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Replacing the web in a filar micrometer



The E. BOUTY Paris filar micrometer worked fine, had no rust or any other issues, it was just missing the reticles. This article will therefore explain only how to replace the missing reticles with spider web (thread).

The following information comes from personal observation: there are (at least) two kinds of spider thread: the frame thread and the sticky kind. Spiders can move all over their web and not get stuck – that is because the one kind of strand is not sticky – it simply goes from point A on the web frame to point B. Then the spider makes the frame, and then makes the sticky strands and hooks it to the frame thread to make the familiar web. Then an insect or whatever comes along and gets stuck in the web. So, what we want to use is the first type of strand, otherwise the reticle will attract dirt, dust, or anything else, plus be hard to use because it will stick to everything.

I just used an existing thread from an unknown observatory spider. No spiders were harmed in the gathering of material – it was not difficult to find a thread here or there that was the start of a web. I found a thread that looked to be very small diameter.  It is easy to see if it is the sticky kind, too – I just put my finger on it and tested to see if it was sticky. I started with a piece of wire bent in a “U” shape, with about 2” between the ends. This is not critical, you just need a long enough piece to reach both sides of the frame that is missing the reticle plus a little bit more. In my case, there were two missing threads, each a little over an inch long. I made my wire frame, and then sprayed glue on about 6 inches of the wire. You could just as easy dip the ends in lacquer or something, I just used what was handy. I took one end of the thread and hooked it over the outer end of one of the wires and started twisting, leaving space between the ends so I could put the metal frame between the wires and have the thread centered over the frame. The next part took a little time and practice. I tried something easy first – a glue stick. I simply rubbed the stick on both sides of the frame. This assumes you are replacing a reticle that has already been installed, so there should be a mark or groove or some way to tell just exactly where the thread goes.  If not, you need to make such a mark.

I tried using the fork shaped wire and centering the thread over the marks on the frame but this proved very difficult. I then took two pairs of very fine tweezers, and grabbed one end of a thread in each pair. Then it was easy to put one end over the tiny groove on one side of the frame, and then stretch to the other side the frame, and put that end in the groove. The glue stick method did not work, so I sprayed a little of the spray glue on a paper and put a dab of it on both sides where the spider web would be. After it dried, I reassembled the micrometer and it works just fine. The spider web in the following pictures is a little difficult to see, I did what I could.

Filar micrometer with eyepiece removed

Filar micrometer with cover removed

Slide removed, grooves for web barely visible

Spider web on fork

Spider web held between two pair of tweezers

Getting ready to put spider web across frame

Oops! Try again

Spider web embedded in glue, in the grooves.

Spider web on base

View through eyepiece