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Comments on ER11 Collets

ER11 Collets

ER11 Collets

The new 24K RPM spindle has an ER11 style collet holder. Attempting to measure the TIR (Total Indicated Runout) is not possible with the measuring tools available at THMS. It should be well under 0.0004 inch.

With ER collets, TIR of .0006” (.015MM) is considered Class 1, .0004” (.010MM) – Class 2, and .0002” (0.005MM) is Class AA (5 microns). Of course, the cost increases with accuracy. Class 2 and higher is my recommendation. A holder with excessive TIR negates this accuracy.

The internal surface of the holder looks well finished. I am going to depend on the fact that a spindle of this design and cost should certainly be well machined. First operational tests confirm this hypothesis.

Of most concern after assessing spindle TIR, is the quality of the ER11 collet used. The spindle is shipped with a ¼” ER11 collet in place in the holder. It is good practice to always have a lightly oil-protected collet, finger tight in the spindle holder. This helps prevent contamination and corrosion of the mating surface. Wipe out the spindle protective oil before use.

ER style collets are self-ejecting, so a sticky collet is not an issue. I have read negative “user reports” from clueless owners of ER16 and larger collet retainers (the nut — that has a double meaning) telling of the threads being very poorly machined. The off-center ridge inside the nut is an ER design feature. Not a manufacturing fault. Do some study of the ER collet system.

The ER11 collet has the retaining ridge but it is too small to be made off center. I bought a second nut to be sure. Therefore, the ER11 collet is much harder to insert and remove than the ER16 and larger collets because the retainer ring is centered and has no gap. If I need to change collets with any regularity, I will purchase a nut for each size. I now have two.

The spindle was purchased from Amazon.com. Amazon also offered a considerable number of very low cost ER11 collets. The low cost of a set of seven for around $18, ($2.50 Ea.) should have been a warning. They are horrible. Precision bits will not slide completely into the full depth of the collet.

Some ER11 individual USA made collets are priced as high as $60 EACH! Good imported collets can be obtained in the $10 – $30 each cost range, in the class 2 quality range, with the low end of that very good for most of my needs. Stay away from the $2.00 to $3.00 ER11 collets.

One of the defective cheapies was used in initial tests. The first ¾ of the collet depth was useable. It was used in the video of the previous post. A new set of ER11 collets have been ordered from a different source. Once inspected and tested, results and the source will be posted here.

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