Re: barber colman #12 gear hobber questions

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Posted by BillS on September 16, 2009 at 21:56:18:

In Reply to: Re: barber colman #12 gear hobber questions posted by Jim Pollock on September 15, 2009 at 08:42:15:

Sorry, I wasn't very clear - the axial play I was thinking of is between hob cutter shaft and bearing. What you want to do is remove the outboard bearing and the cutter. Check for up/down looseness and end play looseness between shaft and back bearing housing. There has to be some play here (.001-.002 maybe?), but should not be excessive.

When the cutter and outboard bearing are mounted, it is very hard to see this looseness, but cutting pressures can expose it through poor finish.

Well, 1" rotational backlash in the cutter may seem like a lot, but this accumulates for a number of gear pairs in the cutter drive. I think 1" at 3" OD represents some wear, but I don't know how much one would expect from a "tight" machine.

Anyone got an idea about acceptable cutter drive backlash?

The machine is not really designed for small backlash in the cutter drive, but is operationally set up to always load the cutter drive backlash and to even out irregular cutter loading with the flywheel.

One thing about table drive direction - don't try to climb cut with this machine. I'm guessing your table drive screw has considerable slack. To keep from breaking a cutter when climp cutting, the table screw and nut should probably have no more than a coupla thosandths play.

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