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Shopmade Handscrews

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Shopmade Handscrews

Thread your own wooden screws

By Steven Bunn


Even though I have a small fortune invested in tools, I always seem to be short of wooden handscrew clamps. But daydreaming about buying ten more of these versatile tools runs smack into the reality that such a purchase requires spending anywhere from $200 to $450, depending on the size of clamp. Ouch!

Several years ago, I resolved to satisfy my need for clamps by making my own, using the chunks of this and that from my scrap pile, which waxes and wanes with the seasons. In September, this pile spills out across the shop floor, but by late December, the frigid Maine weather has reduced it to nothing. Until spring, the morning race to get some heat in the shop becomes a little like the Mississippi River steamboat races of the 1800s, the crew dismantling cabins and upper decks to provide fuel for the roaring boilers. So, my rule of thumb is to make clamps before the heating season starts.

The first batch of clamps that I made were similar to Jorgensen handscrews, except for having wooden screws. I turned maple and ash on my lathe to make my own wooden screws, and threaded them with a screw box. The resulting clamps worked well, with one important exception: They were a bear to adjust; cranking them open and shut was laborious. When a tricky glue-up was writhing on the bench like a crazed anaconda, and speed was of the essence, these clamps wouldn’t do.

Then, while flipping through a book I purchased at a flea market, I spied two wooden clamps in a photograph taken at Old Sturbridge Village in Massachusetts. These clamps were similar to the ones I had made, with a crucial difference. Where both screws on my early clamps threaded completely through the opposing jaw, the Sturbridge examples had one screw that passed through the threads and one that seated in a stopped hole. Both screws were secured to this jaw with garters. So as the screws turned, they either forced the jaws open or pulled them closed. Shouting the (unprintable) Maine equivalent of “Eureka,” I rushed to the shop to build a prototype. There must be an unwritten rule sacred to cabinetmakers (at least to me, anyway), that the paying work isn’t nearly as interesting as the harebrained schemes that we invent. Several hours later, I held in my hands a clamp which effortlessly twirled open and shut. Here’s how to make your own wooden handscrews, like the one I devised.


Make the jaws

I usually make these clamps in batches. Start by milling and sawing kiln dried stock for the jaws. The dimensions for each jaw block are 1-3/8” wide on the clamping face, 1-1/2” inches thick, and 9” long. Arrange the blocks in pairs and mark the outer side or cheek of each pair with a triangle that points to the mouth of the clamp (1). Open each pair of blocks to their clamping faces and mark two points on one, 1-1/4” and 4-1/2” from the back end. Hold the blocks together, with their ends flush, and use a square to strike lines across both faces, running through the points you’ve marked. Mark the center of each line to locate the screw holes. Then label the diameters and indicate whether the holes go through or are stopped (2). Taking this step avoids confusion if you make these clamps in multiples. Also, mark the jaw faces “left” and “right” and “top” and “bottom.”

Chuck a 5/8” brad point bit into your drill press and position a fence so the bit’s point lines up with the center points you’ve marked on the jaw block. Always keep the marked cheeks of each pair of jaw blocks pointing outwards (3). This ensures that the drilled holes will be equidistant from the fence in each block, so that the holes—and the jaws—will be coplanar when the clamps are assembled.

If you’re making a batch of handscrews, now is the time to clamp a temporary stop block to the fence, to ensure that holes are drilled consistently in each set of blocks. Place the left jaw blank on the table, against the fence. Bring the bit down and align its point with the mark that’s nearest the block’s top end. Clamp the stop block behind the jaw block.

Drill a 5/8” hole completely through the block. This will become the threaded hole for the top screw. After drilling matching holes in all your remaining left jaw blocks, reset the stop block and drill the second (lower) hole in each left block.

Remove the stop block and reset the depth stop to drill the 5/8” x 1” deep stopped hole in each right jaw block. Place the right jaw, clamping-face up and marked cheek out, against the fence, with the brad point centered on the location of the top hole. Install the stop block and drill the 1” deep hole. Do the same for any other right jaw blocks. Install a 3/4” brad point bit, reposition the stop block and drill a 3/4” inch hole completely through the jaw block at the location of the lower screw. You should now have left jaws with two through 5/8” holes and right jaws with one stopped 5/8” hole, and one 3/4” through hole (4).

Clamp each left jaw block clamping-face up in your bench’s shoulder vise. Then, using a 3/4” tap, carefully tap both 5/8” holes (5) to accept the 3/4” dia. screws you will make next. A 3/4” woodthreading kit (tap and thread box) is available from Woodcraft (#12T14). Note: I start with 5/8” dia. holes, because the root diameter of my tap is 19/32”. The holes’ additional 1/32” dia. make it easier to get the cutter started. Check your tap’s root diameter and adjust the size of the starter holes you drill, if necessary.

Cut the angled face on the outside corners of each pair of jaw blocks to form the clamp’s mouth (6). Clean up the angled cuts with a disc or belt sander. Finish the jaws by easing the outside edges with a 45° chamfer router bit.


Turn the screws

I have lots of split-off pieces of green maple and ash lying around, because I primarily make Windsor chairs. I turn my screws from this leftover material, because it turns and threads easily. I split out 1-3/8” to 1-1/2” square billets, trim them to 16” lengths and turn them on my lathe to 1-1/8” dia. Then I mark out the handle, allowing for some waste on the end. My handles are based on the profile of the handles on a set of chisels of which I am particularly fond (7). Personalize your clamps by turning the shape of your handle as you wish.

Turn the remainder of the shaft to 3/4” dia. I have always found it best to turn my screw shafts slightly undersize at this stage. Whether or not my calipers are slightly out of sync with my drill bits (and every other blessed thing), it is a fact that a shaft that’s turned too large will bind when its fed into a screw box. So don’t get fixated on being overly precise (see “Performance vs. Art,” below).

Mark out and cut the grooves in the screws that will engage the garters in the jaws when the clamp is assembled. Notice that these grooves are located at opposite ends of the two screws. On the lower screw (the one that installs nearest the jaw mouth), the groove is located near the handle (8). On the top screw, the slot is on the opposite end. I turn the end of this screw down to just under 5/8” dia., and then cut the garter groove. This section should be a little longer than 1”, to allow for trimming.


Thread the screws

Cutting the threads is a simple process, because green wood works so easily. Clamp the screw in your bench’s shoulder vise, shaft up. This frees up both hands to turn the screw box. The box’s guide (or starter) block keeps the shaft aligned with the thread cutter as you start to feed the work into the tool. The threads on the bottom screw run from its tip to the flat section that precedes the garter groove (9).

The top screw threads start beyond the garter section on the end and extend all the way to the handle (10). The screw box’s guide block will bottom out against the handle before the last threads can be cut; the block must be removed to finish the job.

First, back the screw box off the threaded portion of the shaft. Then unscrew its guide block. Removing this block exposes the V-cutter that actually cuts the threads. Take the partially-threaded screw out of the vise and rethread it into the screw box: Carefully turn the screw by hand, until its threads engage the screw box’s threaded body. Then turn the screw box like a nut to move it down the threaded shaft. The exposed V-cutter will engage the final unthreaded section and cut threads very close to the handle before it bottoms out (11).

Before you try out your newly threaded screws, set them aside for a week to dry out. They will shrink enough in diameter to turn easily in the threaded jaws. If you are working with kiln dried stock, you don’t have to wait, but you may have to run the threads back and forth through the screw box several times, and do the same with the tapped jaws, to get a looser fit (see “Kiln Dried Screws", below). Loose is good. Remember that threads are really spiral wedges, so they tighten as they close. A loose fit allows the clamps to twirl easily when you are adjusting them.


Assembly

Make sure the non-threaded 3/4” and 5/8” dia. portions of the screws fit smoothly in the appropriate holes drilled in the jaws. Resize the shafts, if necessary. Test fit both screws to ensure that the two jaws will seat tightly together when closed (12). First, seat the 5/8” end of the top screw into its stopped hole in the jaw. Then trim the end, if necessary, until the threads seat against the jaw’s clamping face. Next, test the non-threaded portion of the lower screw in its 3/4” dia. hole. The threads should extend slightly into the jaw’s body. If necessary, take another turn with the screw box. But be careful not to cut the threads too close to the garter grooves. (Clamping puts pressure against the garters, which in turn put a lot of pressure on the garter groove shoulders—they can break out if there isn’t enough heft between the threads and groove.) Complete the screws by trimming the waste off the end of the handles.

Mark the location of the garters for both holes in the right jaw. The best way to do this is to lay each screw in place on the jaw and tick off the garter locations with a pencil (13). I drill 3/16” x 1” deep holes (14), being careful that they are far enough apart so that the garters (3/16” square pins that are driven in) don’t rub or bind the screw shaft as it turns. I aim for the garters to protrude 1/16” to 3/32”. Any less, and the screw grinds the garter to dust and runs over it. Any more, and the shaft binds when the screw is turned. When I have an overly tight garter, I have two choices: keep working the screw back and forth until the garter and screw wear in, or be patient and wait until the green screw shrinks a bit more.

Make the 3/16”-square garter pins out of any available hardwood. I cut mine about 1-1/2” inches long. Thread both screws onto the jaws and seat both garter sections. Then drive the garter pins into the round holes and trim them flush. Finally, clamp the assembled handscrew on your workbench and belt sand both sides until the jaws are flush. This removes any misalignment introduced when the holes in the jaws were machined at the start of the project. Once you have made one handscrew, you can use the same technique to create them in any size. The process is the same.

Click any image to view a larger version.















Performance Vs. Art

First and foremost, these clamps are tools which I expect to put to hard use in my shop. I have gotten to the point where I no longer sand the screw handles, or do more to the assembled clamps than give them a quick pass or two with a belt-sander to flush up the sides of the jaws when the clamp is closed. I find that the turning-tool marks, left unsanded on the handles, add to their “grippyness.” I also don’t worry about wane, small checks or other defects in my handles, because the screw doesn’t have to be visually perfect to work. In the same vein, small chip-outs in the wooden threads are acceptable, because a screw thread is, in reality, an inclined plane. Even with small chip-outs, there is still a lot of bearing surface between the male and female threads of the screw and jaw. Only if a number of adjacent rows of threads are chipped out or broken off is the screw ruined.



Kiln dried screws

Green wood cuts like a dream, but dry stock can be both tough and brittle. Threads can chip off if the wood is really dry. If you use kiln-dried material for screws you can (1) either run the threaded tap back and forth through the threaded jaw while applying side pressure, to help open up the width of the threaded opening, or (2) carefully adjust the depth of the V-cutter in the thread box itself, so it cuts deeper while threading. Another option is to liberally wipe the screw shaft with turpentine before you cut the threads—I’ve found that wetting the wood this way helps the screw box cut more cleanly.