# Does blueing tools really hurt anything?



## hwebb99 (Nov 27, 2012)

I recently bought a used lathe. It came with a bunch of tools. All except two are Robert Sorby. The previous owner sucked at sharping. The profiles are all messed up, and most of them have been overheated sharpening. Does this really hurt anything.


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## Steve Neul (Sep 2, 2011)

I thought you were talking about gun blue. Yea heating the tool to the point of blue will soften the metal a little. All that will really happen is you will have to sharpen them a little more often.


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## Tennessee Tim (Dec 15, 2010)

There's ways to correct this.. one is when ever sharpening always keep a small container of motor oil or wd-40 to quench the ends in EVEN if not overheated. This is a basic way to reharden edge. I've made a chisel from spring stock and watch people make knives but the technical part of when and what orders to heat and cool I just refresh my mind prior to building.

As with a good knife/saw/chisel edge is to keep lightly touched up through out use not when dull as I tend to do.....bad habits are hard to break.

Looks like a great find!!!


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## Bill Boehme (Feb 9, 2014)

hwebb99 said:


> I recently bought a used lathe. It came with a bunch of tools. All except two are Robert Sorby. The previous owner sucked at sharping. The profiles are all messed up, and most of them have been overheated sharpening. Does this really hurt anything.


Yes, it does degrade the quality of the steel a bit, but not to the degree that it does with high carbon tool steel. Sharpening, when done correctly, should not do more than make the edge feel barely warm. If the edge feels hot then you're doing something wrong and if it turns blue you're doing something terribly wrong. I would say by the look of the tools that you are right in the assessment about the sharpening skills of the previous owner.

My guess is that he was using a silicon carbide grinding wheel. The thing about silicon carbide is that the carbide grit gets dull after a while and they don't slough off like the the grit on an aluminum oxide wheel. So, if he wasn't using a star wheel dresser regularly then the tools were just rubbing against the wheel and wearing down the edge from scuffing rather than cutting.

Common folklore among woodturners is that bluing the edge is OK. That's not exactly true. The difference with HSS is that the blued steel develops microscopic cracks that cause the edge to fracture off sooner than an edge that hasn't been blued. A little bluing isn't anything to worry about and it's hard to quantify in woodworking terms how much the effect will be on a tool that is very significantly blued.

One thing that I would not do is quench HSS tools that get really hot. Quenching ruins the temper and is just a crutch for bad sharpening technique. Done correctly, heating is not an issue.

The thing that caught my attention was the SRG in your pictures. It could be an optical illusion, but it sure does look like it got pranged ... really bad.


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## hwebb99 (Nov 27, 2012)

What is an srg?


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## saculnhoj (May 18, 2015)

SRG is a spindle roughing gouge. Your large one appears to be bent at the tang. Probably got a really good catch one time possibly using it as a bowl roughing gouge which is not good. 
Despite what Bill said it's my opinion that you don't really hurt HSS by bluing it. Yes microscopically I suppose you can but did all the wrong things for years when learning and never could tell that it hurt my tools at all. I ground too hard and blued the ends and then quenched them while hot. All are not considered things to do today but I never did notice a problem with edge holding.
I would have to look up the exact temperature but temps to blue steel are somewhere around 600 degrees, maybe a little more. To take the temper out of HSS you have to heat it red hot or higher. It's designed to handle heat when used to cut metal. I've had my HSS cutters on my metal lathe get red at the tip and it didn't seem to hurt them. 
The old adage about grind away the steel until the blue is gone is wrong for HSS also. True with Carbon steel because blue heat does change the hardness of the steel on them. However on HSS just go about your normal sharpening procedures and eventually you wont' have any blue left.


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## hwebb99 (Nov 27, 2012)

Yes the srg is bent at the tang. IMO the tang was too small to begin with. Should I try to straighten it or can I use it like it is? There are two other srg's and they are also bent.


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## Maylar (Sep 3, 2013)

Depends on what the tools are made of. High carbon steel loses its temper when heated. If heated too hot for too long (subjective) they won't hold an edge for squat. I have however inadvertently blued chisel blades on a grinder and after slowly grinding back got back to hard steel again.

HSS metal cutting tools can glow red and not lose their edge. Dunno how that applies to woodworking tools though.

And yeah, I'd prolly straighten the tang on that roughing gouge. Just because.


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## epicfail48 (Mar 27, 2014)

In short, yes. I can go into a nice explanation of the hardening and tempering process for steel, but the moral of that particular story is once you've heated the steel far enough to get a color change, you've affected the temper and made the steel softer. High speed steels are more resistant to the effect than carbon steels, but still, the metal is now softer than what it was. They mipay still be usable, but be prepared to sharpen more often


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## Bill Boehme (Feb 9, 2014)

hwebb99 said:


> .... Should I try to straighten it or can I use it like it is? There are two other srg's and they are also bent.


It depends on how many times it was previously straightened. :laughing:

And, perhaps it was bent much further and this IS the straight position. Too much bending back and forth will work harden the bend and make it more likely to break ... if used incorrectly.

The fact that there were two other SRGs that also were bent is funny.


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## hwebb99 (Nov 27, 2012)

He must not have been a quick learner. He also had about 10 bowl gouges. I don't know why he needed to use a spindle gouge for bowl turning.


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## Bill Boehme (Feb 9, 2014)

hwebb99 said:


> .... I don't know why he needed to use a spindle gouge for bowl turning.


Maybe he loved a great catch. :devil2:


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## saculnhoj (May 18, 2015)

For HSS to be damaged by heat it has to be heated above Cherry red. Blue doesn't hurt it. Heat treating HSS is difficult process and requires very exacting temperatures above what we use to heat treat carbon steels. When I wrote the article on making your own tools for American Woodturner I did a lot of research into HSS. Don't remember all of it because it was well beyond what home woodturners would ever try. What I did find out was that the steel withstands a lot of High Heat and can do so continuously when in use. 
There has been a lot of talk by very knowledgeable people about quenching HSS saying it can cause micro fractures and hurt the edge. I'm not doubting them but like I said above I didn't know any better when I first started turning and grossly overheated the tools while grinding and conseqently felt like I needed to quench them so I did. I don't every remember it causing problems with the tools.


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## Bill Boehme (Feb 9, 2014)

One of the things that happens with quenching is some of the retained austenite gets converted into untempered martensite. The untempered martensite has higher lattice structure stresses than tempered martensite. This is at least the theory behind the micro-fractures. How does it impact woodturning tools? Hard to say since the main concern in these tool steel alloys is for machining metal and not wood. My guess is that the impact on our use of HSS tools is minimal.

Noticing a difference in edge longevity requires having a baseline for comparison ... but in all likelihood, we wouldn't have a baseline if all of our tools have undergone the same sharpening treatment where the tools get very hot followed by quenching. Even if we did have a baseline, comparisons are very subjective at best anyway.

The other side of the coin is that if we get the tools very hot during sharpening and then don't follow it with rapid quenching there is the problem of some of the tempered martensite being converted back to austenite.

The solution is avoiding getting the edge too hot. Generally, bad sharpening technique is the culprit for steel getting hot enough to blue the edge. Don't use silicon carbide grinding wheels. Aluminum oxide are great, AO/ceramic matrix even better, and CBN is better yet. Well, probably the best is a slow speed water cooled system (AKA Tormek). If you do blue the edge, it is generally the very thinnest part of the edge and not further back on the bevel where there is enough metal to conduct the heat away, so don't sweat it. Just work on improving sharpening skills.

Lastly, there are dozens of HSS alloys intended for a wide variety of purposes, so blanket statements about cutters getting cherry red when machining metal without adverse consequences can't be generalized as true for all high speed steel alloys.


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## saculnhoj (May 18, 2015)

Ditto on your last statement about dozens of alloys and that also goes for the heat treatment procedures. Shouldn't have made such a blanket statement. I've had some really crappy chinese made HSS turning tools that wouldn't hold an edge worth a darn. And then other such as Dway tools that are fabulous. 
Mostly what I was trying to get across is, don't worry too much about bluing tools. It doesn't ruin them. It's far better to simply learn to sharpen correctly. One trick is to touch the metal near the tip frequently when sharpening. If it's too hot to touch it needs quenching. This is still a low enough heat to not hurt the tool. If it burns your finger your getting it way too hot.


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## hwebb99 (Nov 27, 2012)

I can sharpen a tool with an established profile and it barely gets warm. It is trying to reshape these tools that have been severely screwed up is when I get impatient and over heat them. This is why I always recommend a beginner to buy a jig. I think this poor guy even used a jig. If I had to guess why he gave up wood turning I would say because he sucked at sharping.


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## Bill Boehme (Feb 9, 2014)

saculnhoj said:


> ..... If it burns your finger your getting it way too hot.


Have water next to the grinder to cool the tool and A-1 Steak Sauce for your finger. :laughing:



hwebb99 said:


> .... If I had to guess why he gave up wood turning I would say because he sucked at sharping.


That thought was rattling around in my head when I saw the pictures.


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