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Author Topic: Calling all bug mavens--just what does this "Lightning" screw do?  (Read 1606 times)
N6GND
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Posts: 317




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« on: June 10, 2012, 12:35:26 PM »

On my Vibroplex Lightning there is a screw threaded into the [corrected from previous statement] right side of the proximal part of the pendulum (part 13 in the Vibroplex machine drawing on their website). The screw hole is threaded and impinges upon the trunnion pin. If the screw is tightened this prevents movement of the pendulum independent of the yoke (part 10), so that dash motions are not independent of the dit motions. So the screw must not be tightened if the bug is to operate properly. If I take the screw out or leave it in untightened there is no difference in operation.

It seems as though the screw might originally have been a means to keep the pendulum and yoke from moving up and down the trunnion pin. The way my pendulum assembly is made the yoke is a tight friction fit on the trunnion pin and thus no up and down motion of the pendulum and yoke is possible.

The screw is not shown or otherwise identified in the Vibroplex machine drawing.

Maybe it was an original design feature which was later made obsolete by changing the fit of the yoke onto the trunnion pin. It may have been that originally neither the yoke or the pendulum was a tight fit on the trunnion pin and the screw was used to prevent up and down motion of the loosely-fit yoke and pendulum. If this is the case, I will christen this  the "appendix" of the Lightning. And you thought that only you had an appendix!

Looking at the Alberto Frattini website photo of his copy of the J-36 bug (which is nearly identical in design to the Lightning) there is a screw in the very same location--although it's a setscrew rather than a Philips head. I don't think it would have been included there, in his very refined design, unless it had a purpose. Possibly on Frattini's bug this screw keeps the pendulum from sliding up and down the trunnion pin.



« Last Edit: June 10, 2012, 01:33:14 PM by N6GND » Logged
WV1N
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Posts: 18




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« Reply #1 on: June 11, 2012, 08:42:49 AM »

The vertical position of the trunion pin is controlled by the the upper and lower trunion screws (46).  The lower trunion screw is locked in position by a set screw to hold it's position.
 The only screw in the proximal pendulum is the dash contact screw.  It holds the silver dash contact on the left side and   protrudes to the other side to hold the dash tension spring.  Over tightening
the dash tension spring nut would make it difficult to form dashes.  You should have a spring wrapped around the screw that adjusts the tension needed to make a dash. 
Or am I missing something?

Bill, WV1N
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N6GND
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Posts: 317




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« Reply #2 on: June 11, 2012, 10:35:13 AM »

Thanks Bill, you are confirming my theory that my Lightning bears an artifact from an earlier design and manufacturing technique.

My Lightning is #271578 which was made in 1973. On earlier, pre-'73, models, my guess is that both the yoke and the pendulum were free to  rotate independently or to slide up-or-down on the trunnion pin. A setscrew (for which the pendulum on my bug bears a threaded hole forward of the dash-tension screw and right next to the trunnion pin) was used to fix the pendulum to the trunnion pin. With the pendulum thus fixed for up-or-down motion, the yoke was also prevented from moving up-or-down but was free to rotate independently.

The revised design tightly friction-fit the yoke to the trunion pin so that the pendulum would be fixed regarding up-and-down movement but could rotate independently.

My Lightning seems to have the older design pendulum, with the threaded trunnion pin setscrew, along with the newer friction-fit yoke. There is a setscrew present on mine which serves now only as a cover for the hole in the pendulum. I have the setscrew in the hole untightened but with a tiny dab of threadlocker to keep it from falling out.

Interesting that Alberto Frattini's high-end copy of this design uses the older method for fixing the pendulum to the trunnion pin.
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WV1N
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« Reply #3 on: June 13, 2012, 10:46:37 AM »

I posted this question on one of the Yahoo bug groups and the consensus is that it is a set screw that sets the height of the pendulum.  I find this interesting since I don't have it on either of the two early lightnings I have.
Bill wv1n
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K3STX
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Posts: 955




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« Reply #4 on: June 13, 2012, 11:23:34 AM »

I think what you are talking about is the screw on the arm. Look at my website , under "My Morse Code Keys"  and the "1959 Lightning bug" picture with the "screw" highlighted  www.k3stx.com.

Is this it?

paul
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N6GND
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« Reply #5 on: June 13, 2012, 12:09:54 PM »

Yes, that's exactly the screw I'm talking about. I don't see it on the Lightning machine drawing or the parts list available now from Vibroplex.

Your 1959 Lightning is earlier than mine so this supports my theory that the screw in question was part of the earlier design. When they made my bug in 1973 they apparently used an old-style pendulum drilled for the mystery screw with the newer friction-fit yoke/trunnion assembly which obviated the use of the mystery screw to determine the height of the pendulum.

Now, for the first time in many weeks, I can sleep at night.
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