Built during the 1960s, the Mitsui Jig Borers Types 4B, 4BMT and 4BN were direct descendents of the Company's earlier models and, as before, of a design that followed closely those being built in Switzerland by SIP. The specification of the range was rather unclear, the makers listing the Model 4B as lacking automatic traverse milling feed in each direction and the 4BMT with power feeds fitted only to the table - might it be that something was lost in translation as an all-sing-all-dancing version appears to have been lacking. The 4BN was a version fitted with NC (numerical control), a huge free-standing control console with punched-tape drive being part if its standard specification.
Power feeds were hydraulically driven (ensuring shock-free changes of speed) with positioning by the usual Mitsui combination of optical scales and high-precision standard scales, the latter calibrated on a Mitsui Seiki photoelectric standard scale comparator. Accuracy of positioning was claimed to be within 60 millionths of an inch.
Full details of all models can be found below.