Bourn & Koch 25H

The Bourn & Koch 25H is the smallest of the four H-Series horizontal CNC gear hobbers, a compact machine for fine-pitch work. It takes workpieces up to 25 mm (1.0 in) in diameter, has a pitch range of 1 Module and offers 178 mm (7.0 in) of axial travel. That places it with small pinions, splined shafts and miniature gearing, not with general power-transmission gears.

Everything at the hob end is sized to match. The hob can be up to 31.75 mm (1.25 in) in diameter and 31.75 mm (1.25 in) wide, and it runs from 750 to 3,000 rpm, double the 1,500 rpm upper limit of the 100H. Small hobs need that speed to reach a useful cutting speed. Hob shift is 25.4 mm (1.0 in), handled by an automatic hob shifter with a parts per shift counter, and the work spindle turns at up to 400 rpm.

Two things besides size separate the 25H from its larger siblings. It is listed as 4 axis CNC gear hobbing, and the hob swivel is set by hand: a manual hob swivel with a maximum of 30 deg. +/-, where the 100H has a power-programmable CNC swivel. A shop that changes helix angle often will notice that at every setup. Lubrication is manual grease as well.

Control is a Fanuc 0i CNC with Bourn & Koch's conversational HMI on a touch-screen PC front end. Cycles include automatic single or double cut with speed and feed change between cuts, plus crown and taper hobbing. Only two options are listed, a NUM Flexium CNC control and a loading/unloading system. The machine weighs approximately 900 lb (408 kg), on a stress-relieved steel weldment base with polymer concrete, and the maker says it hobs without hydraulics.