I have been re-reading about climb versus conventional cutting, sampling various sources:
+multiple posts here on the forum.
and I must say I feel somewhat confused now by the contradictory statements, exceptions, dependencies to the specific material/cutting situations…so I wonder if it is possible to come up with a (simple) definitive guideline for when to use which.
Here’s what I have gathered, and I would appreciate if you shared your opinion/experience/tips !
- the backlash thing and climb milling being “dangerous” due to this on “older manual mills”. It seems to me there is a consensus that on CNCs in general and the Shapeoko in particular, this is not a concern, so I would cross that parameter off the list.
- multiple sources concur that climb milling is better for finish since it pushes chips “behind the cut” , “toward the back of the tool”, while conventional would “carry chips upward, falling in front of cutter”. Try as I might, when I visualize a vertical endmill, I just don’t understand how conventional would be worse, the chip gets cut from the inside to the outside of the material, surely it can be evacuated to the outside of the cut just as well as behind the cut for a climb cut?
- Bob recommends “Try climb for roughing, because you can rough faster and the tool deflection effects on accuracy don’t matter–the finish pass will deliver the accuracy” while the wiki says “The sliding and biting behaviour [of conventional] leaves a poor finish on the material”
- tends to be perpendicular to the cut for climb, but articles imply that deviation can be either towards the outside or the inside ? outside I get, I don’t see how the tool can be pulled inside the cut with climb ?
- tends to be parallel to the cut for conventional, sounds better for dimensional accuracy yet statements like “the cutting forces are heavier and the tool is more likely to deflect” or “During conventional milling, the cutter tends to dig into the workpiece and may cause the part to be cut out of tolerance” raised my eyebrows.
heat: conventional produces more heat since by definition at the very beginning of the chip formation (thin-to-thick) the cutting edge is rubbing before it starts cutting/biting into the material. This part makes sense, but I do not understand the statement about climb that “chip width starts from maximum and decreases so heat generated will more likely transfer to the chip”. Why ?
power: climb is supposed to use less power, I just do not understand why ? Is this a corollary of the heat thing ?
tool wear: stated to be lower with climb, with “tools lasting up to 50% longer”. I guess this is a corollary of heat and power being lower ?
downward/upward force on the stock: conventional is supposed to create an “upward force” pulling stock from the bed, requiring stiffer workholding, while climb would push it down. This makes no sense to me, for a vertical endmill going through stock, I must be missing something…
climb causing “negative rake/cutting” at high stepovers : why ? The following guideline went completely over my head:
– When cutting half the cutter diameter or less, you should definitely climb mill (assuming your machine has low or no backlash and it is safe to do so!).
– Up to 3/4 of the cutter diameter, it doesn’t matter which way you cut.
– When cutting from 3/4 to 1x the cutter diameter, you should prefer conventional milling.
Finally, this nugget of wisdom from @RichCournoyer back in 2016:
And repeated hints from @gmack in the chipload thread, to use climb.
My personal take on all of this, is that overall climb wins on the Shapeoko, and that the guideline to use climb for roughing and conventional for finishing passes (for dimensional accuracy) is simple and good for 90% of cases ? (which would leave many users in the dirt, since as far as I remember CC still only generates conventional cuts ?)