Replacement crosshair material

[Pixies]

Our household is a bit lacking in thick dark heads of hair! Not balding, I might add (esp for the missus) but fair and fine.

Any suggestions on suitable wire for replacing a broken crosshair that is easy to get hold of and not requiring buying a large amount for just a few centimetres' worth!

 

Cheers

[johninderby]

Piano wire is very good and comes in lots of thicknesses so just pick a fine one. You can get it on Amazon or eBay and normaly comes in 1m lengths. Or a local music shop of course.

Edited February 14, 2022 by johninderby

[inFINNity Deck]

In the old days cross-hairs were either made of spider's cobweb or horse-hair. The former is a bit tricky to install, while they may be a bit too thin for astronomical purposes, the latter is fairly easy to install and should be thick enough. I have restored several geodetic instruments using both types of material, here are three examples:

http://www.dehilster.info/geodetic_instruments/1919_keuffel_esser_transit.php

http://www.dehilster.info/geodetic_instruments/tavistock_theodolite.php

http://www.dehilster.info/geodetic_instruments/graphometer.php

Nicolàs

 

[wimvb]

One strand of ordinary copper wire can do the job. This also comes in different dimensions.

[Astrobits]

I have used silk threads for this application.Easily obtained from any bit of silk cloth, thread,  haberdashers or silk moth cocoon ( where I got mine from).  The best spider threads are those from the Orb Web spider as they are remarkably strong. I have yet to find any wire thin enough and readily available in small quantities for my liking.

Nigel

[johninderby]

#12 piano wire is 0.7mm and comes in a 1m length. Strong stiff and doesn’t kink like copper.

Violin E string is 0.54mm

You don’t want to go too fine otherwise the crosshairs can be hard to see.

Edited February 15, 2022 by johninderby

[Pixies]

I have opened up an old pair of wired ear-buds. The individual wire strands are very thin. I might try these first.

[Pixies]

Sorry - another question. I was going to use fast-acting 2-part epoxy - but would superglue work as well?

 

Cheers

[inFINNity Deck]

I use colourless nail polish for the spider threads, it comes in small quantities and with a nice small brush. May also work for horse-hair and even thin copper wires. Normally the thicker wires (e.g. horse-hair, copper wire) are not glued but attached with small cylinder-head screws.

Nicolàs

[Astrobits]

Putting a 0.5mm thick wire into a 25mm eyepiece it will appear to be 5mm thick visually as that focal length eyepiece is a 10x magnifier. I have found that such a thick crosshair will occult a focussed star making it difficult to get it onto the centre. The only way round this is to defocus the star sufficiently so that the crosshairs show up against the bright disc. It does make seeing the star patterns a bit more difficult but it means that you can have any reasonable thickness wire/thread that you like.

Nigel

[CCD-Freak]

I have used the smallest strand of wire I can find and as mentioned above the strands in old headset or microphone cables are very fine.  I solder a small loop in each end of a three or four inch piece of the wire.  I fashioned a V shaped tensioner from an old coat hanger so that the small loops on the wire connect to a hook shape at the ends of the tensioner.  The wire is pulled tight by the spring action of the V and then lined up with the eyepiece barrel.  I then put a small weight on the tensioner to get the wire straight and tight then put a drop of super glue or epoxy to secure the wire.  When the adhesive is set I remove the wire ends from the tensioner and trim the ends with an exacto knife.   I have replaced many finder eyepiece crosshairs this way.  The fine wires are not affected by humidity so they stay tight and straight.   My $.02    Hope this helps