ok to use water to cool down a forstner bit?

[Jacob Reverb]

Keeping your bit cool will not hurt it. Although, you do not want to get it really hot as that WILL remove the temper. I always keep some water handy when grinding my plane irons and chisels, and dip them often to keep them from getting hot. That's also the idea of the slow speed grinders with the water pan. Don't overheat your tools. But don't soak your wood.

+1

I would have a can of cold water handy, and maybe dip the chucked Forstner bit into the can of water between each hole (assuming you have a lot of holes to bore). That way the wood stays dry and (assuming you don't get the bit roaring hot between cool-downs) the hardness stays in the steel.

[johnny means]

How can going too slow cause a bit to heat up? A sharp forstner, should be able to bore a clean hole at 1 rpm. The problem is that most users seen to destroy the cutting ability of the bit on the very first cut buy spinning at excessive speeds. The goal is to have the bit cut a continuous spiral shaving similar to what a hand plane would make. This requires that the bit move through the wood as fast as it rotates around the hole. What I always see done is that the user gs the bit spinning then starts to feed slowly. The cutting edge of the bit skims around the bottom of the hole and is burnished in the process. After this initial burnishing the but never cuts the way it was designed to and the user discovers that he needs to burn his way through the cut creating sawdust instead of clean shavings.

[Jacob Reverb]

How can going too slow cause a bit to heat up?

Dunno. Maybe they mean the "feed rate," rather than the "cut rate," is too slow.

[Howard Acheson]

Is it a good or bad idea to cool down (while it's revolving) a forstner bit? Will a wet bit which is then somewhat wet harm the stock?

I wouldn't do that.

The best and traditional way to cool the bit is to sharpen it and to slow down the speed.

[Tom Esh]

I wouldn't do that.

The best and traditional way to cool the bit is to sharpen it and to slow down the speed.

+1.
I've also found a vac hose positioned near the bit helps immensely. It pulls extra air across the bit and more importantly clears the cuttings. With a sharp bit and proper speed / feed, sufficient heat should be removed with the cuttings to avoid overheating.

[Peter Quinn]

#2+ on sharp bit appropriate speed, clean chips. I like to use a vacuum and sometimes compressed air too. The trouble with keeping the steel cool is how to know you haven't gone too hot. At the tips of the cutting edge it doesn't take so much for a clogged dull cutter to get very hot. Same on a grinder with chisels. The water itself won't hurt the steel, but the rapid change in temperature if you get too hot wont do you any favors. A good HSS Freud diablo at my local Borg costs $12-$22. Mostly by the time I've bought wood and spent time working it, I have a lot more invested in it than that. I know a guy that spent 6 months building a beautiful guitar, then wet sanded the finish with water/ soap instead of mineral oil or spirits. Wanna know what that looks like today? All that water went into the holes for electronics, absorbed , released through the finish over time. Think water wont hurt wood? Think again.

[Jacob Reverb]

The water itself won't hurt the steel, but the rapid change in temperature if you get too hot wont do you any favors.

If you get it hot enough to reduce the temper, the edge is already toast, whether or not you quench it again. Actually, quenching will make it harder (but probably too hard, which was the reason for tempering in the first place – to reduce the hardness).

[Steve Jenkins]

One thought that occurs to me is that this may be a production set-up and even with a sharp bit if he is trying to bore numerous holes in a timely manner the bit will get hot. I had a similar problem with a router bit making rope molding. I went to the MSC catalog and bought a "cool gun". It uses compressed air and emits a jet of air that is about 70 degrees cooler than ambient temp. Using this directed at my router bit I reduced sharpening by a factor of 10.

[Gary Kman]

..... I know a guy that spent 6 months building a beautiful guitar, then wet sanded the finish with water/ soap instead of mineral oil or spirits. Wanna know what that looks like today? All that water went into the holes for electronics, absorbed , released through the finish over time. Think water wont hurt wood? Think again.

Now someone has added SOAP to the equation. Last time I taste tested soap and water has different properties than plain water, much different.

Then if one were to study the effects of water on people rather than wood and only used the voyage of the Titanic for a reference I think we would be advised to avoid water at all costs.

And last wet sanding a guitar with "mineral oil"? That's a new one for me. Perhaps that's the secret to that greasy sound on the Ramones first album. Live and learn.

[John Buzzurro]

Just a thought - I use something to reduce the friction on my drill bits when overheating is a concern. Works with saw blades and router bits too:
http://www.woodcraft.com/product/200...l-1034-oz.aspx

[John Bell]

I have a hunk of aluminum that I picked up somewhere that I lay stuff down on like sawzaw blades and drill bits to cool.
And for my drill press I use a clamp-on heat sink for small bits and a large spring clamp for larger bits. Just remember to remove the clamp before turning it on. Its not as fast as water, but effective just the same.



I’m going to make a larger heat sink out of an old CPU cooler attached to the spring clamp, but just haven’t got around to it yet. I don’t have time this week, but maybe next weekend.

[george wilson]

It is true,heat removes temper,not water. I was toolmaker for Colonial Williamsburg,now retired. Don't post here much.Keep in the Neanderthal section. It is still not a good idea to quench HSS bits,anyway,because it can cause cracks in them. The best thing to do is not let your bit get too hot in the first place. I've seen many a Forstner bit burned blue,and THAT will have ruined it already. Most of them are carbon steel unless you pay good money. Keeping them sharp is an excellent idea. So is having more than one to use if drilling a lot of holes.

[Tom Esh]

Just a thought - I use something to reduce the friction on my drill bits when overheating is a concern. Works with saw blades and router bits too:
http://www.woodcraft.com/product/200...l-1034-oz.aspx

I didn't notice much difference with Forstners, but it sure improves chip ejection on twist / bradpoint bits. Saves a lot of time pulling the bit to clear chips when you've got a bunch of deep bores to drill - like dowel joints. Only downside is it STINKS (like a pile of burning tires) until it dries.

[Lee Schierer]

I'm not a metallurgist, but I don't think you can get a forstner bit hot enough drilling wood to lose the temper. It seems to me you have to get it cherry red and then let it air cool for the temper to change. I don't think wood will get it that hot. As others have mentioned dull bits and improper speed will cause problems. Heating steel to cherry red and quenching it in oil or water will harden it. Water generally cools too quickly for good crystal structure so oil is normally used.

[george wilson]

Carbon steel will lose its temper at MUCH lower heat than red hot. I'm a retired master tool maker. Depending upon what you want carbon steel to function as: 750º for springs,normally about 400º for things like drills. Red heat in normal light is going to be about 900º or higher. You can EASILY ruin the temper in a carbon steel bit by overheating while drilling. By the way,if the drill got red hot,the wood would long since have caught fire!!

HSS steel is so called because it has alloys that make it able to stand much more heat. It is TEMPERED at about 1000º. Much higher tempering than water or oil hardening steels. HSS is air cooled,by the way,which is why pouring water on it when it is already hot is not a good idea. It will cool it to quickly and can crack it. Some machinists abstain from quenching HSS tools while grinding,but it's o.k. IF the HSS is not allowed to get too hot while grinding it. I quench every 2
or 3 seconds if the tool has a thin cutting edge.

Carbon steels(the common ones) are either water or oil quenched. If it is oil quenched,quenching in water will cool it too fast and can crack or distort it,and make it much too brittle. If it is water quenched,oil will not cool it rapidly enough to harden fully,except in very small tools like awls. In either case,steel as quenched is very hard,but brittle,with no mechanical strength. Tempering is how you take away some of the excessive hardness and add toughness. A spring is quite tough,but can be filed. Saw blades are spring tempered(hand saws). Generally,for a knife blade,you want a harder temper,and might go for the 400 degree temper. I am greatly simplifying this whole business just for a quick explanation.

In the ancient art of starting fires with a rotating stick against another piece of wood,most frequently using a bow drill type mechanism,you had to reach 451º F just to get paper to burn. And that was with wood,not a steel drill.