Posted by BillS on March 12, 2010 at 08:12:11:
In Reply to: Re: Non Differential Hobbing Seting Teeth When Second Cut posted by jon banquer on March 12, 2010 at 03:41:30:
Jon, It makes sense that reversing is the most reliable way. Once the feed is disengaged, synchronizing gear to cutter is, as you say, a crapshoot. And by the time you see that things are not in sync, the gear is most likely ruined. After all, reliability is the important thing here. My earlier post was wishful thinking at best.
Bilal, a non-diff hob doesn't have a synchronizing dial like a threading attachment on a lathe, or anything like that.
However, moving the cutter slide might hold promise, since it reminds me of a similar adjustment on a Prat&Whitney thread mill which moves the cutter axially, independent of the workpiece.
How about this? with machine off, try to jog machine to bring a work piece tooth nearest to cutter.
Raise workpiece above and move cutter table out in front of but near the start of cut area.
Manually move table toward work to position top center of cutter just beyond
front face of work.
Engage table feed. Keep table feed engaged for rest of procedure.
Pull machine belt manually to bring cutter teeth near top of arc.
This should also take care of any remaining backlash in drive components.
Loosen cutter slide.
Move work slowly into mesh with cutter as you shift cutter slide to center work tooth in cutter space.
Move slowly so you can rock the cutter back and forth by hand to detect when cutter contacts work.
Put a dial on cutter slide to more easily observe its movement. Keep rocking cutter and
shifting slide until cutter slide can't move either way without locking cutter in mesh.
Cutter depth might not be exactly at original depth since cutter slide is loosened.
Pull work away from cutter mesh. Run machine in reverse to get sufficiently in front of work.
Since you did the adjustment near front face, this should shorten time to get out in front. And
you don't need to move as far as required for the first cut. Remember, feed is still engaged!
Set to depth and make the (hopefully!) final cut.
Actually, I still like the idea of loosening the work piece and moving it slightly as you move it to depth, rather than moving cutter slide. I never did the cutter slide thingee, but we used to check angle of throated worm gears off the machine and put them back on machine. Rocked the loosened workpiece by hand as it moved into mesh with cutter, then locked the work down. Much easier to rock the workpiece and feel the mesh. Still have to have feed engaged with machine backlash out, and then move out of mesh and run in reverse to keep things in sync. But the killer is if you originally had to indicate the blank in, taking it off will mess that up.
Remember, when you run the machine backwards, set an electrical stop. Don't walk away if the machine doesn't
have an electrical stop when moving in opposite direction! I had two Barber Coleman #12's like that.
Also a mechanical stop that disengages feed will mess everything up!