Thread: 3 sharpening questions if I may....

Originally Posted by Tiger

3 things have been puzzling me during my wonderful venture with sharpening chisels.

1 Most of the time I get the chisel razor sharp straight off the grinder, sharp enough to dry shave arm hair. After this, I take to the oilstone, first coarse side, then smooth side, I find this does nothing to increase the sharpness of the chisel. Sometimes it actually reduces the sharpness. Now I'm very careful with holding the bevel down on the stone, could there be another explanation for the reducing sharpness or have I overestimated my ability to keep the chisel's bevel in full contact with the stone?
If you use a jig to hone with you eliminate the problem

2 When a chisel's tip is slighlty blued, does the chisel need to be re-tempered or the blued tip simply ground off.
Theoretically


3 The razor sharpness doesn't last very long, do you guys just give it a quick hone on a strop or back to coarse and smooth stones to get that really sharp edge again?

.

Originally Posted by Tiger

Most of the time I get the chisel razor sharp straight off the grinder, sharp enough to dry shave arm hair.

I'd love to know how you manage this! Straight from my grinder the chisel is next to useless.

Originally Posted by Tiger

After this, I take to the oilstone, first coarse side, then smooth side, I find this does nothing to increase the sharpness of the chisel. Sometimes it actually reduces the sharpness.

I find that I have to get down to 0.5 micron honing compound to get it sharp enough to shave with. If you're using a combination Silcone Carbide/Aluminium Oxide (Norton or Bear) Indian stone from Bunnings then this is no surprise to me. Waterstones, honing compounds and diamond paste are the only things fine enough to get a seriously smooth, sharp edge as far as I'm aware.

Originally Posted by Tiger

2 When a chisel's tip is slighlty blued, does the chisel need to be re-tempered or the blued tip simply ground off.

In theory you can simply grind this part back, but there is evidence to suggest that the softening of the steel could go much further than the blued region. It seems many a chisel has been ruined with a heavy handed grind.

Originally Posted by Tiger

3 The razor sharpness doesn't last very long, do you guys just give it a quick hone on a strop or back to coarse and smooth stones to get that really sharp edge again?

For me a quick trip back to the honing compound on some flat MDF is enough for the first two or three micro bevel touch-ups. After this I tend to go back to a 1200 grit waterstone for the primary bevel then move through the 4000 stone before finishing on the honing compound again for the new micro bevel. I only bother with the grinder when the 1200 stone takes too long to recover the small micro bevel area.

Regarding the soft edge, there are three possible reasons for this; a) you've seriously softened the steel through over heating, b) because the edge isn't necessarily smooth straight from the grinder it may wear faster and c) the steel used to make the chisel isn't all that flash. Personally I think a focus on your grinding might show up the cause for this, whether it be the wheel you're using or the technique I don't know.

More information please!

Thanks for the comments.

Bob, I don't like using the honing jig but I'll get it out and see if it makes a difference.

Kman, I use a 80 grit white wheel on my grinder and a very soft touch (usually). I do have a fair bit of experience grinding woodturning tools and the first tools I bought were carbon steel so you learn soft touch and some technique from that. You're right about the stone, I use the Bear from Bunnies. It seems to be a reasonable stone in that it cuts fast but don't know what sort of grit it is. You make some good points on no. 3 and I wish there was an easy way to test whether a chisel has lost its temper.

I must bookmark this thread. Sharpening is an interesting subject to often overlooked on this forum

I think my wheel is a 46 grit or something, but I never bothered to practice getting a good edge on the grinder either, I use the stones for that. I'd considered getting a 120 grit wheel also, maybe I will

Tiger

A couple of points ..

If you are grinding a sharp edge off a 80 grit wheel, then you are grinding to the edge of the blade and this will likely burn the edge (blueing) since it will create a lot more heat.

The subsequent edge may shave hair but it is still only 80 grit. Compare this to 8000 grit on a waterstone!

The edge will be quite serrated, which is weak as it will break down quickly, hence it will not last long.

You can grind back a blued edge, but you do need to go beyond it. I consider that bluing is not the danger colour - get the steel dark brown and it has been overheated.

Regards from Perth

Derek

Hello,

Originally Posted by Lignum

I must bookmark this thread. Sharpening is an interesting subject to often overlooked on this forum

Right...

I feel at the same time excited and uncomfortable when following these descriptions about different kinds of branded Mythical Lapping Rocks and Rouge Ectoplasmas offering both progressive cutting action and obviously a large amount of midichlorians or just plain Chakra packed in them. Then we shave our hair off (to show off to everyone we have lotsa hair to shave off ), some even remove them hair roots (extreme sharpness, only for them Truly Sharp Guys ).

Despite always exciting, sharpening is also a bit grindy and uncomfortable topic to follow, one of the most passionate subjects ever, especially amongst us males. I feel it's hitting the bullseye of one of our weak spots like nothing else, like someone taking advantage of some incurable inborn addiction of others. Sharpening must be surgically designated topic to us males, especially when we are also by nature eager to grab at anything causing some kind of trouble. I just pray, may our souls be saved from bad when engaging the battles of high-intensity sharpening discussion .

I'd like to be aware of the true relations and interaction between different types and hardnesses of steels and sharpening mediums. But, because Mother Nature has one helluva sense of humor, she arranged it so that abrasive wearing is probably one of the most difficult areas of combined thermodynamical phenomena there is. Every effective factor is constantly altering, causing a situation where things are moving almost, but not quite to the same direction. It's an ingenious joke, she will be never getting bored because of what these tiny variations in phenomena will cause amongst males. Oh my, what a lovely b*tch she is .

I really want to know something more than just brands of sharpening mediums. Commercial brands have sometimes a bad tendency to degrade in quality, especially if some particular brand suddenly experiences a sudden and intense credibility boost. There is blood in a water, and a business sharks will soon appear.

Therefore I'd like to look under the hood, to see what actually is going on there. It is a fact that during a period of time, quality costs are about the same no matter where it is made. If something is made from real materials, to achieve the same strength, finish and performance, there is needed about the same materials, process design and labour and machinery. Business courage and character between operators may be very different, of course.

It is true that sometimes there appears so called distruptive technology, questioning the efficiency of current mainstream technologies and methods, like some new manufacturing process or principle. But it does not generally happen that suddenly.

Sorry guys, I have been today again worrying about some quality issues. My bad, hope you did not get disturbed about me venting hereabouts .

kippis,

sumu

Thanks, Derek, some good points. I thought I was saving time by grinding to a thin edge but maybe not the best thing to do in terms of longevity for the chisel's edge. Interesting about the bluing too, won't feel quite so bad next time I go too far with the grinder.

Think in terms of shaping on the grinder and sharpening/honing on stones or W&D.

Shape the primary bevel but sharpen the secondary IMO.

Originally Posted by derekcohen

You can grind back a blued edge, but you do need to go beyond it. I consider that bluing is not the danger colour - get the steel dark brown and it has been overheated.

I can't say with any certainly what temp is required for the steel to change colour, but Rc61 hardening means tempering at ~200 degrees Celcius. I'm sure it would be very easy to go beyond this with a grinding wheel.

From this example for plain carbon steel, a blue temper colour might indicate a hardness change to around the Rc56 regoin based on this temper hardening chart.

I'd seen somewhere that a tempering colour of pale yellow was good for blades, this is also consistant with the charts.

A reference for hardness and home tempering of O1 tool steel is here. I think the colour that you're talking about, Derek, is probably where the hardness changes to around Rc40/44.