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Robert Hankins

Robert Hankins

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May 19, 2003
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What is your experience - opinion of using Polymer Clay for knife handles?
Most likely for stick tangs not for scales. This is the stuff you bake at 250deg F in the oven.
 
the way i see it, if you put it on the tang and then bake it you would kill the temper. but i do think it would be interesting. i would suggest making it into a block and then bake it and then drill and shape it like normal. post pics if you make a handle with it.
 
I've seen a guy who does this, but I can't find the link to his webpage again. I'm not certain of the durability of sculpy, etc. but it's cheap and easy to test :)

-d
 
Tempering is a time and temperature process. You won't alter the temper much at 250 degrees F. unless you bake it for a day. You can take a good knife steel up to about 300 degrees F. for about 4 hours before you begin to alter the temper very much. At about 250 degrees F., you can hold it for about 8 hours before altering the temper very much. At 200 degrees it takes about 16 hours to begin altering the temper.

This information is based on research at Timken Steel and Bearings. Most knife steels are tempered similar to bearings and the steels used are very similar and in some cases they are identical. BG42 and 52100 are examples of knife steels that began their lives as bearing steels. By the way, the BG in BG42 stands for Bearing Grade.

Scott (Ickie) Ickes
 
Perhaps a stupid question: What if you tempered the blade after you finished with the handle?
 
hmm...that's the first time I've ever heard of being able to over temper something with time, perhaps someone who knows more about it could explain the reason for this? :confused:
 
There was a long discussion about this a while back. Try a search to find all the threads.

A lower temper (250) will not affect the temper at a higher original temp (say 400).

The clay would be destroyed at 400.

Polymer clay would only work for decorative knives,like letter openers, it is not all that durable or wear resistant IMHO.
 
I don't know how well they would hold up to use, but they sure give interesting possibilities for different looks.

Rick
 
I am under the impression that they only cook the PVC once to get the stuff to set up, and you do not HAVE to heat the stuff again to install it. You would have to call em and ask em to see if heating the stuff up to mold it to a stick tang would be doable.
 
I've used polimer clay's for handles but mainly spacers and guards. They hold up well. They are on some of the work knives at the farm. Like said they cure at 225/250 for about an hour so that won't affect the temper.

Larry
 
mrstenoien said:
hmm...that's the first time I've ever heard of being able to over temper something with time, perhaps someone who knows more about it could explain the reason for this? :confused:
Click to expand...

Here is another way to think about the tempering process. You're baking the steel, just like you're baking food in the oven. If you bake food at a higher temperature, it get's done quicker. If you bake it too long, it burns. When tempering steel, you're transforming the steel microstucture via a baking process. The higher the temperature the quicker the transformation will occur and the more quickly you'll get done. The lower the temperature, the slower the transformation will occur. I can't give you the specifications (time and temperature) that we at Timken use to temper our 52100 bearings, as it is company confidential information, but I can give you some basic guidelines as to how the tempering process works.

The above is why the time that we temper our knives for is just as important as the temperature that we temper them at. If you were to take a knife and temper it at 200 degrees F. for 16 hours, this would be approximately equivalent to tempering it at 250 degrees F. for 8 hours or 300 degrees F. for 4 hours. At 350 degrees F., you'd need about 2 hours and at 400 degrees F., you'd need about 1 hour. This scale is not exactly as linear as it seems, but close enough. Each steel type will have it's own time and temperature transformation rates to achieve the optimal hardness vs. toughness balance. The above examples are not what you should use for times and temperatures, but showing how the time changes with temperature. Some knifemakers temper at 400 degrees F. for two hours, some at 425 degrees F. for two hours. The type of steel and size of the knives' cross section determines the temperature and the time that is required to achieve the tempering process.

My best advice is to look at the time and temperatures that have been mentioned here ("here" means on the various threads on this forum site) for different steel types and experiment with your own knives, based on what others are successfully doing. Test them with different processes, until you get the edge holding, toughness and hardness that you're seeking to have in your knife. Cut some rope and chop some two by fours and compare the results of different tempering processes until you get the most out of your blades.

We're just baking really hard bread when we temper!

Scott (Ickie) Ickes
 
Scott, would it be fair to suggest that the larger the cross section of the part, the lower the tempering temp and the longer the time? I've been sitting here thinking about this and reading some, and it struck me that the lower temp would allow for more homogeneous temp throughout a larger piece because of the extended equilibration times between inside and outside.

Have you seen the actual tempering time versus temp curves? I bet those are intruiging and insightful.

I read that the higher the alloy content, the more this applies. In Verhoeven's guide, for simple AISI 1045, the hardnesses were (approx) within two points between 1 and 4 hours for any given temp up to 1000F. I would have loved to see 8 and 16 hour data. I would have also loved to have seen a curve for a higher alloy. If anyone has an online reference, I would appreciate seeing it. Thx.

Very interesting subject.

To keep topical: I convinced my wife this week to get some poly clay so she can make handles and we can make some desk knives for Christmas gifts. We will try some millefiore-style flowerette onlays and stuff and also some damascus-style patterning. She found that there are differences not only between brands but within each brand there are several categories with different characteristics such as strength, sag in heating, etc. Not all poly clay is created equal.
 
fitzo said:
Scott, would it be fair to suggest that the larger the cross section of the part, the lower the tempering temp and the longer the time? I've been sitting here thinking about this and reading some, and it struck me that the lower temp would allow for more homogeneous temp throughout a larger piece because of the extended equilibration times between inside and outside.

Have you seen the actual tempering time versus temp curves? I bet those are intruiging and insightful.

I read that the higher the alloy content, the more this applies. In Verhoeven's guide, for simple AISI 1045, the hardnesses were (approx) within two points between 1 and 4 hours for any given temp up to 1000F. I would have loved to see 8 and 16 hour data. I would have also loved to have seen a curve for a higher alloy. If anyone has an online reference, I would appreciate seeing it. Thx.

Very interesting subject.

To keep topical: I convinced my wife this week to get some poly clay so she can make handles and we can make some desk knives for Christmas gifts. We will try some millefiore-style flowerette onlays and stuff and also some damascus-style patterning. She found that there are differences not only between brands but within each brand there are several categories with different characteristics such as strength, sag in heating, etc. Not all poly clay is created equal.
Click to expand...

Scott, would it be fair to suggest that the larger the cross section of the part, the lower the tempering temp and the longer the time
Click to expand...
?
I don't know the answer to that one. I would think that it seems like your statement is correct, because if you don't lower the temperature for a larger cross section piece that the longer soak time to ensure tempering all the way through will overtemper the surface layers.

Have you seen the actual tempering time versus temp curves?
Click to expand...
It's been about 15 years since I've seen them. It was during my engineering training (I went through a 15 month bearing technical training program before going to the field as a Service Engineering field rep). I do remember that it was a very generalized chart, and didn't give specific steel types, because we use quite a lot of different steels for bearings. I remember that it was fairly linear, and that are standard statement to customers for bearings is that we suggest that the maximum temperatures for installation purposes is 300 degrees F. for 4 hours, 250 degrees F. for 8 hours and 200 degrees F. for 16 hours. Those three guidelines are in my presentations for seminars that I teach to mechanics and engineers. If you go beyond those temperature and time guidelines, then the temper of the steel is compromised. What this says is that for 52100, if you temper at 300 degrees F. for 4 hours, you actually do not affect the knife too much. You won't begin to get any effect until you go beyond that temperature or beyond that time, or both.

Scott (Ickie) Ickes
 
Interesting info about your industry, Scott. Operational parameters like "service time at elevated temp" are not something we face as knifemakers, so this was nice insight. Thank you!
 
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