I'm afraid that this will be a bit of a cheat --- I'm going to try to crowdsource an understanding of this. Let's start by looking at all the variables:
Material being cut --- this should be groupable into a couple of categories, ideally matched up with typical endmill manufacturer recommendations:
- Soft plywood
- MDF/Particle board
- Plastic (hard)
- Plastic (soft)
- Metal (ferrous/non-ferrous), specific alloys and elements (are there any elements in their native form which are usefully machined?)
(from: http://www.pdsspindles.com/engineering-speeds more-or-less --- other useful suggestions would be welcome)
- Shapeoko 3/XL/XXL --- note the sub-variant issue of attached spindle (Dewalt, Makita, other) and possible speed range
- Nomad 883
(going to limit it to current production Carbide 3D machines)
Number of flutes and flute length and geometry
Endmill material (carbide/HSS)
Spindle RPM --- as part of this, filled in the chart: https://www.shapeoko.com/wiki/index.php/Materials#Router_Speed_Chart
Machine Feed rate (and plunge rate, which is often half or one-fourth of that) --- One thing I'm surprised at is that there isn't a specific inter-relation between SFM and the feed rate and climb / conventional milling. Logically, when doing conventional milling, the feed rate is effectively added to the effective speed of movement of the circumference of the endmill against the material, while in climb milling, it should be subtracted (and if one could move the machine at a feed rate equal to the SFM, then the rotation and movement would cancel out and the endmill would just revolve around the perimeter of where it should be cutting, as if it were a wheel).
Chip Load --- this creates something of a circular effect, since it is derived from a number of values, but the desired chip load is determined by the endmill, its diameter, number of flutes, and material being cut per the endmill manufacturer's recommendations.
Additional information which may be calculated:
I would like to fill in this post with additional information as it is found, puzzled out, derived or asked about.
Okay, I've gotten everything filled in and calculated for the official feeds and speeds at: https://www.shapeoko.com/wiki/index.php/Materials#Shapeoko_3
Harvey Tool has a PDF on climb vs. conventional milling: http://www.harveytool.com/secure/Content/Documents/Tech_ConventionalMillingVsClimbMilling.pdf and of course, there's a wiki page on it. https://www.shapeoko.com/wiki/index.php?title=Climb_vs._Conventional_Milling