BladesByBaz

[BladesByBaz]

G'day,

Absolute beginner here. I've just made a handful of knives from lawnmower blades and files.

This current knife I annealed using an oxy-acetylene torch, got it glowing cherry red then let it cool down slowly. It made it soft enough to grind, file and sand.

Did I do that right?

Next thing I need to do is harden/temper. I've been reading around and it seems that heating it up cherry red but then instead of letting it cool naturally, I am to quench it in some preheated vegetable oil is that right?

From what I read to temper it I need to put it in the oven at around 400 degrees Fahrenheit (My oven is in Celsius) for a few hours, let it cool then repeat.

Should I sharpen it before or after tempering?

Baz.

Lawnmower blade knives.

File knives

 

[GHEzell]

As for the annealing, if it got soft enough to file you did it right. If you didn't go hotter than cherry red you probably didn't grow the grain.

As for hardening, you want to go a little hotter than cherry red, in fact you don't want to judge the temperature by color at all, except to see that the blade is heated evenly. Get a magnet. Heat the blade up until the steel is no longer magnetic, being careful not to overheat the edge or the point, as the thin areas heat up fast. When the magnet no longer sticks to the blade, heat it just a bit hotter... you'll want it about 150 degrees Fahrenheit hotter than the 'currie' temperature (this is the point where the blade looses magnetism, and I apologize for being metrically challenged). It would be nice to be able to soak the blade at this temperature for a few minutes, but this is virtually impossible with a torch, so dunk the blade point first into the oil (which needs to be heated to 'uncomfortably warm bathwater' temperature beforehand) and swish it forward and back (not side to side, this can cause warps) until the blade is no longer glowing red, let's say 7-10 seconds. Pull the blade out of the oil and sight down the blade to see if it has warped... if it has, straighten immediately, while the blade is still very hot ( thick gloves are suggested). If it has not warped, go ahead and let it cool in the oil. Once the blade drops down to 400 degrees or so (this is approximately where the oil stops smoking), it is starting to transform into untempered martensite, which is very hard and very brittle, so stop trying to straighten it and put it back into the oil until it cools to room temperature/cool to the touch. Wipe off the oil, and immediately stick it in a pre-heated tempering oven.

As for tempering, files are very high carbon steel usually, and from my experience 400 degrees Fahrenheit is going to leave you with a somewhat brittle edge... try at 450, and temper it for at least one hour (I usually go 2 hours), then cool the blade in water, then sharpen a portion of the blade and test it. There are a lot of different ways to test a blade, but since we are primarily concerned with brittleness, try whittling on a piece of brass with the sharpened portion, this will quickly let you know if the blade is still 'chippy'. If it chips, try another round of tempering 20 degrees hotter.

And that is basic grandpa-tech heat-treating of unknown steel, and should give you a good knife. Meanwhile, read up on such things as thermal cycling and decalesence, these things can help make it into a very good knife indeed, once they are understood.

By the way, that is a very good looking blade. One thing I forgot to mention, leave the edge a little thick until after hardening, maybe 1/2 mm, this will make it less likely to warp or over-heat and you won't have to worry as much about decarborization. Thin the edge back down after you have heat-treated it.

 

[Stacy E. Apelt - Bladesmith]

Welcome to Shop Talk.

The stickys at the top of the page have a whole section on file knives with HT and other info. The Count will soon be posting his extensive list of things to help you.

One thing I spotted on your knife is the 90° angle where the tang meets the blade. This is a bad thing, and can lead to the blade breaking there. Make those transitions rounded, like the file tang was to start with. This prevents stress risers from starting and making cracks and breaks.

Harden the blade at 1500F/815C and temper at 450F/230C. Temper for one hour and cool off in water, then temper a second hour. The stickys have detailed info on this.

From the photos, it looks like you have fitted the guard before HT. It is better to leave the slot fitting until after finishing the blade or the gap will be quite sloppy.

The shape of the brass handled knife is a good shape. I would use that as a pattern for the next several knives.

I see you like holes in knives. To some degree this is a personal taste issue, but be aware that hole in the blade lead to broken blades in both quench and use. In the handle they are places where moisture and gunk gather....causing problems later on.

Finally, lawn mower blades are a very poor choice of steel for knives. there is a current thread running in Shop Talk about it. You will be doing you nad your knives a great service by ordering some 1084. It is the simplest to HT and makes a very good blade.

 

[DallasB]

Baz, What a great knive!

I too have a question. I polish to a mirror finish then I temper my blades(from old files) at 400 for an hour or so. After doing this I am finding small cracks throughout the blade.
Any sugg

 

[BladesByBaz]

Gentlemen, thanks very much for all the suggestions and advice. I am very new to all of this and learning fast. For the time being, it is a cashless hobby that causes me to use whatever is on hand. The lawnmower blades were lying around and a lot harder than the standard blades you get in the hardware store, so I used them. The holes in the knives are not deliberate, they are the bolt-holes that held the mower blade on to the bottom of the mower. I just went around them and incorporated them in the design.

I've just been given some knife-grade steel pre-annealed so I will keep you posted. I'll also try the hardening/tempering suggestions above on my current file-knife and let you know how I go.

Cheers!

Baz.

 

[GHEzell]

Baz, What a great knive!

I too have a question. I polish to a mirror finish then I temper my blades(from old files) at 400 for an hour or so. After doing this I am finding small cracks throughout the blade.
Any sugg

We will need more information (heating methods, how you are judging temperature, what you are quenching in, and pictures are always helpful) before we'll be able to give a good answer. I'd suggest starting a new thread.

 

[BladesByBaz]

Made a forge today after work. Scrap metal and a mix of galvanised, rusty and painted. I didn't bother measuring anything or cleaning anything. Quick cuts with an angle grinder and just eyeing it.

Limited time, but a working forge. All there is left to do now is pack the inside with insulation and pop in the gas on the back pipe.

 

[Salolan]

Someone much more knowledgeable will hopefully be along shortly, but galvanized + forge temperatures is a big no no.

 

[GHEzell]

I was thinking the same thing. Without knowing which parts are galvanized it is hard to say.

When galvanized steel is heated it gives off very dangerous gasses. Very, very dangerous gasses....

 

[BladesByBaz]

The hinge tube is the only galvanised piece. I can grind the galvanising off or put it outside, light the burner and burn it off for it's fist time.

 

[Stacy E. Apelt - Bladesmith]

The galvanized pipe hinge isn't any problem.

 

[BladesByBaz]

Another finished knife.

 

[BladesByBaz]

File knife finished. Not quite how I expected the multi-layered paint to turn out, but I'm happy with it.

 

[BladesByBaz]

Made a longer forge out of scrap metal. Now I can make longer knives.

 

[BladesByBaz]

Speed-building! 20 minutes, cut, drill, weld, paint. Not a rule or scribe in sight! Voilà! One knife-making vice, ready to screw down to the bench.

 

[BladesByBaz]

Built a new work bench for knife-making out of rusty scrap angle-iron. Thick hardwood slats, a place to house both forges, the knife-vice and to stow the gas bottle and quenching oil. Adjustable feet to level it on the uneven slope of the concrete, (Drainage) and bolted to the frame of the building for stability.

 

[BladesByBaz]

I thought I'd take a bit of a break from the Iron Man suit today and started on three new knives. I'll put different handles on each and change the file-pattern design on the spine of the blade.

1. I've been playing with the mix and the venturi to get the fire right in the forge. This is the crap I have at the moment.

2. Three identical blade blanks to cut out.

3. File-pattern number one on the spine.

 

[BladesByBaz]

FINALLY! I've been fiddling around with the gas/air mix and flames have just been shooting out the front of the forge. None of the heat has been building up inside. So, I filed out the port in the side and positioned the venturi further into the forge. BINGO! I'm now able to get temps above 1000 degrees Celsius. Aluminium melts at around 660 degrees Celsius. This first picture was a tall pyramid of aluminium off-cut. You can see it has collapsed into a molten blob in around one minute.

It's still a little rich so I have to tweak it a bit more.

Now to really get some heat into the steel for good annealing!

Ahhh! That's more like it!!!

 

[BladesByBaz]

I've now got blade 1 of 3 roughed out and most of the file work on the spine is shaped. Some fine filing and sanding then it's ready to start tapering the blade to an edge.

 

[Hengelo_77]

some good looking stuff there