# ER milling collect chuck typical accuracy



## jdm23 (Jan 26, 2021)

I'm new to milling, so far the only thing I did has been watching videos. I'm not fixated about precision although that is a long term goal for me.

I've got cheap ER16 and ER25 collect chucks for my MT2 milling machine which is integrated in the 250 x 550mm lathe.

On the milling spindle I have between 0.01 and 0.02mm total runout on the edge of the taper.
Fitting the chucks on with moderate tension I read some 0.03 - 0.04mm on the collet chuck taper. That is pretty much the same for both of them.
This improves a bit if I rotate the chuck in the spindle, but I did not spent a lot of time with this approach. A test bar into the ER16 has a little more than 0.05mm TIR not far from the collet.

Are these errors typical in this class of machines? Can give me trouble in producing "reasonably" parts?
Is it a normal practice to indicate a chuck for the best position and possibly mark it?


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## RJSakowski (Jan 26, 2021)

While not desirable, you can still mill with that amount of runout.  It will resulting increased wear on the milling cutters and a slightly larger apparent diameter of your tools.  0.05mm TIR is 0.025 (.001") non-concentricity which, for most operations, is within the acceptable error.  If it bothers you, you can compensate with your tool diameter.  Even with micromachining (less than 1 mm tools), you should still be OK.


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## Mitch Alsup (Jan 26, 2021)

In Dec, I got an MT5 ER-40 chuck, and depending on the rotation angle it has 0.000,3" to 0.001,5" runout (on the ER-40 tapered clamping surface). So I found the point of least runout, and marked it based on the mark on my lathe spindle. Now I can assemble it onto the spindel, as good as it goes, easily.


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