request advice on honing tool design

[sharpandsafe]

Hello All,

I am designing a tool to maintain high-end kitchen knives that are in frequent use. I have drawn up plans for a base that has many holes in it to hold a pair of honing rods at various angles for different edge bevels. My current design has pairs of holes for holding the rods at 15, 17, 19, or 21 degrees per side. It is designed to hold the rods in an X-shape while the user gently draws the knife edge along the top of where the honing rods cross (like those little pocket pull-through sharpeners, but on a much larger scale). I am planning for the tool to have two sets of honing rods to use with it. One set will be a fine alumina ceramic for a very gentle sharpening action as the blade is hones and the other set will be glass rods in the tradition of HandAmerican's borosilicate glass butcher's steel.

First questions: what do you think of this concept? Do you have any suggestions for improvement?

Second questions: what kind of glass should be used for the glass honing rods? Should the glass rods be smooth/polished, or should they be "frosted" by tumbling them with some SiC grit?

Before researching glass types, I was under the impression that HandAmerican chose borosilicate glass because it is a harder material than regular soda-lime glass, but it turns out that this is not the case! Borosilicate glass is quite a bit SOFTER than regular glass, so is is best to use soft boro glass or harder fused quartz glass or soda-lime glass. I can also guess that HandAmerican chose the boro glass for thier butcher's steel because it is less brittle than soda lime glass, rather than for any benefit in it's honing ability. If this is the case than I see no reson to use more expensive boro glass when soda-lime glass rods are available so cheaply.

FYI, these are the Knoop Hardness (kg/mm^2) values I have found online for glass products from various manufacturers:
Borosilicate Glass : 448-481 (softest)
Fused Quartz : 487-600
Soda-lime Glass : 565-605 (hardest)

 

[Obsessed with Edges]

I personally would avoid the 'X' config for the rods, and instead use a 'V' with some open space between them at the bottom (like a Sharpmaker, for example). One of the things I've never liked about the ceramic pull-through sharpeners, is that many or most of them are configured that way. The bottom of the 'X', being ceramic, is a very hard and unforgiving place for the apex to bottom out at the end of the stroke. If the blade is slightly off-angle and abrading the shoulder of the bevel to one side, the apex will be grinding too obtusely against the rod on the other side at the same time. Very difficult to maintain a crisp apex this way, UNLESS great care is taken to avoid bottoming out at the end of the stroke. If the rods are lengthy enough, that should be do-able. But, I'd just separate the rods a little bit instead, and eliminate the hazard completely. If the stroke goes all the way to the bottom, it'll just bottom out against wood/plastic or whatever base material you're using, and that won't harm your edge like ceramics will.

Edit:
Another small downside to using an 'X' config, is that the portions of the rods below the intersection will be unusable. Maybe not a big deal, if the rods are very long. But, with a 'V' config and a forgiving base to mount them in, you can extend the stroke all the way to the bottom.


David

 

[sharpandsafe]

I personally would avoid the 'X' config for the rods, and instead use a 'V' with some open space between them at the bottom (like a Sharpmaker, for example). One of the things I've never liked about the ceramic pull-through sharpeners, is that many or most of them are configured that way. The bottom of the 'X', being ceramic, is a very hard and unforgiving place for the apex to bottom out at the end of the stroke. If the blade is slightly off-angle and abrading the shoulder of the bevel to one side, the apex will be grinding too obtusely against the rod on the other side at the same time. Very difficult to maintain a crisp apex this way, UNLESS great care is taken to avoid bottoming out at the end of the stroke. If the rods are lengthy enough, that should be do-able. But, I'd just separate the rods a little bit instead, and eliminate the hazard completely. If the stroke goes all the way to the bottom, it'll just bottom out against wood/plastic or whatever base material you're using, and that won't harm your edge like ceramics will.


David

Thank you so much for your feedback, David! I think I understand your concern. Part of my intention with this design was to minimize risk to the apex with the smaller "pull-through" sharpeners. This design uses short, fat rods, and is also designed to be used with a "pull-through" draw/horizontal stroke, and NO vertical motion - keeping the apex in the crotch of the rods the whole time. I figured using fat rods (10mm diameter, in the current design) would minimize risk to the apex because you would have to be WAY off angle to be grinding the apex at a high angle to the rods - the thickness of the rods naturally provides a separation between the two grinding points along the edge, which helps to stabilize the knife blade also. Does this make sense, or am I totally flawed in my thinking?

What do you think about the glass rod options?

 

[Omega Leather Works]

I don't really have anything to offer on a technical level, but I'd like to say that your concept sounds very interesting.

I'm betting that you'll get the most satisfaction by experimenting with your design. Of course there's nothing wrong with asking for opinions! I'm most intrigued with the concept of the rods being apart by nature of their width. Who knows, you may be on to something there. :thumbup:

 

[Obsessed with Edges]

Thank you so much for your feedback, David! I think I understand your concern. Part of my intention with this design was to minimize risk to the apex with the smaller "pull-through" sharpeners. This design uses short, fat rods, and is also designed to be used with a "pull-through" draw/horizontal stroke, and NO vertical motion - keeping the apex in the crotch of the rods the whole time. I figured using fat rods (10mm diameter, in the current design) would minimize risk to the apex because you would have to be WAY off angle to be grinding the apex at a high angle to the rods - the thickness of the rods naturally provides a separation between the two grinding points along the edge, which helps to stabilize the knife blade also. Does this make sense, or am I totally flawed in my thinking?

What do you think about the glass rod options?

I'm more concerned about the apex rolling into and contacting anything at all on the opposite side, while working the bevel on one side. Not so much an issue of how much linear separation there is between contact points on each side. The 'crotch' of the sharpener, to me, is the troublesome aspect in itself. Even a small variation in angle (even 1 degree or less, which is likely much tighter than most anyone could maintain through an extended sharpening session) is going to put at least part of the apex at risk, and more so if the edge is very thin. I've always gotten better results by working the bevel itself, and just barely 'sneaking up on' the apex from one side at a time. When there's contact on only one side, it's much easier to focus on protecting the apex when there's no chance of contact from the other side. Even if the angle is off a little to make the shoulder roll into the rod, the apex will be clear of any contact from the opposite side and no additional harm is done to it. If there's simultaneous contact on both sides of the blade, and the blade pivots or rolls even slightly toward the shoulder of the bevel on one side, the apex is always going to be detrimentally affected from the other side. It's the simultaneous contact on both sides that places a premium on perfect angle control throughout the full stroke and again on each and every subsequent stroke, whereas working only one side at a time is more tolerant of the blade rolling a little into the shoulder on the side being honed, without harming the apex (or altering the apex angle) from the other side in the same stroke.

As for the glass rods, I haven't used glass rods at all, so I don't think I can offer much there.


David

 

[sharpandsafe]

I'm more concerned about the apex rolling into and contacting anything at all on the opposite side, while working the bevel on one side. Not so much an issue of how much linear separation there is between contact points on each side. The 'crotch' of the sharpener, to me, is the troublesome aspect in itself. Even a small variation in angle (even 1 degree or less, which is likely much tighter than most anyone could maintain through an extended sharpening session) is going to put at least part of the apex at risk, and more so if the edge is very thin.

Hmmm, I have read through your latest post several times, and I think we are still not understanding each other. Can't the same criticism be made of the Sharpmaker? That is a very popular tool. What is the real difference between alternating strokes on either side of the bevel if the time between strokes is second (sharpmaker) or a tiny fraction of a second (my design) caused by crossed rods that are offset 10mm from each other? Besides, I am envisioning this as a HONING tool, not a sharpening tool. A sharpened knife would be drawn through the glass rods or the ceramic rods very lightly, and just a very few times after each use (as an alternative to a butcher's steel). I am envisioning this as a tool that can sit on my kitchen counter and can be used to maintain a sharp edge on my kitchen knives after each and every use. This is not intended as a tool to sharpen a dull blade.

I've always gotten better results by working the bevel itself, and just barely 'sneaking up on' the apex from one side at a time. When there's contact on only one side, it's much easier to focus on protecting the apex when there's no chance of contact from the other side. Even if the angle is off a little to make the shoulder roll into the rod, the apex will be clear of any contact from the opposite side and no additional harm is done to it.

This makes sense to me as well. If using a Sharpmaker, would you then advocate working one side of the bevel at a time, rather than alternating each side of the bevel with each stroke, as most do?

If there's simultaneous contact on both sides of the blade, and the blade pivots or rolls even slightly toward the shoulder of the bevel on one side, the apex is always going to be detrimentally affected from the other side. It's the simultaneous contact on both sides that places a premium on perfect angle control throughout the full stroke and again on each and every subsequent stroke,

Just to be clear, the contact on either side of the bevel is NOT simultaneous. as the rods are round, even though they are crossed against each other, the blade only contacts a very small area near the center of each rod, and the two contact points are offset by the radius of the first rod plus the radius of the second rod. The edge bevel would contact rod #1, move away from the contact area of rod #1 and then contact the center of rod #2 on the opposite side of the bevel a fraction of a second later. Perhaps you understand this, but it is not clear to me from your post. I should look for a way to post my CAD drawings to make it more clear what I am trying to describe.

In addition to a honing tool, I am thinking this could be a good tool for burr removal AFTER sharpening, but I am not intending my design to be a sharpening tool itself.

 

[BluntCut MetalWorks]

Good thinking on how to make a better ubiquitous 'v' pull through sharpener.

There are potential problems:

1. The contact area for the ceramic rods could quickly loaded up, even with nice rotation & clean. Soon after that area will be worn out. Of course, flip the rod end will double the short lifespan but over all still too short.
Example. a geometric contact area for a 2mm height bevel = 2mm line per rod.

2. Good chance of side-to-side bending edges with micro-bevel. Or rod only in contact with micro-bevel edge shoulder.

3. Lop-sided tip when it came off the back-rod, now pressure on the front-rod is too high and one sided.

4. Excess pressure would bend the edge, one way by the back rod & other way by the front rod.

5. Burnishing (glass rod) works better to pull metal away from edge than along the edge (and the entire bevel in this case).

6. High hrc + thin blades edge fracture - from lateral contact with very hard surface.

 

[sharpandsafe]

1. The contact area for the ceramic rods could quickly loaded up, even with nice rotation & clean. Soon after that area will be worn out. Of course, flip the rod end will double the short lifespan but over all still too short.
Example. a geometric contact area for a 2mm height bevel = 2mm line per rod.

Yes, I knew this would be the case. Are you suggesting that, even if the rods are cleaned, that they will lose their effectiveness?

2. Good chance of side-to-side bending edges with micro-bevel. Or rod only in contact with micro-bevel edge shoulder.

One would have to know the angle of the micro-bevel and hone to that angle. I have also known that this is a potential limitation. Regarding the side-to-side bending: why wound this be any more of a risk than for example, using the Sharpmaker UF rods to touch up an edge as many do.

3. Lop-sided tip when it came off the back-rod, now pressure on the front-rod is too high and one sided.

This is a good one. Thank you. I had not thought of this.

4. Excess pressure would bend the edge, one way by the back rod & other way by the front rod.

Again, how would this be any more of a risk than with the Sharpmaker on any other round hone (butcher's steel) used to touch up an edge?

5. Burnishing (glass rod) works better to pull metal away from edge than along the edge (and the entire bevel in this case).

Hmmm, this is interesting. This is the first time I have heard this. Are you saying that an edge must be drawn down the length of a glass rod, edge-leading, for their to be any benefit as in the HandAmerican borosilicate honing rod?

6. High hrc + thin blades edge fracture - from lateral contact with very hard surface.

This is why a light honing stroke is required. Edge chipping does become a real concern above HRC 61-62, in my opinion, though there are many that hone Japanese kitchen knives of up to HRC 64-65 on ceramic rods like the Idanone rods. Are these people tempting fate in doing this and risking serious damage to their knives?


Thank you, Bluntcut, for all your thoughtful feedback. I really appreciate it!