"PrecisionmachinisT" wrote in message ...

"Jim Wilkins" wrote in message ...

"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote in message
.70...
I've been learning on the Darex E90. It's very easy to use, but it
took
a while to figure out exactly how to adjust the stylus height and
position vs. the wheel location in order to duplicate the original
factory primary relief angle on a given cutter.

0.5" times the sine of 1 degree is about 0.008", so for a flat-cutting
cup or dish wheel you lower the finger below the tool's center height
by 0.008" times the angle times the diameter of the cutter. Lowering
the spring finger 0.040" rotates a 1" cutter by 5 degrees (close
enough for mental math and cutter relief).

For a round wheel you leave the finger at tool center height and raise
the wheel 0.008" times the relief angle, times the wheel diameter.


With the Darex, you ALWAYS leave the finger at cutter centerline when grinding your primary--in order to change relief angle, move the entire finger assembly left or right along the keyslot, this changes the point along the helix where actual contact with the wheel is made in the axial plane; moving it left increases clearance; moving to the right

( correction--moving it left DECREASES clearance angle, and to the right INCREASES it )

decreases it, the actual amount being co-dependant on individual cutter helix angle and effective wheel diameter. ( the air bar height is fixed, at a position appx 3/8 below the cup center line )

Only place I can think of where the above doesn't hold true being with straight flute ( non-helical ) cutters.