Certain year group of Keuffel & Esser's cursors for duplex
rules are known to crumble as the years go by. It is known among
the collectors as "KERCS" (K&E Rotten Cursor Syndrome.)
I own a few of those and wanted to do some repairs as much as I
Cursor parts suffering KERCS. Cursor bars crumble
down like cray.
- Only cursor bars are affected. Frames, glasses and screws are
- We must rebuild cursor bars.
- The tension spring within the cursor is completely pulverized
due to oxidation. So, this has to be remade.
- The original screws are "inch screws." Taps for inch
screws, for example, are expensive outside of US and England.
- I decided to use Delrin because this "Engineering Plastic"
material is easily handled by normal machining process as if it
- Actually, Delrin is Dupon's product name. It's generic name
is "Acetal", and Mr.Yukio Kubota, a collector pal of
mine, kindly got a piece of this material for me. Thanks.
- I cut out this piece from a sheet of 0.2mm thick phosphor bronze.
This thickness seems to give just the right strength as a spring.
- The original structure was that the metal female screws were
cast inside the cursor bar plastic. This structure is impossible
to recreate. My initial plan was to "self tap" the screws
in the cursor bars. After several "tapping", however,
the original screw wore down and become unusable, So I had to
use a real tap to cut a female screw into the cursor bar.
- The inch taps are hard to get outside of US or England. So I
decided to use ISO screws and associated tools.
- Mr.Kimutra kindly sent me a set of screws of an appropriate
size, 1.7mm x 2.5. Although they are Phillips headed, they seem
to be just fine, perhaps because they are black.
(Left: Half assembled cursor, Right: Restored K&E 4081-3)
(Another rule, restored K&E 4088-3. I used brass screws for
- Somewhere I read that Delrin could cause allergic reaction.
So I hardened myself with a mask and saved every small pieces
of dust of Delrin in a bag. Luckily., I did not develop any skin
rashes. Good grief.
- The newly refurbished rule is in great shape. Delrin glides
smoothly over celluloid body.
- I had to remake cursor bars several times. The "yield"
was about 1 out of three including initial failures. Good grief.
Addendum: Use of Inch Sized Screws
On my inquiry to the Slide Rule Mailing List, Dave Martindale kindly
told me that the screws for K&E cursors were Unified No.1-72
and gave me suggested metric drill sizes for making tap holes. I
was also able to locate a shop in Japan which stocks Inch taps.
Now I can repair cursor using original screws.
Restored K&E 4081-3