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Jacobs Gear Hobber

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Bazyle21/05/2013 12:14:52
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4643 forum posts
185 photos

Further to Joey's earlier question re calculations this site might help. It is not clear if Duncan ever finished his hobber but he has a nifty program for calculating gear ratios for it. (thanks Duncan if you ever read this).

This program is also useful if you have a universal dividing head but not the gears listed in Machinery Handbook for differential indexing. Just calculate the ratio given by the listed gears and then use the program to find the combination using the gears you do have.

I wonder if it wouldn't be easier to adapt a very small horizontal milling machine. The simple production ones even smaller than a centec come up on ebay but get little interest. Probably end up as scrap but they would provide the necessary X & Z axes plus spindle leaving only a blank rotator and gear drive to make.

Found my copy of MEW 108. Somewhat hard to understand the explanation but found a much better description by JS on another forum.

david lockwood09/04/2019 14:01:13
41 forum posts

Does anyone know what rpm I should be running the Jacobs hobber at ?

I am just about to machine up the belt drive and I have to work the ratios out

many thanks to anyone who can help

David

Pete Rimmer09/04/2019 19:07:31
364 forum posts
12 photos

The manual for my hobber (which uses 32mm diameter hobs) says the hob speed is 300rpm for steel and 980rpm for brass.

david lockwood10/04/2019 18:38:31
41 forum posts

Thank you Pete

Mark Rand10/04/2019 23:02:59
728 forum posts

That speed gives about 100 feet per minute for steel, which is the accepted cutting speed for HSS cutters on mild steel blanks.

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