End Mill Question from a Novice

CNC Machines Shapeoko Pro
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So, if the 1/4 end mill in my Shapeoko Pro only plunges a millimeter or so at a time, then why is the cutting length so long? Can I cut an inch deep with the end mill and just go slower? I’m thinking the answer is “no.” But if the end mills should only plunge a fraction of an inch, why is it made like it is. Especially with a down-cut, the longer flutes aren’t removing material further away.

Help me see what I’m missing.

ND

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Because the machine needs cutting flutes for the length of the endmill which will be in potential contact with the stock.

Having the full length of cutting flute also allows for full-depth finishing passes which remove only the roughing clearance which was left previously which will result in better surface finishes.

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Try to not cut below the flutes of your end mill. The reason is the flutes can cut some but carry out chips. Plus the flutes may not be quite as big as the shank and when you get the bit cutting with the shank rubbing you can burn your wood.

When installing a bit you want the bit inserted the minimum amount the length of your collet. So if your collet is 1" long the bit needs to be inserted at least 1". You can insert it further but do not bottom out a bit in the router shaft. The first reason not to do that is the bit is actually pushed up an inclined plane when you tighten. If you have the bit all the way up it has no where to go. Secondly the top of the router shaft inclined plane may be rough and can cause your bit to not be centered in the collet. Having the bit inserted the minimum the length of the collet gives you the best grip on the bit when you tighten up our collet nut.

Carbide3D publishes the cutting length of each of their bits. So going a little over can be done but do not try to cut 3" deep with a #102 1/8" bit that has about a 1/2" cutting depth. The collet will start rubbing when you try to use a bit that is too short for the pocket you are trying to create.

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Hi @Noeldear,

Funny, this was one of the main question I kept asking myself when I first got my Shapeoko, since it seemed strange that I would only ever wear the tip of the flutes of my endmills while the rest of the flutes was pristine. Which lead me to a rabbit hole or understanding the different approaches one can take to create toolpaths. I wrote a section about balancing width of cut and depth of cut here:

The main answer is that in traditional toolpaths (pockets, contours), the machine deflection limits the depth of cut you can pull off, so you can almost never cut deep enough that the full length of cut is utilized.

But there are at least two situations where you can use the full length of cut:

  1. a finishing pass along a contour, that has previously been cleared with a regular (multi-passes) toolpath. Those finishing passes are used to shave off just a little bit of material, so they are easy on the machine (not much resistance), and then it’s possible to cut at full depth of cut (it’s a situation of “large depth of cut, but very small width of cut”)
  2. adaptive clearing toolpaths, which keep tooling engagement constant, so it’s possible to decide to keep a very low radial engagement (width of cut) but compensate by a large depth of cut.

This is much more info that you need, but I figured I would share the result of my own musings :slight_smile:

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Thanks for all the replies! This helps.

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