Re: Synchronome contacts pitted


Stephen Hibbs
 

Hi, Naing,

Thanks for re-sending me Norman’s picture. It is very much more like the Synchronome original part. It differs only, as far as I can see, in the way it retains the gathering arm. The very thin wall embracing the pendulum rod makes for easy clamping with a small screw. This part would also be difficult to fabricate. The text further up the page isn’t visible, but I expect it mentions that making this part begins as a casting. Achieving that thin, circular outer shape would be difficult even by that method, almost impossible by any other. My other comments as to the importance of curves vs. straight lines, etc. would still apply to the making of this part. The dimensioning convention used here only alludes to the formation of the ramp as a section of the surface of a torus; it’s not explicit. That would be complex to set up for machining, someone one would only do if it was thought to be truly necessary (and I don’t think so), and was going to be made in quantity.

An additional comment about the other design:

5.   Unless I’m missing something, it would put the gathering arm off center. That is, it would miss the count wheel. Perhaps it’s intended to work with a gathering arm of a different design, one with a jog in it that puts the gathering jewel back on the centerline.

Best regards,
Steve

Stephen Hibbs
PO Box 536
Markleeville, CA 96120
530-694-1045




On Feb 20, 2021, at 5:02 AM, N Linn <naingtlin@...> wrote:

Dear Stephen,

Your advices are very much appreciated and giving me a lot to think about recreating a part to work with. That helps expanding the idea by various perspectives and thank you so much. 

It would be great if you can examine the picture provided by Norman. Let me send you the file attached.

Best wishes,
Naing

On Sat, Feb 20, 2021, 3:21 AM Stephen Hibbs <oldtimemachines@...> wrote:
Hi, Naing,

I can’t seem to get Norman’s .jpg to download. Wish I could see it. But as a mechanical engineer who has designed thousands of parts for manufacturing, I have some comments about the .pdf from bailey.services that might simplify its fabrication with no loss of functionality.

1. The curved ramp is shown as a segment of the developed surface of a toroid. Again, this could be simplified. If it was simply the surface of a cylinder instead, it could be generated by the simple motion of a milling cutter instead of a complex motion, if you follow me. The roller on the Synchronome’s gravity arm won’t know the difference if it is truly rolling instead of sliding (which it might do if its pivots aren’t sufficiently lubricated). There might be a very slight tendency to twist the pendulum if it rolls down either edge rather than the surface, but I think that would be negligible. If the correct suspension spring is used, it has considerable torsional stiffness and the pendulum bob has huge torsional inertia.
      And I still suspect a straight ramp is as good as a curved one. If I were making this part, I’d make the flat ramp long enough that the roller would land below the top of the ramp and be lifted off before reaching the bottom. This is what Gents’ does and it extracts all the potential energy available in the time the roller and pallet are in contact with each other.

2.  I believe the 45-degree facets are intended to act as elastic hinges where thin material embraces the pendulum rod. But they are so long that I’m not convinced that a single 4-40NC screw in brass will be able to generate adequate clamping force around the rod. And the effort to generate enough clamping force will likely strip the female thread, leaving you with no clamping force at all. The safe way out is two screws, though there is still risk of stripping one of the female threads if they are tightened unevenly.
     You’ll likely be starting with .50-inch thick stock, or maybe the nearest metric equivalent. There’s really no need to machine it down to .44 inch thick, nor is there a functional need to machine the two 45-degree facets on the end opposite the ramp; only an aesthetic one. Nor is there a need for the counterbore if those facets are omitted.

3.   The .035 dia. thru hole gives the gathering arm a place to be, but I don’t see what keeps it there unless the 2-56NC hole below it is part of a retaining scheme not shown. The original pallet part, of course, has an elegant but complex retaining scheme machined into it that was wisely avoided in this design.

4.   The .38 radius on the underside can actually be any radius that’s convenient. It does happen to match the specified radius of the ramp.

Kind regards,
Steve

Stephen Hibbs
PO Box 536
Markleeville, CA 96120
530-694-1045




On Feb 19, 2021, at 1:29 AM, Norman Heckenberg <heckenberg@...> wrote:

<pallet.jpg>




--
Naing <pallet.jpg>

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