# Hobbing Attchment



## Maurice (Dec 9, 2016)

I teach at a local community college and we have a hobbing attachment for a correa horizontal mill with no instruction how to set this up would anyone have any information on this . Mostly on how to set up gear ratio. From the picture I have, I think we could hook it up but I'm not sure about how to set up the gears. Any info would be a start.
Thanks
Maurice


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## Chipper5783 (Dec 9, 2016)

Hobbing?  Or are you simply referring to a spiral (helical) milling attachment? 

There are some nice you tube videos ("Littlest Hobber") to learn more about gear hobbers.  If you are just looking for the ratio calculation for a spiral milling unit then you can use most any manual, figure out the ratio for your machine (ie. do you have a 40:1 head, 5 tpi lead screw etc).  The manuals provide a chart (which probably won't work for you) and the formula to apply for off chart ratios.  Once you have the constants for you machine, the formula ought to work fine and you can make your own chart.

Let us know how you make out.  Regards, David


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## Billh50 (Dec 9, 2016)

There are some UTUBE videos on hobbing with a horizontal mill.  Here is a link to one.


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## willthedancer (Jan 24, 2017)

Maurice said:


> I teach at a local community college and we have a hobbing attachment for a correa horizontal mill with no instruction how to set this up would anyone have any information on this . Mostly on how to set up gear ratio. From the picture I have, I think we could hook it up but I'm not sure about how to set up the gears. Any info would be a start.
> Thanks
> Maurice



I have not set up a horizontal mill with a hobbing attachment, but have set up lots of gear hobbers. Often in the change gear area there will be a plate with the ratio you need to work with like: 15/number of teeth you need to cut, or 25/number etc.

Hobbing straight teeth and splines isn't hard once you get it. If you don't have the magic ratio on a plate somewhere, you might set it up anyway and put a slug of aluminum in the indexer. By trying some gear combinations and counting the light gashes made by the hob, you can sort out the ratio.


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## kd4gij (Jan 25, 2017)

You could probably  get a manual here.
http://www.correa.es/en/contact/


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## vtcnc (Jan 25, 2017)

The hob must rotate with the work piece at a ratio that represents the number of teeth you want to cut. E.g., hob rotates 20 revolutions to 1 revolution of the work piece = 20 tooth gear. You must have a hob that matches your pressure angle and DP. I can send you some additional information that could help if you PM me.


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