Milling cutters

I'm new to milling and I would like a general rule of thumb about the maximum size of cut, relative to the cutter dia, for profiling and slotting. I'm only cutting mild steel and aluminum. I am OK on cutter speeds and feeds.

Good stuff from way back - as good as any place to start. You can see you gave no clue as to capability/mass/power of machine tool involved

A treatise on milling and milling machines .. : Cincinnati Milling Machine Company : Free Download, Borrow, and Streaming : Internet Archive

I'm new to milling

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Jackamus said:

I'm new to milling and I would like a general rule of thumb about the maximum size of cut, relative to the cutter dia, for profiling and slotting. I'm only cutting mild steel and aluminum. I am OK on cutter speeds and feeds.

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Mainly you have to consider the total depth of the feature you are going to mill. The diameter might be commonly about 1/3 to 1/4 of the length of the flute (a 1/4 inch diameter endmill might have a 1" long flute). Even that is not particularly stiff: a 1" diameter endmill sounds pretty beefy, but when it is 4" long, it is not.

So short (or stub) series endmills are best whenever they have long enough flutes to do the job. And when you go up in length then you have to cut back on the other cutting parameters. So the job guides the decision making.

Nice slots are not cut with a single pass with an endmill. The endmill will flex and pull off to one side, making a decent cut on one side and a scabby cut on the other side. So best mill a slot with a smaller diameter tool, and then open it up by cutting a finish pass down each side. This will put the feature location where you expect it, and a nice finish to boot.

Although the majority of my work involves inch dimensions, I often make use of metric endmills because they are common and come in convenient diameters that are slightly under some common fractional inch size features. For example, I use 3mm to mill 1/8" slots, 6mm to mill 1/4" slots, 12mm to mill 1/2" slots

Vertical or horizontal machine?

Jackamus said:

I am OK on cutter speeds and feeds.

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I'd be willing to bet that you're not.

Jackamus said:

I'm new to milling and I would like a general rule of thumb about the maximum size of cut, relative to the cutter dia, for profiling and slotting. I'm only cutting mild steel and aluminum. I am OK on cutter speeds and feeds.

Click to expand...

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depends on many things including
1) what material you are milling
2) what is cutter made of hss or carbide
3) length of cutter stickout of holder
4) length of tool holder
5) hp of machine and its rigidity
6) part and fixture rigidity and strength.
7) type of cutter that is a roughing mill with wavy teeth tends to have less
vibration as the cutting is spread out more per rev or less of a wack wack wack
.
for example a short length 2" dia end mill might be able to take milling 1.75 wide by 1.75 deep, but if it was 12" of flute length it might have trouble with 1.75" by 0.1" cutting without vibrating a lot.
.
feed rate per tooth is often related to material being machined. softer materials often can feed at 200% to 400% thicker feed per tooth
.
rpm and sfpm is often limited by cutter vibration. longer length cutters cannot take anywhere near max sfpm or rpm without severe vibration
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same with part vibration, a rigid part can take more depth and width of cut at much higher sfpm and feed per tooth cutting 200% to 1000% faster cubic inch material removal rate as long as machine can supply the higher hp. if big cutter needs 20hp and machine has only 10hp that its a hp limit. same as taking too much moving part in fixture or vise. vibration can often move a part like a impact wrench can remove a tight bolt. its the combination of vibration pounding and force