Marking Knife From Saw Blade




Introduction: Marking Knife From Saw Blade

About: I'm not an expert in anything. I just enjoy making things sometimes for the process sometimes for the end product.

I got the idea to make this marking knife based on the shape of a fountain pen tip and the shape of the handle is based on an artist brush handle. I used an old saw blade for the blade portion and walnut with brass pins for the handle. This was one of those knife builds that I had to get out of my system I kept imaging it in my head and finally decided to make it. Marking knives are usually used to make fine marks on wood in order to get more accurate cuts they are also used in hand cut joinery like cutting dovetails or mortises.

Here is a video of my build:

Step 1:

The first thing I did was to cut a piece of steel from an old saw blade. The width was approximately 3/4 of inch wide and the length was roughly 7-8 inches, I say roughly because I didn't measure the length I was more concerned with the width of the blade.

Step 2:

I clamped the blade to my workbench and used my angle grinder fitted with a cut off wheel and cut out the rough shape of the blade.

Step 3:

I filed off the burrs left from the cutoff wheel and then used a template to draw the point on to one side of the blade. I wasn't going for extreme accuracy at this point I just wanted to make sure I was close to a 45 degree angled blade shape. I would fine tune the blade shape later. Using my angle grinder I cut out the shape of the blade.

Step 4:

Next I needed to make sure the blade spines were straight. So I chucked my blade in to my vise and using a straight edge I checked the spine for straightness. I used a marker to highlight the areas I would have to file down. This was the trial and error portion of the build, I would file a little and then check the straightness. I repeated this process until both narrow sides of the blade where straight and flat. I confirmed this by standing the blade on its spines on a flat surface. If the side was flat then the blade would stand unsupported as seen in the last picture.

Step 5:

To make this look more like the fountain pen tip I was picturing I added curves to both sides of the blade just past the beveled sections. I accomplished this by using a coved or half round file. I removed most of the material with the file and then using my 1x30 belt sander I refined the shape until I was happy with the overall look.

Step 6:

Once I was done with the shaping of the blade I moved on to the handle. I freehanded a rounded over shape on the handle portion and used my angle grinder to remove most of the material. I cleaned up the cut on my 1x30 belt sander.

Step 7:

Now that the majority of the shaping was complete I focused on cleaning up the blade first I evened out the surface by draw filing the whole blade. Draw filing is when you place a file flat on the surface of the blade and pull it towards you much like you would use a draw knife. This serves to flatten the blade and remove any minor imperfections. You can see in the second picture how smooth and clean the surface looks after draw filing. At this point I also defined the bevels of the blade. I didn't sharpen it but got it pretty close to sharp. It is easier to remove material now than after hardening the blade.

Step 8:

I decided on what shape and size I wanted to make the handles and drew a reference line on the blade. Then measuring from that line I marked and then center punched two spots that would be the locations of my pins. Now it was time to head to the drill press.

Step 9:

Using a drill press vice I drilled a 1/8" hole in the handle. I started to drill a second hole but my drill bit began to chatter which means either the drill bit is too dull to cut or the steel is too hard for the drill bit to cut. So I got a brand new drill bit and tried to make the second hole it chattered right away. This told me that the steel was too hard for drilling and would require that I anneal the steel. In order to anneal the steel I used my blow torch to heat up that portion of the steel until it was red hot and then let it air cool. Once it was cool enough to handle I chucked the blade in my vice and drilled the second hole.

Step 10:

It was now time to heat treat the blade. I turned on my mini forge (click here to read the instructable I wrote on how to make a mini forge) and heated up the blade until it was no longer magnetic. I use a small magnet on a stick to intermittently check the blade as it heats up. Once it stops being magnetic I put the blade back in the forge for another 10 seconds and then quench it in a container of peanut oil. You can see what the blade looks like after quenching in the third picture.

Step 11:

After quenching I have to temper the blade. But before tempering I sand off all the scale from the heat treat. I use a flat surface and 400 grit sand paper to clean up the blade.

Step 12:

Then I preheat my oven to 375 degrees Fahrenheit (in my oven setting it to 375 degrees Fahrenheit will reach the 400 degree Fahrenheit mark I suggest testing your oven to see what temperature to set it at so that it reaches 400 degrees Fahrenheit) and placed the blade in the oven on a baking sheet for 1 hour. At the end of 1 hour I turn off the oven and let the blade cool inside with the oven door closed until it was cool enough to handle. You can see the blonde-ish or light bronze-ish color that the blade turns after tempering.

Step 13:

After tempering I sand off the bronze color using 400 grit sander paper. I make sure to sand the blade on a flat surface or with a flat surface like a sanding block.

Step 14:

I noticed that after drilling the pin holes that the top hole was not centered. In order to correct that I removed some of the material from the blade using my 1x30 belt sander. This gave the top portion of the handle a more narrow shape which in the end I really liked. This was one of the few occasions that an error added to the look of piece instead of detracting from it.

Step 15:

I also cleanup the bevel and sharpened the blade using a flat surface and various grits of sand paper beginning with 400 grit up to 2000 grit. I stop at 800 grit for the overall finish of the blade.

Step 16:

Next I trace the handle section on to a piece of walnut. I use my table saw to cut a 1/4 inch strip off the walnut. I trace my second handle on to the walnut to make sure I can get two pieces from the one slice.

Step 17:

Then I move to my scroll saw and cut out the rough shape of the handles. I do a test fit to make sure that the handles will actually cover the tang. Using my 1x30 belt sander I clean up and shape the bolster or rather the top portion of the handle. I do this now because once the handles are glued on to the tang this small area is very hard to reach and may result in scratching the blade.

Step 18:

At the drill press, using a 1/8 inch drill bit I drill the holes for the pins through the wood handles. Once I drill one pin hole I put a spare 1/8 inch drill bit in that first hole. This will keep the handle in place while I drill the second hole, if I don't do this then the wood can shift while drilling and will not line up when I try to glue them on to the tang. I repeat the process for the other side and then do a test fit to make sure everything is lined up.

Step 19:

Next I tape off the blade for glueing and I wipe everything that will be glued with denatured alcohol to remove any dirt or grease.

Step 20:

After everything is dry I mix up some five minute epoxy and slather on a generous amount on to the glueing surfaces. I assemble all the pieces and make sure to wipe off any excess epoxy before clamping. I also make sure to wipe off any epoxy squeeze out after clamping. I leave it clamped for 24 hours until the epoxy is fully cured.

Step 21:

After the epoxy is dry I unclamp the knife and cut off the excess pins with a hacksaw. Then I begin the rough shaping of the handle using my 1x30 belt sander.

Step 22:

The final shaping of the handle is all done by hand sanding up to 400 grit. You can see in the third picture that I am using a small file to remove some epoxy that squeezed out that I didn't notice until after the epoxy had cured. This is why it is very important to clean up any epoxy that may have squeezed out during clamping.

Lastly I applied 5 coats of Danish Tung oil dark walnut finish to the handles.

Step 23:

Here is the finished marking knife. I was very please with how this turned out. It was pretty close to what I pictured in my head. I gave this knife to a hand tool woodworker who absolutely loves it. He really enjoyed the shape and feel of the knife. So with that I consider this one a success. Thank you for reading all of this and please feel free to leave a comment or ask a question. I will try my best to answer any questions you may have.

Video of the build:

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    40 Discussions

    I saw a comment that mower blades are mild steel?
    Every time I've changed mower blade they have always been 'heat treated carbon steel' Even the cheapest ones I could get were still carbon steel (although the heat treatment may not be so good on real cheap ones?) I'm pretty sure the comment is wrong?

    3 replies

    No, lawn mower blades are definitely mild steel, sorry to say. When you see "heat treated carbon steel" on the packaging, it's most likely a marketing technique that uses a couple loopholes in the phrasing. They are able to say that the blade is "carbon steel" because technically it is. All steel has carbon in, mild steel just has a far smaller amount of carbon than hardenable steels. If you want to know you are getting a product with hardenable steels in it, look for key words like "HIGH carbon steel". As for the words "heat treated" on the packaging, it probably is heat treated, it's just that heat treating has little to no effect on mild steel.

    A while ago I welded a high carbon edge to a pair of old blades, and the difference was incredible. They hardly ever need to be sharpened and they cut cleanly through the grass instead of just ripping it like a lot of blades do.

    Strange, the ones I've changed behave more like a high carbon spring steel? I’ve hit various things including 'tree' stumps about 5"~6" diameter and bent blades, they cannot be straightened 'cold' which I know mild steel will. I tried welding high speed tool steel edges (lathe parting off blades) but the main part of the blade got too brittle and they broke off (I would expect the weld or HSS 'edge' to fail first if blade is 'mild steel?) I now know I should have normalised blades after welding but didn't think it would be necessary at the time. (HSS isn't affected by 'red heat') I'm not an engineer, I trained as a precision machinist so have some idea of different material properties. I very much doubt they are in the 4340 range but they are a 'high carbon' even if the 'lower end' of 'high carbon' range. BTW, these are for a ride on lawn tractor/42" mower not a walk behind mower, don't know if that makes a difference?

    That's just it though, if you hit something with a blade and it plasticly deforms, it isn't high carbon steel. Or at the very least it isn't heat treated high carbon steel, but that would be completely pointless for a company to spend extra on a better material then not utilize it to its full potential.

    And I've never seen 1/4"+ thick mild steel that can be cold forged much at all. It's just far too elastic to fully take a bend out cold.

    It's a little hard to picture what you were talking about with the tool steel blade, but if you are saying that the edge you welded on cracked during use, then that makes perfect sense as well. Since it is far harder than the mild steel blade it is welded to, any flexing of the main blade could cause a fracture in the harder edge. Instead of using a tool steel for this, I'd recommend something tougher with less carbon, like 1084 or 1070. At the very least, if you're dead set on using tool steel, I'd opt for a hotter/longer temper.

    In the end though, if you REALLY wanna use your old lawnmower blades to make a knife or something, there's nothing stopping you. You'll just end up with a knife that has horrible edge retention, and is prone to nicks and dents when used on anything slightly hard. Why you would want to spend so much time and effort on a blade made from an inferior material doesn't really make sense to me. You can buy a 4 ft flat billet of 1095 with a similar amount of material to 2 lawnmower blades for around $20-$30, and 1095 will hold a fantastic edge.

    I could be wrong and maybe you do have some hardenable lawnmower blades, but you should at the very least do some serious testing. Start by cutting off a 2"-3" piece of a blade, quench it, put it in a vice, and whack it with a hammer. If it doesn't snap in half or shatter into a million pieces, it isn't worth your time. If it passes that test, take another section, grind a 20-25 degree edge in to one side, then harden it and temper it at 350-400 F. Sharpen the edge up and start hammering it through increasingly hard things. Start with end grain wood, then edge grain wood, then dead soft copper, work hardened copper, mild steel rod, and a medium steel hardened nail. After each test, check the edge for any damage and do a paper cut or shaving test. If it can pass all these tests without any damage, it is likely to be high carbon steel. If it fails at the mild steel or medium steel rods, it is likely either a high carbon or medium carbon steel that may have some use in tough blades. If it fails the wood or copper tests, it is most likely mild steel and shouldn't be used as blade steel.


    1 year ago

    Wow, awesome instructable! Tons of detail, and the blade you made is very cool and original. I don't think I've ever seen anything quite like it before. I wish I could try it out, I might have to make something like it eventually, haha.

    Just for future reference, heating steel and cooling it in air is referred to as normalization. Annealing is very similiar in process, but results in a very different molecular structure in the steel :)

    1 reply

    Thanks for the compliment and the clarification.

    I have also seen a design for making a woodturning parting tool from a saw blade, but incorporating the carbide tipped tooth.

    Thanks for this Instructable, I need a marking knife.

    3 replies

    I've considered doing that myself, but there are a couple of considerations to take into account. 1. Carbide is very hard, which also means that it is very brittle and likely to chip in a catch or even if you hit a very dense knot. 2. The tooth should be a square tooth, or it will cut and pull to one side, increasing the likelihood of a catch. 3. Parting tools are a type of scraper, with the point presented closer to the center of the wood than the top. Most circular saw blades have a positive rake angle (if you draw a line from the gullet of a tooth to the center of the blade, the tooth pitches forward into the cut). That will make a parting tool much more aggressive than it was intended to be and may be more prone to catches. I could be wrong about that, but for safety sake, I thought I'd toss that out there. Also, you might be able to reduce the rake angle with the right layout on the blade.

    Good thoughts , Carpenter.

    Someone in my woodturning club had the design details, but of course now I have lost my copy. Darn, now that I need it.

    (1) There are a lot of carbide tipped turning tools out there now, like the Easy Wood tools. And I occasionally abuse some of my saw blades without damaging the carbide tip. Have knocked the saw tooth tip off, however - another story.

    (2) Good point about the tooth profile.

    (3) Yes, we would need to consider the rake angle, good point (no pun intended).

    Maybe I will finally find the plans.

    That parting tool sounds pretty cool. Using the carbide teeth in that way gives me another idea. Thanks for the inspiration and for the compliment!

    I'm going to make one of those but will use an old lawn mower blade as I have several busted/worn out blades ;o)

    3 replies

    I don't think mower blades will harden at all. They are very mild (low carbon) steel.

    I recently watched an episode of 'Forged in Fire' where a contestant used an old mower blade to create a knife. They said it was 'high carbon' steel at the the time. So are there low and high carbon steel type mower blades being used? His knife was very tough and kept an excellent edge even through the various tests it was was put through.

    For safety, a mower blade needs to bend before breaking and deform before chipping. Basically, a low carbon mild steel is actually preferable for this application... and cheaper. So most of the companies that make mowers will go with the best (and cheapest) material.

    A few of the better companies out there will use medium carbon material and then selectively harden ONLY the cutting edge. If you happen to have one of these, then it may work for you.

    Advice... do NOT go through a bunch of work making a blade unless you know what material you're working with. It would be a shame to put all that work into something you can never harden! Cut off a small chunk and test harden it.