Gear Hobbing Attachment (milling machine) Part 2

In part one I made the spindle  and frame of the attachment.   And explained a bit about  the theory of gear hobbing. If you haven't seen part one this will  probably make more sense if you go back   and watch that first. The spindle is driven by  a stepper motor via a toothed belt and pulleys The large pulley needs to be keyed to the spindle. Next i need to make a nut  for the end of the spindle. The saw cuts allow the nut to be clamped  in place to set the preload on the bearings So that's the mechanical part done but how am I synchronizing the spindle to the milling machine and how am I setting the division ratio   I'm reusing the control box I built  for my previous hobbing attachment   this has some other features such as controlling  the feed rate which I'm not using. This machine doesn't have power feed yet but the way it works  is quite simple. The first thing I need to do is add an encoder to the mill spindle. This lets  the control unit know its position and speed. This encoder disc I made with a small slitting  saw. I want to attach it to the outer rotating part of the mill spindle so I can still  use the up and down motion of the quill. The encoder disk has 150 slots using quadrature  encoding. This gives 600 pulses per revolution .  The stepper motor I'm using has 200 steps per  revolution and the pulleys have a 3 to 1 ratio,   which also gives 600 steps for one revolution of  the hobbing spindle. This means I can easily divide   by any whole number by simply counting that number  of pulses from the mill spindle before sending   one pulse to the stepper motor. For example  a one-to-one ratio for every pulse received one pulse is sent. But that's not very useful for  cutting gears. If i want to cut a 42-tooth gear, then i want one revolution of the  hobbing spindle for every 42 revolutions   of the milling spindle to cut  42 teeth around the gear blank. So I count 42 pulses between each pulse sent. These pulses happen very fast  so the rotation of the spindle   is smooth, rather than a series of steps. Should the mill spindle turn backwards, then the count is decreased instead  of increased so i never lose position   and can cut in both forwards  and backwards directions. The teeth on a gear cutting hob wrap around it  in a spiral this means they are at an angle to   the horizontal the head on the milling  machine must be tilted the other way   so that the teeth line up  with the direction of cut . This angle is normally stamped on the gear hob. The  gear blank is first turned to the correct diameter. The number of teeth is set the y-axis is slowly  advanced until the cutter just makes contact, then it is zeroed. and advanced to the full depth of  cut three millimeters in this case. The cut is taken along the x-axis. Since the hob is cutting all the way  around the gear the feed rate has to be slow. To cut helical gears it's just a case of  tilting the spindle to the correct angle   the angle of the hob does not need to be changed. You might be wondering why i made the spindle  able to rotate all the way up to 90 degrees well there's one more trick it can do... This cutter I also made with the hobbing attachment Technically this is no longer gear  hobbing. This is known as gear skiving   and it's one of the few ways to produce internal  gears or cut gear teeth up to a shoulder   on a normal rotary milling machine. I can hear what you're thinking. That was  only a plastic gear, will it work on steel? I was actually surprised how well that worked.

Channel: AndysMachines

Views: 593,380

Keywords: hobbing, hob, skiving, shaping, gear skiving, gearhobbing, gear hobbinh, gear hobbing

Id: VJOem40ggkI

Length: 21min 18sec (1278 seconds)

Published: Mon Jul 05 2021