Herters chronograph questions

[mroliver77]

I was not sure where to put chronograph posts so I picked here.

I have a Herters Mark VII from 1964. It came without cables or screens. I do have the instruction book and the tables are glued inside the lid. According to the booklet skyscreens were available for it back then but were very expensive. Does anybody know about these ole girls? Anybody used one with skyscreens?

I would like to make this thing work just for giggles. I have a CED but though it would be cool to watch the lights blink. ;)

It would also be cool if somebody traded me something neat for it!

Jay

[Rocky Raab]

If I'm not mistaken, the "screens" for it weren't skyscreens, but printed screens you shot through. There was a fine grid of conductive ink that the bullet would cut. They were only good for one shot, so every shot took two new screens you had to go out there and replace.

Whether your unit would work with current skyscreens is doubtful.

[mroliver77]

Rocky,
The screens in the book are really wire screen. There are two sets of wires interwoven and insulated from each other. The way it was set up you could move the leads(attached with alligator clips)after a shot and get up to3 shots per screen. There were different makers that used screens according to an older loading book I have so I bet one of them used the screen setup you remember.

My booklet does clearly mention and sell skyscreens as we know them. If you think about it they would relay the same impulse to the machine.I am not sure how to wire it as the connectors are different and are not marked for polarity.

Maybe some pics tomorrow.
Jay

[Rocky Raab]

If I understand correctly (and I'm no electrical engineer) the wire screens serve as on and off switches. The first screen closes a circuit that starts the timer, and the second screen opens that same circuit, stopping the timer. The machine then counts the number of voltage cycles that happened while the circuit was working. The fewer the cycles, the faster the bullet went.

Chronographs with skyscreens may be a bit different, because they use a change in light level (the bullet's shadow) to trigger the on/off action.

That's oversimplified, but it serves as a Joe Sixpack explanation.

[btroj]

That is how I always understood it also Rocky. I do remember reading an article in a 70's era magazine about a guy who was making his own screens using pinking shears, a computer punch card, and light gauge copper wire. The shears left notches on the edge of the cards which spaced the wire wound around the card evenly. The ends of the wire were connected to the appropriate leads and worked fine.
Sure makes me glad for technology. The fact we can get a chronograph with sunscreens for 100 dollars today is amazing. Hard to imagine many individuals owning a chronograph in the 60's or 70's. Too much work and expense.

[OuchHot!]

Is this the machine that has rows of lights that give a number and you turn a rotary knob to get each number in sequence and then refer to a chart? My memory is really bad, but a friend had such a machine. We made two screens using a serpentine of aluminum foil supported on fiberglass screen. At each shot we walked forward and jumped the hole in each screen using foil strip stuck down with silver paint we bought from an electronics house. The wind tended to catch the screens but triggering was 100%.

I hated that machine, it worked very well but always gave me numbers far less than I wanted. It was my understanding that the sky screens were very finnicky but we didn't have those.

[mroliver77]

Thats the one!

[Rocky Raab]

Screen spacing is absolutely critical to readout accuracy. Even a fraction of an inch off can change the velocity reading by a distressing amount. That's one of the very many advantages of today's skyscreens: they don't flop around in the wind and change their spacing at random.

[scrapcan]

Jay,

Send Pressman a pm. I would be willing to bet "Mr. Herters" can come up with more info for you. I would like to see a picture also.

You might think about doing a search on the net for homemade chronograph. There are instructions for making skyscreens usig photocells and I think infared dectector/emmiters. It has been a while since I looked it up though. You might be able to adapt something as all you need are two trigger mechanisms fo rthe timing circuit.

[skeettx]

Found this old thread :)
I had one and made my screens with regular paper and the wire from
a Ford ignition coil. Just insure the wires are glued down close enough
to insure the bullet severs the wire.

Mike