cooling hot tool while grinding

[mark ravensdale]

Hi all!!!
i'am new to this so if this is posted in the wrong place or whatever then PLEASE forgive me.

Anyhow, I was reading some of the older post today, and one really interested me, it was regarding whether one should dip a high speed steel tool into water while grinding to cool it (something I personally would NOT do) however no one replied with the tactic I use, if I am grinding/sharpening I have my shop vac close by and if I feel the tool may be getting a little too hot I simply turn on the shop vac and stick the tool down the hose for 5-10 seconds, it cools the tool in a matter of a few seconds but does not affect the steels temper as its not a shock cooling like a dip into water, I seem to remember reading once that water is (I think) 400 times more quicker at removing heat than air, hence the reason why people die more quickly from hyperthermia if they are wet!
So there you go, stick it down your hose it works a treat :)

[Steve Schlumpf]

Mark - I have cooled the metal using both methods and I honestly do not think dipping the tool in water would affect the temper. The only reason I dipped the tool in water was because the metal was getting uncomfortable to hold onto while reshaping a grind. Temper would only be affected if the tool became extremely hot... and is why HSS is preferred over carbon... it requires higher temps to change the temper.

[Dale Miner]

Cooling HSS in water; an opinion with some background in the matter.

There are those that say that a HSS tool should not be dipped in water to cool, and then there are those that say it makes no difference. Both are correct with certain criteria.

When a HSS tool is sharpened to a very thin edge, and quenched in water, the edge cools extremely fast compared to the heavier sections. As the metal cools, is also shrinks, and the difference in the cooling rate and corresponding shrinkage results in micro cracks in the edge. However, the effect is generally not an issue unless the metal is cooled from very elevated temperatures. It the metal is warm to the touch and quenched, micro cracking will not take place. If the metal is red hot, the effect is much greater and micro cracking is very likely in the thinnest portions of the edge. A blunt edge typical to a scraper will withstand quenching from red heat with little if any micro cracking as the section change from edge to body is minimal. A bowl gouge with a fingernail grind is probably the most susceptible to micro cracking from quenching from elevated temperatures, and the wings of the gouge have a very acute edge and will see the greatest difference in cooling rates. In dim light, metal will be a dull cherry red at about 900 degrees F. In normal shop lighting, about 1200 to 1300 F is needed for the metal to be visibly red. Grinding the tool until it turns blue will heat the tool to about 700 F. Quenching from 700 F will not cause micro cracking in HSS. Heating a HSS too to visible red heat while grinding will not have any appreciable effect on the temper (hardness of the too), and quenching from visible red heat will not have any effect on the temper of the tool, although it may cause micro cracking.

The high vanadium content metals that some gouges are made from do suffer from being heated to a red heat while grinding to a slight extent. Heating to a blue color while grinding those metals does not have any appreciable effect on the temper.

While both metals are able to resist being heated to 700 F while grinding with little if any effect on the properties, I feel that if a tool is going to be reshaped/repurposed and will be subjected to substantial grinding, it is better to frequently dip the tool in water when it becomes uncomfortable to touch (140 to 150F) and resume grinding.

[Bob Bergstrom]

Stuart Batty was demoing at Turn on Chicago and said that he has been quenching his tools for years when sharpening them with no visible effect. I would say that not allowing the tool to get too hot before quenching is good judgment.

[Bernie Weishapl]

I generally dip my tools when I am reshaping but other than that I just sharpening and go. We have metal specialist here in town who has worked with metal over 40 yrs. He said HSS turning blue while sharpening is no big deal. He said even if reshaping it he said it does not hurt at all to dip your tool in water to cool it so it can be handled. I have never had a problem or noticed any difference in my tools using this method.

[mark ravensdale]

Wow thanks for your replies, this seems a very good forum!!!
yes I watched a video on you-tube yesterday of Gary Gardner talking/demonstrating to a woodturning club in the US and he mentioned that HSS is able to handle a much higher temp before its temper is affected, also my father used to work in a steel mill in Sheffield England (11 miles from my home, I have passed the Robert Sorby, Henry Taylor, Crown factories many times over the years) and delt with many different high speed steels and he told me that on the whole this is true!
So yes it seems that cooling HSS with water while grinding should/would have no affect on the makeup of that steel
however I think I will continue to use my vac for cooling as me/water/and electricity don't usually get on well:)
i wasn't trying to say who is right and who is wrong, but just trying to offer an alternative.
your posts are VERY much appreciated and I look forward to learning a great deal on this forum, and dale your reply was very interesting and I am now a little smarter than I was yesterday :) (many thanks)

Again, many thanks and great forum!!!

[Mel Fulks]

Good point,Steve .HS takes heat to dull red without degrade. While that is the technical definition ,unfortunately there is no legal definition. One of the web sites recently posted as a source for steel machine knives had "TM" after its VANADIUM HS name. Interesting, if small ,step toward truth in advertising.