Wooden Jaw Jig
Introduction and Safety
I’ve found that I can easily extend the capabilities of my
four-jaw chuck by making special purpose wooden jaws.
By using wood I can shape the jaws to whatever shape I need, and I can
grip even already finished parts of the work without marring.
I use a One-Way Stronghold chuck, but most modern four-jaw chucks are
similar enough to use the same technique.
When I first started using wooden jaws I’d turn a disc, drill holes, and
then cut it into quarters. It was
hard to get the holes drilled accurately, particularly since each hole requires
two operations to drill and countersink.
I tried
Please keep in mind that the mounting power of wooden jaws is less than that of metal jaws. A serious catch can break a jaw away from the mounting screws. You aren’t limited to finishing cuts by any means, but do use common sense in regards to the size, weight and balance of the work you mount with wooden jaws. This jig will make jaws that are up to 3 inches in radius, although I usually use about 2 to 2-½ inches. If you want big jaws, to reverse a bowl to turn the base or the like, use the special bowl jaws or the metal jaws designed to mount wooden jaws.
Measuring Mounting Hole Separation
The first step in making a set of wooden jaws is to determine the separation of the mounting holes. It’s not easy to measure this distance directly, especially on the base jaws, because they’re threaded. It’s much easier to measure the distance indirectly if you don’t mind doing just a little arithmetic.
It’s more accurate if you use a caliper, but an accurate ruler will do. First measure the diameter of the top of one of the mounting screws (and write it down. The diameter of the mounting screws of my One-Way Stronghold is .460 inches). Now screw a mounting screw finger tight into both holes of a base jaw and measure from the inside rim of the inside screw and the outside rim of the outside screw (mine measured 1.460 inches). Subtract the screw diameter from the second measurement and you get the hole separation (1.0 inches for my Stronghold).
You can also measure on one of the jaws. With calipers a two-step procedure is best. Using the inside measuring points, measure from the inside of the inside hole to the outside of the outside hole, then measure and subtract the diameter of one of the holes.
Hopefully the results will agree. If you don’t trust your caliper skills, to double check you can drill a pair of holes that distance apart in some thin stock and make sure you can mount it on a base jaw with both screws.
Making the Jig
The three parts of the jig are the Base, the Frame, and the Slide. All three parts can be made out of whatever scrap you have laying about, but I recommend ¾ inch plywood for stability. The only measurement that needs to be exact is the difference between the width of the Slide and the inside of the Frame. Everything else can be altered to suit what you have on hand.
The Base
The function of the Base is to hold the Frame and to allow the jig to be clamped to your drill press table. Cut out a piece of wood about 8 inches wide and 20 inches long or a little longer than your drill press table is wide.
The Frame
The function of the Frame is to align the Slide in two positions that are the same distance apart as the mounting holes on your chuck. Cut a piece of ¾ inch plywood that is about 8 inches long and 11 inches long. Draw a line parallel to and 1-½ inches below the top, and another parallel line 5 inches below the first line. Now draw a line that is perpendicular to the first two lines and that is 3 inches to the right of the left side of the Frame. You now should have a rather fat “C” drawn on the Frame. Cut out the inside of the frame. You can use a band saw, but cut slowly so that it will be reasonably accurate and plan on going back to square up the corners. Now fasten the Frame to the Base. The left hand edge of the Frame should be about 7 inches to the left of the center of the base. You can use screws, nails, glue or any combination.
The Slide
The function of the slide is to hold a wooden jaw for drilling. Cut out a piece of ¾ inch plywood about 4 inches wide (or so the difference between the width of the Slide and the opening of the Frame equals the hole separation of your jaws) and 8 inches long. Cut carefully, this piece should be cut with square sides and corners. Measure 1 inch to the right of the lower left corner, and draw a line that angles up 45 degrees to the right. Now measure 1 inch to the left of the right corner and draw a line that angles up 45 degrees to the left. Carefully cut out the resulting triangle. Set the Slide into the Frame and make sure it fits up against the left edge of the “C” and that the corners allow it to move all the way to the top and to the bottom. Now check how much travel is allowed. It should match the hole separation of your jaws. If the travel is too little, you can file, plane, or sand a little from the bottom of the slide. If the travel is too much, you can shim it with paper or thin cardboard. Before making jaws you can test the jig on a triangle of ¼ inch plywood and see if the resulting holes match the mounting holes on your chuck.
Making Jaws
You can use any wood to make jaws. I usually use maple because it’s easy to turn, strong, and I have a lot of it about. I cut a board so that the width of the board is the radius of the jaw I want, usually 2 inches. Then I cut this board into triangles. I use a sliding miter jig on my table saw, but you can use a chop saw or a band saw, as long as the result is a consistent set of right angle isosceles triangles. You only need 4 triangles, but why not cut more while you have things set up?
Pick one of the triangles and draw a line that bisects the 90 degree angle to aid in orienting the jig. Your holes will lie along this line. You can vary the location of the holes depending on how far you want the jaws to open and whether you’ll run anything through the center. To start, measure ½ inch down from the 90 degree angle along the bisecting line and make a mark. Put the jaw into the slide. Make sure that the jaw is all the way to the top of the Slide and that the Slide is all the way to the bottom and against the left side of the Frame.
Mount a drill bit in your drill press that is slightly larger than the diameter of the jaw mounting screws your chuck uses. I use a ½ inch bit. Position the jig on your drill press table so the drill bit is centered on the mark. Clamp the jig in place on the table. Check again that the jaw is to the top of the Slide, and the Slide to the bottom and left of the frame and that the drill bit is still centered on the mark. Take the jaw out, and set the drill stop so that the bit stops about ¼ inch from the frame. You may have to adjust this to fit the length of your chucks mounting bolts.
Turn on the drill press, and put the jaw back in the Slide, making sure (at the considerable risk of repeating myself to much) that the jaw is at the top of the Slide and the Slide at bottom left of the Frame. Drill the first hole. Now slide the Slide to the top left of the Frame (making sure wood chips don’t prevent this) and drill the second hole. Repeat this for the other three jaws.
Now change the drill bit to one a bit bigger than the thread diameter of your chuck mounting screws. I use a ¼ inch bit. Adjust the drill stop so that the bit drills a little ways into the Frame. If you have to adjust the table height at this point make sure the drill bit is still centered the same. Now using the same procedure drill the second set of holes in all the jaws. You can, at this point, cut the corners off the jaws on your band saw or you can turn them off after they’re mounted on your chuck.
Mounting and Shaping Jaws
Mounting the Jaws
To mount the wooden jaws, first take off whatever jaws are mounted on your chuck and set the mounting screws aside. Check to make sure that enough of the screw extends through the wooden jaw to fasten securely. Align a jaw’s holes with the mounting holes on a base jaw, and screw one mounting screw in loosely. Then start the other screw. If you can’t start the screw straight in, stop. You’ll really regret stripping the threads on your base jaw. Enlarge the hole in the wooden jaw a trifle with a round file and try again. Once both screws are started, tighten them both securely. Repeat for the other three jaws.
Shaping the Jaws
Once you have all the jaws mounted, screw the chuck on to your headstock. The jaws will hold better if the radius you cut into the jaw matches the size piece you want to hold. However, you want to have some adjustment left in case some of your pieces are a little oversize. The chuck may not hold it’s setting if it’s not gripping anything, so you can’t just open it up. Instead clamp a piece of scrap wood about ¼ to ½ inch thick in between. Then turn on your lathe, and turn the jaws. For safety you’ll want to turn the perimeter round first, and probably put a radius on the outside edge.
If you want to grip a disk, just turn a recess in the jaws. A depth of 1/8 to ¼ inch will probably be fine, and won’t put you in any danger of hitting the mounting screws with your turning tool. . To grip a flat square, such as for a rosette, turn a recess that intersects a set of mounting holes, then put the points of the square in the holes and tighten.
If you want to mount a tenon or dowel, mount your drill chuck in the tailstock and drill the appropriate sized hole. If you use Forstner bits you’ll get a truer hole, just be careful you don’t hit the metal chuck. To grip a turning square just drill a round hole like you would to grip a dowel or tenon
If you want to grip spherical or hemispherical items (such as tippy-tops or scoops) you may want to make thicker jaws. You don’t need to try to mimic the spherical or hemispherical shape, just turn a cylindrical recess. The recess should be a little deeper than the hemisphere. You add a lip at the front of the recess for a more secure grip.
Moon-Roarer Toy
At the 2000 AAW Symposium I watched Rude Osolnik turn a bracelet, holding the stock between a wooden pressure pad attached to the headstock and tailstock. He then turned what he called a “moon-roarer” with the left-over center piece. It’s a simple toy, a two hole wooden button with a string looped through it. You hold the loop at each end with the button in the middle, swing it around to wind up the string, then pull rhythmically. When it gets to going fast it makes a roaring sound. No batteries are required and kids can work it at a younger age than tops.
Pressure turning leaves a central area unturned, so I made
a set of wooden jaws to make the toy.
I clamped ¼ inch thick piece of scrap between the jaws and turned a 2 ½
inch recess about 1/8 inch deep. I
found a piece of ½ inch thick Padouk, roughed it into a 2 ½ inch circle on the
bandsaw, and drilled a pair of 1/8 inch
holes about ¾ of an inch apart in the middle of the disk.
I mounted the disk in the jaws and turned the front half of the rim true
and cleaned and recessed the face.
Then I flipped the disk over and repeated it on the back side.
Using the toy with just string loops (actually I used nylon cord) pinched my fingers a bit, so I decided to make some handles. One could turn handles between centers of course, but this is an article on wooden jaws, so I clamped a 1/16 inch thick scrap between the jaws and used a 3/8 inch forstner bit to drill about 3/4ths of the way through the jaws. I cut a 1/2x1/2x6 inch piece of Padouk on the bandsaw, and drilled two pairs of 1/8 inch holes, then clamped it in the center of the jaws. I brought up the tail stock for support and turned the handles, parted off the first, cleaned up the end of the second, then parted it off too.
Coffee Scoop
If you share my addiction to good coffee as well as the one to turning, you might like making this combination scoop and bag closer. I hate those little covered wire closers that come with most coffee bags because they never miss an opportunity to fall off and get lost. You probably know the scene; you retrieve your stash of the good stuff from the freezer, fumble with the closer, search for where you spouse has hidden the coffee measure, and then can’t even reach down far enough into the bag when you find it. This scoop/clip solves all those problems (I should add that my wife doesn’t consider any of the above to be problems, focusing instead any specks of coffee that might get brushed off the counter to cling to the sawdust already littering the floor). The clip allows easy opening and closing of the bag and won’t flutter to the floor. The scoop is always right there where you need it. The long handle lets you reach way down in, and if that isn’t enough you can cut off the top of bag and still seal it just as well.
To make the jaws for this jig, find or glue up some 2 inch stock, then cut, drill and mount them as usual. Clamp a ¼ inch spacer in between the jaws and turn a 2 inch diameter recess a little deeper than 1 inch. You can add a lip on the rim for extra security. Take two adjacent jaws off of the chuck and cut about 3/8 inch off what will be adjacent sides on the band saw to make room for the handle of the scoop.
To prepare stock for the scoop/clip, glue two 1x2x7.5 pieces together with a paper joint between their faces. Give the glue a day to cure unless you’re lacking excitement in your life. Trim the ends square, then mount it in the regular metal jaws of your chuck. You can get more details on turning scoops in Richard Raffan’s Turning Projects. But briefly, turn a 2 inch sphere on the end, whether you use a template or a layout system is up to you, but do make it accurate, as any irregularities will be painfully obvious when it’s hollowed out. Turn the handle to a shape you like, but leave the handle where it joins the sphere fairly fat for strength. Once you’ve sanded it smooth and parted it off, split the paper joint.
Remount your wooden jaws on the chuck and mount the scoop in the jaws. Hollow the inside of the hemisphere, being wary of that 5 inch handle swinging about. You may want to make a cardboard template so you neither cut through the bottom nor leave it overly heavy.
Once the hemisphere is hollowed and sanded, remove the scoop/clip from the chuck and clean up the paper joint. Drill a 1/8 inch hole though the handle about ¼ inch from the edge of hemisphere and use a straight edge to lay out cutting lines from the center of the end of the handle tangent to the outer edges of the drilled hole. Then cut along the lines. A scroll saw is better, but you can also use a bandsaw. If the slot tapers it will clamp the bag better. Round the inside edges of the end of the slot so that it will slip over the bag easier. Then sand the inside of the slot and apply a food safe finish if you like.