Monroe KA Teardown

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Introduction

Ever been at a garage/boot/stoop/yard sale, flea market, or junk shop and seen a weird thing that looks like a cash register and a typewriter mated? These are electromechanical calculators which our dads and granddads used in the office because electronic calculators were far off in the future.

There are many of these now on eBay, but many of them are less than functional. The last time they were used was probably in the 1960s, and all the grease has probably congealed and picked up dust and twigs and things. Also, decades of being moved around and not being serviced means that parts go out of alignment or get broken by the well-meaning and the inquisitive.

Worse, the manuals and repair guides for these machines are either rare or nonexistent. My dad tells me that a man came round the office every month to maintain the calculators. It's likely that any repair information stayed inside the company.

And so, this disassembly guide will help you take this calculator to pieces so that the pieces can be cleaned, repaired, or replaced. And hopefully you'll learn a bit about the mechanisms that make these machines go.

The specific calculator we're going to be taking apart is the Monroe KA. The KA is of the K series of Monroe calculators produced from 1921 to 1928, with the A meaning Automatic, that is, with an electric motor attached. This model came with various sizes of accumulator and counter, and can multiply and divide (manually) by successive addition and subtraction.