Understaning linear bearings in sharpening systems

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norhther

Joined
Feb 9, 2024
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Hi! First post!
I was searching for some reviews on the Hapstone RS system, and I came across a comment critisizing it. He said the following in a comment:

On YouTube, you can find some sharpeners using alternative kinematics. They don't have a central pivot and are based on a linear bearings instead. They are much better. With this schema, the cutting edge angles do not depend on the thickness of the abrasive stone or plate. Moreover, when the amount of removed metal is considerable, it also doesn't change the angles.
He also posted several videos of different sharpening systems , but I don't understand the difference between them and the hapstone.
One of the several he shared is this one

So if someone can provide me with a explanation (a pic I think would be enough) I would be very grateful!
Thanks
 
In the video, it looks like the arm that holds the stone is always horizontal. It does not pivot up and down like on most sharpeners. Instead, the arm is attached to a column that slides vertically up and down. To set the angle, the clamps that hold the blade pivot up and down.

This scheme is kind of like the thickness compensator on the TSProf Kadet. On the Kadet, you need to set the thickness compensator yourself. On the device in the video, the thickness compensation is done automatically as a consequence of raising or lowering the vertical column to position the stone resting on the knife edge. Perhaps the Kadet would work similarly if it were possible to lock the arm in a horizontal position.
 
Ok.

On the KO3, the rod holding the bushing the guild runs through has to be lifted to compensate for the different thickness of the plate. To maintain the same edge angle.

A diamond plate is thinner then CBN. So going from diamond to CBN, the thickness has to adjusted for. Same for a strop. It's thicker then diamond but not as thick as CBN.

He also touches on the point that edge angle changes as metal is removed. And in my opinion, that's OCD. You'd have grind an entire reprofile, removing more then 1/16 of an inch of steel. But then again, that's what the angle cube is for. To verify the edge angle. Regardless on how much you grind off.
 
The principle behind this idea is that the angle won't change when your stone thickness changes, articulated arms do the same. I have seen several Russian sharpeners do this. The downside is they have to be much stiffer to have the same repeatability as the EP style sharpener and the angle adjustments are much coarser, which I think is the biggest issue. I would like to see how much movement is in the system before getting too excited about it. Is it just eye candy or does it really work well. The one in the video I don't think has enough length in the Z axis guide to work properly for where it is located so it may not hold the angle as constant as I would like, and I wonder how much preload is on the bearings? It also will have a heavy stone arm which I consider a negative compromise.
 
Diemaker said:
The principle behind this idea is that the angle won't change when your stone thickness changes, articulated arms do the same. I have seen several Russian sharpeners do this. The downside is they have to be much stiffer to have the same repeatability as the EP style sharpener and the angle adjustments are much coarser, which I think is the biggest issue. I would like to see how much movement is in the system before getting too excited about it. Is it just eye candy or does it really work well. The one in the video I don't think has enough length in the Z axis guide to work properly for where it is located so it may not hold the angle as constant as I would like, and I wonder how much preload is on the bearings? It also will have a heavy stone arm which I consider a negative compromise.
Click to expand...
I see. Which system would you recommend?
 
norhther said:
I see. Which system would you recommend?
Click to expand...
I can't answer that question as I don't have enough experience with all of them. For me, it's the one I made for myself. I think it is second to none in precision, repeatability, and stiffness, which I feel are the most important qualities in a guided sharpener. I have made videos of me using it but don't have any photos so a video link is the best I can do. I still have a bunch of changes I would like to make but they are mostly minor. I have been playing around with different designs for years and may make one of the auto compensating type. My latest idea is to make it modular so you could have the traditional EP style stone arm or auto compensating and a blade table or clamps. You could start out with a basic sharpener and add to it as you wish to try out the different options. This way if you want to try out a different sharpener design you could just swap a module vs buying a totally new one. One big advantage of the articulated arm types is they don't have that long stone arm shaft that makes it hard to ship or store because of the box size needed for it. You can make that rod 2 piece but that is a compromise I would never make.


 
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A myth about guided systems is that they're easy. When in reality, it takes a learning curve for each one.

Recommend a system?

Lansky. If you can master that. Then the $300-$500 system will be more user friendly. But not unless you can get an edge down with a Lansky.

It's remarkably easy to destroy a knife. With the expensive system making it super easy.

Don't think you're going to pull a system out the box and lay an edge like you see in pictures on here.

Just know that before you take out the money. There's commitment involved.
 
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Diemaker said:
I can't answer that question as I don't have enough experience with all of them. For me, it's the one I made for myself. I think it is second to none in precision, repeatability, and stiffness, which I feel are the most important qualities in a guided sharpener. I have made videos of me using it but don't have any photos so a video link is the best I can do. I still have a bunch of changes I would like to make but they are mostly minor. I have been playing around with different designs for years and may make one of the auto compensating type. My latest idea is to make it modular so you could have the traditional EP style stone arm or auto compensating and a blade table or clamps. You could start out with a basic sharpener and add to it as you wish to try out the different options. This way if you want to try out a different sharpener design you could just swap a module vs buying a totally new one. One big advantage of the articulated arm types is they don't have that long stone arm shaft that makes it hard to ship or store because of the box size needed for it. You can make that rod 2 piece but that is a compromise I would never make.


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Looks wonderful! Hope one day I can be able to make something like that.
 
Grasshopperglock said:
A myth about guided systems is that they're easy. When in reality, it takes a learning curve for each one.

Recommend a system?

Lansky. If you can master that. Then the $300-$500 system will be more user friendly. But not unless you can get an edge down with a Lansky.

It's remarkably easy to destroy a knife. With the expensive system making it super easy.

Don't think you're going to pull a system out the box and lay an edge like you see in pictures on here.

Just know that before you take out the money. There's commitment involved.
Click to expand...
I have been sharpening with stones for some years now, and I have a Worksharp Ken Onion with all the extras, and I just want to have a sharpening system for that high end profile that is really hard (impossible I would say) this systems give to the edge.
 
norhther said:
I have been sharpening with stones for some years now, and I have a Worksharp Ken Onion with all the extras, and I just want to have a sharpening system for that high end profile that is really hard (impossible I would say) this systems give to the edge.
Click to expand...

In that case. TSProf. When you're tired of dicking around.

(That should be their company slogan.)
 
norhther said:
I have been sharpening with stones for some years now, and I have a Worksharp Ken Onion with all the extras, and I just want to have a sharpening system for that high end profile that is really hard (impossible I would say) this systems give to the edge.
Click to expand...
What exactly do you find impossible?
 
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