A Gear Cutter Backing Off Device, aka Eureka

I am in process of building a Jan Ridders Glass Cylinder engine and it requires T2.5 timing pulleys. I am not fond of spending money (it is a hereditary thing I think) so I intend to make my own pulleys. Originally I was going to use the fly cutter technique but with the tiny tip size I am concerned that the tool will not last cutting 3 pulleys.So, I need to make proper cutters and then relieve them. As Duplex states in his original article series in Model Engineer 1949, more teeth is easier on the machine. Not wanting to cave in and use the alternatives, I need a relieving device. I researched a lot of patents, including the Hendley cross slide version but it turns out the Eureka is more feasible with the tools I have. I found Balzer’s original 1895 patent for a previous version of the Eureka but the article I am basing this off is from the Centennial Model Engineer archive. A patent describing a more recent version (1906) resembles the Eureka. Off to the metal pile to find the chunks of steel from which to carve this thing. I opted to make the anchor and ratchet plates first so that the mandrels can be turned for a good fit. Not having a large boring head I bolted the 2 plates together after laying out and drilling a .125 guide pin hole in the centre. This was mounted in the 4 jaw and centred on the hole. A boring boring operation later and I reached the 1.500 dimension.

Off to the bandsaw for some rough trimming and then to the horizontal milling machine for cutting the slots and cleaning up the straight bits. The round portions were trimmed on a belt/disc grinder and filed to the lines.



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