Knife Edge Suspension!

**Scottie-TX** · 09-02-2009, 11:06 PM

Thot you may enjoy reading about my latest "acquisition" -
Scottie goes off th' deep end again. SHEESH.
A knife-edge suspension for my keyhole Wiener!
Bless 'is patient heart, my hero, "LAB" - aka David J. LaBounty CMC FBHI - indulged my follies once more and made me a knife edge suspension!
(THANKS!)
Now, whut in 'ell's a " Knifedge " suspension?
O.K.; Here's one. It consists of the post (knife edge) and the bed that hangs from it, attached to the pendulum. Note that the bed is articulated!

**Scottie-TX** · 09-03-2009, 12:24 AM

So why a knife-edge suspension? What's the point - edge?
Well, I know it seems like overkill for a Wiener that runs on five ounces with less than a one inch swing with healthy overswing:
How much pendulum error can be produced in a one inch swing? Not much.
Not much but; Not much but the knife-edge suspension was designed to reduce CIRCULAR ERROR of the pendulum.
You can readily see how ribbon or thread suspended pendulums are prone to - can move in a plane other than a straight line. Because they can, pendulum can wander off a straight line course necessary for accurate timekeeping.
Machining of it is very critical because in order for proper performance, bed must always rest fully across the knife edge. Otherwise it can rock fore or aft on the knife.
Why articulated? SAME reason! If pendulum doesn't hang in the same plane as the knife - again it can rock fore or aft - not fully seated on the knife, defeating all the benefits of it.
Also very important that the knife edge be in the same plane as the pallet arbor as not so doing defeats some of the benefits provided by it.
In some old clocks, the bed and knife are inverted. That is, the bed is stationary and mounted to the backcock, while the knife edge is fixed to the pendulum.
Hope you liked my new akkazishun! (I do)

**DanJeffries** · 09-03-2009, 08:04 AM

Very interesting clock....I love it when I see another Knife Edge suspension.

I have a French tower clock that has knife suspension with a pinwheel escapement, the pendulum barely moves. It also does not take nearly the amount of weight to run as does my other tower clocks. It is very accurate especially for a tower clock movement.

Anyhow, great clock and I hope you enjoy!

**Scottie-TX** · 09-03-2009, 05:22 PM

Both observations are very interesting.
Certainly I imagine few if any other type suspension could be more efficient or have less friction.
But more interesting I find that it's used to suspend probably, a VERY heavy pendulum. Penman notes in his book that this is seldom used to suspend a heavy pendulum due to the nature of it's construction and ability to do so.
Now I don't expect this suspension to decrease the power necessary by even a measurable amount, but I do know it's threshold with a ribbon and I WILL retest with the knife.
To it I will also add a rotatable post type attachment. It's purpose will be to ensure that bob will be perfectly parallel to the case.
Thanks for sharing your experience with the knife-edge.

**Sooth** · 09-05-2009, 08:22 PM

Nice. Is there some sort of standard as far as the angles of the "bed" and the angles of the knife?

**Scottie-TX** · 09-05-2009, 08:43 PM

No, I don't believe there is a standard, but I think design considerations and application to some extent guide the design. The knifedge may be a little more standard. Penman in his book recommends sixty degrees for the knife-edge. I believe LAB chose 65. For the bed, angle must take into consideration amount of swing anticipated and two other related factors:
That it's not so narrow as to cause restriction, and that it is not so wide as to lose control of the edge. Penman chose 120 degrees for his treatise. For my app. would not want that - too wide - less control. LAB, knowing this, chose 75 degrees - optimum control; adequate spacing for oscillations. That will provide ten degrees total oscillation without interference. I doubt my pendulum oscillates five degrees total.
THANKS for your interest.

**Mike Phelan** · 09-09-2009, 02:01 PM

Most English bracket clocks with verge escapements use knife-edges for portability; the pendulum rod is attached directly to the verge staff; no crutch or suspension.

**Scottie-TX** · 09-09-2009, 09:44 PM

Yep! Thanks MIKEY!
I read that also in PENMAN altho English bracket was not a reference.
That'd probably be the type where the BED is mounted perhaps to the backcock and the pendulum hanger contains the knife-edge.
I did test it last eve and was impressed. with a light toss, oscillated FORTY minutes before coming to rest. I have not yet performed dynamic efficiciency tests in operation.