Posted by BillS on March 28, 2013 at 09:36:23:
In Reply to: Re: Chatter marks on gear teeth posted by Tim on March 28, 2013 at 01:34:14:
RonV has made some excellent points that are true for any hobber, but mainly apply to vertical setups.
Your machine is horizontal, so you are not able to use a large backing support between table/worm drive and workpiece.
Here are some suggestions, all of which could likely help:
Shorten the arbor to minimize distance between machine and workpiece.
Use large diameter arbor. Or beef up the arbor with solid spacers, preferably grey iron. Stiffness is what you want. Change gears with spokes or concave faces are not as stiff as you might think.
Add mass close to workpiece. Mass could be added to outboard side of workpiece (center side). This can reduce frequency of vibration.
Check for looseness in bearings supporting the worm drive (up/down motion of worm should be very small). Check and adjust worm to wormgear clearance. Not tight, but minimal. Keeping an eye on temperature to generate heat but avoid excessive heating is a good rule of thumb to optimize adjustment. I used to use a good hypoid gear grease for the wormgear bath.
I like RonV's suggestion to run machine as slow as possible. There are change gears on motor shaft to step down speed.
If you can slow down the machine, try increasing the table feed. .015 is very small. At this feed, maybe climb hob to minimize cutter wear?
Make sure that center makes full contact with pilot center hole in arbor. If center is bearing type, check for any up/down bearing play. Try a solid center if you have one to see if this helps.
Anything that dampens vibration is good. If you can put drag on the arbor; e.g. a smooth pulley-like surface on the arbor with a wooden clamp around it. Use spring-loaded carriage bolts through both halves of the wood clamp, and leave one long wooden side to "dog" against the overarm support. It shouldn't take much drag to dampen the vibration.
If the feed table drive has minimal backlash, I would suggest trying to climb hob (cutting toward the center).
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