Making a Better Coping/Dovetail Saw

As the lads I'm writing for have made good progress in the last year, the next article I write for them is gonna be on something a bit more complicated than basic tools and joinery:

http://pic3.picturetrail.com/VOL12/1...9/68646821.jpg

Store-bought coping saws never work to their potential because those flimsy steel frames don’t hold the blade sufficiently taut. Their frames can be bent outwards for more tension, but with hard use they quickly bend back to their original mediocre performance. I want one I can speed up dovetail work with, cutting dovetails that require minimal paring in two cuts of the saw. Making that tight, 90-degree turn neatly at the bottom of the dovetail requires a taut blade, and I’ve made a number of frame saws over the decades to achieve that goal. This model is the just the latest refinement of time-tested designs made by my family for generations.

http://pic3.picturetrail.com/VOL12/1...2/50978326.jpg

I’m using some very special wood for these…a 240-year-old Pacific Madrona growing at the high tide line of Hood Canal. Termite-ridden, it had to be taken down. While it’s the largest and straightest-grained Madrone I’ve ever seen, the salt water seems to have had a stunting effect in spite of full sun, and the diffuse-porous growth rings are so tight I need magnification to count them in places. Truly exceptional, it is so dense it cuts like tough butter without the splintering normally common in the faster-grown examples of this wood. Normally a twisted understory tree and both harder and heavier than American Beech and Sugar Maple, we use the straighter trees for flooring and stair treads here in its Pacific Northwest native range. Like beech, it shrinks severely in drying, but also like beech, is sufficiently stable once dry for making tools. You can use mahogany, cherry, walnut, maple, ash or any number of hardwoods successfully for your saw. Because of the orientation of the holes in the design and the stresses on them, I recommend you use quarter or rift-sawn stock for the handles.

http://pic3.picturetrail.com/VOL12/1...9/67802779.jpg

I’m making a run of 8 saws for economy of scale and full use of the rift sawn, 5/4 board I selected from the drying stack. When making saws, handles, hand screws or other tools, I always use up all the stock I devote to the project, saving any finished pieces leftover for completion later when the right offcut becomes available or for use as spare parts. In the picture above I’m laying out the mortises and holes in the handles, using the jointer fence as an index for efficiency and speed. I build furniture and boats the same way; gang cutting stock for multiple parts and cutting joints in sequence so I can both feel and see the perfect match I’m trying to achieve between each part.

http://pic3.picturetrail.com/VOL12/1...9/67802788.jpg

As there are only 16 mortises to make, I chop them with the half-inch mortising chisel. Predrilling and paring aren’t necessary once you get the hang of this simple, basic tool, and it takes 45 minutes…. less time that I would have spent making a jig and using the router.

http://pic3.picturetrail.com/VOL12/1...9/67802791.jpg

I bore the holes for the quarter-inch drill rod I’ll use for blade mounts and tensioning rod, counter boring for the handle’s ferrule and evaluate hardware fit after each task. I use brad point and Forstner bits for accuracy and ream the .25-inch holes to .27 using a wire gage jobber bit for clearance. I also like to use a 45-degree countersink where the drill rod emerges from the handles…just for neat. If your bit wanders and you have a hole slightly off center, that 45-degree countersink can also be offset a bit to fool the eye, hiding your mistake.

If you don’t have a drill press, this can also be done just as well using a hand drill. Simply use a long, bell hanger’s bit that’s easy to keep plumb, and have a helper sight plumb from the end of the piece while you sight the face side as you are drilling.

http://pic3.picturetrail.com/VOL12/1...9/67802832.jpg

Before turning the handles, I square up the ends of the rough stock and bore a small pilot hole for the drill rod blade mount, to be bored full size later. If I drilled the full-size hole before turning the handle, the hole would be too large for the lathe’s live center. A faster alternative is to fabricate and epoxy mount the drill rod before turning, using the drill rod stub to mount the turning square in the lathe’s 3-jaw or Jacob’s Chuck…but most woodworkers don’t own a chuck for their lathes, so I’ll do it without using a chuck.

http://pic3.picturetrail.com/VOL12/1...9/67802795.jpg

I turn the handles on the lathe using a sizing gage on the parting tool matched to the ferrules I’m using. Any brass or copper pipe the correct size will do, but these are ready-made brass ferrules used by larger hydraulic repair shops to fabricate hoses…they are readily available in an amazing array of 50 sizes for 5 dollars a dozen. Acquire your hardware first…I rarely begin a project before all the hardware is on hand, as I prefer to pick my own challenges.

If you don’t have access to a lathe, simpler, 8-sided handles can also be made, fitting the ferrules using rasps and files. Using thickened epoxy demonstrated below to mount the ferrules; the fit doesn’t have to be perfect, as the epoxy will fill those gaps perfectly.

http://pic3.picturetrail.com/VOL12/1...9/67802836.jpg

With the handles turned and ferrules mounted with epoxy, I drill the final .25-inch holes with a jobber bit that will follow the pilot hole neatly in preparation for installing the blade mounts, also using epoxy.

Continued…

http://pic3.picturetrail.com/VOL12/1...9/67802840.jpg

The blade mounts are merely two saw cuts in the end of drill rod cut to length and filed where necessary to fit the stock coping saw blades.

http://pic3.picturetrail.com/VOL12/1...9/67802848.jpg

I bevel the ends slightly using an electric drill and grinder, both for neat and in preparation for cutting threads where required…

http://pic3.picturetrail.com/VOL12/1...9/67802922.jpg

…and a ¼ X 20 tpi die is used to cut the threads, again checking hardware fit as I go.

http://pic3.picturetrail.com/VOL12/1...9/67802923.jpg

The forward blade mount is drilled for a pin used to aid in turning the blade. I cut the slots for the blade over deep and use the end of the slot as my pilot hole for drilling.

http://pic3.picturetrail.com/VOL12/1...9/67802927.jpg

The pins are mounted using silver braze ground in its own flux and MAPP gas. Easy and very strong, but you can also use soft solder to the same end. Simply heat the surgically clean, reamed and sanded surfaces until the braze material melts…this braze at 1100 degrees. The pins are #4 screw blanks available at gunsmith supply houses heated to cherry red and the heads hammered flat. Also available is a Silver Solder Black to completely hide the braze material that doesn’t color to match the steel.

http://pic3.picturetrail.com/VOL12/1...9/67802852.jpg

Finally, I finish all the steel parts with wet-or-dry paper and phosphate blue. The bluing doesn’t interfere with epoxy bonding these mounts in the turned handles, just be sure you don’t oil them per the bluing instructions until after the glue has set.

http://pic3.picturetrail.com/VOL12/1...9/67802912.jpg

The handle blade mounts are set in dyed marine epoxy and cleaned up with a vinegar-dampened towel. For uniformity, the handle holes were drilled slightly over deep and the mounts installed using the depth gage.

http://pic3.picturetrail.com/VOL12/1...9/67802915.jpg

With the hard parts done, I cut out the handles using the patterns in my plan.

Continued…

http://pic3.picturetrail.com/VOL12/1...9/67802967.jpg

I counterbore holes for the necessary washers that distribute the considerable stress of the blade mounts and tension rod across a wide area of the handle. As the hole for the drill rod is already present, and it would have been difficult to bore these to the correct depth while the stock was still rectangular, I index the flats of the handle on the drill press table using blocking and fill the hole with a tight dowel to better index the pilot of the Forstner bit. This is another opportunity to hide an off center hole by offsetting the washer within the tolerances of its fit around the rod. If I were using wood prone to splitting at the holes, like any flatsawn ring-porous wood, I would bed these holes in dyed marine epoxy. The best method for this is to drill the initial holes oversize, fill them with epoxy under light heat to better soak into the wood pores, damming one end of the hole with masking tape, and redrill them to the correct size after curing.

http://pic3.picturetrail.com/VOL12/1...9/67899727.jpg

I clean up the saw marks on the drill press using a drum sander, and round over the edges using a router with 3/8 round over bit. Then I do some minor rasp and file work that distinguishes these pieces from something that can be done in a factory. I change the radius of the curves so as to better fit the hand, and add some subtle curves in the handle’s thickness between the stretcher and tensioning rod…just for pretty. Then I finish sand from 80 through 220 grit on the drill press using an aircushion sanding drum that follows the curves, followed by hand sanding through 400 grit. Between each grit I raise the grain with a damp towel…a practice that saves sandpaper by swelling the scratches so they are more easily attacked by the next grit. It also prolongs the life of the finish if the piece ever gets wet.

http://pic3.picturetrail.com/VOL12/1...9/68418073.jpg

As soon as each piece is finish sanded, and before the tenons are cut, I soak the pieces in hot “Boat Soup” over night and allow them to dry for a few days. My soup is merely a mixture of 60-40 boiled linseed oil and turpentine with a healthy portion of both pine tar and Japan Drier added, mixed in a double boiler. It adds some lovely natural color to the wood, but I also believe adding oil to the wood, as deep as I can get it will benefit the piece several decades from now when old wood begins to get dry and brittle from age.

As sculpting and sanding change the dimensions of the handles, slightly, I don’t cut the tenons until last. The shoulder-to-shoulder dimension is simply the measurement between the handles at the blade. If I have shaved some wood off so the inside edges of those handles are no longer perfectly flush with the face of the mortise per the design, I also make that adjustment in the shoulder-to-shoulder dimension of the stretcher.

http://pic3.picturetrail.com/VOL12/1...9/68418078.jpg

As I usually set these aside once the major work is done and finish them individually after hours, I simply cut the tenons using multiple passes on whatever blade happens to be in the contractor’s saw…cutting them oversize and trimming them to fit using the shoulder plane. If I were doing all the saws at once, I’d still fit them individually but use the stack-dado set for efficiency.

http://pic3.picturetrail.com/VOL12/1...9/68418084.jpg

I make a practice of cutting the stretchers a half inch overlong. That provides me waste stock at the ends to fine tune the table saw tenon settings to fit each mortise, and I trim the tenons to length as my last step in finishing the tenons.

http://pic3.picturetrail.com/VOL12/1...9/68672696.jpg

I make up two prototype saws and give them to two professional finish carpenter friends…tradesmen who still cope joints the old-fashioned way… for a few weeks of hard use to prove the design, and incorporate their comments in the final design above.

http://pic3.picturetrail.com/VOL12/1...9/68250708.jpg

After finishing with a few coats of renewable, polymerized oil, curing, and rubbing out with 0000 steel wool lubricated with carnauba wax, the final result has the look and feel I’m after. The curves remind me more of a sculpture than a tool factory product, the handle fits my hand perfectly and the warm finish is sensuous to the touch, inviting me to pick up the tool. It’s the least I can do to pay tribute to that magnificent tree.

Bob,

Those are mightily pretty saws.

- Ed

Thank you, Bob. Almost too purty to use...almost.... :)

Dumb question: The stretcher isn't glued in is it? It seems you need slight angular movement over that joint to get the high tension you desire on the blade.

Did you also make the blade?

No glue...the saw comes apart.

Stock coping saw blade in packs of 4 at Tacoma Screw, my jobber.

To keep a gap from opening up at the tenon shoulder, simply don't screw the lower acorn nut down all the way....then you have room to adjust both upper and lower nuts fro even bearing on the tenon shoulder.

What a great idea for a much better saw - and pretty too.
Nice job!
Any chance you might be selling some in the future?

Dave...these are gifts made after hours for a large crew of framers and finish carpenters I'm putting together in a month or so.

My intent is for you to make your own...too much labor in these, and adding the efficiencies necessary to make the price something reasonable takes all the fun out of it.