Posted by BillS on December 03, 2006 at 17:35:54:
In Reply to: hobber recommendation posted by Bob M on December 03, 2006 at 02:01:55:
If the gears are *throated* worm gears, you need a hobber that has infeed. In other words, the hob cutter can be automatically fed in a radial direction to an automatic stop. G&E (Gould & Eberhardt) hobbers and many more modern hobbers can infeed.
A hobber without infeed can be used to throat worm gears by manually infeeding the cutter to an indicated depth, so your need for automatic infeed depends on a trade-off between productivity versus "hands on" operation.
If your gears are cut as helical (no contour of teeth to fit the cylindrical worm) then an ordinary hobber with table travel only will work.
There are other choices to consider - with or without differential, hydraulic or change gear table feed, capacity, change gear inventory, etc.
Capacity varies among hobbers, but you need to be sure the machine is not too small to accept a standard 10 NDP hob cutter. Again, if the diameter of the hob cutter must be smaller than a typical 10 NDP shaft mounted cutter, you will probably need a machine that accepts shank hob cutters. This will depend on the spec for cutter radius to get the correct fit to the worms.
Since your gears are relatively small in size, the machine's minimum capacity is important - i.e. how close can the workpiece be moved to the cutter. A large capacity hobber (24" OD say) may not be able to cut the small pieces you require.
Off hand, you might find that a 6" or 12" diameter capacity machine would suit your needs.
Also it doesn't sound like you need a machine with a differential, but that would add some flexibility for future work.
Like with anything else, don't expect to get good service from a worn out machine. If you aren't willing to rebuild a machine, check everything for tightness and minimum backlash.
Service? Well, I hope others will share their experiences on this topic.
Tooling is commonly available for hobbers (cutters, mandrels, arbors, change gears, etc.), but repair parts may be another story.
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