How to Build It
Common Hardware, Tools and Skills
All the parts of this jig are made from 3/4-in. medium-density fiberboard (MDF), primarily because it’s very flat. Baltic birch or ApplePly plywood would work well, too (see Sources, page 110), but shop-grade birch plywood won’t cut the mustard. MDF is fairly inexpensive (about $30/sheet)and you’ll only need half a sheet or a bunch of scraps.
Most of the hardware for the jig is garden-variety stuff (see Shopping List, below). A few crucial items can only be found in a catalog (see Sources, below.) Altogether, the hardware costs about $30.
As for power tools, of course you’ll need a drill press, but it doesn’t have to be a floor model. A 10-in. benchtop will do, and you can buy one for less than $100. (The only requirement is that the drill press must have at least 10-1/8 in. of clearance between the bottom of the chuck and the top of its table.)
You’ll need a set of twist drill bits up to 1/2-in. dia., a metal-cutting countersink, 1/2-, 5/8-, 3/4- and 1-in.-dia. Forstner bits and a 3-in.-dia. sanding drum. A self-centering hinge bit is optional (see Sources, below). You’ll also need a tablesaw and a stacking dado set. A bandsaw helps with cutting the round parts, but a jigsaw is okay.
You’ll also need a hacksaw with an 18- tooth-per-inch blade, an 8- or 10-in. flat ***-cut file, an 8-32 NC tap and
handle and household lubricating oil.
Getting Started: Laminate the MDF
Begin building the sharpening system by gluing together all the parts that are made from two thicknesses of MDF.
1. Rough cut pieces for the driver (A1), the fixed support (C1), the moveable support (C2), the crank (C4) and the lapping plates (E1) (see Cutting List, page 74).
2. Clamp and glue the pieces together (Photo 1, page 68). It’s okay if the pieces don’t perfectly align while you’re gluing, because they’re meant to be at least
1/2-in. oversize in width and length.
Make the Lapping Plates
Now make a set of flat blocks, or lapping plates, for flattening and polishing the back side of your chisels and plane irons. Lapping a tool requires removing a fair amount of very hard steel. The secret to getting this tedious job done quickly is to use many different grits of sandpaper, just as if you were sanding wood. Our lapping system uses a set of five double-sided plates made from laminated MDF. Each is the size of half of one sheet of standard sandpaper.
1. Cut the blanks (E1) to final size.
2. Flatten both faces of each plate by sanding them on the top of your tablesaw (Photo 2).
3. Spray the plates with three or four coats of clear lacquer. Sand the lacquer smooth.
4. Tear your sandpaper into halves and coat each piece very lightly with a spray adhesive, such as 3M Super 77. Apply the paper to the lapping plates (Photo 3). When your sandpaper wears out, simply peel it off the plate and stick on a new piece. Clean off adhesive residue from the plates with mineral spirits.
Suggested Grits for Lapping Plates
Ordinary sandpaper works fine for most grits, but for the finest ones go with special microfinishing paper, with grit sizes measured in microns (see Sources, below). Each lapping plate has two grits, one on each side.
Coarse: 100 and 120
Medium: 150 and180
Fine: 240 and 320
Extra-Fine: 400 and 600
Superfine: 15 micron and 5 micron.
Make the Twist-and-Lock Disks
This sharpening jig has three major components: a driver disk mounted in the drill press chuck, a set of five interchangeable abrasive disks that mount on the driver disk and a tool holder that clamps to the drill press table (Fig. A, below). Begin by making all the disks.
Three of the disks are test pieces for setting up the tablesaw and drill press in the steps ahead. The disks twist and lock together as a unit, so they have to be carefully cut. Try out your cuts on the test pieces first, so you won’t mess up any of the parts that really matter!
1. Cut rough blanks for the driver disk (A1) and abrasive disks (A2) to final size.
2. Lay out the dado cuts. Draw one straight and one angled dado on three test blanks (Fig. B, below). Use your tablesaw’s miter gauge to draw the angled dado. Draw a circle with a compass on all the blanks, both test and real.
3. Cut straight dadoes exactly down the middle of each blank.
4. Cut angled dadoes in the abrasive disk blanks only (Photo 4). Use a test piece to set up the saw. Make a partial cut, turn the piece over, and see if the cut falls on the layout lines. Move the stop block on your miter gauge until you’re right on the money.
5. Cut little pieces of hardwood for stops (A3) from a long blank. Glue the stops in place on both the abrasive disks and the driver disk (Photo 5).
6. Drill 1/2-in. diameter holes with a Forstner bit in the center of each blank (Figs. B and C). Drill shallow holes in the dadoed side of the abrasive disk blanks (Photo 6). Drill a deep hole in the plain side of the driver disk blank.
7. Remove a small triangular-shaped piece of wood at the intersection of the two dado cuts on the abrasive disk blanks (Fig. C, below). Simply drill it out with the 1/2-in. Forstner bit.
8. Lay out holes for rare earth magnet cups and washers on one of the test pieces (Figs. B and C). Then set up the drill press fence and stop block to drill these holes in both the driver disk and sanding disks. Be particular about the depth of all of these holes. The washers and magnets should be either flush with the surface of the disk or slightly below it.
Round the Disks Without a Lathe
1. Cut all the blanks into approximately round shapes. Then make a simple sanding jig for the disks to rotate on (Fig. D, below). Put a coarse sanding drum in your drill press and mount each disk on the jig (Photo 7, below). Secure the jig to the drill press table with a single clamp. By hand, rotate the roughly circular disk against the sanding drum, hitting only the high spots.
After each rotation, tap the corner of the jig with a mallet to nudge the disk slightly closer to the drum. It won’t take long before the disk is perfectly round. Small differences in diameter between the disks won’t matter.
2. Epoxy the shaft (A4) into the driver disk (Photo 8). (First, be sure to check that your table is absolutely square to the shaft, both front to back and side to side.)
3. Epoxy two pieces of square key stock into the dado on the bottom of the driver disk (Fig. C, below). If you can’t find two pieces the right length, buy three and cut one shorter with a hacksaw.
4. Fasten washers and cups for the rare earth magnets to the disks (Photo 9).
5. Flatten the bottoms of all the sanding disks on a medium-grit lapping plate. Spray the bottoms of all the sanding disks with three or four coats of lacquer, and sand out the bumps.
Suggested Grits for the Sanding Disks
Use standard 5-in. sanding disks without holes. You can use disks with an adhesive backing or make your own from regular sheet sandpaper and a low-tack spray adhesive. Disks come in standard sandpaper grits or in microns.
Coarse: 80 grit
Medium: 120 grit or 100 micron
Fine: 320 grit or 30 micron
Extra-fine: 600 grit or 15 micron
Super-fine: 1200 grit or 5 micron
Make the Adjustable Base
and Tool Rest
1. Rip the blank for the fixed support (C1) and moveable support (C2) to final width.
2. Cut the rough blanks for the two guides (B1), the table that adjusts for the squaring of a tool’s bevel (B2) and the table that adjusts the angle of the bevel (B3). Also, rip a piece for the base (C3) and trim it slightly oversize in length.
3. Cut a 45-degree bevel along one side of the guide blank (B1) (Fig. E, below). Caution: Tilt your tablesaw blade away from the fence, so there’s no kickback hazard. The blank is oversized in width so there’s plenty of support for this cut. Then reset the tablesaw blade to 90 degrees and rip the blank to final width.
4. Crosscut all pieces to final length.
Drill Holes for the Tilting Mechanism
1. Test drill a hole for a 1/4-20 coupling nut. The coupling nut should fit tight in the hole, so it can’t spin. Make this hole 1/64-in. smaller than the maximum outside diameter of the coupling nut, measuring across its points.
2. Set up a fence and stop block to drill a hole through the moveable support (C2) with this bit (Fig. H, below). Drill a smaller hole in the same place through the fixed support (C1) for a piece of threaded rod.
3. Cut the blank for the micro-adjust crank (C4) to final square size and drill holes for two coupling nuts and a threaded rod (Fig. J, below). Cut the crank into a rough circle and sand it round, as you did with the disks.
4. Drill holes through the base (C3) and pilot holes into the fixed support for the screws that hold the two pieces together (Fig. G, below).
5. Cut a shallow kerf in the bottom of the movable support for a pointer (C5) (Fig. H). Cut the pointer, glue it in place and file a bevel on its end. Radius the top edge of the support with a file or sandpaper.
Install Good Hinges on the Tool Rest
The lower half of the jig is ready to assemble, but first you must dado two parts to receive two high-quality hinges (see Sources, below). Typical door hinges don’t work, because there’s too much slop between the pin and the hinge. That slop will cause the jig to shake while sharpening.
1. Cut dadoes in the bevel angle table (B3) and the fixed support block (C1) (Figs. E and H).
2. Place the hinges in the dadoes and drill 3/4-in.-deep pilot holes for the screws (Photo 10).
3. Drill holes in the bevel-angle table (B3) for the adjustment screws and T-nuts. Install the T-nuts.
4. Screw the hinges in place to connect the support block and bevel-angle table. (You may have to file a bit off the end of the screws first so they don’t protrude through the bevel-angle table.)
5. Screw and glue this assembly to the base (C3).
6. Glue the two guide blocks (B1) to the bevel-squaring table (B2) (Photo 11). Rip the assembly to final width.
7. Drill holes for rare earth magnet cups in the guide blocks (Fig. E, below). Install the cups and magnets. Drill a large hole in the table for the adjustment bolt to pass through and a small hole between the guides for a pivoting bolt.
8. Assemble the entire base (Fig. A, below). Epoxy the coupling nuts in their holes. Paint or lacquer the whole jig so it’s easier to keep clean.
Drill and Tap Holes for the Tool Holder
1. Clamp a machine bolt (D3) in a vise and saw off its head. Then file a notch in one end with a sharp, flat ***-cut mill file (Fig. F, Detail 3, page 73).
2. Make a V-block to support the bolt. This is simply a 12 in. or so square of MDF with a long V-shaped notch cut down the middle, about 3/8-in. deep.
3. Mark the center of the flat area you filed on the bolt with a center punch and drill (Photo 12). Cut threads in the hole. (See Q&A, page 14, for tips on tapping holes.)
4. Drill and tap holes down the middle of a short piece of flat bar stock (Fig. F, Detail 2).
5. Fasten the bar to the notched bolt with a small screw. Cut off the excess length of the screw and smooth the end with a file.
6. Cut a piece of T-slot extrusion to length (see Cutting List, page 74). Smooth the ends with a file. Drill and countersink a hole near one end (Fig. F, Detail 4). The T-slot extrusion is too narrow to use a standard countersink bit, so use a 5/16-in. twist bit instead.
7. Make the handle (D1) and clamping block (D2) from wood that doesn’t easily split and has hard end grain. Maple is ideal. These two pieces are pretty short, so cut foot-long blanks to make machining easier and safer.
8. Cut a groove in the handle blank (Fig. F, Detail 4). Cut the handle to length, and round over the edges and corners to make it more comfortable to grip. Fasten it to the T-slot extrusion.
9. Cut rabbets on the edge of the clamping block blank with a dado set (Fig. F, Detail 1). Then rip the blank so the offcut (the edge with the rabbets) is 3/8-in. wide and the thickness of the finished clamping block. Drill the screw hole and cut to length. Round both ends with a sanding drum in the drill press.
Calibrate the Jig
The last job to do before using your jig is to draw a scale on the base to indicate the sharpening angles (Fig. K). Use a drafting triangle to mark a baseline angle of 30-degrees (Photo 13), then copy and tape our scale in place or draw your own. Also, mark the gauge line on the jig’s base for setting your tools (Fig. A, below).
Photo 1: Laminate two pieces of MDF to make an oversize lapping-plate blank. Cut the blank to final size after the glue is dry.
Photo 2: Flatten each lapping plate by rubbing it on two sheets of 120-grit sandpaper glued to a tablesaw with a spray adhesive. When pencil lines drawn on the face of the plate disappear, the plate is flat. Spray each plate with lacquer to seal it.
Photo 3: Mount a half sheet of sandpaper onto the lapping plate with spray adhesive. Put a different grit on the other side of the plate.
Photo 4: Cut dadoes in a set of square blanks to begin making the twist-and-lock mechanism of the abrasive disks.
Caution: You must remove the guard on your saw for this cut. Push down on the blank with a hold-down block to keep your fingers out of harm’s way.
Photo 5: Glue short stop blocks into both ends of the dadoes. Make sure the end of each block is flush with the side of the blank. Put pressure directly on each stop block with a small clamping block.
Photo 6: Drill a hole with a Forstner bit in the center of the abrasive disk and driver blanks. Then saw the blank into a rough circle. (The center hole will help you sand the disk perfectly round.)
Photo 7: Round each disk on the drill press with a sanding drum. Rotate the disk on a sanding jig (see Fig. D, below) to turn it into a perfect circle.
Photo 8: Glue a shaft into the driver disk with epoxy. (The shaft is simply a hardware-store bolt with its head and threads cut off.) Lower the shaft into the disk, then lock the chuck in place so it stays put while the glue dries. This ensures that the shaft is absolutely perpendicular in the driver.
Photo 9: Screw special magnet washers to the abrasive disks and cups for securing the rare earth magnets to the driver disk.
Also, epoxy metal bars to the driver disk. They’re simply square key stock from the hardware store. Now all the disks are ready to go.
Photo 10: Drill pilot holes for two hinges to begin making the base of the sharpening jig. Use a self-centering bit in the drill press to make perfectly aligned holes.
The base is hinged so you can adjust sharpening angles. Two hinges side-by-side are more rigid than a single hinge.
Photo 11: Clamp every which way when you make the part of the jig that receives the removable tool holder. The T-slot extrusion must fit snugly in the jig’s guide slot, and the best way to ensure a tight fit is to use the T-slot extrusion itself as a spacer.
Photo 12: Drill through a hardware-store bolt to make the clamping mechanism for the tool holder. The bolt has its head cut off and a notch filed on the unthreaded portion. The V-shaped cutout in the support block keeps the bolt from rolling while you drill.
Photo 13: Calibrate the angle setting of your jig with a standard 30-60-90 drafting triangle. Turn the crank handle until the jig’s tilting table lines up with the top edge of the triangle. Make a mark opposite the pointer, and label it “30 degrees.” Then line up our scale (Fig. K, page 74) with this mark and transfer the remaining angle settings to the base of your jig.