The first challenge was to dismantle this caliper and clean it thoroughly but it's not a bed of roses. Built n the 70's, little was known how it was assembled and I had a boggling 3 days of thinking. Finally I placed the bezel against 2 blocks of wood and gave it a hard push.
Inside was so filthy , filled with dust, accumulated dirt and dry grease. So I took out all the parts and cleaned it thoroughly. The bottom picture shows a magnified view of the dial pinion
The main pinion placed against an Australia 5 cents.
Below shows the process of derusting parts in a degreaser solvent.
Below shows a cleaned part
Cleaned up item vs a dirty part. Quite a contrast.
Now everything clean, dry and ready for assembly.
After the cleaning process, I assembled the caliper and check for significant signs of wear and tear. The caliper was still accurate.
Then comes the next wave of challenge . Replace the broken crystal that has no spare parts. The crystal takes a dome shaped so that it clears the movement of the hand dial during operation but a brand new crystal replacement is just a flat piece of polycarbonate that has to be pressed into the bezel. That means the crystal is slightly bigger that the bezel but it cannot be too big otherwise it will crack during installation. Just a tat bigger.
The second challenge is to cut a perfectly round polycarbonate. Conventional scissors and penknife is not going to make it.
The third challenge is to introduce a 5 degree bevel angle to the edge of the crystal's circumference so that when it is pressed in, the crystal's circumference sits squarely to the bezel ( hard to describe)
The crystal must have a thickness of 0.65mm for it to flex to a dome shape, not any thicker and thinner is not ideal for protection against impact.
The only way to cut the crystal with all the above properties is the use of a lathe. I used a dremel parting wheel to achieve this . With a special attachment that I have made so that the Dremel tool can be mounted onto the tool post and angled to the required 5 degrees.
It took 3 attempts to get the right diameter before it was pressed into the bezel.
Below you can see the bevel angle of the crystal. Without this angle the crystal will be seated poorly on the bezel .
The final product that's cut out perfectly round .
The last challenge is pressing the crystal to the bezel.
Professional workshop uses a hand press and a dome shaped cup that uniformly presses the crystal into the bezel ( one minute job). I had to use sone household items like a plastic bottle to work the crystal slowly into the bezel. It's one hell of a struggle. When it finally went in, it was such a relief.
Took me slightly more than one month to crack this puzzle of crystal replacement .
No comments:
Post a Comment