Messages

As a side note, you can also get an accurate value of this offset if you use one of the many calculators available (calcapp, tormekcalc, etc.) by both changing the diameter of the wheel to 254mm *and* reducing the distance to top of the wheel by 2mm.

The work being done can be measured by the material being removed (bonds being broken within the steel) and the generation of heat. You need to maximise the first and minimise the second. We want as little heat as possible and as much material removal as possible for maximum efficiency.

Agreed 100%.

To complement my response to OP's objection, the Higher MOH of the abrasive relative to the material being ground allows it to scratch said material. In doing so, there is resistance to the relative motion of the abrasive and the material. This resistance is precisely friction, and overcoming it generates heat (due to resistance to gliding at the molecular level AND to the the energy released by the breaking bonds within the material AND to the wear within the abrasive).

Lubricants work by separating surfaces. A lubricant that would work so well that there would be no resistance to the relative movement of the abrasive with respect to the ground material would also prevent the abrasive from scratching the material. For grinding to be effective, surfaces have to be allowed to come into contact. Where they come into contact, the kinetic friction coefficient depends only on the surfaces, not the lubricant.

Machinists know that a dry bit removes material much faster than a lubricated one. Unfortunately, it also breaks down so much faster that it is impractical to use it dry.

Water for the Tormek is a good compromise : it properly transfers heat away from the point of contact, lubricates a bit but still allows grinding to happen quickly enough.

TL/DR : the better the lubricant, the less abrasive and steel come into contact, the slower steel is being ground.

I apologize if this is a stupid question but, I was wondering if anyone knows the degree difference on the angle master setting of 250mm to the middle scale of 10"?

It's not stupid at all. If you play with the model here, you'll see that for a given setup (USB height set, projection distance set), the difference in angle when the stone diameter varies from 250 to 254mm is about 1 degree. So for a given position of the WM-200 on the wheel while resting on the flat of the blade, the angle read on the WM-200 should be off by the same amount.

This is patently false and a myth that needs to die. Friction is nothing more than generating heat.

Thank you for your kind, nuanced words.

Still, from a physics standpoint, in a situation where a solid moves in relationship to another, the friction coefficient is the ratio of the tangential force to the normal force. If there is no friction, there is no tangential force applied to the material being cut, so no work being done and obviously no matter being removed.

In the same fashion, a frictionless action of a knife blade on a tomato will press down on the tomato but not cut it. Our job as sharpeners is to make sure friction happens over such a tiny surface that the cells are instantly sheared in two by the focused tangential force without the tomato being deformed by the normal force.

Heat is a byproduct of friction, heat reduces cutting of abrasives, and increases wear ; hence the need to use a coolant in many situations where friction generates a lot of heat, or to reduce friction using a lubricant where the unlubricated action would generate more heat than the tool (drill/belt/wheel) or piece would be able to withstand locally. Cutting fluids act as both.

In my experience, the SG is okay for most stainless and carbon steels. Only carbide steels or one type of very scratch-resistant carbon steel require the SB or a diamond wheel. Could it be an issue with applying too much pressure on the wheel ?

If you reduce friction you will reduce sharpening efficiency. In another post, you seem to complain that the stone is glazed and needs refreshing... If the stone wears down it means that new abrasives are exposed, therefore maintaining sharpening efficiency. If the stone wears down too quickly, it means it is not hard enough for the material you're trying to sharpen.

I'd contact Tormek support.

Phil,

I'm not sure I understood properly, but I think what you're measuring with your AngleCube or such is the angle between the horizontal plane and the side of the blade.

The main part of the difference here is that the knife does not contact the wheel exactly at the top of the wheel. So to find the correct angle, you'd have to mark the radius of the wheel at which the apex of the knife makes contact, then measure the angle between this radius and the vertical, and subtract this angle from what you found previously (if the contact happens further away than the top of the wheel, which is usually the case).

You are also dealing with a lesser error : the blade is usually tapered, so the side of the blade is usually at an angle with the plane of symmetry of the blade. So you'd have to measure the taper angle : you can clamp the blade in a vise and take one measurement on each side, then divide the difference by two. Once you have this difference, you have to subtract it to the angle you read on the angle cube resting on the side of the blade.

For more on this, here is a link to a geogebra page I designed where you can easily play with this subject, no advanced mathematics involved. The first error is the angle between the dashed line (from the center of the wheel to the point of contact) and the vertical axis. Or the other dashed line (tangent to the wheel at the point of contact) and the horizontal axis.

Hope this helps !

Hello !

Have you tried Rich's website ?

A bit more food for thought on this ultrasonic deburring thing :

https://www.blackstone-ney.com/blog/ultrasonics-deburring-fact-or-fantasy/

This report was shared by the author and discussed in this thread on the forum

I was lucky to find this, it's classified as a reading light but it's led with three colors and flexible.  It's perfect for sharpening.

Wow, it looks very nice, not only for sharpening but also for having around the workshop. Care to share a link ?

I have found that it is much easier to get low BESS scores when I sharpen at low angles (sub-15 dps). In my experience diamond stones tend to produce lower scores than the SG-250, and higher grit finishes (1000+) produce lower scores than lower grit finishes.

Just to make sure : when you talk about lower scores, do you mean lower BESS number or lower sharpness ?

I used to chase BESS scores initially. It is a good tool to measure progress while you develop a technique. After a while I got too lazy to fire up the BESS tester, but I still do occasionally. In my experience you quickly get a feel for a sharp burr-free edge by how effortlessly it glides through phone book or cigarette paper, you don't even need to test.

I wholeheartedly agree, once you get comfortable with the process, there is little need for systematic BESS testing. When I get a new, exotic steel I usually test it before/After.  Plus high BESS does not necessarily translate to higher edge retention, so I use it only as a reference to see if a given sharpening is consistent with the lot, if I have a doubt.

Although this may be the case in some instances, but for me, there have been times that I'm finishing off with the above numbers, but still running the knife through my microscope and it clearly shows no burr is present.

In my experience some steels never get under 130 BESS. I have a few french Sabatier knives that won't get under 150, 130 at the very best, no matter what. And they get back to a lofty 250 after a few uses in the kitchen. Those I don't trust to care for knives get to use them, but my 8 y.o. son uses my japanese knives.

Also, I've experienced some situations (edge leading with SJ-250, on soft steels) where there is still a layer of very soft steel at the apex of the edge. It is however invisible under a typical optical microscope.

In my experience, the composite wheel has less feedback than the leather wheel with the compound. Still, John's advice is excellent advice.

When honing with the composite wheel, I prefer to add a few drops of water or the friction feels too high. Also, to be honest I don't think your edge will roll over due to the angle being (reasonably) too high, or the pressure being a (reasonable) bit too high. What I found is I tended to be apply a more constant pressure and moving more slowly when using a jig, therefore being much more efficient.

You may learn a lot by conducting a few experiments :
- If you hone a knife freehand, test it, then hone it righ afterwards at a controlled angle, then retest it : does sharpness increase ? If yes, you are not dulling the edge freehand, you are not honing efficiently.
- If you do it the other way around, does sharpness decrease ? If yes, you may be misjudging your honing angle *a lot* when freehanding. Using a sharpie might help.

You could also confirm your findings by looking at your edge under a microscope after freehanding : do you see a burr ? Does cutting a taunt nylon wire (BESS or DIY) leave a dent in the edge ? Those would confirm that freehand honing is not efficient, or not enough.


Also, honing with a jig but not honing enough might be just what it takes for the knife to feel sharp when testing it on a sheet of paper. But there will still be a burr. If you don't hone enough freehand, the burr will be there but will not have such a consistent angle, so it will not feel as sharp. I feel that I have to hone for a longer time when using the composite wheel compared to the leather wheel.

Very nice job !