[CW] Stuttering Dots on Vibroplex - Info from Two Experts, Frank W7IS and Jim W0EB

[Richard Knoppow]

    Very interesting. I tried something on two keys I happen to 
have in front of me. One is a Lionel J-36 and the other a 
Vibroplex Original c.1920. What I did was simply flick the dot 
spring, i.e. the spring with with the dot contact on it. On both 
keys its vibrates, actually makes a sort of twanging sound. I 
suspect it must do this while its vibrating during keying. My 
guess is that all bugs do it. A damper of some sort may stop it. 
Whether this has anything to do with stuttering dots I don't 
know. Certainly the amount it can move depends on the strength of 
the spring and probably on the spacing from the fixed dot 
contact. Probably also the force applied by the pendulum. I am 
trying to think what the dot stabilizer does during keying. When 
neutral, i.e. the pendulum is parked, the dot spring can't 
vibrate because it is held by the stabilizer, however, during 
keying, when its making dots, it can not be held by the 
stabilizer of it will not store energy needed to keep the system 
vibrating. Without the dot spring the pendulum would probably be 
stopped pretty quickly because of the energy lost to the fixed 
contact. The spring must be able to move no matter how its 
damped. A foam damper or a string around part of the spring must 
have some effect on the number of dots the key will make. I have 
not tried this experimentally.
     If a damper is really desirable it seems to me one could be 
made of a blob of damping gel, probably in the U of the spring. 
This would allow the spring to move but would dissipate the 
energy stored in it quickly.
     I wonder if the TAC keys, made by a company McElroy owned 
part of, has the same problem McElroy's keys have. I have no idea 
whether he designed it, or perhaps more accurately, the same 
person who designed the McElroy keys designed it.
     I tried a 10 power magnifier, because it was handy. I could 
not see the vibrations clearly but certainly did when tweeking 
the spring.
    I certainly agree about making sure keys are aligned 
correctly. There is more too it than it might seem.
    I have not tried tying down the swinging arm of the swing arm 
damper. Seems to me a rubber band of the right size would do it. 
I have three keys with them one of which is very sloppy. That is 
a 1944 Original that appears to be made of re-worked parts. It 
was sloppy in a number of ways, I mostly fixed it. I don't think 
it was ever used very much. After the work it feels OK.
     I do have a couple of TAC keys but am too lazy to get them 
and look at them. Probably later when my curiosity overcomes the 
fatigue from house cleaning today.
     I do not have a McElroy key, too rich for my blood. I can 
work only one key at a time although I would not be surprised to 
find out there are people who can work one with each hand and 
maybe each foot too.
     I knew a fellow at Fox in the local news department, who was 
born without arms. He did everything with his feet including 
power typing. This is more difficult than you might think because 
you don't have opposable toes. I wish I had a better memory for 
names. I am quite sure he could have worked a key with his feet.
     Anyway vy 73 and -30-


On 7/7/2020 6:27 PM, D.J.J. Ring, Jr. wrote:
> THE REAL REASON FOR SPEED KEY DOT STUTTER
>
> The reason McElroy invented the dot stabilizer is all of the 
> McElroy speed keys suffer from self oscillation of the dot 
> contact assembly.
>
> What McElroy should have done was improve his dot contact 
> assembly design so that it didnt self oscillate rather than 
> place a goofy metal arm onto the U shaped dot contact assembly.
>
> Take any McElroy key and place a magnifying light on the dot 
> contact assembly ... and watch what happens when you stop 
> making dots.
>
> In-between dots and after the dot contact comes to rest it will 
> continue to self oscillate.. which you will be able to plainly 
> see with a 3 power magnifying lens or light.
>
> And its the serious self oscillation that causes dot stutter on 
> McElroy keys.
>
> McElroys fix for the self oscillation was to place a metal 
> brace on the dot contact assembly to prevent the self oscillation.
>
> But the metal arm can only just barely touch the long dot 
> contact spring or it will kill the dots.
>
> So the adj of the metal arm is very very critical and will go 
> out of adjustment constantly.
>
> I've tested hundreds of other speed keys of all different types 
> and its only the McElroy keys that have the self oscillation 
> problem with the dot contact assembly. What McElroy should have 
> done was to redesign the dot contact assembly so that it didnt 
> go into self oscillation.
>
> What's happening is users are becoming confused with what 
> really causes dot stutter and there are many reasons.
>
> What works best to prevent self oscillation of the dot contact 
> assembly is to simply wrap dental floss around the U shaped dot 
> contact assembly .. or to place some thin foam behind the U 
> shaped dot contact assembly and hold the foam in place with 
> dental floss.
>
> Below are the real causes of dot stutter:
>
> 1. Using too much return coil spring tension for the dot arm. 
> Which causes the dot arm to hit the damper with too much 
> force.. which can and will cause dot stutter.
>
> 2. If the damper is adjusted wrong--- it will also cause dot 
> stutter.
>
> 3. The idea is to use minimum force necessary for the dot side 
> coil spring tension and then adjust the damper for best 
> dampening (which will help prevent dot stutter)
>
> 4. The spacing of the dot contact to the dot post can also be 
> adjusted for least amount of dot stutter.
>
> 5. If your key has an articulated damper assembly-- (rather 
> than a simple dampening ring).. then what I do is lock the 
> articulated damper in place by placing fish line or dental 
> floss around it. And then all the dampening will take place on 
> the dampening wheel. And that articulated damper wont fly up in 
> the air .. which causes dot stutter as it comes back to rest.
>
> 6. Something else that helps dampen the round dot arm keys is 
> to place a 3" long 1/4" diameter trombone speed control on the 
> round dot arm keys. The larger diameter of the 1/4" hollow 
> trombone provides better dampening on the damper wheel.
>
> 7. And lastly and most important--- if all the piece parts on 
> the key are not perfectly lined up... it can and will cause dot 
> stutter. And that's because if all the piece parts are not 
> perfectly lined up.. it will unbalance the key and make it 
> difficult to send with due to the dot stutter.
>
> I hope this helps settle the dot stutter issue problem once and 
> for all.
>
> Try placing a magnifying lens on your "U" shaped dot contact 
> assembly to see if it self oscillates when coming to rest or 
> in-between making dots.
>
> If you see the self oscillation, then wrap dental floss around 
> the U shaped contact assembly per the above info.
>
> 73 de Frank W7IS
>
> Jim W0EB has more info on his "Dot Stabilizer" here:
> https://www.w0eb.com/DSmain.html
>
> They help greatly in getting rid of scratchy dots.
>
> 73,
>
> DR
> N1EA
>

-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL