Tool Grinding...How'd I Do?

[Ray C]

Sorry,it is a BAD idea to quench HSS in real cold water. Some don't quench it at all because it may cause small cracks since it is an air cooling steel,meaning it hardens when cooled real slowly. Quenching it in water would best be done at room temperature at best.

Personally,I have not cracked a HSS lathe tool dipping it in water,but I dip quickly,take it out,and dip again. Plus,I don't let the bit get REAL hot to begin with,to avoid cracking in the quench. I'm saying I know how to quench at the grinder,by cooling HSS a little slowly.

Cooling ANY tool steel in ice cold water,even water hardening tool steel,is a bad idea as it causes too much shock,inducing warping and possible cracking. Old blacksmiths would start their cold mornings by heating up a steel bar good and hot and putting it into the quenching tub(slack tub) to take the chill off the water.

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Hi George... I hear what you're saying about creating stresses and am aware of that. The outside surfaces expand/contract many times faster than the core and this places pressures indeed. But they are just that, pressures... because at these temperature ranges the metal is no where near any boundary from spheroidized structure to austenite structure -not by many hundreds of degrees. At the temperatures we're talking about, in the eyes of metal, that's like the difference between a human walking from a room that's 75 degrees to a room that's 65 degrees. Do you feel it? yes. Does it make a difference? No.

Most tool steels have annealing temps that don't start until 400. -That's why I leave a little water on the bit because it starts to slowly evaporate around 150 degrees and at that temp, there's no harm in dunking in very cold water. Consider that car engines in Minnesota can go from -20 to 350 in a matter of moments... (the stresses of rapidly going from hot->cold or cold->hot are identical). And the reason all but the most critical parts of an engine are kept at/under 350 degrees is because that's approaching the annealing point. As far as cryogenic structure change, the first signs of crystalline reorganization occur at -150 and occurs fully at -320.

Dunking warm HSS in cold water is +/- 200 degrees from any boundary of crystalline change...

One thing for sure, if you warm it up till it's blue (or even dark amber) that's a sign that atmospheric oxygen has started to bind molecularly -and that occurs WELL after the annealing point so, by definition, it has become softer.

Respectfully...

Ray

 

[Ray C]

I'm definitely with Bill on this one... As mentioned before, if those are your first grinds, YOU DONE GOOD! -And to further bolster Bill's commentary, the reason I mainly started using carbide was because I spent so much time grinding and more often than not, struggled to get consistent results. For the simple bit styles (LH, RH, Threading), I could do those repeatably but anything more complicated than that... -Forget it! It took me way too much time.

Now please don't abandon HSS because of what I said. Please learn how to do HSS right because it will come in handy.


Ray

Yes, the grind looks good from here. But one thing I will say is the a pretty grind is not always a good thing. The proof of the grind is in the cut. If it works, you did well, if not, try again. If I grind a tool here, and someone grinds one in California, and we send them to someone in Texas, I'll bet the Farm they are not the same, if hand ground. It takes practice. When you think you have it, practice some more. You are on the right track.

"Billy G"

 

[Tony Wells]

I seriously doubt you could hurt HSS with a grinding operation. Tempering after the initial quench (>2000°f generally) during manufacture happens around 1000°f or a little more. It's tough to properly anneal HSS. In fact, I have melted some, and later found it to be just about as hard as it was. It's pretty hardy stuff. One of the things that earned its name is the fact that it will retain its hardness running at speeds that no other material at the time could approach. In fact, even at red hot, it is still harder than the carbon steels is soon replaced and will cut many materials. So even if you get it red at the grinder, it's not hurt........unless you quench it. Stay away from the ice-water for sure, and even the thermal shock dunking it in room temperature water from red or near red temperatures causes micro-crystalline fractures that will ultimately result in chipped and broken tools. They will fail not because they got too hot in grinding, but because the oft recommended water quench. Best way to grind it is to use an open, coarse wheel, substantial pressure and get with it. Ignore the temp. When you get it close to size/shape, etc., slow down to a finer wheel, then hone an edge on it. You will do less damage to the tool, and save tons of time if you are aggressive with the initial grinding and skip the water altogether.

A lot of this thinking has probably come from the slow, wet grinding done in surface grinding of other metals, and the production grinding of most HSS tools. However, the reasons for all the light touch and flood coolant is not to protect the metal from heat effect but to provide a stable, non-moving part to grind. Cooling it accomplishes this. Offhand grinding has no such need.

 

[Ray C]

Thank you... Exactly my point. Yes, when going from many hundreds -or thousands of degrees to cool/cold water, bad things are going to happen. But going from 150 to cold... No problem. As mentioned, if you leave a little water on the metal, it starts to evaporate at/around 150 (just about the time it feels uncomfortably hot). When it starts changing colors, you're getting waaarrrmmmerrrrr... By the time you say, CRAP and your brain figures-out this thing is too hot to hold... That's when you don't want to dunk the thing.

I seriously doubt you could hurt HSS with a grinding operation. Tempering after the initial quench (>2000°f generally) during manufacture happens around 1000°f or a little more. It's tough to properly anneal HSS. In fact, I have melted some, and later found it to be just about as hard as it was. It's pretty hardy stuff. One of the things that earned its name is the fact that it will retain its hardness running at speeds that no other material at the time could approach. In fact, even at red hot, it is still harder than the carbon steels is soon replaced and will cut many materials. So even if you get it red at the grinder, it's not hurt........unless you quench it. Stay away from the ice-water for sure, and even the thermal shock dunking it in room temperature water from red or near red temperatures causes micro-crystalline fractures that will ultimately result in chipped and broken tools. They will fail not because they got too hot in grinding, but because the oft recommended water quench. Best way to grind it is to use an open, coarse wheel, substantial pressure and get with it. Ignore the temp. When you get it close to size/shape, etc., slow down to a finer wheel, then hone an edge on it. You will do less damage to the tool, and save tons of time if you are aggressive with the initial grinding and skip the water altogether.

A lot of this thinking has probably come from the slow, wet grinding done in surface grinding of other metals, and the production grinding of most HSS tools. However, the reasons for all the light touch and flood coolant is not to protect the metal from heat effect but to provide a stable, non-moving part to grind. Cooling it accomplishes this. Offhand grinding has no such need.

 

[Tony Wells]

My point was that at 150°f, you don't need to cool it. Go ahead and grind it until it gets red.....still no damage, unless you quench it. Of course, you shouldn't hand hold a piece and grind it until red, use a holding device of some sort. If you do grind to 150° and cool, true you won't do any damage. In fact, this is a good practice for nice high quality woodworking edged tools. But we are talking about HSS metal cutting tools. Different rules apply. If you do take such a slow approach to grinding lathe tools, you will waste time, and grinding wheel.

 

[Ray C]

So, I hate to say this but, what other way is there? You got my curiosity going now. Don't clam up on me.

My point was that at 150°f, you don't need to cool it. Go ahead and grind it until it gets red.....still no damage, unless you quench it. Of course, you shouldn't hand hold a piece and grind it until red, use a holding device of some sort. If you do grind to 150° and cool, true you won't do any damage. In fact, this is a good practice for nice high quality woodworking edged tools. But we are talking about HSS metal cutting tools. Different rules apply. If you do take such a slow approach to grinding lathe tools, you will waste time, and grinding wheel.

 

[george wilson]

Let me clarify why I quench at all. I,as I've stated,know that red heat doesn't hurt HSS,in full agreement with Tony. I make repairs to mechanical antiques and do other work wherein I need special shaped miniature form tools like ogees,etc.,which I need to inspect carefully and diddle around getting them just right. So.I quench in order to hold the bits and closely inspect them.

If I can find the pictures,here's a model cannon barrel I made recently with moldings all over it. I made form tools to speed up the process of making repetitive moldings. This cannon is about 8" long. It has not been polished yet in the picture. Just from being turned.

Also,a pair of wax seals I made from brass,with buffalo horn handles. Typical of orders I get from customers. They are about 6"" overall length.

I'm not the usual type machinist. Most of my work is artistic in nature,especially from being the toolmaker for an 18th.C. museum setting.

For ordinary left and right hand turning tools,etc.,no need to quench.

View attachment 98226

 

[Ray C]

Beautiful, George... Really beautiful! You're right, I don't see how you could do that with typical carbide inserts of the usual variety. Definately a job for custom HSS. Like I said, it took too much time when I tried to make complicated bits so, you must have the knack down pat.

 

[Tony Wells]

I'll give you an extreme example. I wanted a 2.000 radius slab tool. I had a piece of 1" HSS. I took a oxy acetylene torch and burned it in according to a scribed line, then took it to a 10" 36 grit OA wheel to get it close to profile. Then I used another trick (to be given at some later date) to finish the radius with a smaller grinder. Never touched water with the tool. Never had a problem cutting 4140 @36 Rc.

 

[Bill Gruby]

George, your work is impecable. Simply amazing.\

Ray -- Take a piece of 1"X1" Steel. Cut a slot length-wise to fit the tool. Use setscrews to hold it fast and have at the grind. Length is up to you. Old school technology come full circle.

"Billy G" )