Confused about Compression End Mills

I guess I’m a little confused about compression end mills. So if the start of the end mill has an up cut and then switches to a down cut, the idea is that both faces of a veneered piece like plywood would have clean cuts and very little if any chip out. How is that possible? If starting with an up cut, doesn’t the first pass cause chip out or is that created once the bit has gone deeper so the first pass would be ok. Or do you have to make sure the first pass is deeper than the up cut portion to prevent the chip out?

I see. So what would be a good bit to use for through cuts where there is very little chip out on both faces? Or is it best to start with a down cut bit, then switch to an up cut bit and complete the through cut with that?

Compression bits can be used in some cases. The don’t have to cut full depth as in only make one pass. They just should make the first pass at a depth greater than the up cutting portion of the bit so the top surface doesn’t tear out. Likewise, the final pass should be planned so that the upcutting portion lifts the fibers so as to prevent tear out. Certain machines can handle these bits. It also depends on the material, speeds and the depth of the upcutting portion on the particulr bit. Downcutting bits can produce good results also as long as a spoilboard is positioned underneath the work to prevent tearout on the bottom face.

I think using a down cut end mill with a spoilboard is a much better option for an xcarve

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