Jerwag Milling Machines - Germany
Types FW, FWP & FWU 355/1000
From what must have been one of Germany less well-known machine tool makers, surviving Jerwag milling machine sales literature appears to show that the Company were active until perhaps the mid 1950s.
Although Jerwag made a number of conventional milling machines - they appear to have concentrated on horizontal models - one particular machine stands out, the Model FW 355/1000 standard horizontal and the FU 355/1000 "Universal". Massively built, the millers were unusual in having the entire body set at an angle to the right with the rise-and-fall knee supported on a bar at each side. The millers were sold on the premise of a greatly improved cutting performance, this being achieved by allowing them to perform what is known as "cut-down" or "climb" milling. In conventional milling - especially as practised by amateurs in light work on an inexpensive machine tool, the cutter rotates up against the advancing workpiece, so thrusting it back against the feed screw and automatically tacking up backlash in the feed train. The result of this process is that the start of a shaving cut is very thick, the end thin and the cutter "rubs" against the work so helping to blunt it and spoil the surface finish. In addition, the forces involved will tend to left the job from the table and so need very rigid and, in some cases, complex and time-consuming clamping arrangements. It was realised - and confirmed by experiments - that if the cutter could be fed downwards into the work, the start of a shaving would be thin (and hence easy to start), the end would be thicker and the cutter working positively (not rubbing) - with both tool life and surface finish improved. A further benefit was that the resolved cutting force was downwards, so acting to clamp the job to the table. Of course, there was a snag - and a big one - any backlash in the table feed drive would cause the cutter to grab the job and lock up, followed by the possibility of mechanical mayhem. Hence, some provision for taking up backlash automatically was essential - and numbers of milling machines have, over the decades, had this facility built in.
Jerwag's system was particularly well engineered, with the fitting of two feed screws working in opposition to each other while also providing the machine with the ability to mill conventionally and to have a rapid table return.
More details are shown in the two catalogues below.