Conventional milling is when the cutter rotates in the opposite direction of table travel. The milling table moving to the left, while the cutter is turning clockwise. In other words, the flutes are cutting the chip from “underneath”.
Climb milling is when the milling table, and cutter, are moving in the same direction. Table moving to the right, cutter turning clockwise. The flutes are cutting the chip from “above” the workpiece.
The effects can be illustrated while slotting.
This is the preferred method when working with an underpowered milling machine, or one that has some wear in the gibs……..etc. It gives a rougher finish at high feed rates (I’m virtually hogging the material in the above cut), but is generally acceptable at slower feed rates.A light cut with very slow feed rate.The plate which hasn’t been bevel ground for welding was conventional milled with a 4 flute cutter, again proper SFM with a slow feed rate. A reasonable finish in my opinion.
The second pass was done with the cutter trying to “climb” up onto the material. You can feel this with a manual milling machine. It feels like the milling table is being dragged along. It does make for a smooth finish.
HOWEVER…………………………….LOOK CLOSELY AT THE CLIMB CUT
Comparing the second pass to the first, leads you to believe that the smooth cut is the way to go. But notice how the second cut has deflected from the desired line of travel. The finished surface is closer to the camera. The milling head, cutter, and table, has deflected enough to move the cut a few thousands away from the conventionally milled cut.
If you have a tight, heavy, machine…….by all means climb cut. BUT if you’re working with a small light machine, or one that has some wear on it…….conventional milling will hold a better tolerance. Stuff isn’t trying to flop all over the place.
A Closing Note
The above pictures were for demonstration. In the real world, I prefer to cut a rough slot full depth……one pass.A single pass cut for a 7/16 bolt to move in an adjustable sliding assembly. Nothing uber precise. Otherwise, a smaller cutter would have been used to remove the bulk of the material, then the slot widened to exact tolerance with a second and third pass on either side of the cut.