Replies

1. 
   lwilliams | Aug 07, 2010 02:01pm | #1

   You do need to harden the tool before you temper it. You should be able to get a 1/16" chisel to critical temperature with a small propane torch but avoid a MAPP torch. MAPP torches produce hot a pencil-point flame that makes uniform heating difficult or impossible. If you have one, put a flame spreading attachment on the propane torch and closely watch the cutting edge which is easy to overheat becaue it's so thin. Even if the chisel is made of water hardening steel, you can effectively quench something as thin as your chisel in oil. Use a vegatible oil, not motor oil.

2. 
   derekcohen | Aug 08, 2010 01:00pm | #2

   Hi Mark

   I have treated many blades - chisels are easier than plane blades as the area is small.

   Step 1 - play the flame from the tip to about 2" back and get the steel cherry red. It is best to do this in a darkened area as daylight can trick you into seeing a brighter red than reality. Be sure to do this is a safe place. Some like to use a magnet - if the steel does not attract a magnet then it is ready. I must say that I have never done this.

   Step 2 - the moment that the steel glows cherry red, plung it into a tin of oil. I prefer peanut oil - smell better, has a higher flash point. Now hold it there, move it about. The idea is to cool off the steel as fast as possible. The steel should come out rock hard - so hard that a file will skate off it (and not cut). If it does, then it is ready for the next step. If it is cut by a file, either it did not get hot enough (Step 1) or it did not cool down fast enough. If the latter, then heat if again and this time quench it in water. Water cools faster. Some steels are meant to be quenched in water, and some in oil.

   Step 3 - The steel will be blackened at this point. Clean the steel with a fine sandpaper until it is bright again.

   Step 4 - Tempering the steel is the process of softening it to the desire level of hardness. So light the torch again and this time aim it about 2" behind the bevel end. Watch the steel getting red again. As it does, the colour will run up the steel towards the bevel end. As it get to a dark yellow, quench it rapidly in water/oil again. The idea is to halt the tempering at this point.

   Step 5 - clean the steel, flatten the back on stones, and hone the bevel.

   Done.

   Regards from Perth

   Derek

3. 
   lwilliams | Aug 08, 2010 10:43pm | #3

   Mark,

   If it was me, I'd temper the chisel in a household oven or toaster oven. Bake it at about 350ºF and 30 minutes ought to be plenty for something as small as your 1/16" chisel. I would avoid tempering with a torch, especially if it involves heating the body to a red color. This will leave a soft area that will be prone to bending. The color you're looking for is a faint straw color. You won't necessarily see any color because the color will be slight. You'll probably have to put it next to some steel that's been polished but not heated to see the color difference.

1. 
   derekcohen | Aug 09, 2010 04:34am | #4

   Hi Mark

   Larry's recommendation is the safer option. I'd go for it. Using a torch requires a quick hand and eye.

   For reference, the colours represent the Rockwell hardness of the end result. Here is a guide:

   http://www.anvilfire.com/FAQ-article.php?bodyName=/FAQs/temper_colors_hardness.htm&titleName=Temper%20Colors%20and%20Steel%20Hardness%20:%20anvilfire.com

   Another article with good links: http://www.dfoggknives.com/hardening.htm

   The difference between pale yellow and dark straw is not big, but the harder the steel the more brittle it will be. Is your 1/16" for paring or morticing? I assumed it would be the latter, in which case I stand by the colour I recommended. However it could be a paring chisel, in which case I would go with Larry's choice.

   Regards from Perth

   Derek

4. 
   sapwood | Aug 09, 2010 12:40pm | #5

   Can it handle the heat?

   Depending on the type.... a hot oven might no be too kind to the handle.

5. 
   marking | Aug 09, 2010 09:26pm | #6

   Reply to All

   Thanks to all who have thrown in their two cents!

   In  the process of trying to glean  information that is new to me from many sources it is truly helpful to have personalized responses.  Many thanks!

   So am I to gather from the the response ("step 4") from Derek of Perth that the heat treating step is to harden and then the tempering (oven or otherwise) is to partially reverse the hardening to reduce brittleness?  Can hardening be achieved at lower oven temperature?

   Thanks also for the point about heat's affect on the handle.  I did think of that, but it never hurts to ask.  I may wait until it is less humid  to aid in it's removal.

   One point I did learn elsewhere that I can share:  quenching is best done in oil.  In the knife making video I saw on youtube, the blacksmith preheated the oil (to somewhat slow the quench?? and get just the right level of hardness??)  Somewhere I saw the point made that water quenching is less desirable because a layer of steam is formed between the metal and water thereby cooling the metal too slowly.

   I may  play with different angles and never get around to dabbling in metalurgy, but it's always great to learn.

   Again, thanks for all the information.  Keep "em coming.

   peace

   mark

1. 
   derekcohen | Aug 09, 2010 11:09pm | #7

   Hi Mark

   A few points to consider.

   Firstly, you can put a chisel handle in an oven - but you must wrap it in a wet cloth to prevent it scorching. Otherwise remove the handle first.

   Secondly - more importantly - it is not simply an either-or regards oil or water as the quenching medium. One will suit the steel type better. The idea of the quench is to halt the process dead. Oil does this slower, which suits some steels better (the "O" in O1 steel stands for "oil hardened"). Water quenching is faster (actually I think brine is the fastest). The "W" in W1 steel stands for "water hardened". This was a favourite of LN until they switch to A2 (which stands for "air hardened" steel). A lot of the old steel is W1.

   Now I have found that using oil for some blades is too slow and the end result is that the steel is not hardened enough, or tempered too little. And on some steel, the use of water is too fast and the result can be a crack. Consequently it is safer to start with oil (I like peanut oil - smells nice) and switch to water if it does not work. I have also done both - first dunked the blade in oil, then finished the process in water.

   Regards from Perth

   Derek