Posts Tagged ‘dovetail’
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…
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.
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.
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.
Now add glue and clamp up the joint. I like to use small spatulas for working glue between the tails.
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.
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.
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?
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.
If you have been following along in parts one through four, you should have your tail board finished and your pin board dimensioned. The next step is to transfer the tail locations to the pin board by using the tail board as a template. This is why you don’t need to precisely follow the angle you laid out when sawing your tails, any slight deviation from the pencil line will be transferred to the pin board and copied exactly. Missing your slope is purely cosmetic and the joint can still go together seamlessly. To transfer the tails, align the pin board so it’s even with the side of a bench plane or block of wood as pictured below, then clamp it in the vise. Slide the plane/wood back and use the tail board to bridge the gap. Now the shallow rabbet that was created in part 1 becomes extremely useful. Slide the tail board up to the pin board until the small shoulder from the rabbet hits the pin board. You should immediately feel the rabbet’s shoulder align the board. This accurately solves two of the three alignment problems you can encounter in this step: 1) skewing or rotating the tail board relative to the pin board and 2) sliding the tail board too far forward or not far enough. All you need to do now is slide the tail board side to side until the edges are aligned. A block of wood can help.
Now use your off hand to press in the middle of the tail board, locking it in place. Use your dominant hand to hold a marking knife and scribe the tail locations into the pin board. I’m using the thin kerf knife from Blue Spruce Toolworks as it can fit between any tails I cut. For larger work I typically use a larger knife. Press the knife firmly against the tail with the flat face touching the tail. If the beveled face of the knife is against the tail the knife line will be offset and your pins will be far too thick. Draw the knife along the tail with light pressure, but repeat this a few times until a clear line is visible. Again, be sure to keep firm pressure on the side of the tail so the knife doesn’t stray.
Once the tails are transferred, mark the waste (the tails obviously, we want to keep the wood that will go between the tails which are called the pins) and using a marking gauge, scribe the baseline as was done in Part 1, but this time only mark the faces. The edges will not be cut off so there is no need to carry the baseline all the way around the board. Be sure to reset the gauge to the thickness of the tail board as it is typically not the same as the thickness of the pin board. Having a dedicated gauge for each measurement is helpful when several joints need to be cut.
Now clamp the board in the vise for sawing, being sure to align it vertically first. If it’s clamped at a slight angle you will have a hard time hitting your vertical lines right off the saw.
Now use a square or dovetail guide to mark vertical lines, these will help guide your saw. I like to draw them in the “good wood” portion of the board so they aren’t sawn off. Then when the joint is cut I can see how parallel my cut was to the vertical line. This will give me an indication of any clean up work I’ll need to do with a chisel.
Now to saw the pins. The same sawing techniques apply that were discussed in part 3, but you aren’t sawing square across the board this time, you are trying to split the knife line. This means with saw cutting on the waste side of the line, the edge of the kerf should land right on the center of the knife line. The cut must then go straight down, parallel to the vertical lines that were just drawn.
With the sides cut, saw out the waste with a fret or coping saw, then chisel the baseline exactly as was discussed in part 4. Be sure to check that the baseline is square and without humps that could prevent the tail board from seating fully when assembled.
For the next (and likely final) part of this series we’ll be fitting the pins to the tails, gluing the joint, and cleaning it up. Until then, happy joinerying.
Part 3 of this series wrapped up the saw work for the tail board. Now there’s just a little chisel work to take care of before moving onto the pin board. For smaller work, I like to lay the parts on my shooting board. This gives me something to back the work against and also provides a sacrificial surface that can be gouged with a chisel on occasion. Make sure the board is clear of debris before you start working or you may press something into the face of your board, denting it. This is quite aggravating if you’re working on a drawer face or the outside of a box. I can say “quite aggravating” now because I’m typing, but if this happens in the shop and potentially ruins an otherwise flawless piece of work… well, my grammar may be quite different. The real issue here is at first the work surface may be clean, but as you start chiseling out the waste those bits of wood fall on the bench or shooting board. Then without thinking, you flip the board over and start chiseling from the other side and one of those stray wood fragments gets embedded in your board. So every time you move or flip the board, make a habit of clearing the debris.
When chiseling to the baseline, there’s a few things to keep in mind. First of all, unless you’re really good with your fret or coping saw, you probably have a decent amount of waste to clear… maybe 1/16″ – 1/8″ of material for most people. Typical advice is to remove half the waste at a time until there is such a small amount left that you can’t split it, then drop the chisel in the baseline and finish it off. That’s actually a good method to use. Chopping through too much waste at once drives this chisel back into the board, crushing wood fibers behind the chisel in the process. If you drop right into the baseline and the chisel is driven back, you’ve just crushed good wood and you’ll be looking at an unsightly gap when the joint is assembled. So don’t get greedy, take the 2-4 chops you may need to take and work your way back to the baseline. Another important tip if you’ve never considered this is which way to pry the chisel. If the chisel gets stuck in the board you need to pry it loose. Not a big deal, but you need to push it away from the baseline. Prying back against the baseline will again crush the wood fibers and carry the chisel across the baseline.
As to the chopping process itself, I stand on the side of the board hold the chisel vertically (basically what is pictured above). If you’re positioned in front of the board you can’t tell if the chisel is vertical or not. If you have to, undercutting the joint is perfectly acceptable 90% of the time or better, at least in my opinion. Chop about half way through the board, then flip it over and chop the remainder in from the other side. This avoids blowing out fibers which is almost a given if you chop entirely through the joint.
Once the waste is chiseled out between the tails, clamp the board back in the vise and clean up the outside shoulders, then check everything for squareness.
When checking for square, the smaller the tool the better. My square is a vintage Millers Falls model, but Starrett and Vesper Tools also offer nice squares similar to what’s shown. Check your shoulders, baseline, and the cheeks of the tails. Any humps in the baseline should be removed, with an undercut if need be. The tails should never need squaring if you’re sawing correctly… but if they are out of square you have to fix it now or you’ll never have a tight joint. If you can’t get a chisel between the tails to fix a skewed cheek you may be out of luck and need to start again. The joint can still go together obviously, but you’ll be filling gaps for sure. Again, with a little practice at sawing you should never need to adjust the tail cheeks, just the baseline.
Next up we’ll be tackling the pin board.
Accurate sawing starts with accurate layout which was covered in part 2, but there are several other factors that should be considered from body position to how the saw is held and more. For solid information on basic sawing techniques (and a whole lot more) I’d recommend The Foundations of Better Woodworking by Jeff Miller. What I will say here is that a moxon vise and properly tuned saw will make a world of difference.
A moxon vise raises the work to a more comfortable sawing height (your back will thank you). My moxon was made with the kit from Benchcrafted, but you can also get a more affordable kit from Texas Heritage. Your saw should be sharp, filed with a rip tooth pattern and a fairly high tooth-per-inch count, 15 is common. The set on the teeth also needs to be minimal, a couple thousandths on either side of the plate to ensure straight sawing. And when you clamp the board in the vise, align it vertically. If the board is tilted slightly hitting angles or sawing vertically becomes unnecessarily complicated.
Now lets get into it. When you start sawing across the end grain, sawing square to the front face is absolutely critical. A skewed cut will never yield a tight joint so you will either have gaps or have to do extra chisel work to square up the cut after sawing. This is okay, but chiseling takes extra time and adds another opportunity to make mistakes. What we’re shooting for here is saw-cut-to-saw-cut joinery. So how do you saw squarely to the face? Place the saw on the waste side of the layout line and lift the saw slightly. This means the saw teeth are only touching the far edge of the board and the saw can pivot around that point. Next, place the thumb from your off hand next to the saw plate and bias the saw plate against it. Using your thumb to steer the saw, align the teeth so they’re parallel to the layout line and start sawing with very light pressure. As the saw starts to cut into the board, lower the handle so you’re sawing straight across the board.
At this point the saw shouldn’t be very deep, just a light kerf cut squarely across the end grain. With this kerf established, focus on angling the saw to match the layout line and begin taking full, even strokes with the saw, not short, choppy cuts. I have found this to be an important part of saw-cut-to-saw-cut joinery. Full, smooth strokes means the cut can be finished in a few strokes, 4-8 is typical for most of my dovetails. This helps ensure a straight cut which is crucial. Short saw strokes means you may need 15-20 strokes to finish the cut… each time the saw may stray slightly. The kerf can also become enlarged which makes tracking the saw more difficult, so practice your sawing until you can fly through a cut smoothly and with confidence. A good way to practice sawing or just warm up for dovetailing is to run through several cuts on scrap wood.
Once you’re comfortable sawing to your line and squarely across the board, cut the sides of all the tails. I recommend cutting one angle first across the entire board, then go back and hit the other angle. This helps keep your muscle memory on track where as switching between angles can make it hard to get in a rhythm.
Before moving on, lets examine the cuts and understand what’s critical. We’ve already talked about cutting squarely across the board, but what about hitting the angle precisely? Well, having a straight cut matters, having that cut run to the exact angle laid out with the dovetail guide doesn’t really matter, it’s just for looks. In fact, you could cut the joint with no layout lines at all on the face, just cut squarely across the board and the angle can be whatever it wants. The reason to lay out an angled guide line is just to help keep the tails as consistent as possible, but it’s purely for appearance sake. For the joint to fit tightly you only need to saw squarely and in a straight line. Skewed cuts or wavy cuts will always result in gaps. The only other sin to avoid when sawing is cutting beyond your baseline. There’s really no fix for that besides wood filler.
Saw out the waste with a fret or coping saw (I opt for a fret saw) being careful not to cut below the baseline or into the tail itself.
The last step before moving onto the chisel work is to cut the waste off the edges. Flip the board 90 degrees (making sure to align it vertically again) and grab a crosscut saw if you have one. You’re sawing right against the baseline, so make sure to stay on the waste side of the line. One thing that can help is chiseling a small shoulder up to the baseline. This little valley gives the saw an accurate “kerf” to start the cut and leaves a super clean shoulder on the joint which will be visible when all is said and done.
Flip the board and cut the other shoulder, then it’s time to get out a chisel to clean up the baseline.
With the boards prepped as discussed in part 1, it’s time to lay out the tails for sawing. To do this, you will need two sets of dividers (also referred to as a compass, but I don’t want to get into that right now). I own four Starrett sets which covers just about anything I’ve ever done. The tips should be ground to a point and I prefer to have them all in different sizes so I don’t confuse which pair has which setting.
Use one set of dividers to mark the side pins. These tend to be a little thicker so they don’t split, I’m using 1/4″ here. Mark that distance in from each edge of the board, then set that pair of dividers aside to use on the following joints in the other corners.
The second set of dividers will walk off the number and width of the tails and consequently the pin space between each tail, all without the fuss of measuring. To do this, guesstimate the size of the tail, set the tip of the divider into the pin hole (on the left in this example) made by the first set of dividers and step it across the board until it passes the far pin hole (on the right side). Each step will be a tail, so if you want three tails, you need to take three steps, four tails, four steps, and so on. Be careful to walk the dividers lightly across the board. You don’t want to create any pin holes until you’ve finalized the setting on the dividers.
The distance the dividers overshoot the pin hole on the right will be the gap between each tail. Don’t actually create a pin hole here, just gauge the gap by eye and decide if it needs to be thinner or thicker.
Adjust the dividers and repeat the process until you have the correct number of tails and are satisfied with the gap size. Now you can step the dividers off one last time, this time pressing hard enough to mark the board. When the dividers cross the pin hole on the right, stop. Do not mark a pin hole here. Instead, shift the dividers over so the leg falls into the right side pin hole, then step the dividers back to the left. Now you’ve got a board with pin holes in the end… so what? So now we pull out our trusty friend, the dovetail marking guide. There are a variety to choose from, I wrote about some here.
Place a pencil in the pin hole on the far left, slide the guide over until it hits the pencil, then mark both the face and end of the board. I stop the pencil line on the face of the board at the baseline of the joint. This helps avoid sawing too far which we’ll discuss in the next blog entry. Sliding the guide to the right, mark every other hole, then repeat the process from the other direction using the opposite slope.
When the layout is complete, mark the waste areas so you don’t get confused…
…and get ready to start sawing.
Fitting supremely gloat-worthy dovetails starts with having the right tools and proper board preparation.
Each of these tools will be discussed as they are used in the process, but the first step is board prep.
I’m making a sample joint so I have two relatively small boards. If you’re making a drawer, box, or casework of some sort you’re typically going to have four sides and four corner joints to deal with. Begin by planing each board to the desired thickness with parallel edges. If you’re using a powered planer, make sure to at least plane off the machine marks before starting the joint. The ends are critical and must be square to the face and edge of the board. This probably means you can’t just cut your board to length on a chop saw and call it “good enough”. I always square up the ends on a shooting board before dovetailing.
For clarification, I’m using cherry as the tail board (which I cut first) and the poplar will be the pin board.
I don’t care if you prefer the tails-first or pins-first method, whatever gets you the best results. I go tails first for three reasons listed in order of their significance:
1) It’s how I learned to do it. 2) I think it’s easier to cut the pin angle by skewing the saw to the face of the board and cutting straight down, but I’ll go into more detail on this when I get to cutting the joint itself. 3) I can gang-cut two tail boards at once which saves time.
Before actually laying out the tails there is one more step, cutting a small shoulder on the tail board. First, use your marking gauge to scribe the baseline of the joint. Measure the thickness of the pin board, then run the line around the entire tail board.
Now add the shoulder on the inside face of the tail board. This is often known as the “140 trick” because you can use a #140 block plane to cut the shoulder. For larger work I use a rabbet plane, but for narrow boards like this I’ve become fond of using a router plane. Check out my blog post covering this technique here.
The point of adding this shoulder will become clear when we transfer the tail locations to the pin board. For now just add it to the inside face of the tail board and you’re ready for laying out the dovetails which will be the focus of the next blog entry… stay tuned.
When fitting a dovetail joint I cut the tails first, align the tail-board over the pin-board, and transfer the tails with a marking knife. Pretty straightforward, but it can be tricky keeping the joint aligned while transferring the tails to the pin-board. If the tail-board is cooked the drawer/case/etc will be racked when assembled, there will also be gaps at the joint’s baseline. If the tail-board is square, but slides a little forward or back relative to the baseline the joint will have gaps or may not assemble at all. Finally, if the board is perfectly aligned to begin with but then shifts while marking… good luck realigning.
For all these reasons, I put a small rabbet on the tail-board which creates a barely visible shoulder. This shoulder slides against the pin-board and instantly aligns everything except the sides of the boards, but that’s simple to do. If you don’t rabbet your boards already, you should. At least give it a shot. Once you decide to use the rabbet you have to figure out how to make it. The generic answer for a large number of joints is to set up a table saw or router. That works great, but for working on a few joints (making a box or just a couple drawers) it’s faster by hand. Since you’re cutting a rabbet, it makes sense to reach for a rabbet plane or fillister. After all, this technique is known as “the 140 trick” named after the model #140 block plane often used to cut the rabbet. These planes work well for larger cases or drawers, but I find them completely unsuited when working with narrow parts. The planes can be sensitive to set up and a narrow board doesn’t give much surface area for the plane to rest on or the fence to register against. Clamping small pieces securely for use with a rabbet plane can also be a challenge.
Enter the router plane. I typically have two boards (a left and right side) to rabbet, so I lay them next to each other on the bench, throw a clamp on the back side and let the front register against a bench dog or some other backstop. Using the router plane, I support half of the tool on each board (which should be the same thickness), set the depth with extreme simplicity and accuracy, and cut across the grain to my baseline. The baseline is already cut into the board with a marking gauge as part of the dovetailing process so no extra work there, but you do have to be careful not to cut across the baseline. This may sound difficult, but I’ve never had an issue. The knifeline from the marking gauge severs the fibers should cut deep enough that as the router plane gets close the fibers simply lift up and fall off. When all is said and done I find this approach far superior for narrow components. Less tool set up time, no risk of tipping the tool resulting in a non-square rabbet, and work holding is much easier. If that’s doesn’t convince you, check out the video of the technique in action, then give it a try.