How much pressure you apply when free hand sharpening?

[Fidel Fernandez]

Hi,

I had a marathon session last weekend sharpening all my blades and I developed numbness in all the fingers that touch the blade (Thumb, index and middle finger of each hand).
It is not carpal tunnel because there is inflammation in all those fingers. The inflammation has subdued and the feeling is back in most of all my fingers, but a small area of my left thumb and my right index finger. The inflammation continue on those fingers.

I can tell that I am applying too much pressure when I am sharpening. How much pressure is need to free hand sharpening?

Words like moderate pressure, not that much, etc. won't help. Those are very subjective to the person.

I also like espresso coffee and I have to tamper to 30 pounds of pressure to get a good cup of coffee. That gives a concrete answer of how much pressure to apply.

I know 30 pounds is too much for free hand sharpening, but I need a real idea how much pressure is needed. I don't want to develop arthritis because sharpening.

Any help is welcome.

Fidel

[john zulu]

Numbness? I do a lot of free hand. Never had numbness before. Some pressure is required but not downward force. The key is steady and repeatable sharpening angles.

Here is a thought. Just mark the edge with a sharpie. Take 5 full strokes on a 120 or 220 grit stone. Most of the sharpie should be removed by then. If it disappears after 2 strokes. Then it is too hard.

[Jim Koepke]

Fidel,

I have absolutely no way to know how much pressure is used when sharpening my blades.

Water stones need a much lighter touch than oil stones if you do not want to damage them.

The only suggestion might be to start with light a pressure and increase only enough to be removing metal. Woodworking for fun, hobby or business should not leave your body in a bad state from just one weekend's work.

Even though much enjoyment can be derived from a sharpening marathon my practice is to sharpen as needed, before, during and after the actual work process. It is rare for me to go to my shop just to sharpen, unless it is the kitchen knives.

jtk

[Robert Hazelwood]

Unless you are trying to remove a lot of metal to get rid of a ding at the edge or something, you generally want to apply as little pressure as possible. As the edge approaches zero thickness, the pressure on the edge metal increases towards infinity, and this fatigues the metal which leads to lower edge life. Also heavier pressure results in a bigger burr that you will need to remove. For me during normal sharpening (not re-profiling an edge), I will use just a bit of pressure (if I had to guess a number, 5 pounds) on my 1000 grit stone until I raise a burr. Then even less on the 5000 grit, and essentially none on the last few passes on the 10000 grit stone. If I were freehand sharpening as with a knife, I would actually be holding the blade up slightly on the final passes so that the force on the stone is less than the weight of the blade- but this is harder to do with a honing jog.

This is one reason why you want good fast cutting stones, because you won't feel the temptation to bear down to increase cutting speed.

Also, I wonder what kind of shape your blades were in when you started sharpening this last session, to have developed finger numbness? Except for the initial prep when I first get a blade, it only takes me 5 minutes at most to sharpen, usually much quicker. That includes setting up the honing guide and everything. You may be trying to remove too much metal. As soon as a slight burr is formed across the whole edge on the coarse stone (1000 grit waterstone in my case), you no longer need to remove metal, but focus on polishing the edge and getting rid of the burr.

Hope this helps.

[Tom M King]

I think the pressure would be measured in ounces, rather than pounds.

[Jim Koepke]

I think the pressure would be measured in ounces, rather than pounds.

My thought process was tempered by are we talking per square inch or square millimeter?

From back in my days of wrenching on my vehicles, the torque wrench used was a small one and measured in inch pounds.

For the big stuff a bathroom scale and a yard stick were used.

jtk

[Tom M King]

Even with a guide, it's a feel thing. I would think if you put a whole lot of pressure, you couldn't feel what was going on. The wider the edge, the more pressure it takes, of course, but it's still done more by feel than a given amount of pressure. At least, that's the way it seems to me when I do it.

[john zulu]

Too much pressure will also dig into the waterstones. That is not a good thing at all. It is just like planing. Too much force and the shavings become tearouts.

[Pat Barry]

For the big stuff a bathroom scale and a yard stick were used.jtk

That picture is worth a chuckle. Thanks Jim :)

[george wilson]

I don't use soft stones. Tried them years ago and went back to harder ones. Anyhow,I do put a good amount of pressure on a tool when sharpening. I taught many people in other trade shops to sharpen while at the museum. When they just could not get their blade sharp,I decided they did not know how to bear down.

As a well known knife maker once said:"The only thing honing lightly does is it makes you feel good."

You can lighten up when final finishing a sharp edge. I do strop fairly light.

[Jim Matthews]

I wonder if the numbness can be traced to the steel pressing into your palm.

Carpal Tunnel syndrome and other nerve pain in the hand come from the
sort of repetitive motion you have described.

If your sharpening bench is above your belt line - you are also forced to extend
the wrist while applying pressure to the stone. That sounds like the culprit, to me.

If your sharpening bench is below your belt line - you can get your body weight engaged.
That position also allows me to use both hands.

You need enough pressure that the sound of the steel on stone is audible.
Mine sort of "rumble" when I get it right.

If it's "whisking" like a broom, I can't raise a burr.

If the steel is dragging, it makes a chattering noise - like a loose muffler.

I couldn't say how many pounds of force that translates into,
but it's the best feedback I have.

FYI - I don't have the hand strength to rehab more than three irons in a day.

[Warren Mickley]

A "marathon session" is not a good idea. Better to sharpen the tools mid stream as they need it. That way you get a rest from the other work you are doing and are sharpening only for short periods of time. There is no virtue in abusing your fingers; if your fingers get tired do something else for a while.

The optimum pressure is different for different stones. There is usually a pressure where the stone grabs the steel nicely, not so little friction that the tool skips over the stone and does not engage, not so much that the tool is hard to control. This is something we get a feel for, not something we measure.

Keep in mind that pressure is pounds per square inch. A 1/2 inch chisel 3/32 inches thick will have a bevel area around .09 square inches while a plane iron 2 3/8 inches wide and 3/16 thick will have a bevel area of around .89 inches. The force needed for one is almost ten times that for the other. And if you are making a "secondary" bevel or hollow grinding, you have less surface area in contact with the stone.

[Fidel Fernandez]

The finger numbness is where I touched/grabbed the blade and the jig. I started with the jig and gave up, no good results. That is what it caused the pain, but I continued free hand. I had to fixed the mistakes I did with the jig.

I never had that pain with just free hand, only some bleeding fingers :)

I guess it was part of my inexperience with a jig that it made me press harder than normal.

I didn't sharp again yet, but I tried to see what happen. I placed a blade into the jig and my hands like I was going to sharp and the pain/numbness is right where the fingers are touching the metal.

[Jim Koepke]

Anyhow,I do put a good amount of pressure on a tool when sharpening. I taught many people in other trade shops to sharpen while at the museum. When they just could not get their blade sharp,I decided they did not know how to bear down.


The best bit of sharpening advice given to me was from a co-worker on my last job. While we were waiting for an assignment he was playing with a three oil stone set up to sharpen his knife. He said, "you have to push the blade into the stone like you mean it."

I will use more pressure on an oil stone than a water stone, one just has to learn the limits. There are a few digs in my finest water stone from "meaning it" just a bit too much.

jtk