint

But will it assemble?  Maybe, it depends how good you are with a dovetail saw and if your pin board is a softwood or hardwood.  Softwoods are much more forgiving of a slight interference fit.  Try to assemble the joint dry, just enough to get a feel for if the joint is too loose (gaps), too tight (get out your chisel), or just right (time to glue it up).  The biggest risk here is if there is too much pressure on the outside pins.  There is no wood supporting them and they can easily split at their base if the outer tails are too large, wedging the pins apart.  This is why we size the outside pins a bit thicker than the rest, to add some strength and lower the risk of a split.  So, if the joint slides together with almost no hand pressure you likely removed too much material with the saw and will be faced with gaps.  Minor gaps can be addressed in a variety of ways.  Some people use generic wood filler, some mix glue with saw dust from the wood being used in the joint for a better color match, you can also try to glue in some wedges of the same wood if the gap is large enough… though if it’s really bad you should probably just start over.  It’s all part of the learning process, but after even a few test joints you should be getting respectable results.

My first dovetail from 2008, not pretty.  The one above it was just a few joints later.

My first dovetail from 2008, not pretty. The one above it was just a few joints later.

Lets assume you don’t have gaps, but you don’t have a perfect saw-cut-to-saw-cut fit either.  This is when a little chisel work may be required, but that’s not a big deal.  Chiseling the sides of the pins (an operation known as “pairing”) is a lot easier than working on the tails because we have plenty of open room to work with.  Never try to go back and tweak the tails at this point.  Trying to identify where the excess wood is located can be a little tricky.  Look for your knife line from transferring the tails over.  If you didn’t split it there’s a good chance the knife line is still visible and the pin is fat in that area.  Also look for pins that weren’t cut vertically.  If the saw drifted away form vertical the pin will get fatter as it approaches the baseline.  This means the tail may slide on nicely at first and then bind up when it’s part way home, never fully seating itself.  If everything looks good but the joint is still a little difficult to assemble look for burnished areas at the top of the pins or any other signs that there is high pressure on certain areas that resulted from test fitting the top 1/8″ or so of the joint.  What you want is a joint that can go together with hand pressure or light hammer taps.  This is again something you will get a feel for after fitting a few of these joints together.

The side of this pin needs a little work.  Mark off any areas that need adjustment...

The side of this pin needs a little work.  You can see the knife line wasn’t quite split by the saw and the saw drifts away from the vertical line.  Proper sawing can save a lot of extra chisel work at this stage. Mark off any areas that need adjustment…

...then go to work.  Be careful not to push a deep cut through the back of the pin or you will blow out the back edge.

…then go to work. Be careful not to push a deep cut through the back of the pin or you will blow out the wood fibers on the back edge.

Once you’ve got the desired fit the joint is ready for gluing.  I like to add a partial chamfer on the back of the tails as pictured (something I picked up from the Rob Cosman dovetail DVDs).  This does a few things.  If I have several joints in the works, the chamfer tells me “this one is done” and helps avoid confusion.  It also eases the tails over the pins which helps avoid damage to the tops of the pins.  Finally, it gives a little extra area for the glue to go and minimizes the squeeze out.  Just be sure the chamfer is on the inside of the joint (where it will never be visible) and it doesn’t extend to the top of the tail.

Partial tail chamfers on the inside of the joint.

Partial tail chamfers on the inside of the joint.

Now add glue and clamp up the joint.  I like to use small spatulas for working glue between the tails.

Glue the sides of the pins and tails, I don't worry much about the baseline because it's all end grain.

Glue the sides of the pins and tails, I don’t worry much about the baseline because it’s all end grain.

When the glue dries, the joint may look a little messy from the glue, pencil marks, and not-perfectly-flush surfaces.  Plane the surfaces flush, removing any glue spots or other surface defects in the process.  Be sure to plane away from the joint so you don’t blow out the end grain of the mating board.  That’s a mistake you’re only going to make once.  If this were a drawer you were making, this would be the time to plane the sides down to achieve a perfect fit to the case.

The joint after gluing.  Throw it in a vise and flush up the face.

The joint after gluing. Throw it in a vise and flush up the faces.

Below is the joint after its been cleaned up.  I did no filling or “cheating” of any kind.  The tail board is straight off the saw, no chiseling at all (other than chopping the baseline of course).  The tail board is mostly off the saw, but a few of the sides needed some minor adjustments as discussed previously.

Cleaned up joint, ready for finish.

Cleaned up joint, ready for finish.

Finished joint with a basic oil finish.

The end result with a basic oil finish.

After gluing, cleaning up, and finishing the joint, it’s finally done.  One thing worth discussing at this point is the baseline which is obviously still visible below the tails and pins.  Is that normal?  It looks ugly. Does it serve a purpose?

Visible baseline on the finished joint.  To keep it or remove it?

Visible baseline on the finished joint. To keep it or remove it?

Well, the baseline knife mark is there because we made the joint by hand and a lot of people like to leave it visible for that reason alone.  Another sign (along with skinny pins) that this joint was not machine made.  That’s fine.  Other reasons to leave it there is because it takes more work to exclude it than include it.  If the joint isn’t going to be seen often (the back corners of a drawer or a case joint that will have molding covering it) than leaving it is just more efficient.  If you’re making a box or something where it will be visible then it becomes a question of appearance and largely boils down to personal preference.  If you don’t want to see the baseline in the end, there are two common approaches I take.  First, I won’t cut the baseline so deep with my marking gauge, then when I’m done I just plane off enough material to remove the scratch.  The other option requires a little more planning.  You need to lay out the joint first and then only mark the baseline on the areas that will eventually be removed.  So you basically end up with a dotted line instead of a solid baseline.  Anyway, there’s no right or wrong here.  It’s your joint, make it how you want to.

And that takes care of that.

-WMT

Tags: , , , ,