Kater's Gravity Pendulum Metrology Project

[Boswell]

if you frost the edge of the glass then shine a light into the glass from another edge it might allow the edge to show up clearer.

 

[zondar]

Yes, I've been thinking about ways to make it more visible. That's an idea, or possibly just some black paint along the side might do. I can't disturb the main face, though, since that has to be as flat and friction-free as possible.

I'll probably go back to mounting knives on the pendulum, though. The main reason is so I can let the knives extend slightly past the bob for easier measurement. For that, I have to cut a triangular grove across the bob (as seen in the first post), plus an additional shallow cut to allow the knives to sit in it square in the bottom of the groove. Or else maybe grind some off the back edge of the knives.

I also have to cut the tool-steel blanks I bought for knives in half or smaller so they will fit. I bought some cheap diamond-dust cut-off wheels which might work, but I'm skeptical.

If anyone can point to the most appropriate Dremel-scale cut-off wheel for cutting tool steel, please do so. Thanks.

 

[whitmore]

Serious planning must go into how the fully constructed pendulum will be measured.

The usual approach is by stacking blocks (Johanson blocks for machinists, etalons for science labs).
While invar is a nice low-tempco material, it does have mechanical properties; it will
stretch when the brass is down, but shrink when the brass is above the support.
Young's modulus for invar is 137 x 10**6 psi ( convert to bar, * 0.068947573)
and you want its length while it's hanging...
This is the province of granite surface plates, differential measure, height gages..
calibration of cheap 1-2-3 blocks would be useful, and a 68 F/20 C measurement room.
Do you have some white gloves?

 

[RJSakowski]

If anyone can point to the most appropriate Dremel-scale cut-off wheel for cutting tool steel, please do so. Thanks.

I use the abrasive cutoff disks for the Dremel for cutting steel.

 

[zondar]

Do you have some white gloves?

No, nor a national lab's facilities at my disposal. Sad.

My current idea for the over-all physical construction looks more like this:

* Two glass anvils rest on a squared-up 123 block assembly.
* The assembly is clamped or bolted to a fixture plate.
* The fixture plate is bolted to a heavy aluminum profile stand.
* The stand is mounted to a granite surface plate or similar.
* Dampening and leveling feet are mounted under the surface plate.
* Finally, an optical reader is positioned via a flexible arm (e.g. Noga-style).

Unfortunately, work on this project will be interrupted for a while. SAD!