Thread: A question on geometry

Just a few thoughts - from a restorer rather than blade manufacturer:

- As you already mentioned, the wedge will create a bow in the scales - the recommendation is that the taper in the wedge should be approximately the same as the taper in the tang.

- The positioning of the pivot hole in the scales should not allow too much overhang of the scales. My theory here is that because the scales are bowed, and the tang is tapered, when the blade is opened at 180 degrees there is a danger of splitting the scales at the pivot. This can be overcome to an extent by using internal washers at the pivot.

- My conclusion from the above is the same as Richard has already stated, taper angles and scale design are best based on old razors - there are literally thousands of photos in the SOTD archive that should provide enough top views to give you a guide.

Inserting information about pinning in Blue

Originally Posted by UKRob

Just a few thoughts - from a restorer rather than blade manufacturer:
...snip...
- The positioning of the pivot hole should not allow too much overhang of the scales. My theory here is that because the scales are bowed, and the tang is tapered, when the blade is opened at 180 degrees there is a danger of splitting the scales at the pivot. This can be overcome to an extent by using internal washers at the pivot.
Adding... Always! do your final pin tightening with the blade fully extended!! I have not followed that a few times..to my chagrin and remaking a scale.

- My conclusion from the above is the same as Richard has already stated, taper angles and scale design are best based on old razors - there are literally thousands of photos in the SOTD archive that should provide enough top views to give you a guide.

~Richard

Here is a good post on making wedges, a discussion and photos, of what you are asking. (How wide the rear of the wedge should be?)

In my experience and when I make a wedge, I fit the blade in the scales and mark the top of the blade where I want it to hit the scales. Then measure the thickness at this point and taper the wedge to half that thickness on the other side.

Most of the wedges I have measured are half the thickness from one end to the other.

This will bow the scales enough, about ¾ of an inch and around the widest part of the tang. Looking at old Sheffield razors, you will find ¼ inch tangs with thin 1/8 to 1/16 inch wedges, and that are, and have been, keeping tension on a blade properly for a hundred years or more in some cases.

When I pin the wedge end I slip a rubber eraser on the tang side to keep the proper taper of the scales on the wedge.

Many old blades are tapered on one side, or more on one side than the other and makes centering the blade difficult. Tapering both sides equally will center the blade tip in the scales. A very little bit of adjustment will make a big difference.

You want the scales to be under tension through the full arc of the scales without hitting the blade or tang. A loose set of scales is dangerous, for shaving, honing and stropping.

Thanks for the info, I think I've got the basic idea, maybe. It's just a bit different concept than any other blade I've made, especially folders where everything has got to be flat and square.

I'll do some more reading and more looking at pics, and maybe see about getting my hands on a vintage razor or two to study.

Thanks again

I don't know much, learned a bit reading this thread, but I'll mention one thing that a pro custom razor maker made a mistake on when he made his first few ...... not allowing a long enough distance between the heel and the pivot for comfortable stropping. Just something to keep in mind.

No worries on that, the first I did was a bit on the long side. Still playing with designs and trying out tail shapes for comfort, taking a little getting used to after shaving with normal razors for 30 years.

Originally Posted by will52100

No worries on that, the first I did was a bit on the long side. Still playing with designs and trying out tail shapes for comfort, taking a little getting used to after shaving with normal razors for 30 years.

As you are still in the design stage, here is another consideration to do with tang/monkey tail length and shape. When it comes to stropping a razor, it's preferable that the monkey tail fits inside the opened scales from a comfort point of view. Some modern designs do incorporate eccentric tail shapes but if you look at original designs you'll notice that tails are quite modest.

A good idea when you design both the razor and scales is to draw them in both the closed and rotated 180 degrees into the fully open position. Ideally, in my opinion, the tail should be mostly covered by the scales when the razor is fully open.

Good suggestion, thanks. For something so simple, it's surprisingly complex, but am learning.