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Sharpening - Lathe Tools

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After a couple rookie mistakes with my lathe, I found I had a dull carbide turning tool. The tool itself was inexpensive, only 5 bucks, but it looked so easy to sharpen. And it was! I chucked a diamond sharpening steel - the kitchen type for touching up chef's knives - raised up the tool holder with a fender washer to raise the cutting edge up over the center line of the sharpening steel, and with the steel turning slowly, cranked in the tool until the carbide pad touched the diamond sharpening steel. The edge was sharpened and undercut from the radius of the sharpening steel. Now it is sharper than when it was new! I think I just found a way to extend the life of my turning tools by several-fold.  (Darryl Hayashida)

Do you have any suggestions on what grit to use and any suggestions on sharpening suggestions of the easiest way of sharpening lathe bits and saw blades?  I am sharpening challenged.  (David Ray)

I sharpen my metal lathe tools on a 6" circular sanding disk with 300 grit paper. Make a quick pass at the wheel and immediately dip the warm too in water. Make another pass, repeat.  (Don Greife)

Are you sharpening HSS or carbide bits?  That's a pretty gritty subject...  If they're just HSS, you can sharpen with a 60 or 80 grit grinding wheel.  The lathe bits aren't quite as critical as our plane blades.  If they're carbide, you need to get one of those "green" grinding wheels.  Not sure what grits they come in.  (Mark Wendt)

I've finally got my new bench to a point were I can start using my Craftsman lathe and wondered if anyone has any tips on bit sharpening/tuning.

I've got a grinder but have been warned not to use it, lest I ruin the temper of the bit. Does anyone know of any good online resources on the subject?  (Jim Lowe)

Here's a good basic introduction.  (Rick Hodges)

I sharpen my tool bits on my Tormek low speed water grinding wheel. I do the sharpening on the side of the grinding wheel and not the surface used for sharpening my planning blades. I don't notice any problem since the tool bit is being cooled with the water the same as the planing blades.  This may help.  (Frank Paul)

You might want to check into atlas_craftsman@yahoogroups.com

It's the Atlas lathe user list and they have tons of info and resources.  I've go a 12x36 101 with a 54" bed.  Talk about overkill for rodmaking!  (John Dotson)

If you are turning HSS bits on a grinder,  don't worry about temper.  Grind one side and dip it in some water close by.  Do all the sides in this manner. The bits will be fine.  (Don Peet)

Yeah. You don't need to worry about the bit. You'll have a harder time keeping your fingers cool. (Larry Swearingen)

Yer getting yer fingers too close to the wheel...  ;-)  Saw you had a post up on the Practical Machinist forum.  Nice looking reel.  (Mark Wendt)

I have used a grinder to shape bits for as long as I have had a lathe, over 50 years. You grind cool in water grind and cool. Don't let the bit change color from the heat. I have been around a lot of machine shops and that is how they do it, that is where I learned.  (Tony Spezio)

One option for preventing altering the temper (over heating) of your lathe bits is to use a grinder with a speed of about 1750 rpm and equipped with white aluminum oxide wheels, as they supposedly grind cooler than gray carbide wheels. This is the grinding setup for sharpening my tools that was highly recommended to me when I first started turning wood  about 15 years ago, and almost all turners of my acquaintance use.

I have made some of my own turning tools from lathe cutter stock and sharpened them with no problems on my grinder with the white wheels (yes, I also have one with gray wheels!).  (Frank Schlicht)

Machinists have been grinding High Speed Tool Steel since the beginning of time.  You just have to be cautious about material removal.  Start with a very coarse wheel to develop the desired shape relatively quickly, dunking the tool in water frequently to keep it from getting too hot.  You know it’s too hot if it starts to turn yellow or worse yet, blue.  Usually, if it is that hot, you can’t hold onto it anyway.  When you’ve got it roughed out, move to a fine wheel to finish it up.  A fine wheel puts a smooth edge on the tool so you get clean cuts but it tends to remove little material and overheats the tool easily.  Again, dunk it a lot.  (Al Baldauski)

Someone correct me if I'm wrong, but doesn't high-speed steel retain its hardness even at high enough temperatures to turn it red? Isn't that the technological-metallurgical improvement that makes it superior to carbon steel? If so, does it really matter that it turns blue when it it's sharpened?  (Steve Weiss)

I wasn't going to speak but now that you bring it up Steven, you are correct sir!  Machinists have NOT been grind HSS since the beginning of time, since maybe the early 20th century. I'm petty sure it wasn't in common use during WWI but available for a high price.  Kind of like Carbide tooling during WWII.   I've got some OLD rusty small tool bits that I got at a Garage sale that are NOT HSS and I do have to be careful grinding them or they WILL turn blue pretty easily. Modern HSS bits are no problem for me. You CAN turn them blue but I burn my fingers before that happens. That said I'm still careful when I have to grind my high priced plane irons.  It's much easier to concentrate the heat in the very thin cutting edge of a plane iron than it is in the blunt cutting edge of a lathe bit. So when I'm grinding a lathe bit fresh from a new bit I keep some water handy to cool off the bit so I don't burn my fingers, not because I'm afraid I will "draw the temper" of the HSS bit.  (Larry Swearingen)

Since you insist on crossing T’s and dotting I’s, technically you are correct.

Some HSS materials will retain their hardness up to 1400F but the hardness/temperature curve is a “curve”.

As you approach 1400F the material loses hardness as it approaches that point.  It doesn’t all-of-a-sudden change from hard to soft at 1400.001 degrees. In sharpening an HSS tool, if you see the color turn blue, that indicates you have exceeded a temperature of about 600F. At the very thinnest edge of the tool I can guarantee you the temperature has gone MUCH higher because the naked eye can’t detect it and the hand can’t move the tool away fast enough to prevent it.

So, in an effort to provide a technique which will give a visual indication of a SAFE procedure for sharpening HSS I took some liberties in absolute correctness.  And “Since the beginning of time” was poetic license to indicate that it’s been in use for quite a while, today’s HSS alloys since the early 1900’s.  (Al Baldauski)

That's true... archeologists have been turning up hammered High Speed Tool Steel arrowheads all over the place. It was the concept of a "wheel" that took it so long to catch on, though.  (Mike St. Clair)