There are 2 types of people in this world; those who have used a pencil to mark a cut line on a piece of wood and dirty liars. Now, a pencil is an excellent tool, and one of the most used in a woodshop, its hard to beat the convenience for marking a cut line. For some tasks though, like laying out dovetails or other precision joinery, a pencil mark doesn't, ermm, cut it. I'm so sorry, i tried to find a better pun... Anyway, the line is too thick, and its hard to get a pencil butted right up against a straight edge to put the line right where it needs to be. What to do?
The traditional solution to this conundrum is a special tool called a marking knife. Made with a sharp point and a chisel-ground blade, this knife is meant to sit flush with a straightedge and reach into tight corners, and leave an extremely fine line where you want the cut to go by actually cutting the top few fibers of the wood. The resulting cut is finer than even the finest pencil line, is located right where you want it, provides an excellent groove to start a chisel or saw in, cant be erased or smudged, and the fine point of the knife can reach into right corners better than any pencil.
Really, a marking knife is a brilliant tool for just about any carpenter to have. Sound interesting? WHo am i kidding, of course it does! Lets make one, shall we?
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Step 1: Step 1 - Gathering Materials
This is an extremely simple project, from start to finish you need a hacksaw, a file and a drill. No complicated tools or materials needed, although to be fair the complicated tools do make the process easier. Im going to list the essentials first, then the non-essential but handy items
1. Steel - No, the cold-rolled from your local home improvement store wont work. What you want here is a good, high carbon steel. If you've never made a knife before, i recommend O1 steel, its easy to work with and heat treat. Youll need a piece 1/8" thick, 3/4" wide and 6" long. A place like Grainger will have this if you need a source.
2. Handle material - You could use nearly any type of wood, micarta, G10, metal, whatever you want really. Whatever you use, you need 2 matching pieces of it, 1/4" thick, 3/4" wide and at least 4" long, though i recommend starting with an oversize piece. Ill be using a some stabilized Walnut
3. Pin material - you'll need a piece of round stock 1/8" in diameter. This can be brass, stainless steel, copper, whatever really. You'll need about 6 inches worth. I'll be using brass here
2. File - You'll need this for shaping the blade and putting in the bevel, as well as shaping the handle.. A good 10" bastard cut mill file is again an excellent investment, for the whopping price of $10
3. Blow torch - You'll need this for heat treating the blade, provided you choose to heat treat it yourself. Also usable are a fire with an air blower for the low tech, a gas forge if you have one, or what ill be using, an electric kiln. You can also send out your blade for heat treatment
4. Sandpaper - For smoothing and polishing the blade, as well as the handle
5. Drill with 1/8 bit - For putting the holes for the pin in the blade and scale materials
6. Sharpie - Layout work
Thats all you need, though one of those things isn't strictly needed. Now, a few tools that aren't necessary but do make the process easier:
1. 2x72 Belt grinder - Used for shaping the blade and grinding the bevels, as well as shaping the handle. Not needed, but awesome to have. A hand-held belt sander could also be used, its just slower
2. Portable bandsaw - Ill be using this to rough cut the blade, it's faster and involves less work than a hacksaw
3. Drill press - Makes drilling holes in metal so, so much easier. Seriously, get one, even if you cant find a sweet 1950's floor press to restore.
4. Layout fluid with a carbide scribe - I use Dyechem, makes better lines than a sharpie and won't wash off
5. Digital calipers - Again, helps with layout work. I recommend getting a set, they're dirt cheap and are useful for everything. I use this Wixey set, as they display fractions as well as decimal inches.
Alrighty, got the essential materials and tools? No? Dude, what are you waiting for, we've got to get to the next step!
Step 2: Step 2 - Layout, Rough Cutting, and Shaping
Alrighty, time to start making stuff! First, take your bad of steel and cut off a piece 6" long. Go ahead, I'll wait.
Got it? Okay, time to lay out the point. I've found about a 35 degree point to give a sufficiently pointy edge. No protractor? Geez, you just aren't prepared at all, are you? 'S okay, neither am I. Make a mark 1 3/4 back from one of the corners on your piece of steel, then draw a straight line from that mark to the opposite corner. That'll give you roughly the right angle, its close enough for this application. No, go ahead and use your hacksaw to cut off most of the waste, then use your file to bring it right up to the line. Take your time, you can take more off but you cant put it back. Consult the pictures to get an idea of the shape, if you don't already have one.
Now you've got the rough profile of the blade down, so lets put in some bevels. Since the angled edge, the one you just cut, is going to be the cutting edge, we'll be putting the bevel there. The angle were shooting for here is about 25 degrees. To approximate that, draw a line parallel to that angled edge just a hair over 1/4 of an inch away. Once you've got that line draw, go ahead and use your file to remove the metal between that line and the edge, but don't go all the way down. Leave about the thickness of a dime on the edge. make sure to keep the bevel nice and flat, with a consistent angle all the way across. It sounds a lot harder than it is, just take it slow and work to the lines. A word to the wise, the side of the blade you put the bevel on does matter. The knife shown is a right-hand bevel, meaning that when held the flat side of the blade will be on the left, and the bevel will be on the right. South paws should put the bevel on the other side
Now, i used my belt grinder for this, so it took me about a minute and a half, taking my time. With a file, this shouldn't take more than 15 minutes. If you have one, a belt sander with a 60 grit belt will put in a decent bevel in less time, but I'm keeping my instructions simple. At any rate, once the bevels have been roughed in, meet me at the next step!
Step 3: Step 3 - Pop Some Holes in It
Here's the easy step, drilling some holes for the pins that hold on the handle. First, youll want to draw a line down the center. I coated mine in layout fluid, then used my calipers to scribe a line dead center, but a ruler and a steady hand with a sharpie works too. Now, on that center line, make a mark half an inch from the back of the blade (the side opposite the cutting edge), then make a mark an inch and a half from the first one, then another mark an inch and a half from that. Check the pictures if that didn't make sense, it barely made sense to type it...
Anyway, once you've got those marks laid out, drill a 1/8" hole through each. A drill press works best, but a handhel drill works fine too. Heck, use a brace and bit if you want, itll give the same results, it just takes longer.
PRO TIP: Use a center punch to make a divot at each hole location to prevent the bit walking off position!
Step 4: Step 4 - Heat Treatment
This is the step that takes this from a lump of steel to being an actual knife. Forewarning though, this step involves extremely high heat and flammable substances. If you don't have the facilities to safely proceed, lack the necessary equipment or this just makes you nervous, don't do it. Instead, you can send out your knife to a commercial heat treatment service. Tru Grit is a delight to work with, just download the packing slip, write down the steel type (O1) and desired hardness (61HRC) and ship it out, then join us at the next step.
Those of you still around, here's the general order of operations:
1. Heat the blade really bloody hot
2. Quench (cool rapidly)
3. Temper (heat again, just not as hot)
Pretty simple process really. O1 is extremely easy to heat treat, use a blowtorch to heat the cutting edge to about 1500f, which will make the steel glow cherry reddish in a dim room, and keep it there for about a minute. After that minute is up, dunk the blade in some warm oil, canola or peanut oil both work well. Hot tip, hold the blade in a set of pliers instead of by hand to avoid an ER visit!
Now, after quenching, the steel is extremely hard, harder than glass and just as brittle. It will shatter like glass if you drop it, so don't bloody drop it! Instead, wash off the oil and pop the blade into an oven preheated to 450f and let it bake for an hour. Take it out, let it cool, then send it back in for another hour. Do this one more time. This is called tempering, and doing this will soften the steel and toughen it up, so you'll actually be able to use your knife without cracking it. Once you're done tempering, proceed to the next step!
A quick note, heat treating steel is an extremely complex process, and this is the bare minimum of information needed. it should also be noted that every grade of steel has a different process, so if you happen to be using anything other than O1, these instructions may not produce the best results. If in doubt, consult the data sheets for your grade of steel, O1's can be found here.
Step 5: Step 5 - Polish and Sharpen
Alrighty, now that you've got your heat-treated blade, time to finish up the metal part of things. First things first, you need to flatten the back (the side opposite the bevel), so it sits nice against a straight-edge and makes a sharp edge. To do this, stick a piece of sandpaper on a flat surface (table saw top, kitchen counter, granite surface plate, piece of mdf), mark all over the blade with a sharpie and scrub it on the sandpaper until the sharpie disappears. Repeat with higher grits of sandpaper, up until you hit about 800 grit. Flip the flade over, repeat with the top side to make it look nice.
Nows also the time to fully finish the bevel. Use your file to bring it down almost to a sharp edge, then go back to the sandpaper to sharpen it. If you've ever sharpened a chisel, its the same process. The key things here are to keep both the back of the blade and the bevel as flat as you can, and to polish both those surface as high as you can, so make for the best edge. Its a lot easier to do these steps before you get the handle on, so get it right now and make your life easier later!
Step 6: Step 6 - Making the Handle
Alrighty, now that the blades cleaned up, time to attach the handle scales! First, lets drill the pin holes in the handle material, which is hopefully oversize. First, stack the 2 piece of handle material on top of each other, then center the knife on the scales. Drill one hole, then insert a piece of your rod stock (cut down to a 3/4" long pin) through that hole. Drill a second hole, then stick in another pin in that hole. Doing this will allow you drill the third and final hole in exactly the right spot, so everything lines up right.
Once you've got all the holes drilled with the pins maintain alignment, trace around the knife, then cut off the excess material. The front of the scales should be cut square 1/2 forward of the pin hole closes to it, to match the spacing of the rear of the knife. Once you have the front cut, you need to do some shaping. Round over the front, bevel it, do whatever yous like, then sand down the front. You need to do this now, once the scales are attached you wont have access to the front of the scales. Now that the front of the scales are finished, time to glue them on.
Degrease the knife and the inside of the scales with some acetone or denatured alcohol, then mix up some 2 part epoxy. Apply the epoxy to the inside of the scales, then insert the pins. Use the pins to line up the scales properly on the blade, then clamp up the whole assembly and let the glue cure. be sure that you've got a little less than 1/8" of the pins sticking out on both sides of the knife. Once you've got the clamps on, be sure to clean any glue from the front of the scales before it dries, otherwise you'll scratch the blade trying to remove it
Once the epoxy is set, use a ball peen hammer to peen over the pins, then shape the handle to fit. I cant really tell you how to do this, just use files and sandpaper to shape the grip to be comfortable to hold. Once you've got the handle shaped and sanded, apply an appropriate finish. Again, cant tell you what to use for that without knowing what handle material your using
Step 7: Step 7 - Use It!
Taadaa, you're all finished up after sanding. In my case, i sanded the scales up to 400 grit, then buffed with some white rouge. Since the wood has been stabilized, it takes a lovely polish and doesn't require a finish.
Hopefully this has inspired to you get to work making your own marking knife, its an extremely hand tool and a fun project. This style blade is also handy for loads of other tasks, its an excellent general-purpose utility knife. Ive use mine for everthing from leather work to paper-craft, in addition to layout work.
Like the style knife, but not up to making your own? Check out the listing for them at my Etsy shop, where i sell both the completed blades, as well as just the knife portion if you feel like making your own handle