leaf spring blades again(newtake)

[john warren]

ok i'm just begining the jurney into knife making. ive been a welder since 1971 and have worked all sortsof steel an aloys of all types.
doing the best research i can this is what ive come up with.
i started with the bottom spring from a cj5 jeep.
using the tapered end so i wouldn't have as much grinding.
i cut it out way oversized with my o/a cutting torch so as not to decarbonise the steel i would be working with.
heated it to none magnetic and tapped it flat on the anvil. (read railroad iron here)and let it air cool.
reheated to nonemagnetic and let it air cool a second time.
im told you can repeat this a third time and oil quench, i didn't do this.
i have now ground and sanded to design.
and will heat rreat it this weekend.
im told all that needs to be done is a one hour soak at 400 degrees. let it air cool and repete.
i will let you know on monday how this comes out. i have no way of testing on a rockwell scale , so i will give my best judgement using a file test.
if nothing else i have learned a lot about which tools i have that give the best results. i don't think i would sell any knives made this way, prefering to use a known quality if i were to be charging for them. but as a hobby made knife im happy so far.
P.S. that stuff sure polishes up nice on the sample i tried.

 

[birdog4]

You're in the ballpark there, John.
After heat-treating and final grinding. do a brass rod test. This consists of pulling the blade edge
across a brass rod (held in a vise) at approx. the same angle used while sharpening. You'll see the edge deflect as it rolls across the brass. If it stays rolled over, it's too soft. If it chips, too hard. Go back and retemper at 25º higher temp.
Have fun bruce

 

[shappa]

Sounds like you are having fun experimenting.

Lets see some pics if you can.

 

[shappa]

double tap...no idea how it happened.

 

[Jeff Clark]

As I read your explanation you are missing a heat treating step. It sounds like the last thing you did was to heat the steel up to nonmagnetic and then allowed it to air cool to room temperature. You need to heat it up to nonmagnetic and quench it in oil before it will really get hard. After you do that you bake it in an oven at somewhere around 400-500 degrees for something like an hour. Without knowing the alloy in your leaf spring it is hard to know how long you will need to bake the knife to soften it down to the right hardness level for a knife. Try 400 degrees for an hour. Then see if you can cut the surface of the blade with a new mill bastard file. You want to just be able to cut material off the knife. If the file just skates across the knife the knife is still too hard and can break like a file. Try another hour at 400 degrees and repeat the file test. If you don't see any change jack the oven up to 450 and try that for an hour. This is the trial and error approach, but it should work. You might try 475 or 500 if you have trouble getting the blade properly tempered. When you can just barely cut the knife with the flat of a new file you are up around 58 RC.

PS. If you don't heat the knife up to nonmagnetic and quench it with oil the blade will probably only be in the 30 RC range of hardness and won't benefit from baking in the oven at 400. Baking in the oven is to reduce the hardness after quenching. The quenched hardness is probably in the mid to upper 60's RC.

 

[Robert Dark]

Hi John:

Welcome to the forums..........great place to share information and gain new friends.

While I am not qualified to give "dead-on" advice, I have messed around with a few "springs" with good results.

I don't think you mentioned in your post how you were heating your blade.......... Forge?.... Oxy-Acetylene?..... Doesn't matter as long as you can do it consistently (even heating). The magnet is one of your best friends with those springs.

May I suggest the following:

If you are satisfied with your blade design and have ground and sanded to almost the finished blade...........

1. Heat to non-magnetic and let it air cool to a black color.........

2. Do it again...........

3. Do it one more time, only this time you need to cool it VERY slowly... maybe stick it in a bucket of "vermiculite (you can get this at Lowe's or Home Depot) or even some fireplace ashes completely covered in ash............

4. After it has cooled slowly (annealed), and you are ready to "harden" your blade, get yourself some oil (peanut oil, transmission fluid, or even old motor oil will work for an initial quenchant)

5. Pre-heat this oil to around 140-150 degrees F.

6. Bring your blade up to non-magnetic....... when it is there, heat it just a tad longer and quench it in your pre-heated oil.

7. When it has cooled down to the point that you can actually touch it without being uncomfortable, wipe off the excess oil and put it in an oven (toaster ovens work well) set at 400 degrees F. for one hour.

8. Let it cool to room temperature, and do it again.......

9. Get ready to do some more sanding........ If it has excessive scale, soak it in white vinegar over night (works wonders loosening that nasty scale)

10. Get ready to sand some more (did I say that already?)

11. Sharpen it and see what it will do.

12. The main thing to remember.........Have fun and learn from your mistakes.

In making knives, there are many variables.........Find what works for you.........Make blades and test the hell of of them..........

NOW.......Maybe one of the "big boys" will step in and give you some "REAL ADVICE"....

Have fun................... Robert

 

[crex]

Don't trust your built in oven thermometer! Get one you can place inside and can read easily. It may be off a little, but it will be close enough.

Robert's right, you should try to have an even heat across the entire length and width of the blade to get a good quench and even hardness. Most leaf springs are 5160 in the older model vehicles but there are no gaurantees.

On the tempering heats, a lot depends on the geometry of the blade. I'd only change the temps in 15 - 20 degree increments (50's a big jump). I'd recommend the tempering soak to be extended to 2 hours if the blade is thick and heavy (bowie type).

Do your oil quenching outside or at least in a well ventilated area. Be careful, the flash fire often experienced with an oil quench can startle you first time around. It's short lived and mostly just for looks. I'd stay away from the used motor oil, lots of nasties in there get out when heated. Go by Micky D's and get some used fryer oil. It'll bring kids and dogs from everywhere downwind.

You could always cut off a thinner piece of the same steel and run your test quenches and tempering on it. That way all the work you put in the blade won't be ruined with simple miscalculation.

The magnet trick only works on the rising temp so be alert as the temp and color start to come up.

Above all have fun.

 

[john warren]

ok will do, i remember them saying to do that. is the purpose of oil to slow down the cooling rate as opposed to water?

As I read your explanation you are missing a heat treating step. It sounds like the last thing you did was to heat the steel up to nonmagnetic and then allowed it to air cool to room temperature. You need to heat it up to nonmagnetic and quench it in oil before it will really get hard. After you do that you bake it in an oven at somewhere around 400-500 degrees for something like an hour. Without knowing the alloy in your leaf spring it is hard to know how long you will need to bake the knife to soften it down to the right hardness level for a knife. Try 400 degrees for an hour. Then see if you can cut the surface of the blade with a new mill bastard file. You want to just be able to cut material off the knife. If the file just skates across the knife the knife is still too hard and can break like a file. Try another hour at 400 degrees and repeat the file test. If you don't see any change jack the oven up to 450 and try that for an hour. This is the trial and error approach, but it should work. You might try 475 or 500 if you have trouble getting the blade properly tempered. When you can just barely cut the knife with the flat of a new file you are up around 58 RC.

PS. If you don't heat the knife up to nonmagnetic and quench it with oil the blade will probably only be in the 30 RC range of hardness and won't benefit from baking in the oven at 400. Baking in the oven is to reduce the hardness after quenching. The quenched hardness is probably in the mid to upper 60's RC.

 

[Jeff Clark]

Water may quench a blade too fast and cause it to crack. It depends on the alloy and to some degree the size of the piece. Some alloys tell you how to quench them by their names. O1 is an Oil quench alloy, W1 is an Water quench alloy. It is much more common for carbon steel to work when quenched with oil rather than with water. If you don't know what you have it is best to initially quench with oil. After quenching you can try and file it. If it is easily cut by the file you either didn't get the metal hot enough before quenching (making sure you get it hot enough to be nonmagetic is your best quick way to insure adequate temp) or you didn't cool it quick enough. Assuming that you went straight from your heating step to your quenching step, a soft blade might indicate that you could use water instead of oil. Alternately you might try a different type of oil and start with it hotter or colder.