Thread: Hinge pin mechanics

Another perspective.

You want the tang, scales and washers to be aligned.

A flat tang, meaning no tapers, has the tang, scales and washers sitting flat on one another. They are all three in alignment.

A simple bevel tang with the taper from the pivot to the tail needs a simple wedge to affect (effect?) the alignment. The bow/curve the wedge puts into the scales allows at the pivot the flat alignment of the scales, tang and washers.

A compound bevel wedge does the above plus opens the top of the scales to allow for alignment of the three pieces in a horizontal and vertical plane at the pivot.

Another perspective.

You want the tang, scales and washers to be aligned.

A flat tang, meaning no tapers, has the tang, scales and washers sitting flat on one another. They are all three in alignment.

A simple bevel tang with the taper from the pivot to the tail needs a simple wedge to affect (effect?) the alignment. The bow/curve the wedge puts into the scales allows at the pivot the flat alignment of the scales, tang and washers.

A compound bevel wedge does the above plus opens the top of the scales to allow for alignment of the three pieces in a horizontal and vertical plane at the pivot.

Rolodave,
Thank you for this, another good explanation that helped paint a picture in my mind of how it works. So a "compound bevel wedge" is that a spacer of sorts in between the scales in the middle? Or something else? What is the middle scales spacer called as we see in some straight razors?

Originally Posted by Orville

Maybe it is just me, but I cannot help but think that a wedge, with the inherent flexing of the scales it causes, puts more stress on the scales than a simple spacer which does not cause the scales to flex at all. I can see how a spacer would allow for the scales to loosen over time (due to wear from opening and closing, etc.)

Am I missing something?

Hey Orville

A spacer used on a tapered tang puts all the stress on the scales/washers at the pivot. Sort of like trying to bend the last two inches of a foot long stick.

Using a wedge, simple or compound, allows the stress to be evenly distributed over the entire scale rather than just at the pivot.

Originally Posted by rolodave

Another perspective.

You want the tang, scales and washers to be aligned.

A flat tang, meaning no tapers, has the tang, scales and washers sitting flat on one another. They are all three in alignment.

A simple bevel tang with the taper from the pivot to the tail needs a simple wedge to affect (effect?) the alignment. The bow/curve the wedge puts into the scales allows at the pivot the flat alignment of the scales, tang and washers.

A compound bevel wedge does the above plus opens the top of the scales to allow for alignment of the three pieces in a horizontal and vertical plane at the pivot.

By the way in the workshop tutorials I remember, in the wedge making post, being mentioned that if a wedge is made wider on one side , that side has to go on the top side of the scales. Reasons as you explained.

Originally Posted by MikeT

Another perspective.

You want the tang, scales and washers to be aligned.

A flat tang, meaning no tapers, has the tang, scales and washers sitting flat on one another. They are all three in alignment.

A simple bevel tang with the taper from the pivot to the tail needs a simple wedge to affect (effect?) the alignment. The bow/curve the wedge puts into the scales allows at the pivot the flat alignment of the scales, tang and washers.

A compound bevel wedge does the above plus opens the top of the scales to allow for alignment of the three pieces in a horizontal and vertical plane at the pivot.

Rolodave,
Thank you for this, another good explanation that helped paint a picture in my mind of how it works. So a "compound bevel wedge" is that a spacer of sorts in between the scales in the middle? Or something else? What is the middle scales spacer called as we see in some straight razors?

I said it previously, the scales and the tang have to be parallel. That means the wedge has to have taper angle close to the tang taper angle.

The tapering at the tang ensures variability in the pressure/force that the scales press against the tang with, and corresponding increase in friction when the razor is opened for use. (The maximum static friction where the two surfaces start to slide is approximately proportional to that lateral force/pressure).

With parallel tang you can not have that variability in friction.

The other question is the role of the taper at the opposite of the pivot pin. It is necessary to minimize the stress on the scales that the taper at the shank causes.

With the taper at both ends the scales flex as a simple arc. With taper on one end and no taper on the other you have the curvature changing direction with an inflection point in between, i.e. something resembling a S-curve. This creates more stress in the scales and at the joints than a single-curvature line.

You can certainly have it work without taper(s) and/or with more stress, but that's not optimal. You can also make a spoon out of tool steel, heat treat it to 55-63 Rockwell, sharpen it and shave with it. But it's still not not the best design for a shaving tool aka razor.

Personally, if the scales are not made out of say glass or stone for aesthetic reasons and you are stuck with unflexible material I don't see a reason to not use the tapered design. Probably some people find the look of thick scales very attractive and again have to make the same tradeoff because they end up with unflexible scales, but to me there's a difference between making a functional trade-off over aesthetics, over cost/lack of skill, or using subpar design because of ignorance or laziness.

The other way around

If you do a wedge to follow the tang

You want front to back taper and top to bottom taper just like the tang is made
Most tangs will taper down from front to back and from top to bottom.


Again just follow the tang and everything works with itself rather then against itself

If there is no taper which is quite rare other then in new customs from knife makers I guess you have to figure it out...

The other big difference we are seeing in newer razors is how thick the scales can be, they will not flex so now you have all kinds of new issues to deal with

The new "Strong Materials" also present new problems to overcome.. take G10 at .125" it won't flex you have to get down to near .100" or less before the scale will begin to flex.. These are things you just have to work through and figure out as you build more and more

I find this thread to be fascinating. I enjoy the discussions of the dynamics and mechanics here, and also appreciate designs from both sides of the spectrum. On one hand I have a number of new production TI blades, as well as almost all of my vintage that are wedge designs and the flex is easily noted in their function. I also now see the old wisdom of using soft wedge materials such as lead...which could easily be manipulated to reach the precise and desired shape of the wedge to get perfect fitment.

On the newer side of things I also like a couple of my new razors with a spacer. Of course this conversation largely started with PRC in mind, but I think the best example of a well designed spacer use is my Nate's Straights 11/16 1/4 hollow. The mechanics are quite sound with a non-tapered tang, and the necessary friction (aside from the hex hardware) is achieved using a small Teflon spacer so as not to wear the wood scales. I think, personally, that his work is simple, elegant, and functional. Aesthetically his razors are appealing in terms of that well executed simplicity, of which the use of a contrasting spacer is a big part.

Originally Posted by MikeT

Another perspective.

You want the tang, scales and washers to be aligned.

A flat tang, meaning no tapers, has the tang, scales and washers sitting flat on one another. They are all three in alignment.

A simple bevel tang with the taper from the pivot to the tail needs a simple wedge to affect (effect?) the alignment. The bow/curve the wedge puts into the scales allows at the pivot the flat alignment of the scales, tang and washers.

A compound bevel wedge does the above plus opens the top of the scales to allow for alignment of the three pieces in a horizontal and vertical plane at the pivot.

Rolodave,
Thank you for this, another good explanation that helped paint a picture in my mind of how it works. So a "compound bevel wedge" is that a spacer of sorts in between the scales in the middle? Or something else? What is the middle scales spacer called as we see in some straight razors?

That is whole different cat and I will let Glen/Stefan address that. I was only talking about the wedge/spacer at the end of the scales.

Originally Posted by gssixgun

The other way around

If you do a wedge to follow the tang

You want front to back taper and top to bottom taper just like the tang is made
Most tangs will taper down from front to back and from top to bottom.


Again just follow the tang and everything works with itself rather then against itself

If there is no taper which is quite rare other then in new customs from knife makers I guess you have to figure it out...

The other big difference we are seeing in newer razors is how thick the scales can be, they will not flex so now you have all kinds of new issues to deal with

The new "Strong Materials" also present new problems to overcome.. take G10 at .125" it won't flex you have to get down to near .100" or less before the scale will begin to flex.. These are things you just have to work through and figure out as you build more and more

You cannot say it much more simply than Glen.