Make A Marking Knife

Introduction

After posting to the oldtools list about a simple marking knife I'd made, I got several requests for more details. At least one person wanted to duplicate the knife. Due to this interest, I thought I'd put a few notes and sketches here. Since I don't have a scanner (yet, at least), there are no photographs, at least for now. Since I didn't use any plans to make the knife, there are no detailed dimensioned plans available. They shouldn't really be needed...

I made the blade from an old hacksaw blade. This gives about the same thickness as an X-Acto knife blade. It's a bit flexible, and leaves a very fine mark. I like this sometimes, other times (such as laying out the shoulder of a tenon), I'd rather leave a fatter mark. I think I'll make another marking knife with a fatter blade made from and old plane iron, or maybe a file. I'll keep both marking knives around, of course. I've also considered making sort of a scalpel, a non-disposable knife for use when an X-Acto knife would otherwise be used.

Making the blade.

Take an old hacksaw blade and score it with a file a bit inboard of one of the holes at either end. Try to get the mark square, but don't sweat it too much, that's what files and grinders are for.

Using either a machinist's vise, and/or a pair of gas pliers, snap the blade at the mark. It usually works quite well. The materials are free, so no worry at all.

Then measure off the length of the blade. This is a bit longer than you'd expect, as much of it is in the handle. I'd say mine has a bit less than an inch of exposed blade, and about 1 1/2 inches of blade in the handle. The entire knife is roughly five inched from blade tip to handle tail.

Score the blade and snap it in the same manner that you used previously.

Now grind the saw teeth off of the section that you have left. I used a hand-cranked grinding wheel with a modern carborundum wheel. The blade was hard enough that I got to square up the wheel and remove a groove that the previous owner had made.

Make sure to remove all of the old teeth, including the set, which on my blade extended further into the blade than a casual inspection had led me to believe.

Now square up the ends of the blade, in a similar manner. Don't really worry too much about the end that will become a point, of course.

Now it's time to mark off the shape of the blade. I made both sides curved, so when I ground the bevel on one side, I'd have a knife that would work either right or left handed.

Start by marking the center of the blade where the tip will be. Use a small scale and a scribe. Then, using a try-square and a scribe, mark each side of the blade about 3/4 inch down from the tip.

After making these three marks, connect them with two arcs. I used the bottom of a small paint can as a template.

Now it's time to grind the blade to shape. Since this metal is fairly hard, you might want to snap the blade off closer to the line before you start. Just scribe and snap, as usual.

After grinding it to shape, put a rough bevel on one side and flatten each side on a stone.

I started the bevel with the hand operated grinding wheel. It's much nicer than the electric one for this sort of work, since you can easily turn it at any reasonable speed, or direction. Much less likely to remove too much metal. Or the temper...

Then I followed up with a perhaps 600 grit waterstone, both on the bevel and to flatten it. This is where you'll be happy that you removed all of the metal that was set with the teeth.

I followed this up with a 1200 grit waterstone, which is where I left it until final sharpening.

Scary Sharp methods could be used as well, of course, and they work quite well.

Alternate blade shapes.

My old marking knife had (has) a blade shaped something like this:

Naturally, I tried something different when I made the new knife, why not experiment? Overall, I'm pleased, but under some circumstances, the old knife blade has better control. Most of the time, I like the new, curved blade more.

A few days ago, I was looking through a tool catalog, which offered a double-ended marking knife. One end was like my new one, one end was a modification of my old one! They made pretty much the same comments about each shape having some advantages...

I think I'll make another one with this new profile some day. Maybe along with my experiments with a thicker blade.

Making the Handle

I made my handle from a scrap of chestnut sitting around from another project. I finished with a pretty fair number of treatments with linseed oil/turpentine/beeswax.

Start by cutting out a chunk of your favorite wood and squaring it up. Make it sort of knife-handle sized...

Now make a kerf for the blade to fit into. I have a little turned handle dovetail saw that leaves a kerf that's just the right size for this.

You can use a marking gauge to make the line where you'll be sawing.

Now layout the shape of the handle as viewed from a blade flat. On the tighter radiuses by the blade, I eyeballed it, on the tail, I used a can again, this time, a larger one.

After marking, use the woodworking tools of your choice to shape the handle. I used a chisel and a small block plane clamped upside down in a vise. If this part were bigger I'd have been thinking drawknife/spokeshave, and really it's not too small for them, IMHO. I suppose a rasp and files might work as well. Maybe a coping saw? Lots of ways to do things.

Now do the same thing in the other plane, and break the edges a bit. Actually, you may want to really round off those edges -your choice, of course.

Smooth the wood using any method you prefer. I'll confess to using sandpaper, despite using planes and hand-held scrapers a lot more these days.

Assembling the Blade to the Handle

Here's where all pretensions off Galootdom fall away. I had intended to use copper rivets to attach the handle, but as you'll notice, there are no holes in the blade. It's not that I forgot or anything, holes just didn't seem meant to be. I'll cover that later...

Rough up the area of the blade that will go into the kerf, being careful not to rough up the area that will be visible. I used some coarse sandpaper. this is to give the glue a place to "grip". Probably not necessary, but I felt better having done this.

Clean the blade with detergent, or a decent solvent. The superstitious may wish to use both. From here on in, only touch the part of the blade that will be exposed.

Mix up a small amount of epoxy. Spread a thin coat on the portion of the blade that will be in the kerf.

Slide the blade in, work it around a bit to ensure good glue coverage, and lightly clamp it.

A few minutes later (assuming 5 minute epoxy), remove the clamp and trim off any ejected epoxy with a sharp knife. After removing the excess, I waited until the next day to ensure good curing of the epoxy.

Finish the wood in any manner desired, as mentioned above, I used a linseed oil/turpentine/beeswax finish.

Sharpen the blade in your favorite manner. I did a bit more work with the 1200 grit water stone, then finished up on a leather strop charged with auto paint rubbing compound. OK, I'm a bottom feeder using up supplies from a previous project...

Now go use the knife!

My attempts to use rivets

Initially, I intended to attach the handle with two copper rivets. I still plan to do this on a later version, but it fell through this time.

After snapping off the first section of saw blade, I checked the hardness compared to a few other tools. Pretty hard, it was obvious that drilling through it with an ordinary twist drill would be out of the question.

So I got out the propane torch. If I had a welding torch, or a forge, I'd have used one or the other, but the propane torch is the hottest thing I have.

At first, it looked good. Due to the small size of the piece, it was easy to get it to a bright yellow state, after which I cooled it fairly slowly.

Sure enough, it seemed softer, but not as soft as I expected/hoped.

Still, I figured I'd give it a try. I set the piece on a chunk of soft steel and made some marks with a center punch. Bad sign, the punch needed to be sharpened when I was done making two marks...

Then I tried drilling it, using some light oil to lubricate and cool. Progress was almost non-existent, and then the piece of saw blade snapped into two pieces, under moderate pressure from the drill.

I tried again, this time making a point to let the blade cool even more slowly. Roughly the same result, except that the piece didn't snap.

At this point, I remembered watching a co-worker at a previous job grind a hole in a piece of plate glass on a drill press. He used a large diameter piece of copper wire and some grinding compound.

Why not? I tried this, using some valve lapping compound, but no joy. After fifteen minutes, all I had was a polished spot on the blade. It only took an hour to get through a piece of glass maybe four times as thick. I'll probably give some thought as to why this didn't work in the future, but at this point I decided to attach the blade in another manner.

I got a lot of good ideas on making holes from the oldtools list though.

My favorite is simply to use another source of metal, one that responds to heat differently. A worn out file seems the most likely source. I wanted to make a thicker blade anyway...

Another that I'm interested in involves center punching on a softer surface, then grinding the bump off the opposite side.

One that might work well, but which is probably beyond my abilities coordination-wise, would be to punch it while it's hot from the torch. That little piece of metal cools off too quickly for a klutz like myself to set it down on an anvil with a hole, in proper alignment, then pick up a punch and hammer, align the punch and strike. I figure that I'd have maybe 1.5 seconds to do this. Possible, but not for me...

There were two other good ideas, almost the same, suggested by two different people. They both involved spinning a steel rod against the blade at high speed, one idea was to anneal the metal in that area, the other was to actually use the friction and heat to make a hole. Quite intriguing.

I find myself feeling guilty for not giving credit to the people who suggested these ideas, but I wasn't planning to write this article when they were suggested, and I forgot to write down the info. If one of these ideas is yours, and you want credit, just let me know, and thanks!