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This is a review of the Eureka form-relieving tool, which I made to the design of Ivan Law.

The Eureka form relieving tools first appeared in Model Engineer magazine and is also described in Ivan Law’s book ‘Gears and Gear Cutting’ (Workshop Practice Series Number 17).

The tool is used to make form-relieved cutters such as the gear cutters included in the photo. In operation, the tool is mounted between centres in the lathe, with a silver-steel cutter blank secured to the right-hand end of the tool. One of the button tools is mounted in the lathe’s tool post. A pin fixed to the button tool engages in the long slot on the arm protruding from the Eureka. With the lathe running at a slow speed, the device indexes the cutter blank one tooth per revolution and simultaneously feeds it past the button tool. The cut is taken by slowly advancing the button tool into the work using the cross slide.

The Eureka tool was used to make the set of 0.75 module pitch gear cutters in the photo. Each cutter is used to make gears with a specific number of teeth as shown in the table. These were used to make the spur gears for the differential and gearbox on the 1/5 scale model car described in this website.

Cutter No. Teeth in gear

1 135 – rack

2 55-134

3 35-54

4 26-34

5 21-25

6 17-20

A separate button tool is needed for each gear cutter. The tool with the smallest diameter buttons is used to make cutter No. 6 and so on. I discovered that the design of the Eureka makes it impossible to make the No. 1 cutter due to the lack of clearance on the large button tool required. The No. 2 cutter is just about achievable.

Once I had finished making the tool and the gears, I discovered a far easier way to make spur gears, which is to use a gear hob!

The tool was made on a Warco WMT300/2 combined lathe and milling machine and X3 milling machine from Arc Euro Trade.