Tablesaw DovetailsComments (0)
This article is from Issue 51 of Woodcraft Magazine.
Perfect fits, simply sawn
by Ken Burton
Whether deserved or not, there is a certain mystique surrounding dovetails. Between the checkerboard contrast of end grain versus side grain and the subtlety of the interlocking angled cuts, the joint practically screams “craftsmanship.”
For woodworkers, hand-sawing and chopping out a set of dovetails is almost a rite of passage. But getting to this point takes a fair amount of practice. And once you’ve mastered the technique, cutting dovetails still takes time and involves some risk. Personally, I am a little more results-oriented than process-oriented. After discovering how easy it is to use my tablesaw to cut clean pins and tails, my dovetail saw spends a lot more time in its till.
With a minimum of fuss–you don’t even need some special jig–you can use your tablesaw to quickly and efficiently cut through dovetails that are indistinguishable from hand-cut. The “secret” lies in setting the tablesaw to cut precise angles, and in using a set of custom spacer blocks to position your boards for each cut. Once your saw is set, you can dovetail the next identical part in a fraction of the time it took to do the first. (Note that using this spacer block technique always yields consistently-spaced dovetails. If you want variably-spaced dovetails, you’ll have to take a different approach.)
Scribing shoulders with a marking gauge helps prevent tear out and serves to register a chisel when paring.
Angle the rule to find an easily divisible number. Then mark and extend the center lines for the full pins.
Layout: Pins, then tails
1 Mill your stock to size. While you’re at it, prepare two extra pieces of material the same thickness and width as your good stock to use for test pieces (length isn’t critical).
2 Referring to Figure 1, above, establish shoulder lines on the ends of your pin boards, tail boards, and scrap. Before scribing my lines, I set my marking gauge to 1⁄32" less than the thickness of my material (Photo A). (Scribing a line a hair shy keeps the ends of the tails and pins from protruding past the joint and interfering with clamping blocks during assembly.)
3 Pick a dovetail angle. The angle, or slope, of a dovetail is often expressed as a ratio of rise over run–somewhere between 8:1 and 5:1. This translates to an angle between 7° and 14°. (Here, I’m using a 10° slope.) Whatever angle you choose, set your T-bevel and leave it that way for the rest of the process.
4 Now determine how many full pins you want in the joint and the width of the each pin. (This width must be the same for each full pin.) As for the half-pins, the narrow face can be either the same width as the full pins, which I’ll refer to as “full-width” half pins, or half that measurement–“true” half-pins. (See “Full-Width or True?” on page 42 for a more detailed explanation.) For this 147⁄8"-deep tool chest, I wanted two full-width half pins and five full pins, all 1⁄2"-wide on the narrow face.
5 Determine the spacing of the pins working on the outside face of a pin board. Start by measuring inward from both edges of the pin board by a distance equal to half the width of a pin. Draw a line along each edge to indicate this measurement (1⁄4" in this example), as shown in Photo B.
(If you are using “true” half pins, don’t bother with these lines. Simply reference the edges of your board.)
6 Measure the distance between your layout lines, and divide by the number of pins, plus one. That is, if you want four pins, you should divide by five. In all likelihood, the center-to-center measurement won’t be an easy number to work with. In this case, hold a ruler at an angle across the face of the board, adjusting its position until you do get an easily divisible number (Photo C). (With “true” half-pins, reference the rule against the edges of the board.) Mark the divisions, and then use a square to extend the lines to the end of the board, as shown in Photo D.
7 Lay out the pin cheeks on the face of the board, centering them on either side of the pin centerlines. Then use your pre-set T-bevel to carry the lines across the end of the pin board, as shown in Photo E.
8 Hold the pin board on top of the tail board in their assembled orientation, and transfer the pin cheek lines, as shown in Photo F.
Use your T-bevel to extend the lines down to the scribe line, as shown in Photo G. Mark both faces of the board. (The first few times you cut dovetails this way, you may also find it helps to mark the waste areas with an “X.”)
Full-Width Or True Pins?
Traditionally, the narrow faces of half-pins are not as wide as full pins. With tablesawn dovetails, making “true” half-pins follows this tradition. Your other option here is laying out the narrow faces of the half-pins the same width as the narrow faces of the full pins, creating “full-width” half-pins.
There are times when even half a pin matters. For example, using a “full-width” half-pin for the tool chest case allows the groove for the back panel to fit within the pin, rather than grooving the adjacent tail. With the drawers, using “true” half-pins allows the bottom to run through the end of the tail board without interfering with the pins.
To Lay Out, Or Not To Lay Out
With hand-cut dovetails, you need accurate layout lines to ensure your joints fit well. With tablesawn dovetails, not so much. The accuracy of the joint comes from the spacers. In fact, if you look closely at the photos, you may see that some of the cuts I made are a little off from the lines. If this happens to you, don’t worry about it. As long as your spacers are cut accurately, your cuts will land where they need to be.
Once you become comfortable with the technique, you may discover that you only need to lay out the center-to-center spacing of the pins and the placement of one of the half-pin sockets on the tail board. The spacers will take care of the rest.
Transfer the marks to the end of the board with a square.
When laying out pins, orient the T-bevel so that the pin’s narrow face is on the outer face of your board.
Stand the pin board on the tail board, and transfer the marks indicating the pin cheeks onto the end of the tail board.
Use the pre-set T-bevel to extend the tail lines onto both faces of your tail board.
Make the spacers then cut the tails
1 You’ll need one spacer for each full pin in your joint. Make the spacers as wide as the center-to-center measurement of your pins and about 3" long. (An easy way to make accurate spacers is to rip a long strip of MDF to width, and then cut it into the needed number of spacers.)
2 Screw an auxiliary fence to your miter gauge. Make the fence 3" tall and about 3" longer than twice the width of your workpieces. Center the fence on the blade.
3 Using your T-square as a guide, tilt the blade to match your dovetail angle. Adjust the blade height so the top corner of the blade just barely kisses the scribe line.
4 Stand the tail board against the fence. If you have a right-tilt saw, align the board so that the blade will cut along the left-hand side of the left-hand half pin socket. Place all of the spacers in a row against the fence and the left-hand side of the workpieces. Clamp a stopblock to the fence at the left-hand end of the row of spacers, as shown in Photo H. With a left-tilt saw, do just the opposite: align the blade with the right-hand side of the right-hand half pin. Put the spacers in place, and clamp the stop to the right of the workpiece.
5 Keep the spacers in place and push the board through the cut. Next, pivot the board, reposition it against the spacers, and make the second cut. Remove one of the spacers, and slide the board to the left to position it for the third (and fourth) cut, as shown in Photo I.
6 Remove the next spacer and make the next two cuts, and so on, as shown in Photo J. The last cuts will be made with the workpiece against the stop.
7 Once all the cuts are made, keep the blade tilted, and widen the cuts to remove more of the waste, positioning the workpiece by eye, as shown in Photo K.
Cut all of the tail boards, and widen the cuts as detailed above. You’ll be making any adjustments to the fit when you cut the pins.
8 If you cut dovetails with a regular saw blade, you’ll need to pare the shoulders flat with a chisel, as shown in Photo L.
Clean up the corners of the sockets with a knife, as shown in Photo M. (This is where having a special “dovetail” blade comes in handy. See, “Dovetail Blades” on page 44.)
With all the stops in place to the left of the workpiece (on a right-tilt saw), clamp a stopblock to the fence to serve as a fixed reference point.
After making the two outside cuts with all of the spacers in place (pivoting the board in between cuts), remove one spacer and repeat, as shown here.
Work your way across the board, making cuts and removing spacers as you go.
Remove most of the waste by making repeated passes, positioning the cuts by eye.
Dado out the pins
1 Set up a dado blade on your saw. The exact width isn’t critical; I find 1⁄2" to 5⁄8" is generally about right. Set the blade perpendicular to the table, and adjust the height so the cut just kisses the scribe line.
2 Adjust the miter gauge (along with the auxiliary fence) to match the dovetail angle when measured to the left of the blade, as shown in Photo N.
3 Stand the laid out pin board on end against the fence so that the lines are facing out. Slide the board along the fence until the line for the left-hand half pin is aligned with the left-hand side of the dado blade. Place all of the spacers in a row to the left of the workpiece, and clamp a stopblock to the auxiliary fence, as shown in Photo O.
4 Make the first cut in your test piece with all the spacers in place, as shown in Photo P. (Just nip the edge of the board at first and check the alignment of the cut against the tail board, as shown in Photo Q.)
5 Once you are happy with the stopblock’s position, complete the first cut. Then remove a spacer and make the second cut. Proceed completely across the test piece, removing a spacer prior to each cut. Then make this first series of cuts on each pin board, as shown in Photo R.
6 To set up for the second round of pin cuts, reset the miter gauge so it matches the dovetail angle when measured to the right of the blade.
7 Hold the pin board in place against the fence, and align the right-hand half pin with the right-hand side of the dado blade. Locate the spacers and stopblock to the right of the workpiece, as shown in Photo S. (This series of cuts will determine how well the joint fits together. If anything, err to the side of making the pin too fat, that is, position it slightly too far to the right.)
8 Finish cutting the pins on the test piece, again removing a spacer after each cut. If necessary, trim away any excess waste by repositioning the pin board by eye. Test the fit in the tail board. If the joint is too tight, add a shim or two between the stopblock and the spacers, as shown in Photo T, and recut. Go easy adding shims, as you don’t want to create a joint that’s too loose. Once you are happy with the fit of the test joint, make the remaining cuts on the rest of the pin boards.
9 At this point, your pin boards and tail boards should fit hand-in-glove. Glue and clamp the sides together, and then plane the parts to flush up the ends of the pins and tails.
Pare or chop to the scribe line to clean up the saw cuts.
Once you have trimmed the shoulders, clean out the corners with a knife.
Use your pre-set T-bevel to adjust your miter gauge before cutting the pin board.
Set up the first pin cuts by aligning the left-hand half-pin with the left side of the blade. Then locate the spacers and stopblock to the left.
Cut the left-hand half pin with all the spacers in place against the stopblock.
Check the cut’s placement by aligning the edge of the test pin board with the edge of the tail board and scrutinizing the alignment of the two cheeks.
Remove the spacers after each pass until the pin board rests against the stop.
Set up for the second round of pin cuts by aligning the cutline with the blade and then locating the spacers and stop block to the right of the blade.
Insert paper shims between the stopblock and the spacers to make the pins thinner.
If you do much dovetailing on the tablesaw, having a designated dovetail blade can save time spent paring tails. Some blade companies, such as Forrest Manufacturing, will custom grind a blade with all the teeth beveled in the same direction. The kerf these blades make then aligns perfectly with your scribe line. Forrest dovetail blades cost $144. When ordering one, specify which way your saw tilts and your desired tooth angle.
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