Choosing Endmill Helix Angles

Definitely not, we just gotta message a mod, no problem.

I know alot of what you guys are throwing around is theory and honestly I even have to read these posts multiple times to make a bit of sense.

My new day job is to prove out cut recipes for hobby machines. Would love to start playing with helix angles and how they effect things.

And would love to use that calculator, Haha.


I have enormous respect for you sir! You were an early pioneer in this forum by empirically demonstrating, by seemingly unbiased trial and error, that high cutting speeds can be really useful for maximizing the performance of “hobbyist machines”. Thank you! :star_struck:


This post on aluminium machining has some interesting things to say on

  • the selection of carbide grade, sub-micron vs. coarse grain
  • coating type, specifically PVD coating not being well suited
  • tool geometry

I don’t know enough to agree or disagree with it but I suspect others might.

Interesting - thanks. I don’t know enough either, but suspect it’s “apples and oranges” because of the huge differences in the amount of heat generated that result from the differences in the MRRs and powers.

Note that in all cases, the article mentions “very high speeds”. If you look at the test data, they’re talking about a 1-inch tool at 30k RPM, so a surface speed of nearly 2400m/min.

My endmills are usually running at speeds in the very low hundreds of m/min, so their advice might not be applicable to us.


Thats some gnarly SFM! I just finished a facing recipe with 1" at 10k and it was definitely making some heat.

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Their tests used 1000 times more spindle load (power) than the Nomad is capable of - 1000 times the MMR, cutting power, and heat. Increasing speed decreases cutting forces proportionally for the same MMR and likely decreases heat generation.

Endmills capable of cutting really thin chips like you use (really sharp micro grain carbide?), seem like a better option for “hobbyist” machines to me.

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You know, I always feel like I have a good ‘feel’ for things on my SO3, that is until I come here and read some of the things you guys can do with actual engineering training!!

Well done! And great discussion, it keeps my sights pointed towards an ever expanding universe…

P.S. Though I just replied it is telling me the topic will close in 4 days, I thought 30 days from last response is the way it was supposed to work…

I noticed it too, I’m not sure what’s up with that. Anyway, if anyone needs to contribute to a (recently) closed thread, don’t hesitate to PM me or @WillAdams and we’ll reopen it.

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This topic was automatically closed after 60 days. New replies are no longer allowed.

As shown below Millalyzer can calculate the depth of cut (AP) that should smooth out cutting forces. :slightly_smiling_face:


Does Millalyzer calculate a variance in cutting forces due to helix angles?

Yes - The lower image shows how they should change when endmill flutes are always engaged in cutting because the depth of cut (“AP”) equals the length of the helix (“Full engagement AP”)


I currently use your spreadsheet, which I enjoy, thank you.

Any opinion on the Millalyzer Dynamic vs Static? I suppose I’d like to pick up a copy to play with.


I have dynamic, but really haven’t used that feature yet - too lazy to figure out how I guess! But, its developer (like GWizard’s!) has a Shapeoko, so it should be interesting to see if he develops a good machine model for it/them. :wink:

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Note that this smooths out the forces on the machine but the forces on the endmill can still vary significantly. IIRC I was told you can click on the chart (left or right, I can’t remember) and switch it to the endmill’s frame of reference. When I did that with a “smooth” cut, it showed very different results for the endmill.

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Forces in the machine/workpiece frame of reference:

This means that the forces as seen by the machine structure beyond the spindle bearings, the workpiece and workholding fixture are essentially constant in time. That can be beneficial if the relevant flexibility is on this side (v-wheels and belt drive, I’m looking at you).

(This is an unequal-helix endmill, hence it can’t be completely flat).

Right-click and select “tool coordinates”:

Now these are the forces in the tool’s rotating frame of reference, so a flat line transforms into a phase-shifted sine. This is the force that is exciting the rotating part, endmill and spindle shaft, so this view is relevant for a setup where the relevant flexibility is there, e.g. when using a small-diameter tool or an anorectic spindle shaft.



Those graphs show very clearly how the ‘constant force’ changes when you switch to a rotating frame of reference.