?? Designing Garden Tool

I have some more general questions about heat treating for this design. As mentioned earlier I have been advised to use something like 1045 carbon steel. Since the cutting edge is recessed between those two prongs, I think the only ways to sharpen will be with a bench grinder or metal file. Sharpening will need to go through that whole 3/16" thickness to maintain the angle of the cutting edge.

Will a metal file work with hardened/tempered steel? Should I try to treat the whole piece of metal, or just the area around the cutting edge? Will heat treatment make the tang brittle? This design is not intended for use as a prying tool, but the 60" handle creates a long lever and I don't want it to be weak at the tang.
 
Files usually work well on 1045. It doesn't get as hard as typical knife steel. It also is extremely tough, not prone to brittleness. It is what good shovels are made of.

Diamond sharpeners come in many sizes, but if all goes to plan, you wouldn't need one.

I would HT the whole thing, otherwise the tang will bend easily.
 
Thanks! I'll plan to get the 1045 and heat treat. I'll try the file sharpening with a prototype.

I'd be interested to hear specific tips for heat treating or good places to find information. I have run into a few conflicting descriptions.
 
Thanks again. So do I understand correctly that the steel should first be heat treated at a high temp, and then tempered at something like 400F?
 
Yes. HT has 2 parts.
The first is a hardening, at a higher temp., ended with a quench to suddenly decrease temperature.
The second is a tempering, at a lower temp. to soften the steel a bit.

The modern way is to do it by specific temperature. Here are some specifications https://www.google.com.au/url?sa=t&...-1045/&usg=AFQjCNF8fkxNZMFZmFPD9v-XKExG_2w_Rg

The old fashioned way is to judge the hardening temp with a magnet (non magnetic = hot enough) & then give it a temper using colour change in the steel as a guide.

edit: forgot to mention quench.
 
I'd suggest shooting for something in the neck of 50 RC for your hardness. Tough enough to not chip against rocks but hard enough not to blunt severely the moment it hits dirt. Your bevel will be more important in dirt than your edge apex, and I suggest making sure that the angle of the bevel is low but the edge apex be left about 0.5mm thick. Dirt edges are a little different than knife edges--the bevel does the cutting. At 50 RC it'll be easily filed.
 
Any tips for finding the 1045? I called a couple of the industrial metal suppliers her in town and they didn't have it and sounded like they didn't want to order it in either. Are there any online vendors who might have it?
 
Should work fine.
You don't need perfection in a prototype. Just prove that the concept works. In this case, you would be testing the steel & HT as well.
 
1075 would be fine. The extra carbon is just kind of squandered on it for the heat treatment you'd be giving it.
 
I have another quick question. The HT is going to be difficult. Unless I can find some local shop that can heat treat for me (more expense), the best I can do is a DIY oven made with thermal bricks and a torch. I understand that this method is inefficient and provides poor control.

Are there any other kinds of steel that I can consider? What about stainless? Remember that this is a garden tool for cutting through light plant stems around the soil. I will have another shop cut the blanks with CNC laser.

Yesterday I used the prototype made with cheap low carbon steel for a couple of hours and I don't see much blade dulling.
 
SS is far fussier with HT than simple carbon steels, such as 1070. Perhaps a work hardening SS like 316 would work for you. No HT.

I did my first HT in a barbeque. It is an interesting thing to try. It took me 3 attempts; red hot wasn't hot enough, it had to be bright orange. I used a Buck 420HC blade to test the hardness.
With your tool, you really only need to get the sharp end hot enough, quench in oil, test hardness. Temper in oven. Should be easier than a knife, where the whole blade has to be suitably heated.

Since you already have a version in plain steel, a HT'd version will allow you to compare performance.
HT is the invisible magic in a blade.
 
Since it appears that only a small cutting edge needs heat treatment, is there any reason an acetylene torch couldn't be used to heat it to the correct temp? I wouldn't think it would cost much to have a shop throw on a heating tip and bring it up to orange.
 
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