[KiloOne]

I am trying to machine a human foot shape out of round stock on a standard 4-axis (XYZA) mill.

I have post processed for a Mach_3_Metric_4-axis machine. (by the way Mach_3_Inch_4-axis outputs in mm so I wrote a post-post processor to convert to inches).

I have created a planar finishing tool path which is single spiral cut from heel to toe as pictured here:
Attachment 296226

I am totally confused with feed rates.

The metric G-code has only one feed rate after the spiral has started:

G00 G49 G17 G80 G50 G90 G64
(Ball_750inch)
M6 T1
M03 S4000
G01Z138.546
G00X-10.163Y-0.000A-0.671
Z142.873
Z55.466
G01Z45.941F100
X-10.160Z44.450A0.000 F254
X-10.174Z44.434A-3.435
X-10.186Z44.428A-6.183
X-10.195Z44.430A-8.244
X-10.203Z44.433A-10.305

This seems to set the A-axis feed rate in degrees per minute as I watch the machine in a dry run with no stock.

F254 seems to have been picked up from the tools specified feed rate of 254mm/min (I think).

When the spiral is going around the heel I expected a very slow A-axis feed rate at the heel (nearly 5.5 inches from axis of revolution) and very fast over the top of the foot (only 1/8 inch from axis of revolution) . This does not happen.

I also expected a slower A-axis feed rate when the rate of change of tool distance from rotation axis is high (sides of the heel). This does not happen.

How do I fix this feedrate problem as I can not see how I could machine any metal part with such a change in advance per cutter tooth reed rate with this G-code?

Thanks,
Dale

[KiloOne]

SOLVED!

I decided to add a feed rate on every line that has an A-axis move. The feed rate is based on the distance from the axis of revolution and the distance of the simultaneous XYZ move during the rotation.

I put this in the post-post-processor I had to write to get Mach3 in inches output.

Seems to work fine as Mach3 seems to smooth out any feed rate discontinuities well enough.