Help two blades

[TxMoon]

Not again please tell me what am I doing wrong here!

      look close and there is a crack going threw it!!!!    :mad:   aghahhhhhhhhwww!! I am about to go postal!!! Am I getting it to hot while I am grinding it ? I have way to many hours in this for this to happen. Am I missing something here?    :confused:    http://www.flickr.com/photos/19461788@N04/

[skullworks]

Is it happening during the quench?

[TxMoon]

Can I put it in my forge and weld it back together? I thought I read on here some place that when your grinding when it gets hot dip it in water? I know this would have to make it brittle? I have already heat treated it and now this shows up..

[robtattoo]

Are you just grinding the blade, straight out of the sawmill blade?
Or are you going through the cut out/anneal/gring/hot quench/HT cycle?

I've only ever seenthis happen during the qench, certianly not during grinding.

There are a few reasons that it can happen during the quench;

1) Steel too hot
2) Edge too thin
3) Quench medium too 'fast' (ie; water instead of oil)
4) Quench medium too cold
5) 'Stress Riser' (usually a hard angle, instead of a curve)
6) Quenching the blade 'flat' rather than edge/tip down

Any of these sound like possibilities?

[TxMoon]

I just now spotted it. I dont know didnt see it till I was cleaning it up after the quench.

[robtattoo]

Ah, right'o. 99.999% sure it'll havehappened during the quench then.

What are you using in your quench tank?

[robtattoo]

Think I may have spotted your problem in the middle picture.
Big plastic bucket full of water.

If you're using this as a quench, there's yer problem bud!

I'd stake my reputation on the steel being L6 (probably     ) which is an oil hardening steel.
Water would be far too 'fast' a quench & will cause the cracking.
Buy yourself a couple of quarts of vegetable or corn oil & dump it in a pan/bucket. Before you quench, heat the oil with a few pieces of red hot scrap steel. I like to get mine to around 170-180F
It's the 'shock' of the cold water that's doing it.

[TxMoon]

I used motor oil that I heated up till it was real  warm to touch. then in the oven at 400 for 2 hours. I didnt see the crack before this, but could it happened when it was on the belt sander? when it would get hot then I would dip it in water to cool it so I could keep grinding?

[robtattoo]

You'd have to get it very, very hot for it to crack at that time.
I like to do around 99% of my grinding before I ever put blade in forge. I just leave around 1/2mm on the edge until HT is finished, then give it a final sharpen afterwards, but I'm only on the grinder for maybe 1 minute per side after HT.

[TxMoon]

This is start to finish in short. cut out the blade from the saw mill blade using a angle grinder, then with a belt sander grind it down to what I want, then oil treat, then HT then sand it down to finish.

[TxMoon]

There are a few reasons that it can happen during the quench;

1) Steel too hot
2) Edge too thin
3) Quench medium too 'fast' (ie; water instead of oil)
4) Quench medium too cold
5) 'Stress Riser' (usually a hard angle, instead of a curve)
6) Quenching the blade 'flat' rather than edge/tip down

Looks like it could be #2 or possibly # 5 never thought about #5 before being a problem?
I am new to this and it is something I want to be good at and learn. I want to give them to my hunting buddy's for Christmas. I have put a lot of work into them this sucks but you got to learn some how. back to the drawing board. Thank you so much for your help I really do appreciate your help really.

[robtattoo]

Originally posted by TxMoon:
This is start to finish in short. cut out the blade from the saw mill blade using a angle grinder, then with a belt sander grind it down to what I want, then oil treat, then HT then sand it down to finish.

You may want to anneal the blade after it's cut out & before you start to grind your profile.
Throw the 'blank' in your forge & bring it up to critical temperature (none magnetic) If you can do this with the doors & windows shut & with the lights off, it'll be a very dull red, not bright orange    Try & hold it at this temperature for 1-2 minutes & then bury the blade in either vermiculite or hot ash or embers & leave it to cool very slowly (4-6 hrs) If you can leave it in the embers of a dying fire & then leave it until the fire has gone out & cooled, you should be about right.

This step will releive all the stresses in the steel & bring it back to being soft.

What you are doing is essentially re-hardening a tempered blade, which will increase the amount of stress already in the blade, causing cracks    Also, where you have any transition from thick to thin, or wide to narrow, or any notches (such as just in front of the plunge) try & round off all your corners. It doesn't need to be much, but a sharp angle will become a focus point for any stresses & is more likely to crackon that point.

Hope this helps Tx. Stick with it, you're doing really well from what I can see.

It ain't an exact science (well, it is, but we ain't all Poindexters    ) & 90% of this is trial & error. Unfortunately you can't have one without the other at some point  

[KHALVERSON]

tx
maybe you could grind out behind the crack
and make a finger groove in that area
i really like the profile of that knife
 and its a shame to have  to scrap a blade
especially one as nice as that
kevin

[Bobby Urban]

If you have a mig welder you could grind a bit of the crack out and weld it?  Grind the profile back into it and finish the knife.  Not exactly the best scenario but no one would be wiser looking at the finished product.  

Bob Urban