Wedge design considerations

[MrCrispy]

Wedges, the kind that hold two scales together, not the blade shape.

May I ask some potentially dumb questions?
I'm fabricating some to get the hang of it, but my love of experimentation has me running out of bounds.

-What is the purpose of the wedge? (or purposes)
-When do you know it's just right?
-Is the wedge grind angle relative to anything in particular?
-Is the wedge thickness relative to the anything besides weight for balance?

I have a couple of old pressed honey horn examples where there it never had a spacer. The horn was just brought together and pinned. Early heavy French razors seem to use very thin wafers of bone? as wedges. Early wood scales I often see one piece without a wedge, I have seen several Packwood's that way, and have a Wolf myself with the 'cave man club' handle

If I missed a Wiki section or thread that covers the above, a link be great, I did look!
Thanks
Chris

 

[Doc226]

From Bill I believe

 

[bluesman 7]

-Is the wedge grind angle relative to anything in particular?
-Is the wedge thickness relative to the anything besides weight for balance?


Chris

In the neighborhood of 7 degrees works well for me. This is somewhat dependent on the flexibility of the scales.

The thickness determines where the razor will sit in the scales when closed.

 

[MrCrispy]

Thanks Doc. This confirms what I have seen so far...that the wedge is solving a problem with the scales around the geometry of the tang, and is exacerbated by the inflexibility of the scale material.

The thing is...IMHO there is a better solution for that by carefully chamfering the *interior* of the scales to allow for the wider tang. Even if the spacer is a wedge, this reduces the stress and angle required for wider tangs.

From my limited experiments, it seems only 1/32 or 1/16 off the last 2" of the interior allows free swing of the blade except when the width of the tang swivels to expand the scales at the hinge.

Quoting Bill: "the more the scale if forced outward, the shorter the lifespan will be"

Scales with a flat spacer, and carefully tooled scales *should* have nearly zero outward pressure except when the tang meets friction at the pin swivel, unless the tang is too asymmetrical.

Scales with a wedge, no matter how small, will force scales outward with stress that eventually goes somewhere.
With a flat spacer, the outward pressure is the tang. With a wedge, the outward pressure is the nose AND the tang. This is why I think we see so many thin horn scales bowing out in the middle. Early French tail-less razors often have a REALLY narrow tang, almost reducing any pressure from the tang pivot.

Problem:
- Scales become over-stressed and degenerate with bowing, cracking, etc.

Historical solution:
- Wedges were angled to bow the scales in the middle rather than one end.
- Upgrades of metal capped scale ends were sometimes used for high end models

Are there any other reasons for a wedged spacer? I cant find any, but I certainly dont know all the ins and outs like you guys.

 

[bluesman 7]

If you watch (properly designed IMO) scales while opening and closing a razor you will see them flexing. This allows the fit to be tight when the razor is open, and loose when the razor is closed. If the joint is tight when the razor is closed the materials will creep resulting in a constantly loosening fit. The flexing scales act as springs creating tension when the razor is in the open position. The bow created by the wedge preloads the spring and also keeps the centers of the scales away from the razor while closing. A very elegant design IMO.

 

[MrCrispy]

I completely agree it can be an elegant design, especially with the properties of horn, since it flexes not only with pressure but also temperature.

Are they supposed to be loose when closed? I'd like to see 'stays in place during a wiggle' in every position, personally

If we stay within the constraint that managing hinge tension is the purpose of the intentional stress put on the scales, some quick and un-elegant visio implies many razor designs solve this with a taper in the tang. In fact, I see most tangs have a double taper, one like in the pictures to hold it open, the other from spine down toward blade so that it snugs when closed.

I've only looked at 40-50 blades so obviously I have very limited data, and appreciate your views. When I work with harder material like Black Palm, I know it the 'wing it' approach wont work as well as horn, and I have a pile of 'bad wedges' and want to make a jig, but it feels like the blade drives the sizing. Sorry to be the chatty Cathy or bore anyone with stuff that may just be second nature for some!

 

[Legion]

I was making a new set of scales today, so I thought I would take a pic before I pinned it all together, in order to show (what I think) is the correct angle of "wedginess".

It is probably much easier to see the angle before the scales are bent and peened at the pin end.

 

[RumpleBearskin]

The angle looks a little on the "wide" side to me, but it also depends on how much flex you have in the scale material.

I usually start with the wide side of the wedge, matching it to the thickness of the blade at the point I want it to rest in the scales when closed. Then I thin the "narrow" side to the point I get the "right wedginess" along the length of the blade. That will also depend on the thickness of the tang and the degree that it tapers.