Thread: Hinge pin mechanics

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?

If you feel the tension on the blade as you move it through from closed to fully open, and watch the movement and flexing of the scales on a vintage blade it will show how that torsion changes as the blade moves. It is because of how the shape of the tang is moving through the scales causing different angles and the flexing keeps the movement smooth. If you then did a similar movement on a similar razor that has a spacer instead of a wedge the tension would increase and decrease throughout the range of motion as the contact at the pivot varies as the shape of the tang is not the same throughout the range of movement. Also when the razor is in the closed position the space would have it's greatest amount of tension. The old time designers had stuff fingered out.

Originally Posted by rolodave

This may be right or wrong.

If the tang is flat with no tapers, then a spacer is OK

If the tang, at the pivot, tapers toward the tail you have a simple bevel

If the tang, at the pivot, tapers toward the tail (horizontal) and towards the heel (vertical) you have a compound bevel.

The spacer/wedge should match one of the three.

The taper(s) of the wedge should match the taper(s) of the tang at the pivot.

Bolded seems to be what applies to my PRC Hydra.

Originally Posted by RezDog

If you feel the tension on the blade as you move it through from closed to fully open, and watch the movement and flexing of the scales on a vintage blade it will show how that torsion changes as the blade moves. It is because of how the shape of the tang is moving through the scales causing different angles and the flexing keeps the movement smooth. If you then did a similar movement on a similar razor that has a spacer instead of a wedge the tension would increase and decrease throughout the range of motion as the contact at the pivot varies as the shape of the tang is not the same throughout the range of movement. Also when the razor is in the closed position the space would have it's greatest amount of tension. The old time designers had stuff fingered out.

Yes, they did, but it is not the only method, obviously.

Originally Posted by Orville

Yes, they did, but it is not the only method, obviously.

Can you elaborate please?

Originally Posted by mainaman

Can you elaborate please?

I meant that using a wedge is not the only method of securing scales properly. A spacer can be used as well. There are just different design requirements for both, unless I have read all this information incorrectly.

Originally Posted by Orville

I meant that using a wedge is not the only method of securing scales properly. A spacer can be used as well. There are just different design requirements for both, unless I have read all this information incorrectly.

Elaborate more please. What design requirements are you referring to?

Originally Posted by mainaman

Elaborate more please. What design requirements are you referring to?

Based on what I have read (and I may be incorrect in my interpretation), it is fine to use a spacer, instead of a wedge if there is no taper to the tang. If I am mistaken, then please correct me. I am not a restorer, nor an engineer, but I see no issues with the "action" on the one razor I own that uses a spacer rather than a wedge, so I must assume that it is designed "properly".

Originally Posted by Orville

Based on what I have read (and I may be incorrect in my interpretation), it is fine to use a spacer, instead of a wedge if there is no taper to the tang. If I am mistaken, then please correct me. I am not a restorer, nor an engineer, but I see no issues with the "action" on the one razor I own that uses a spacer rather than a wedge, so I must assume that it is designed "properly".

That is correct, rolodave and I stated it above in the discussion.