Clarity of terms, their meaning and chips vs stress vs cut settings

I was inspired by the MPCNC videos from Thomas Sanladerer to resume work on my BucketMill tool path generator. I notice most people say to watch your depth of cut. Thomas was concerned about wearing out his bit by cutting too deep vertically. I have to wonder if there is a lack of clarity of communication though. One person said the whole width of his bit is being used to cut. Could some people mean “width of cut” and they are saying “depth of cut” because it is too far/deep into the side of the surface to be cut? Can a person cut deeper vertically if they do not cut as deep horizontally? I saw stuff about chip size and cut slower to increase chip size and needing torque and depth of cut and I am trying to put it all together clearly in my mind. Less RPM to horizontal movement ratio means more chip size. More vertical depth of cut means more chip size. More horizontal depth of cut means more chip size and more consistent cutting stress but more cutting stress on average. Can you cut with the full vertical depth of the bit if you do not cut with the full horizontal depth of the bit and then need less chip size because you have more chip count and so you can decrease the horizontal movements (feed rates?) for the cut?

I’ve never heard machinists conflate depth of cut with feed rate.

“Cut slower” here clearly means “slower RPM” not “slower feeds”

To answer your last question you first want to understand climb vs. conventional milling. :slight_smile:

Cut slower means slower RPM? It is not clear to me. I am sure it is not clear to plenty of people. When did I say depth of cut was feed rate?

The only way that “cut slower” can “increase chip size” is for “slower” to mean “slower RPM”

I must admit that I am a bit tired.

Are you referring to “Less RPM to horizontal movement ratio means more chip size”?

Ah. Now I see that. Odd.

Okay. Yeah. In that context cut slower would mean less RPM but if the person did not give the reason for “cut slower” then the person new to the stuff would not know which was meant.

I am frustrated with this subject every time I set up my CNC.
Isn’t the answer “chip load”. What helped me was to go through the logic of the math to calculate chip load.

Interestingly, I used to hate my hand router because it seemed that I was always just burning wood. I steered away from using my router. After tinkering with my CNC where you can only program it and watch is crash, break bits, stall etc. I realized that with a manual router slowing down the feed and increasing the speed was wrong. I actually needed to speed up the feed or slow down the bit. My hand router is now one of my go to tools.


So you were burning your wood and bit? Lovely. I am glad you got it figured out.

Yes, turned out I needed to move faster not slower… not intuitive.

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A lot of my saved speeds & feeds links are now broken, but this one still works:


Thanks @SirGeekALot! I’m just getting started with my OX and all my prior experience was what I like to call “HNC” (manual) milling metal and a little plastic. I’ve definitely been overly conservative on plunge depth.

The closing quote is definitely overall helpful:

NOTE: If you are testing very hard or brittle materials (like mother-of-pearl or non-ferrous metals) start with an initial feedrate that yields a TOTAL chip load less than 2%. If you are testing a thermoplastic , or any material that tends to soften and melt, select an initial feedrate that yields a TOTAL chip load of at least 4% to prevent swarf melting and bit seizure.


Have you heard of the internet archive or the way back machine? We could most likely retrieve info from such dead links.