How to pass Murray Carter 3 finger test of sharpness?

[HeavyHanded]

I reread this thread and now I want to ask: how light IS the pressure required on the 6k stone?? Or any other stone for that matter.

I'd like to know this estimate as well, I only what I use.

I've found if going even a bit too hard backhoning on waterstones with an acute angle the edge can literally sway over a bit - almost looks like a wire edge only more subtle.

On high RC steel it can fracture the last few microns right off the apex. I'd estimate I shoot for an ounce or less but is hard to say, even with a good digital scale the value jumps around and won't accurately read momentary shots less than an ounce or two.

Sometimes if I'm going from a coarse stone right to a polishing grade one I find I can use a bit of force - a couple of ounces for the first few passes as I'm working the high points down a bit. I suspect because the surface area is small, the contact pressure is even more amplified and those come down very quickly. Once I can see a bit of brighter finish along the edge I dial it way back.

I also believe the density and composition of the stone make a big difference - even very hard resin bonded stones will tolerate more force than a ceramic bonded/fired one before getting into trouble.

Edit to add:
I find once I get into brighter levels of polish my waterstone edges tend to reliably feel stickier than other means. In some cases not by a large margin and also tend to require more QC to really get the best.

The "stickiest" edges I have ever made came off of a clear maple strop loaded with Flexcut Gold and a few drops of mineral oil. Absolutely wicked catchy and would barely tug cutting the tops of a fingerprint whorl. Again, they took a lot of QC to reliably achieve and the boards are more prone to contamination than just about anything else you can imagine - not convenient but a great noodling exercise - also tolerated and actually worked best with a solid 6-8 ounces or more. The maple is more forgiving than a waterstone...

https://www.youtube.com/watch?v=gfblDsTy-FY

 

[HSC ///]

I reread this thread and now I want to ask: how light IS the pressure required on the 6k stone?? Or any other stone for that matter.

On the 6000 grit stone for honing I would suggest you just to try it with just one hand. That should give you a sense of the light pressure as the edge glides across the stone

Another stone such as the 1000 if you are trying to thin out the bevel then of course you need more pressure

But as you get to the final strokes and honing on the 1000 I move to lighter and lighter pressure




Sent from my iPhone using Tapatalk

 

[bucketstove]

On the 6000 grit stone for honing I would suggest you just to try it with just one hand. That should give you a sense of the light pressure as the edge glides across the stone

Another stone such as the 1000 if you are trying to thin out the bevel then of course you need more pressure

But as you get to the final strokes and honing on the 1000 I move to lighter and lighter pressure




Sent from my iPhone using Tapatalk

Hi,
yes, one handed is a good way to get a feel,
and with a food scale you can put a number on it
, put stone on scale, zero scale,
then put knife to stone,
and see the reading, and do a few passes
about a 0.25lb/4oz/~100grams and under is usually the goal for final finish strokes
as used for microbeveling/deburring

 

[MichaelMyers]

yup, thats what the test is for, the most important aspect of sharpening, how clean and pointy is the apex, the test lets you feel how crisp and sticky the apex is

paper tests can be fooled and cut with an over polished edge ( rounded apex)

which means your not getting the knife to its maximum potential for cutting and edge retention

When I hand a knife to an experienced sharpener its the first thing they do

and they can tell me right away if I over polished, left some residual burr, or didn't fully apex

all from a quick simple test mixed with a deeper understanding about sharpening

of course
it doesn't tell you if there are chips in the edge though. (Thats where fingernails, paper and visual comes in)

but its just a quick test

Yes I using the test more recently as I have ran out of thin magazine paper and arm hair and wanted a quick way to "feel the condition of the edge as I am sharpening. But I did not expect it to be one of the harder test to pass.

 

[MichaelMyers]

I'd like to know this estimate as well, I only what I use.

I've found if going even a bit too hard backhoning on waterstones with an acute angle the edge can literally sway over a bit - almost looks like a wire edge only more subtle.

On high RC steel it can fracture the last few microns right off the apex. I'd estimate I shoot for an ounce or less but is hard to say, even with a good digital scale the value jumps around and won't accurately read momentary shots less than an ounce or two.

Sometimes if I'm going from a coarse stone right to a polishing grade one I find I can use a bit of force - a couple of ounces for the first few passes as I'm working the high points down a bit. I suspect because the surface area is small, the contact pressure is even more amplified and those come down very quickly. Once I can see a bit of brighter finish along the edge I dial it way back.

I also believe the density and composition of the stone make a big difference - even very hard resin bonded stones will tolerate more force than a ceramic bonded/fired one before getting into trouble.

Edit to add:
I find once I get into brighter levels of polish my waterstone edges tend to reliably feel stickier than other means. In some cases not by a large margin and also tend to require more QC to really get the best.

The "stickiest" edges I have ever made came off of a clear maple strop loaded with Flexcut Gold and a few drops of mineral oil. Absolutely wicked catchy and would barely tug cutting the tops of a fingerprint whorl. Again, they took a lot of QC to reliably achieve and the boards are more prone to contamination than just about anything else you can imagine - not convenient but a great noodling exercise - also tolerated and actually worked best with a solid 6-8 ounces or more. The maple is more forgiving than a waterstone...

https://www.youtube.com/watch?v=gfblDsTy-FY

Great vid! I wish to try a stropping on wood as well. Can i use balsa wood with scrubbing motion?

 

[HeavyHanded]

Great vid! I wish to try a stropping on wood as well. Can i use balsa wood with scrubbing motion?

I'd stick with a hardwood. Red Oak is good as you don't have to scuff it up so often. Maple with a surface treatment per the video worked well too - I picked up a bunch of smaller pieces at Home Depot for cheap.

I also found the black compound at about 20 micron was just a bit too aggressive and would create burring that could be tough to remove on the board. Pretty sure Flexcut is a mix of 3-4 micron and .5 micron.

The scratch pattern is going to be far more pronounced using this method than using on a strop of some sort, even a hard one like balsa. Over time the compound will polish the board as well and the effect will drop off - periodic surface scuffing is important.

Mind the blend, you want to keep it fairly tacky. If it gets too thin you'll notice it stops taking off much steel, too thick and it loads up. Also if you don't apply some force it won't work well for removing damage, touching up a dull edge, refining from a rougher finish. Its not only forgiving of pressure but benefits from it.

Experimenting with this sort of thing will be very informative when it comes to effects based on how the abrasive is presented in terms of mobility and how like amounts of applied force and different materials translates to differing amounts of pressure on the steel. This is sort of between a softish stone and a strop. I was most surprised to find I could scrub away with this - will improve your angle control a bit too as it bites on the board if you get sloppy.

This line of thinking was instrumental to developing my Washboard, and I make use of it often for improvised sharpening - using ash from the camp fire smeared on a smooth piece of wood to touch up my hatchet or machete for example.


The following link should be made into a sticky - was shared by one of the forum members and is a great read for better understanding. At page 21 the use of 'knife board' is covered.

https://bosq.home.xs4all.nl/info 20m/grinding_and_honing_part_1.pdf