Wood Marking Gauge

Marking gauges are used in woodworking because they let you lay out precise markings for mortise and tenon, lap, and dovetail joints. The following instructable describes how to make a marking gauge with a round blade. For this project you will need:

Materials:

1. Hardwood (2" x 2" x 1")
2. Round Brass Stock (5/16" x 12")
3. Round Steel Stock (5/16" x 4")
4. Wood Brass Insert (Hillman 1/4"-20)
5. Plastic Knob (1/4"-20 x 3/4")
6. Oil Hardening Steel (1/16" x 1" x 1")
7. Threaded Brass Rod (#6-32 x 1 1/2")
8. Pan Head Screw (#4-40 x 3/4")
9. Flat Head Screw (#4-40 x 3/4")

Consumables:

1. Masking Tape
2. Sandpaper
3. Scrap Wood
4. Vegetable Oil
5. Shellac
6. Paste Wax
7. Plastic Pipette
8. Thin Leather
9. Green (Chromium Oxide) Buffing Compound
10. Popsicle Stick

Tools:

1. Hand Saw
2. Hand Plane
3. Double Square
4. Bevel Gauge
5. Brad-Point Drill Bits
6. Twist Drill Bits
7. Hollow Punches
8. Drill Press
9. Cordless Drill
10. Hacksaw
11. Metal Files
12. Vise Grips
13. Tap (#6-32)
14. Tungsten Carbide Scriber
15. Tap (#4-40)
16. Countersink (82°)
17. Propane Torch
18. Matches or Lighter
19. Pencil
20. Fine-tip Sharpie Marker
21. Sharpening Stone
22. Utility Knife

The body of the gauge is made of a hardwood block which starts out as square stock with dimensions 2" x 2" x 1". The first step in forming the body is to mark and remove the corners. To do this:

1. Place a tape line 1/2" from all side edges of the block.
2. On face-side and back-side, connect the ends of the 1/2" tape lines to form triangles at each corner.
3. Saw off the edges without damaging the tape.

It turns out that hand sawing wood perfectly straight is really hard to do right, so in the previous step, the corners were rough-cut. A hand plane is used to finish the corners. Do this by:

1. Clamp wood into a wood vise. Protect the clamped corners using leather, cloth, or rubber pads.
2. Plane with the grain. If your plane blade is sharp, it should not bind or skip, otherwise check that you're planing with the grain. Rubbing candle wax on the plane's sole also helps.
3. The process is complete when the corners are flush with (or slightly above) the corner tape lines.

The shaft of the marking gauge is a long (12") brass rod which holds the blade. This shaft needs to slide through the body and is formed by:

1. Mark 4 lines near the center of gauge using a double-square and pencil.
2. Drill through the center with a 5/16" brad-point bit and drill press.

You can use conventional (twist) drill bits for this project, but twist-bit will tend to wander off your target mark. This can be rectified by using a center-punch and drilling a pilot hole, but if you ever have the opportunity to use brad-point bits instead, please do since they tend to be more accurate in staying on target.

The side hole houses the retention mechanism, which is used to hold the shaft in a fixed position. To make the side hole:

1. Use masking tape, a pencil, and combination square to mark the hole's center.
2. Make the hole using a drill press and a 5/16" brad-point drill bit.
3. The drill bit should only extend to the center of the wood.

A 1/4"-20 threaded insert has an outside diameter much wider than the 5/16" side hole that was drilled in the previous step. Fortunately, with the other threads removed, it ends up being exactly 5/16" in diameter. Doing this allows the insert to be slid into the hole, rather than having to be screwed in. To form this slide-in insert:

1. Insert a 1/4"-20 threaded rod into a cordless drill.
2. Use masking tape at the base of the threaded rod as a screw-stop.
3. Screw the 1/4"-20 threaded insert onto the threaded rod.
4. File the outsider threads of the insert off using a flat file as you rotate with the cordless drill.
5. Finish by polishing the insert with buffing compound applied to a piece of kraft paper.

I would recommend against screwing the insert directly into the hole because can easily split the wood, ruining the entire project. In addition, it makes disassembly and repair of the gauge more difficult.

Kraft paper is the inexpensive "brown bag" paper used in lunch bags, grocery bags, toilet paper roles, cereal boxes, etc. It's preferred over regular paper because its rough surface absorbs the buffing compound better than regular paper.

The de-threaded insert needs to be held in place from both the face-side and back-side using #6-32 screws. To do this, form holes on both sides that would meet in the middle of the insert if it is flush with the corner of the side hole. To do this:

1. Drill a hole with a diameter slightly smaller than a #6-32 tap.
2. Tap the hole using a #6-32 tap and use candle-wax as a lubricant.
3. Make sure this is done on both the face-side and the back-side.

Please ignore the large 1/4"-20 threaded hole in the first picture, it was made unintentionally.

The retaining screws are used to hold the insert in place after it is slid into place within the side hole. To form the retaining screws:

1. Take a #6-32 threaded rod and cover one end with tape to protect the threads.
2. Insert the protected end into a cordless drill.
3. Form a tip by spinning the drill and touching the tip of the rod to a powered bench grinder.
4. Before inserting the #6-32 threaded rod into a cordless drill, cover it with tape to prevent damaging threads.
5. Repeat the process for the other end of the rod.
6. Saw the rod in half.
7. Drill a 1/8" hole in scrap wood to hold the screws for the next step. They should pop right in.
8. Form a slot for screwing using a hacksaw.
9. Form a flat-head using a metal file.

In order for the retaining screws to hold the de-threaded insert in place, groves for the screw-tips are formed by:

1. Slide the insert into the side hole until it is flush with the corner.
2. Tighten the retaining screws on both the face-side and the back-side.
3. Loosen the retaining screws and remove the insert.
4. Observe the indentations formed by the screw tips.
5. File the indentations using a triangle file forming V-grooves.

Please ignore the large 1/4"-20 threaded hole in the first picture, it was made unintentionally.

A short 5/16" slider is placed into the side-hole before the de-threaded insert is locked into position. The slider distributes the clamping force evenly onto the shaft so that it does not get damaged while tightening the gauge's knob. The slider jig is used to form the contact-surface of the slider so that it conforms to the shaft's cylindrical surface. To form the jig:

1. Drill a 5/16" hole through a long piece of scrap wood.
2. Drill a 5/16" hole perpendicular to the first hole.
3. Saw the second hole in half.

Use the slider jig to form the slider contact area:

1. Clamp the jig into a wood vise.
2. Place the 5/16" brass rod (shaft stock) into the long end of the jig.
3. Create a notch in the center of the rod using a hacksaw.
4. Roughly match the jig's contours using a coarse round file.
5. Finely match the jig's contours using a smaller fine round file.
6. Use a piece of fine (#400) sandpaper around a 5/16" rod to exactly match the jig's contours.

Finish the slider so that it is less than 1/2" long and has a rounded end for contacting the gauge's knob-screw.

1. Hacksaw the slider off of the 5/16" x 12" brass (shaft stock) rod.
2. Wrap the contoured end of in tape and insert into a cordless drill.
3. Round the sawed end of the slider by spinning the drill against a powered bench grinder.

Having metal to metal contact between the shaft and the slider is terrible because it does not have enough friction to hold the shaft in place and because it can scratch the shaft. To avoid this, a piece of leather is glued to the slider's contoured surface.

1. Hollow punch a 5/16" circle in a piece of leather.
2. Apply contact cement to the slider's contoured surface.
3. Apply contact cement to the leather circle.
4. Allow 5 minutes of drying time.
5. Attach the leather to the slider.

You can substitute the leather with cork or paper gasket material. Rubber has too much grip and would make it difficult to position the shaft precisely.

One end of the shaft is flat and used for holding the blade. The other end is rounded so that it has no sharp and dangerous points. In this step, round the other end of the shaft:

1. Protect one end of the 5/16" x 12" brass rod (shaft stock) using tape.
2. Insert the brass rod (shaft stock) into a cordless drill.
3. Round the other end by spinning the drill while touching it to a powered bench grinder.

In future steps, a blade holder will be made out of the 5/16" steel rod (holder stock). In this step, the ends of both the steel rod (holder stock) and the brass rod (shaft stock) are flattened since there's no guarantee that the ends are square by default. Repeat this process for both rods:

1. Drill a 5/16" hole into a scrap piece of wood using a drill press.
2. Slide the flat end of the rod into the hole so that it touches the bottom.
3. Place onto a sharpening stone or sandpaper on a flat surface.
4. Flatten by moving in a figure-8 pattern.
5. Apply a more pressure to the rod instead of the scrap to keep it in contact with the sharpening stone.
6. Polish by repeating steps 5 to 7 using a kraft paper and buffing compound on a flat surface.

Examples of flat surfaces: a cast iron reference, granite slab, window glass, or medium-density fiberboard (MDF).

Both the brass rod (blade stock) and the steel rod (holder stock) need a hole through the center for a #4-40 tap. The holes is created using a cordless drill and treating it as a miniature lathe:

1. Drill a 5/16" holes into scrap wood.
2. Clamp scrap wood using a bench vise.
3. Protect the unfinished end of the rod with tape.
4. Insert the protected end of the rod into a cordless drill.
5. Insert the flat end of the rod through the 5/16" hole so that it faces up.
6. Spin the drill so that the rod rotates.
7. Mark the center of the rod with a tungsten carbide scriber as the rod spins. The scriber is stationary.
8. Drill the marked center with a twist-drill slightly narrower than a #4-40 tap as the rod spins. The twist-drill is stationary and is held using vise-grips.

#4-40 taps are notoriously easy to snap in half while attempting to tap holes. To reduce the chances of this happening, a tapping jig is used. One end of the jig accepts a 5/16" rod. The end is as wide as the tap. To make this jig use a drill press and:

1. Drill a hole through scrap wood slightly wider than the #4-40 tap's diameter. This is the maximum width of the tap, not just the width of the threads on tap.
2. Enlarge the hole up to 5/16" using a step-bit.
3. Deepen the hole with a 5/16" twist-bit so that it stops just where the tap's threads end.

When tapping threads, it's essential to clean the hole out. Unfortunately a #4-40 hole is so small that it's hard to put anything into the hole to clean it out. A conventional pipette is just too big. Fortunately, the pipette can be heated and drawn so that it narrows enough to fit into a #4-40 hole. To do this:

1. Obtain a clear plastic pipette made of low-density polyethylene (LDPE).
2. Heat the pipette just above the tip with a match or lighter flame until it goes from translucent to clear.
3. Pull on the tip of the pipette which elongates and narrows the nozzle.
4. Let the pipette cool.
5. Cut nozzle to length.

The brass rod (shaft stock) and steel rod (holder stock) already have center-holes. In this step, the rods get threaded with a #4-40 tap. Be very delicate and clean out the hole and tap frequently:

1. Clamp the rod into a bench vise, using leather, cloth, or rubber to protect the rod from damage.
2. Place the tapping jig over the rod with the center hole facing up.
3. Lubricate the tap with tapping fluid and insert it into the jig.
4. Use the twist-bit which made the center hole to clear out metal debris.
5. Use acetone and the pipette to clean out metal debris.
6. Repeatedly turn the tap 1/4-turn clockwise and 1/2-turn counter-clockwise.
7. Repeat step 6 for 2-3 threads at a time.
8. Repeat steps 3 to 6 until the hole is tapped.
9. For the brass rod (shaft stock) provide a slight countersink by manually turning the countersink into the threaded hole.

The brass rod (shaft stock) is almost finished. The last step is to polish it with the help of a cordless drill:

1. Tape the rounded end to protect it from the drill chuck.
2. Insert the protected end into a cordless drill.
3. Spin the drill.
4. Hold kraft paper and buffing compound against the shaft's threaded flat.
5. Hold kraft paper and buffing compound against the shaft.
6. Remove excess buffing compound with a cloth.
7. Repeat the process for the rounded end.

Only one blade blank is needed and can be made out of 1/16" x 1/2" x 1/2" unhardened (annealed) oil hardening (O-1) tool steel. For multiple cut depths or different angles, more than one blade blank can be made. The process for making blade blanks is:

1. Segment 1/16" tool stock into 1/2" x 1/2" squares with a fine tip sharpie.
2. Mark the segment centers using a tungsten carbide scriber.
3. Pilot drill the segments with a drill bit slightly wider than the threads of a #4-40 screw.
4. Countersink the segments until a flat #4-40 machine screw is flush with the 1/16" surface.
5. Cut the segments using a hacksaw.

The steel rod (holder stock) is used to form the blade holder, which is used with an angle cutting jig in a future step to form the blade. In this step, the steel rod is beveled to complement the blade blank's countersinking:

1. Copy the countersink's angle using a bevel gauge.
2. Protect the non-threaded end of the steel rod with tape.
3. Insert the protected end of the steel rod into a cordless drill.
4. Spin the cordless drill against a powered bench grinder.
5. Compare and continue grinding until the rod's angle matches the bevel gauge.
6. Finish the bevel with sandpaper and kraft paper / buffing compound.

The blade jig is used to turn a blade blank into a round cutter. A formula-card and Excel spreadsheet are provided to help in calculating the jig properties. The jig's angle gets transferred to the blade. The distance between the jig's hole and the angle determines the cutting depth. To form the jig:

1. Use the formula-card and spreadsheet as needed.
2. Saw desired blade angle into scrap hardwood.
3. Smooth the sawed area with sandpaper or a hand plane.
4. Drill near the edge of angle for appropriate blade cutting depth.

I recommend using a 30° to 45° angle for the blade. If the angle is too small, it leaves insufficient diameter for the screw to hold the blade to the holder. If the angle is too large, the blade will be too dull. Generally, a wide angle is durable but does not penetrate deeply, whereas a small angle cuts deep and is more fragile.

The blank is rounded and sanded into its final shape with the help of the blade jig. To use it:

1. Use a #4-40 pan-head screw to secure the blade blank onto the blade holder.
2. Insert the assembly into the blade jig.
3. Clamp everything in a vise, with the jig's angle horizontal.
4. Rotate the blade holder while filing with a coarse flat metal file.
5. If corners become thin and flexible, remove the blank and sand on a flat surface until corners fall off.
6. Finish rounding by continuously filing with a fine flat metal file while rotating the blade holder.
7. Remove the blade holder from the jig.
8. Cover the blade holder's end with tape.
9. Insert blade holder into a cordless drill.
10. Finish shaping by spinning the blade holder while pressing the blade's bevel against fine (#400) sandpaper.

The final step in turning the blade blank into a finished blade is heat treating and polishing. To do this:

1. Hang the blade using steel or nichrome wire.
2. Heat the blade using a propane torch until it is bright orange.
3. Quickly quench the glowing blade into low viscosity oil.
4. After quenching, running a file over the blade should feel like glass.
5. Temper the blade in a toast oven for 1 hour at 400° F.
6. Secure the blade to the blade holder.
7. Cover the blade holder's end with tape to protect it from the drill chuck.
8. Insert the blade hold into a cordless drill.
9. Spin the drill with the blade's bevel pressing against fine (#400) sandpaper.
10. Spin the drill with the blade's bevel pressing against buffing compound on a popsicle stick.
11. Polish the blade's flat face and flat back on a flat surface with buffing compound on paper.

By testing with step 4, I found out that using a high viscosity oil (laxative mineral oil) didn't quench correctly. I switch to a low viscosity vegetable oil (peanut oil) and quenching worked as expected. I used plain paper because it was thinner than kraft paper to preserve the flatness of the blade face.

It's been assumed throughout the instructable that your dill press table has been squared correctly. If this isn't the case, you can make a scaper which mounts onto the 5/16" brass rod (shaft stock) to make the marking gauge's face-side and back-side perfectly level and perpendicular to the shaft. To do this:

1. Use a piece of scrap wood (1/2" x 3/4" x 2 1/2").
2. Draw a line down the center of the wood with a pencil.
3. Drill through one end of the scrap with a 5/16" drill bit.
4. Cut along the line with a utility knife.
5. Cut down the line with a flush-cut saw.
6. Drill a side hole and enlarge one side of the jig so that a wood screw can be used to clamp a blade between both halves of the jig.

The process for using the jig is:

1. Insert a wood screw into the side hole of the jig.
2. Slide the jig over the brass rod (shaft stock).
3. Insert a utility knife blade into the slot.
4. Square the knife edge to the shaft using a double square.
5. Tighten the wood screw to keep the blade in place.
6. Insert the brass rod (shaft stock) into the center hole of the the marking gauge.
7. Rotate the jig by hand with the blade touching the face-side or back-side of the marking gauge.

Apply a finish to the jig. I used shellac and paste wax, though any finish should work:

1. Apply up to 3 coats of shellac.
2. Sand with fine (220+) grit sandpaper between coats.
3. Apply a single coat of paste wax.
4. Buff out the paste wax when dry.

That's it! Now you know how to make a round bladed marking gauge.