[mikeg]

When I'm cutting/grinding a blade, how hot is hot enough to ruin the temper? I've been going on the asumption that if it's hot to the touch but not too hot to touch, it's ok. Have I been lucky so far or is that a safe assumption?

thanks,
mikeg

[AlArchie]

Mike, it sounds like you have a pretty good set of guidlines. ANY discoloration while grinding will affect the temper. Especially if it gets blue, but even a straw color will have some adverse effects. And a sharp edge will burn almost immediately, so keep that water close and dunk often!

Al

[Hi_Ho_Sliver]

It takes me a long time, but I just touch the blade to the stone or sander and then into the water, when cutting a blade with an abrasive cutoff saw, I just touch the blade and into the water, I don't take a chance on holding it for even a second, the blade can turn blue right now!

[Thomp]

mike,

if you feel heat quench the blade into cold water and hold it.. till your sure its cold.

maybe rick ferry will jump in here and correct me where i fail, i dont want to pass on bogus info.

it would be the very best if you could cold grind it but thats far from reality,, friction causes heat,

A Little metal heat Properetys here for ya:
known to knife makers, metalurgest and blacksmiths is a heat color rainbow,
if you place a chrome or highly polished surface into a tempering oven and it is slowly heated you could observe the first sign of heat effects in a yellow color like a yellow highlight marker drawn on the surface, then proceeding to heat it will progress to straw on to gold brown,grey, dull blue, steel blue like on a gun then, peacock blue and on into black,

after this point the color will be iridescent and emanate from within the blade/metal as it gets hotter with a maroon, burgundy, red, orange, yellow, and then white just before it starts to sparkle and then melt and evaporate...
(Lot of explanation for your question but i took my meds and am chatty)

when metal removal method of dry grinding is used to make a knife, its best at the first sign of heat to quench the steel And hold it in the water sturring to keep bubbles from sheilding the heat transfer to the water...

if you see color on the blade your damaging it.
and that can happen in the blink of an eye,

i have scorched places on a knife blade before and have quenched the blade and then slowly removed the effected area and think i didn't wreck the blade, but you always wonder what if i didnt scorch that place? would it have been better?
keeping the proper temper, means its rougher to shape the knife its harder to get one sharp, with whet stones, becuse of the toughness of the steel, but once sharp and honed it means lot less maintence keeping it sharp or less stropping and more time spent carving.

removing the scorched places might not effect the blade,
but simply polishing off the color dont fix the steel...

we dont always think of the work it took to make the thing before we are modifying it.
But when a blade is tempered, lots of preparation was taken in selecting the steel shaping and heat tempering the steel. they didn't just go out to the blade tree and pluck one off.

burning the steel will remove the stress that was applied during the tempering process or it can set up a stress in the blade that will make it brittle to the point of chipping while doing regular carving.

keep it cool, one half pass and then cool or a light pass and cool... but light handedness will be rewarded..

anybody can make a 50/50 knife
carve 50% sharpen & hone 50% of your carving time and effort

[rick-in-seattle]

The color required to lose the temper in steel is blue - black.
Any color up to light purple should be okay, but try to stay below dark straw color.
The problem is, that color goes from dark straw to blue-black very quickly.
If you plan to heat-treat the steel later, color during grinding is not too important.

Of course the expert on metallurgy is Captain Bandaid.

[mikeg]

Wow, thanks for the great info guys. I've been making a couple of passes with the dremel, either a cutting disk or a grinding stone, and then quenching in water. I haven't gotten to the point where it's changed color so I guess I'm good to go.

I just won a Kershaw Double Duty on Ebay. It appears to be the big brother to the Double Cross that Rick carries. I'm going to modify the blades when I get it. I figure a slightly larger h andle will make it esier to carve for longer periods.

thanks again for the info,
mikeg

[rick-in-seattle]

Mike,
I did a few tests on some tool steel last night.
I started with tool steel that measured RC 30-32 (Typical hardness of cheap tools).
I heat-treated and then tempered it to a dark straw and it measured RC 54-55 (sufficient hardness for most carving tools) RC 59-60 being optimum hardness.

I took the temper to a midnight blue and the reading was RC 14-15 (this hardness would not hold up to carving butter) well maybe butter, but not wood.

[Thomp]

Originally Posted by rick-in-seattle

Mike,
I did a few tests on some tool steel last night.
I started with tool steel that measured RC 30-32.
I heat-treated and then tempered it to a dark straw and it measured RC 54-55.
I took the temper to a midnight blue and the reading was RC 14-15.

Ok rick,

What is your determination of this test.

My understanding of heat treating was to change the structure to harden a tool as hard as the steel would allow, then draw the temper back to keep it from being brittle.

you got me on the edge of practicality learning something here...

but why would you want to take a tool from 32 to 15 RC unless you was going to shape it with a file. seams more like annealing process went on here,

[Kenny_S]

Thomas, I believe Rick was only doing a few test to see what different colors did to the steel.
Denny Neubauer talked about the exact same thing that Rick just told us. Ya don't want that dark blue to Black stage in sharpening a tool.

Good stuff people.

[Tucson Bill]

Ok, here comes one of those CNN News Anchor type questions - You know what I mean , semi-inane.

How do test the RC hardness of tool steel?