I needed a couple of small masonry chisels for a home improvement project that I have in the works. I couldn't find the right sizes (14mm/0.5" and 10mm/0.4" chisels) at the local stores, and I didn't want to wait a month for an online order.
I figured I can follow those people who make their own knives. I grabbed a couple of table knives made entirely from Stainless steel (including the handle) with straight-enough handles and started working.
Making your own chisel is (1) extremely fun, (2) it's dirt cheap - If you have the tools, it only costs you the utensil from which you'll make the chisel, (3) simple and (4) very fast (about 3 hours, start to finish). On the other hand, don't expect Irwin-quality result. Hell, we're not even working the right kind of steel - Basic tools are made of carbon steel, not stainless steel (which is softer). I expect this tool to need reshaping after a relatively short time.
Step 1: What You'll Need
- Belt Sander - Most of the work is done with this sander. You might be able to sub it with a bench-top grinder.
- Angle grinder - Used for removing large parts of the metal. A very strong sander/bench grinder might be able to replace this.
- Furnace and water container - Used to anneal the steal initially (to soften it for work) and later to heat-treat it (to harden it). My forge is a super-simplified version of what Mike from TheGeekPub made here. You might be able to get away with a simple torch.
- Mini Vice - Of course a large vice would also work. You can also use a clamp which worked great for me. Basically, anything that can hold the work piece steadily.
- Sand paper (optional)- This is used to clean off some of the metal oxides formed during heat-treating & tempering and to sharpen the chisel a bit.
- Magnet - This will help you verify your knives are made of the right kind of stainless steel.
- An oven that can reach 205C/400F - This is used to temper the steel after hardening.
- Any safety equipment you deem necessary - For me this meant ear and eye protection.
The only material needed is a straight stainless steel utensil. You might want to make sure it's actually made of the right kind of stainless steel.
Cutlery is made from either Silver, Pewter, Copper & Nickel or Stainless steel. Most cheap knives and forks you see today are made of stainless steel, but if you're unsure, you can identify the metal with a magnet.
If a utensil is made of Copper & Nickel, it'll be slightly attracted to a strong magnet. This is because Nickel is ferromagnetic (like Iron), but is found in rather small quantities in cutlery, and the copper that makes up most of the mass is not attracted to magnets.
If made from silver or pewter, the utensil will not be visibly attracted to the magnet.
Stainless steel is not a material but a family of materials. The cheaper and more common Martensitic stainless steels are attracted to magnets and can be heat-hardened while the more expensive Austenitic are not (or almost not) attracted and cannot be heat-hardened. Other types of stainless steels are not usually found in cutlery.
TL;DR, if you can lift the utensil with a strong magnet, it's likely cheap stainless steel - Good. Otherwise it's either expensive stainless steel or metal which can't be used here - Bad.
Step 2: Mark and Cut to Shape
I wanted a 14mm and a 10mm pair of chisels. I cut the 14mm before I decided to make this 'ible so I only have pictures for the work on the 10mm, but it's the same, so it doesn't matter.
I marked my knife where the blade is 10mm wide. I also marked the handle in order to round it out. This is necessary since you want to make sure that when you strike the chisel with your hammer you don't strike too far off the center of the chisel's width or the force of the blow will push the chisel sideways, possibly ruining your stone.
Afterwards, I cut the blade above the mark and I cut the handle at the mark. I cut the blade above the mark because during the forming of the blade, it will be further ground down reaching the exact mark.
Step 3: Annealing
Since we want to shape a blade from the metal, we need to anneal it. This reduces its hardness and improves its ductility (think of it as "stretch-ability").
To anneal the chisel we heat it up to several hundred degrees C, until just when it starts glowing red, and then let it cool slowly. You can either let it cool in air (if there's no breeze) or in the furnace as that cools down.
This will take some time, so if you're making another blade, now would be the right time to start working on it.
Step 4: Forming the Blade and Smoothing the Butt
The bolster of this knife (part where the handle chamfers into a blade) was curved, and also that was the point where I wanted the chisel's bevel to be, so I needed to flatten it. To do this I colored it with a marker, so I'll know when I ground the curve down.
This marker also gave me a mark for how far I want to grind that side of the chisel. This will be the shorter - so duller angle - side of the chisel's blade. The duller angle makes it easier for me to sharpen the blade.
The other side of the blade was ground down to make the two bevels meet near the center of the chisel's thickness. This is needed so when I strike the butt of the handle with a hammer, the force translates straight into the stone, instead of at an angle, creating torque pushing the chisel sideways.
To grind the blade, I applied small pressure near the point where the blade contacts the sander. when it became too hot to hold down, I cooled it down in water for a few seconds and continued. Letting the blade overheat will not be good for the metal nor the belt. Keep the temperature safely low by cooling it every time it gets hot enough to quickly evaporate the small droplets that remain on the blade when you take it out of the water.
You're not trying to sharpen the blade, just shape it, so don't overdo it.
I then moved on to smooth out the butt of the handle. Nothing special here, just sanded it round.
Step 5: Heat Treating (making It Hard Again)
The goal here is to harden the steel back up (after we soften it in the annealing step). This is done using Quenching.
The basic idea is to heat the metal until it's glowing hot and then cool it down very rapidly so that micro-structures that form during mid-low temperatures don't have time to occur. I cooled my chisels in water, but oils are also a great option (of course you should avoid oils that would ignite under these conditions).
The resulting metal is very hard but brittle. It might shatter if we strike it with a hammer. We'll fix that on the next step.
Step 6: Tempering to Alleviate Internal Stress
Quenching leaves the steel very brittle. This is partially because the process leaves the micro-structure of the steel under a lot of internal stress. Tempering alleviates a big portion of that stress while only slightly reducing hardness.
To temper our chisel we want to put in an over at just under 205C/400F. A home oven is good for this task. The tempering process should run from several 10's of minutes to a few hours. I set my oven to 1 hour.
When the process is done, let the metal cool down in air.
Step 7: Sharpen and Sand Off Oxides
Sharpening masonry chisels is a bit useless since they'll dull after the first couple of hammer strikes. However, sharpening the knife will still improve its cutting ability a bit. Also, I plan to use these chisels on soft bricks, so it's actually not so useless for me.
Before I can sharpen the blade, I remove the oxides layers that were formed when we heated the metal. This is done with sandpaper (the more coarse the better) and requires a lot of work. If you have rotary tool (i.e. Dremel) with a sanding drum you can do this a lot faster.
Next you sharpen the tool by holding it at a slightly duller angle than the bevel's angle - this will create a micro-bevel at the end of the bevel and slightly improve the strength of the sharpened edge. Work both sides since you have a bevel on both sides.
Step 8: Form a Notch for Hanging
I wanted a way to keep these chisels handy, so I decided I'll cut them a notch to hang them on my pegboard.
A couple of things to remember. First, you don't want to cut the notch too deep into the width of the handle. If you cut through to the metal right under the point where the hammer will strike, you'll create a leaf-spring that will absorb part of the blow. Second, you should make sure to cut at a steep enough angle so the tool will not slip off the hook when it swings (when you hang it).
So, make a mark close to the butt of the handle, at about 30-45 degrees up and 40% deep into the width of the handle. Then cut into the mark with an angle grinder and then sand the edges of the cut.
Step 9: Thanks for Reading
I hope you liked this instructable and that you'll enjoy your chisels.
If you did like it, I'd love it if you could vote for me in the Metal 2016 contest.