Mud Lathe

[Pete O]

(03-08-2018, 06:17 PM)f350ca Wrote: Incredible job on the gears Pete.
So you angle the indexing head to the table axis to make the second and third cut ? Makes sense, how did you measure the angle ?

Thanks for the compliment Greg. The dividing head stays in line with the X-axis, to make the second cut the table is moved across in the Y axis by half of the chordal thickness- which is the thickness of the tooth at the chordal circumference- and then the dividing head is rotated back by 1/4 of the index angle; i.e. one quarter turn of the 40:1 crank handle for my 40-tooth gear. This brings the gap at the small end of the tooth right back to the position in space where the first cut was taken, but moves the big end of the gear to a different position, best way I could understand this was by keeping in mind that the circumference is bigger at the big end, therefore the big end rotates a greater distance when you turn the crank, so moving the table across the same distance that the small end rotated, brings the small end back to where it started but places the big end in a different point in space, so the cutter theoretically doesn't touch the sides as it enters at the small end, but cuts a gradually thicker swathe at it moves along the tooth.
I found this all very difficult to get my head around; I used a book called 'Gears and Gear Cutting' by Ivan Law which presents this complex, difficult to understand information in a complex, difficult to understand format.  I perused a couple of websites and between various sources of info I was able to understand it enough to perform the tasks. I can't claim to properly understand the relationship between the gear surfaces that this creates. This is called a 'parallel depth' bevel, apparently a bit of a compromise tooth form, to get a true bevel tooth form requires specialised equipment where the blank moves during the cut. Maybe I'll try that next time