Introduction: Marking Knife From Saw Blade
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:
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.
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.
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.
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.
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.
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.
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.
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.
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.
It was now time to heat treat the blade. I turned on my mini forge (click here https://www.instructables.com/id/How-to-Make-a-Mini-Forge/ 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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: