Difference between flat and fishtail endmills

What’s the actual difference in result between a flat and a fishtail endmill? I’m looking at 2 endmills here that are the same except that one of them has a flat end and the other has a fishtail end.

Endmill with flat end:

Endmill with fishtail end:

Does the flat endmill give a prettier result on flat surface when facing? What’s the advantage of the fishtail endmill?

I am so confused. Everything I find about fish tail endmills refers to them being the same as flat endmills or standard endmills that we talk about around here. However, the links that you refer to make it look like the fish tail they have instead is not a flat bottom but instead has the center higher than the flute tips. My translation of the difference between the two mentions that their fish tail endmill is good for fibrous materials (and also something about a strawberry (fraise) that I don’t understand). So perhaps if you are milling a lot of pine or perhaps plastics?

I would recommend you just go with the flat endmill. It’s what most everyone uses around here as a standard endmill to get good flat-bottomed projects.

This is the french word for milling bit

From a mechanical point of view the fishtail would be less resistant to high loads. Why and when one would use one I can not answer.

edit: it is explained in the description of the bit: it permits an optimal entry into the cutting material with excellent chip evacuation. It will limit tear out on fibrous and soft materials.

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My understanding is that fishtail endmills have a more pronounced angle at the bottom which results in a crisper/sharper entry when cutting into sheet goods, while a flat endmill has a less acute tip which results in a flatter and more even bottom surface of a pocket when not cutting all the way through.



How would the chip evacuation be better on a fishtail? Do you have experience cutting with a fishtail?

No, I don’t have experience with these bits.
Better evacuation may be due to the fact that there is some extra space between the tips so the chips can align to the channel better, but that is just a guess. (Or maybe it is just marketing talk :sweat_smile: )

It seems to me that the more acute angle of cutting would be better at evacuating chips.

This sounds right to me too. When it’s spinning, there’s essentially a cone-shaped recess at the end of the endmill that is always open to the spiral of the flutes.

In my experience, the big difference I’ve seen is when milling small areas. That is, a hole or pocket that is only 1 - 1 1/2 times the diameter, the bit tends to leave a little nub in the wood rather than a smooth surface. This is most apparent for me when using end mills for clearing a flat depth vcarve


I thought it was the French word for “strawberry”… :no_mouth:

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We discussed the linguistics of this at:

… a free end mill in every box!



And now for more linguistic fun: the French for “trim router” is “défonçeuse”, which never made any sense to me since it is derived from “défoncer” (verb), which literally translates to “to smash/to stave in”, and I definitely don’t want to smash anything with my router.


It is.
Latin languages have lots of meanings for one word and lots of words for one meaning.

I think there’s plenty of evidence on this forum to show a heap of smashed things caused by a défonçeuse :slight_smile:

It seems a défonçeuse is also a type of plough (a tiller of fields). I imagine the grooves cut by such a plough in soil compared to the grooves cut by a trim router in wood might be the inspiration for the name.


Julien, have you ever considered that you’re just not using your défonçeuse for its intended use???

Quite possibly, as I was not even aware those things existed before I got a Shapeoko :slight_smile:
I mean a Défonçe-oko.

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A ripe blackberry murmurs to the wall.


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