Thread: Time-effective alternatives in sharpening

Hi Mark

you didn't mention what type and grade of stone you have in the grinder.
this is probably the biggest variable in respect to controlling heat build up

the next is the type of steel you are grinding -- some wheels are better than others when grinding heat treated "normal" steels.

have a look at this article by Derek Cohen http://www.inthewoodshop.com/Woodwor...ngNirvana.html

My guess is that if you change your grinding wheel to one that runs cooler, you can do away with quenching and produce an edge ready for honing straight off the wheel

Thanks Ian,

Stupid of me not to mention the wheel.

It is a Norton 38A60 JVBE BV200611 (white). When I bought it about 5 years ago I was after approx 60 grit AlOx with friable binding (about J).

Is there a better wheel I should buy now (blue, gel, etc). As soon as I read about these things I forget them....

Cheers
Mark

Mark. I do a lot of sharpening; sometimes over 100 chisels in one session. I never quench any of them and do not get the ends too hot that they burn.
I made my own tool rest as the ones on the grinders when you buy them are hopeless.
I grind the chisel making sure I work the end accross the wheel. For a hollow grind make sure the first touch on the wheel matches the existing grind. This will save you a lot of time. Just adjust the tool rest up or down because grinding the whole chisel bevel again to match the angle of the tool rest maybe causing your long grinding sessions causing heat build up. Do not park the chisel in one position or force it against the wheel. I never grind too long, as once I feel the transfer of heat into my finger tips I stop grinding and start on the next one and then go back to the one that was heating up. I dress the wheel regularly as the clean surface keeps the grind cooler. Sparks coming over the end of the chisel tip will tell you that the grinding is complete.

Yes I do believe that the slower RPM grinders are better and the grinding
stone is important, but saying that I do a lot of sharpening on the faster RPM
one and with a run-of-mill wheel with good results.

I use a 600 grit diamond stone to flatten the back and do the micro bevel with one rub down the stone.


Gary

I don't understand this time business you seem to be flustered over. To sharpen a tool, any tool, takes as long as it takes. The better you want the sharpness the longer it will take to get it that sharp. Use a blunt tool and see how much longer it takes to finish a job

Mark
also have a look at this video
Bench Grinder Basics - Fine Woodworking Video

for later readers, it will go behind FWW paywall around the end of August 2012

Hi Ian

All my dry grinder wheels have a slight camber. These are created with a diamond dresser. The camber makes it very easy to hone accurately and this keeps the heat down (it does not get hot in places where you are not aware).

I still have a 46 grit Norton 3X wheel, which is fantastic (the best available) at grinding cool. However it is a very friable and makes a hellava mess. So-much-so I tend to avoid using it and just use the white 46 grit. I can hone to the edge of a blade without burning it. It just takes a gentle hand and patience. Dunk the blade if it starts to get hot.

Mark, the half-speed grinder does create less heat, but there are a number of factors that are equally important in doing so.

The speed at the circumference of a 6" high speed grinder is (I am told) nearly the same as a half-speed 8" grinder.

Coarse and friable wheels are best: 36 or 46 grit.

Dress the wheels very frequently to keep them clean and cutting at their optimum.

At the end of the day, if you can afford it, a Tormek is the best grinder around. What it lacks in speedy grinding it makes up for in safely grinding to the edge of a blade, which speeds up honing. One can get away with a single 8000 or even 12000 waterstone. Or use, as I do, a 6000 and 13000. The 1000 is not really needed until the bevel is worn a few times.

Regards from Perth

Derek

Originally Posted by derekcohen

Hi Ian

The speed at the circumference of a 6" high speed grinder is (I am told) nearly the same as a half-speed 8" grinder.
Derek

That doesn't sound quite right Derek. I think the smaller wheel at the high speed would be 1 1/2 times faster at the circumference than the half speed 8".
cheers,
Jim

We are using CBN wheels now at Robbos. Hardly any heat generated. Certainly minimal sparks. Beautiful edge. has also made a slower speed grinder which is working really well. 1400ish rev AIR. Jim Carrol has the CBN wheels now. No where near as exy as a Tormec either.

Many thanks to Ian, Gary, Derek, Anne-Maria,

I now get the idea of shaping rapidly on a bench grinder and sharpening on a Tormek, then straight to micro bevel on a fine stone.

Sounds like the fastest way to me when an edge is damaged.

Tangential Velocity
I used an online calculator and found: at the same shaft rotation the speed at the circumference of an 8" wheel will be 33% more than that of a 6" wheel.

This seems to make sense, given "tangential speed of the object is linearly proportional to the distance from the center" and 8 is 33% greater than 6.

A 6" wheel at 2750rpm has tangential velocity of 3.437 m/s.
An 8" wheel at 1425rpm has tangential velocity of 2.375 m/s.
The 6" wheel is 45% faster.

Anne-Maria, what is a CBN wheel?

Regards,
Mark

Originally Posted by MarkInBoatshed

Anne-Maria, what is a CBN wheel?

CWS Store - Optigrind CBN Grinding Wheels | Carroll's Woodcraft Supplies

Tangential Velocity
I used an online calculator and found: at the same shaft rotation the speed at the circumference of an 8" wheel will be 33% more than that of a 6" wheel.

This seems to make sense, given "tangential speed of the object is linearly proportional to the distance from the center" and 8 is 33% greater than 6.

A 6" wheel at 2750rpm has tangential velocity of 3.437 m/s.
An 8" wheel at 1425rpm has tangential velocity of 2.375 m/s.
The 6" wheel is 45% faster.

Hi Mark

Thanks. That helps.... but what is the TV of a 8" wheel at 2850 rpm? You do not provide that info. Your details indicate that the 6" wheel is 45% faster bit this is against the slower 8" wheel. My comment was that a 6" wheel at 2850 rpm would have less surface speed than a 8" wheel dat the same 2850 rpm. Extrapolated from these figures that seems so, but is it really?

That doesn't sound quite right Derek. I think the smaller wheel at the high speed would be 1 1/2 times faster at the circumference than the half speed 8".
cheers,
Jim

Hi Jim

Try this anology: if you have ever waterskiied behind a powerboat and swung in an outside arc when the boat turned, you would know the sensation of crazy speed. By contrast, instead just stay directly behind the boat as its turns, and your speed is much, much slower.

Regards from Perth

Derek

To work out the tangential speed is very simple, just a matter of the circumference of the circle which 22/7*diameter, and then compare the ratios.
6" wheel is 19 inches (close enough)
8" wheel is 25 inches (close enough)

So, 6" wheel at 2700 rpm has an rim/edge velocity of 855 inches per second (19*2700/60)
An 8" wheel at 1400 rpm has a velocity of 583 inches per second, or 68% of the smaller wheel at higher revs. And that's perzackly what Jimbur said (583 x 1.5 = 874 so close enough).

Derek, you're right about the big arcs on a ski rope - I did it just the once!

EDIT: 8" wheel at 2850rpm is 1194 inches per sec

HTH

8" wheel at 2850rpm is 1194 inches per sec

So an 8" wheel at 2850 rpm is indeed nearly 50% faster at the circumference than a 6" wheel of the same motor speed.

Regards from Perth

Derek

Originally Posted by derekcohen

So an 8" wheel at 2850 rpm is indeed nearly 50% faster at the circumference than a 6" wheel of the same motor speed.

Hi Derek, given that there are no square roots or squares (to the power of 2 type squares) involved, the relationship between two diameter wheels at the same rpm is even simpler than I explained - it's a direct ratio between the diameters, so we have a 6:8 ratio which is the same as 3:4.

That simply means that a six inch wheel will be 3/4 of the speed of an 8 inch wheel, or put the other way around an 8" is 4/3 of a 6" (in other words perzackly 33.33% faster). Doing it this way takes out all of my "close enoughs", which at face value led it to be a little closer to 50%, and that was because 25 inches circumference was rounded down, and 19 inches was rounded up.