Problem with Fellows 36-6

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Posted by Ron V on April 18, 2006 at 20:39:49:

The problem I have with the 36-6 is that it’s leaving unsightly marks on both sides of internal and external teeth. The marks run axially along the entire tooth face and even down into the root area. The best way to describe them would be that they look like generation flats around 1.5 mm wide at the tips of the teeth and get thinner towards the root area. You can only just feel them. Cutter condition, cutting speed/feeds and the size of pitch make no difference to the width, depth or shape of these flats. The only thing that seems to change the way the marks look is the number of teeth on the job. The more the number of teeth the more pronounced the marks become. Generally the problem is quite obvious above 50 teeth cutting around 4DP.
In an attempt to fix the problem we started off by adjusting anything on the machine that needed adjusting. We checked and adjusted the relieving mechanism of the table to ensure it was correctly seating in the four points bearing with each stroke. We tried different relieving angles, even though there was no evidence of cutter interference left on any of the cutter’s teeth. We checked the distance the table was backing off from the cutter.
Next we adjusted the upper and lower worms and wheels to specs. Then checked the amount of movement of the cutter spindle or ram fully extended there was just under 0.03mm TIR. Then checked and adjusted the cutter spindles spur guide along with reducing the upper worm and wheel’s backlash we were able to bring down the circular movement of the cutter spindle, on a 50mm radius, to around 0.02mm TIR.
Next was the indexing drive. We found several of the bevel sets were “hard meshing” causing quite a “rough or lumpy” movement of the shafts when turned by hand so we corrected this. All bearings are in good condition.
This is becoming very frustrating as overall the machine appears to be in excellent condition. Any suggestions or leads would be most appreciated.

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