Using One Program to Adjust for Material Machinability

Have any of you used the feed-rate knob to adjust for a material with lower machinability rather than adjusting in the program itself? OR, configured your program to adjust only SFM depending on what you're cutting?

I want to cut the same product in aluminum, brass, bronze, steel, and titanium using one program. I thought I would create a material modifiers for feedrate, depth of cut, and surface speed, then multiply each operation's F, DOC, and SFM by whatever the machinability is for the material being cut within the ranges needed for each type of cut. This way, I specify one variable for each run (e.g. alum = 1.00, brass = 0.8, bronze = 0.6, steel = 0.5, titanium = 0.1)

Note this is pseudocode

Code:

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#1 = 1.0 (alum) vs 0.1 (titanium)

(rough operation - gives 2500SFM and 0.01 IPR for alum but 250 SFM and 0.003 IPR for titanium)
G96 S[2500 * #1] F[0.002 + 0.008 * #1]
... use canned operation to rough material, possibly also multiply DOC by #1 too

(finish operation - same as above, but range of cut is much narrower... this is just an example)
G96 S[2500 * #1] F[0.0015 + 0.002 * #1]

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Same thing could apply to constant RPM (G97) operations for drilling, knurling, etc. The objective is to stay within the range of the insert's cutting envelope as the cutting forces vary due to material type, otherwise my VERY expensive inserts fail at the brazed interface between carbide and diamond.

So depending on each operation and the range of SFM, DOC, and Feed Rate, a single variable can control all three based on an optional base, a constant, and a modifier.
However, insert manufacturers rarely change anything but SFM, so it may be sufficient to modify only SFM in each case...

If you have done this successfully, what is your technique for compensating for a wide range of materials without altering the program for each material?


Torin...

Interesting idea, but to me personally it is easier to generate separate G-code files for each material. The CAM/CAD software I'm using (CamBam) has a nice way to handle it - so-called "CAM styles" where you specify tool diameter, feed speed, spindle speed, depth of cut, milling direction and other parameters. Changing a program from wood to aluminum takes me just a few mouse clicks.

Also, this allows me to switch from climb cutting for aluminum to conventional cutting for wood. Or from 1/8" tool for wood to 1mm tool for aluminum. Or, say, from holding tabs for wood to "onion skinning" for aluminum. Would be pretty challenging to do by modifying variables in the G-code.

P. S. Not trying to discourage you in any way, your idea is very cool, especially if you are dealing with a range of relatively similar materials.

In some CNC control programs (like Mach3, for instance), there's a "feed rate override" which allows you to modify the feedrate on the fly. If I'm carving similar materials that vary in hardness (like poplar and maple, for instance) I often adjust this to go a little faster in the material that's easier to cut.