[Hallicrafters] SX88 Dial belts

[Robert Nickels]

On 9/8/2017 8:30 AM, Greg Gore via Hallicrafters wrote:
> The belt width is 1/8" (.125) and the tooth count is 112. It looks like roughly 4 teeth per inch.

I can confirm what Greg said, and add a bit more from my own 
experience.   The belt from my SX-88 had a patent number on it and I 
used that to research the successor company and potential sources, which 
ultimately led to an application engineer at Stock Drive Products 
(www.sdp-si.com) which is a large manufacture of timing belts today.     
I can't find my notes from that exchange but the bottom line was that 
this patent was for the original "toothed" timing belt, and having been 
designed by a US inventor around the middle of the 20th century,  was 
made to imperial measurements, with 1/8" teeth and spaces, as can be 
seen here:

http://i.imgur.com/Xdq064p.png

My original belt measurements were:  27 1/4" long, .165" wide, 4 teeth 
per inch.

I was told that as timing belts became popular and more suppliers 
started making them, the industry standardized on diametral pitch (D.P.) 
measurements, which is the number of teeth on a gear per inch of its 
pitch diameter.  As a result, there are no products available today that 
match the old pitch of the SX-88 belt and it is extremely unlikely that 
any  such tooling still exists.    Thus ended my search but if anyone 
has that original patent number, I'd appreciate having it.

The design of the dial pulleys would make it difficult to replace them 
with ones that could accommodate modern timing belts.   I did look at 
bead chain as a possible replacement since a "4 beads per inch" type 
might fit the pulleys and the precision and torque required to turn the 
SX-88 band indicator is minimal, but I have not tried it.

73, Bob W9RAN