Climb: Milling is when the cutter rotates in the same direction as the feed at the point of contact. When climb milling the chip goes from thick to thin and the pressure of the cutter will force the work down rather than lift it up.

Conventional: Milling in which the cutter rotates in the direction opposing the feed at the point of contact and the rotation of the end mill opposes the direction of the work piece feed. When conventional milling the chip goes from thin to thick.  Cutting forces tend to lift the work piece.

In today's more rigid, backlash free machines, climb milling can be used for most milling applications and is the preferred method. In conventional milling the sliding action created as the chip goes from thin to thick dulls the cutter rapidly and creates increased heat in the cutting zone. Work hardening of the surface is much more pronounced under these conditions, especially with stainless steels and high temp alloys. When climb milling the cut starts at full chip thickness without the initial rubbing action, thus cutting temperatures are reduced. This reduces the work hardening effect, and substantially improves cutter life. Re-cutting of chips is less of a problem because chips pile up behind the cutter rather than in front of it. Dimensional and finish
requirements of the work piece are usually much improved when climb milling.
Conventional milling will usually produce better cutter life in work pieces with hard and highly abrasive surfaces, since the cutting edge engages the work below the abrasive surface. This protects the edges by allowing them enter on a clean surface.
 As a follow up to last weeks tip regarding HSS thread milling, some have asked for a speed and feed chart to cover those, e-mail me and I will send as an excel attachment.
Thanks and a gift to Brian Baker and Mike Colwell for suggesting this topic.

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