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When the Edge Turns Blue

See the little blue patch in the picture above? Right on the cutting edge. The metal there has been overheated. Has this happened to you? Probably very suddenly. And you know it's a disaster!

In this lesson I want to explain what exactly has happened - what you've done - and various ways to avoid it happening ever again.

But if it does? I'll break the news gently...


| 27 February 2020 16:04

Chris, I think the inside bevel did it. My first one! Thanks!!

| 03 February 2020 08:41

Ann - If you mean the edge is crumbling as you carve then, assuming all is well with the metal as you do, it means the 'wedge' of bevel behind the edge is too acute, too weak.
That outside bevel is no doubt too long. The best thing to do is leave the outside bevel alone and add inside bevel thus increasing the overall 'wedge' angle while keeping that low outside bevel. You can draw the edge back to a white line first or just start adding the inside bevel with slipstones trying to keep a straight cutting edge.
Let us know how you get on!

| 02 February 2020 10:38

Chris, one of my favorite tools, a Stubai sweep 4 x 14mm, won't hold its edge anymore. It never turned blue. My most aggressive grinder is a half-speed with a CBN wheel. I've been successful in recommissioning some other gouges, even more difficult sizes, but this one just isn't coming back to life for me. It's thin and has a low, long angle. Should I try recommissioning it? Does it need a longer or a shorter bevel to try and get it to an edge that will really hold and work?

| 28 December 2017 09:24

Azucena - Not really, with the proviso that cheap machines you get from DIY stores often have cheap wheels, which wear quickly or are not as consistent in structure (so the wheel is a little off-balanced). But you can readily replace them. I use Norton, as a reliable manufacturer.

| 27 December 2017 01:32

Are there other types/brands of wheels that you would recommend?

| 23 December 2017 08:42

Azucena - Yes, a slower speed is a good choice: half the speed means half the friction etc.
Since you are setting up and can choose your wheels, I think I'd not bother having different grits - you can get the fine effect by having a very light touch on the surface. I'd go for the 80 git for both, rounding one over for inside bevels.

These particular wheels wear quickly so you need to dress them regularly. (Use a dust mask!)
If you do want different wheels, 60-100 would be a good spread of grits.

| 22 December 2017 19:16

Hi Chris,
I've decided to invest in a grinding wheel to make the sharpening process go faster. I'm assuming the 1800 rpm is the better choice than the 3600 rpm, but as far as wheels go, the ones being offered are 46, 60, 80, and 100 grit. What are the better choices for an initial and finer grinding combo? The brand I'm looking at are the Norton 3X Super-Cool Grinding Wheels. Thanks for your advice!

| 16 February 2015 10:20

John - Thanks for those thoughts.The only stones that keep 'sharp' (ie sharp edge-cutting crystals) are the quickly wearing waterstones. All others, including diamond, do get their original crystals bluntened and cut less brightly: dressing freshens up the cut. Actually of course ALL sharpening stones - grinder, bench or slip - will wear and need looking after, especially if we want them flat; but that regular, light, maintenance dressing is a good idea for keeping them bright.

| 29 September 2013 07:05

Darlene - Water-cooled wheels such as the Tormek or Scheppach are slow, but safe: impossible to overheat the blade and no flinging out of sparks airborne grit.

| 27 September 2013 10:41

Very informative....great info. I have a Tormek 3 water cooled sharpening system. Any comments on this system and using it?

| 20 January 2013 15:10

Hello everybody,
in Germany one Shop for Carvingtools has an new Grindingwheel with 80's Grit. The Wheel is a special mixture of aluminiumoxid. The heat generated from this Stone is lesser as the heat from a electric buffing wheel.
Somebody has measured the temperature between 97¦Celsius and 126¦C. Normal 80 Grit will heat up to approx. 260¦C. I've tested this Wheel too and this is amazing grinding fun. No blue points.

Greetings from Germany,

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