Crispy fried blades

Re: Crispy fried blades

John, NY

>Firstly, the prediction of depth of thermal damage due to grinding is a very, very new science so there really is no easy answer to how deep...

Secondly, the way I deal with this is I grind the edge flat until I get rid of ALL of the discoloration, i.e. I shorten the blade. I then give it another couple of passes to get rid of more just in case. Then re-establish the edge, grind the bevel and re-sharpen. If you find that it isn't holding its edge well then each time you resharpen it'll get better. There is no reason to trash the blade, at worst, if you don't grind/sharpen off enough you'll have to sharpen a little more often. Eventually you'll get there and I can certainly never get enough sharpening practice...

Tempering Colors

Steve Elliott

>There was probably little or no damage even to the edge that turned brown. When a hardened blade is re-heated to temper it, the surface turns colors in the following order: pale straw, dark straw, brown, vermillion, purple, peacock, blue. Plane blades made from high carbon steel should be heated until they reach light straw, which is somewhere around 380 degrees F. The blue areas on an overheated blade have reached around 600 F.

The very tip of your blade might have been softened a little, but by the time you have reground the bevel, all the damage will be gone.

Reassuring - thanks

Dave (Arlington, VA)

>Hi John -

What you suggested is pretty much what I did. So, thanks for the reassurance. My problem couldn't have happened on a better blade. This blade either has soft spots in the hardening or relatively large, irregular depressions (definitely not pits) on the back of the blade that is making it a bear to flatten.

This is the one blade that is crying out for me to try a back bevel on it because there'd not be too much to lose.

Thanks for your post -

Dave

Now its coming back....

Dave (Arlington, VA)

>Hi Steve -

Thanks for your post! Sometimes I wonder what's happened to my memory. It's probably been less than three weeks when I was reading a book from our local library on making your own hand tools for woodworking and it covered the various colors your describe (pale straw, dark straw, brown, vermillion, purple, peacock, blue) as part of the heat treating process. How quickly we forget! Still there was nothing in there about how far the tempering process might be affected by the heat from careless grinding.

I would hate to waste my time on this blade. So thanks for letting me know that it work the effort to keep working with it.

Regards -

Dave

Re: Crispy fried blades

joel

>As others have mentioned tHe simple solution to a burned blade is grinding past the burn.

However a light straw probably won't effect anything as the blade would normally have been tempered to a straw anyway. so there is no reason to panic. If I get a straw on a blade if it's minor I will usually just ignore it. In a few sharpenings the area will be gone anyway.

On oil or water hardening steel blue will definietly indicate a softened blade.

However - and this is the cool bit. On A2, HSS or other modern alloys you can heat to blue with no problems. HSS can actually I think go to cherry red and not get softer. THese steels have higher tempering temperatures which is why a little extra heat doesn't damage the steel. for me, who always uses a dry grinder it means I can grind faster with no worries if I occasionally get too aggressive.

A few thoughts

jim_reed@marietta

>1. This is a blade for a #4. If it is an original Stanley, it is pretty soft to start with. Try scratching the affected area with a pocketknife and compare it to other spots. You may not be able to tell the difference. Don't worry.

2. Grinding out the discoloration is certainly an option, but why bother? If you use the blade and it works great, you have saved some metal. It may take more frequent sharpenings for a while. Kind of a toss up.

3. Remind yourself to keep good tools away from the grinder. HSS is an exception. Get a good water wheel.

4. Good luck.

Thanks, Joel!

Dave (Arlington, VA)

>Hi Joel -

Sorry for the delay posting. It was a busy weekend and I didn't get much woodworking (or internet) time.

I appreciate your reassurances on the heating problem with this blade. I went really slowly, and I dunked the blades frequently I would even touch them (gingerly) as they came off the grinder and never found them to be very hot at all. That's why I was so surprised at the discoloration. I guess its because at the edge where there's not much metal it can heat up locally quite quickly.

Again, thanks for your post.

Regards -

Dave

Thanks, Jim.

Dave (Arlington, VA)

>Hi Jim -

Been away from the computer this weekend. Sorry for the delay getting back to you on your post.

Thanks for the ideas.

Sadly, this blade doesn't even make it up the quality of a standard Stanley #4 blades. It's a Dunlop - and I've never seen the back of a blade quite like this one. It has four "depressions" on the back of the blade (not pitting) not quite half the size of a pinky fingernail. One of them is fairly close to the edge so I'm really not sure how much I'll be able to use this blade. I couldn't have picked a better blade to de-temper (even if locally).

I don't use my grinder much (at least so far) so I don't think I'll change from my dry to a wet grinder though there's no doubt it be nice not to worry about "bluing."

And, as you suggest, I have a couple of Hock blades and - so far - they've not touched the grinder.

I am hopeful (over time)that I'll be able to learn the idosyncracies of the high speed grinder and use better techniques to get good results.

Again, thanks for your post and your suggestions.

Regards -

Dave

Re: Thanks, Joel!

joel

>Dave,

acouple of things. When I grind I keep my fingers on the blade as close to the edge as I dare. fingers burn at under 200 degrees - steel turns straw at 400. This is how I know when to dunk. If I can't keep my fingers comfortable on the blade I know it's too hot and needs dunking.

My fingers also are applying pressure so the tool gets ground.

from the trouble you are having I would suggest you might not have a dressed wheel. any wheel will seriously benifit from frequent dressings to remove any glazing and run a lot lot cooler. A white wheel or the new blue wheels will run a lot cooler than the old grey wheels.

On a grey wheel any dresser will do. An the white or blue a SC stick is cheap and will work, but you will get better results with a multipoint diamond dresser. (Delta includes on with the grinder which I think is a really nice thing)

Re: Another 2 cents!

John, NY

>I too agree with Joel in that a slight discoloration doesn't really matter and I don't think you're going to be doing significant damage to the steel untill you are at least a deep blue.

One thing I did think of this weekend, since I was doing a lot of sharpening was, I find if I am regrinding an edge then the existing sharp edge will burn/overheat very easily. To stop this I always grind off the sharp edge (about 1/64th to 1/32nd of an inch depending on how many times the edge has been touched up before I decide to resharpen) and create from scratch.

Another thought about high speed grinders... The speed we are concerned with is the linear speed of the grinding surface. A 1750 rpm 8" grinder has a surface speed of ~44000 inches/min, a 3500rpm 6" grinder has a surface speed of ~66000 inches/min. Using a friable wheel makes things a little better too. So a 6", 3500rpm grinder running a friable wheel (a white or pink one I think) really isn't that much worse than a 1750rpm 8". If you are running a 8" high speed, consider putting a 6" friable wheel on it!

Grinder wheels

Dave (Arlington, VA)

>Hi Joel -

Thanks, again for you post.

On putting your fingers close to the edge when grinding: I'm not sure I have enough courage to do that. Frankly, I find it a bit intimidating to stand in front of a device that is spinning at 1750 rpms. Maybe as I gain experience, my confidence will grow. In the meantime, my thought has been - go slow, and if in doubt, dunk (in water, that is)!

On dressing the wheel: yes, I did dress the wheel before griding and several times during the grinding session. It's a garage sale grinder and I have no idea how the machine or the wheel was treated before I got it (except that it had brass in it when I got it).

I use a star wheel dresser and I know my (gray) wheel will run cooler if I keep it dressed. On the color of the wheel, your comment is interesting. For some reason I have a clear recollection of a thread on Badger Pond in which Larry Williams (of Clarke and Williams' fame) argued forcefully that the gray wheels actually run cooler. I can't recall the points in his argument right now, but I do recall that his view was at odds with a number of other posters. Of course, I have too little experience to know anything about this - except what I read.

Again, thanks!!

Regards -

Dave

Thanks, John.

Dave (Arlington, VA)

>Hi John -

I also appreciate your reassurances that I probably haven't done any major damage to the blade.

On grinding off the edge: I had done that on all the blades I was sharpening except for one - and, no surprise, the one I discolored was the one I forgot to take the edge off of. I had read this "tip" someplace and decided to use it. I guess my experience shows the reason that more experienced grinders do this.

Also mine is an 8" 3580 rpm grinder, I will definately keep you idea of using a 6" wheel in mind.

Thanks, again for your post.

Regards -

Dave