George Risk Industries KBM

Contents

• Overview
• Models
• Documentation

Overview

KBM is a series of switches from George Risk Industries. KBM is a subset of Futaba MD. Comparing the Electronic Design Gold Book advertisements for George Risk Industries from 1977/78 to 1982/83 (as collected by Marcin Wichary from an unknown source), KBM appears in the advertisements from 1979/80 onwards.

Depictions and descriptions of KBM vary. In 1978, keyboard model 756 was advertised as having “IBM series key switches”, which makes little sense. In Interface Age, November 1977, KBM is depicted as a Futaba switch. In Interface Age, February 1977, they are depicted as what seems to be ultra-low-profile switches that barely protrude past the keycap, but it seems that the wrong photograph was used. However, no correction was made in the next issue. The description was given as follows:

Build custom keyboards in minutes with the KBM series keyswitch. The model KBM is a low-cost, long life keyboard switch ideal for use in CRT terminals, data entry devices, hex keypads, touch tone encoders, etc. Semi-sealed construction means immunity to environmental contamination and the gold crosspoint contacts insure reliable, low bounce switching for more than 10 million operations. Contacts are rated at 12 volts, 1 ma, with less than 100 milliohms contact resistance. Mounting through an easily fabricated metal panel insures precise keycap alignment, and the rugged 1/16″ terminals make hardwired prototypes a breeze.

The mention of “gold crosspoint” appears to be another error, because Futaba MD is not crosspoint contact; rather, a pair of flat contact leaves with gold plating are brought down over a pair of gold-plated dome-shaped pressings. Additionally, KBM terminals are documented as 0.047″ (the same as the terminals on Futaba MD-4PCS measure, around 1/21.25″), while the advertised 1/16″ is larger at 0.0625″.

Futaba MD switches can have up to three colours: the plunger (typically clear or black), shell (typically cream or black) and base plug (typically matching cream or black, or contrasting orange or yellow). The meaning of the colour code is not yet known, but it seems to indicate at least in part the weighting of the switch.

Keyboards with KBM switches have been found with several colour codes, suggesting that different switch weights were offered, although there is no documented evidence of this, with only two models known. The model numbers do easily allow for additional models to exist. GRI also had custom-branded KBM 01 01 switches produced, with a white shell and black base.

The datasheet for KBM cites 0.03±0.01″ pretravel and 0.12±0.01″ total travel and a 3.5±0.8 oz operating force. George Risk were able to retrieve one of the Futaba part numbers.

Models

Documentation

• KBM catalogue page, provided by George Risk Industries