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Effective cutting diameter Metric help.


Nov 7, 2023
Good day all.
Im new to the forum and im hoping someone could help me out here.

Im machining a part with a 2mm 2 flute ball nose and im getting exessive tool breakage. I started googling "center cutting with a ball nose" and a thread came up about "Effective cutting diameter".
I have a feeling this could be the issue causing the tool breakage. Can anyone help with the metric formulation on how one can accuratly calculate the speeds and feeds for ECD?
I am a self taught operator.

thank you in advance.
Thanks for the response Mtndew. My apologies. The material is 1.2312 tool steel.
The machine is a SureFirst CM365 VMC and spindle max rpm is 10000.
One major speed and feed concern is how big a chip can a cutting tool take.
If with each rotation the tool travels ,001 then each tooth will take .0005.
A drill is stablized by its point so can take a heave chip.
An end mill traveling against its side has very little to stablize it and tends to bend and break with too big of a chip load.
A long 2mm end mill type cutter that one can bend with one finger is not going to take mich stock trsaveling to its the side.

It might take stock better with a plunge feed, and use a larger cutter for the form if possible. if making a 2mm slot in tool steel then it’s a bugger of a job.

A special cutter that has a large diameter, except what is used for the part can be an aid.

looking at / inspecting a ball nose with a jeweler’s loupe can be a huge asset to tool life to see there is a sharp edge. And not a witness land left on the edge.
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The depth of cut im taking is 0.3mm slot. I have attached a PDF of the part im machining. Maybe it can give a better idea of what i am struggeling with. The detailed view B is what im busy with now. In between the 4.06mm islands is area that is giving me the most grief. im doing a 3D contour op to machine around the islands with passes set to order by depth. You can see i dont have much room to use a bigger tool.


  • 4x4 core VT Design Drawing v1.pdf
    217.4 KB · Views: 21
Any chance that you might go in wth a mill saw to rough out a portion of the stock?
It seems that some length of tapered portion might be taken with a mill saw.
Grind a 1/8" mill saw to the taper?
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