The effect of tool runout on mills

[compact8]

Have done a bit of searching, the biggest effect is on tool life, a tiny bit of run out can lead to big reduction in tool life. However, I don't worry too much about that because if the tool bit is frequently changed and the mounting position is random, the wearing on cutting edges should even out over time.

The second thing is accuracy, reamed holes will be bigger which seems to be the case on my mill, a reamed 3 mm hole has a sliding fit with a 3 mm guage pin but I could not feel any play so that's acceptable to me.

How about finish ? side milling does not produce very good finish on my mill but I am not sure if that's due to insufficent rigidity or run out. It's an EMCO FB2 mill that weights about 300 lbs. The current run out is within a thou. I am wondering if it is worthwile to get better ( read : expensive ) tool holders with less run out.

 

[Chipper5783]

I suggest tool life is determined by many factors. If you are approaching the maximum design chip load per tooth, then I think you are correct, that runout would be a negative impact on tool life - most hobby activities don’t come close to maximum chip load. For light cuts, I don’t see tool run out as a major factor effecting tool life (unless the cuts are so small you are mostly rubbing - that’s another issue that will effect tool life). How are you managing chip evacuation, what coolant system are you using, climb or conventional milling, speeds, feeds, . . . . .?

I’m not saying that you shouldn’t try to reduce runout of the end mill. Of course, the more concentric the tool is running, the better. However, there are many factors which effect tool life.

What do you mean when you say “reaming”? A reamer will cut to the size the reamer is ground to (mostly), following the existing hole. Are you plunge milling an existing hole? If so, then the end mill run out will certainly increase the resulting hole size. Strictly speaking, I would never expect an end mill to cut exactly to size. Plunge milling is not the same as reaming. Are you using a CNC machine? You can interpolate a circle to most any diameter you want (though 3m m is pretty small). If so, just tweak the cdc (cutter diameter compensation). I find that interpolated circles are not perfect (you can still feel the stop start location) - if the hole is critical then bore it (or bore it then ream with a reamer).

 

[compact8]

What do you mean when you say “reaming”?

I meant reaming a 2.9 mm drilled hole to 3 mm with a 3 mm carbide reamer

 

[markba633csi]

If I recall the FB2 uses Morse taper #2 spindle, so standard MT2 collets would probably get you in the range of maybe 4 or 5 tenths or less
Should be plenty good enough for hobby work

 

[coolidge]

My tool life is mostly affected by GRRRRRAAAHHHHHHHH STALL oops.

 

[verbotenwhisky]

Have done a bit of searching, the biggest effect is on tool life, a tiny bit of run out can lead to big reduction in tool life. However, I don't worry too much about that because if the tool bit is frequently changed and the mounting position is random, the wearing on cutting edges should even out over time.

The second thing is accuracy, reamed holes will be bigger which seems to be the case on my mill, a reamed 3 mm hole has a sliding fit with a 3 mm guage pin but I could not feel any play so that's acceptable to me.

How about finish ? side milling does not produce very good finish on my mill but I am not sure if that's due to insufficent rigidity or run out. It's an EMCO FB2 mill that weights about 300 lbs. The current run out is within a thou. I am wondering if it is worthwile to get better ( read : expensive ) tool holders with less run out.

I bought a set of R32 Collets and a good set of Mill holders and a Precision keyless chuck and have little to no issue with runout.