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Part 2: an ER40 Chuck Adapter

Two Handy Accessories for your G0602 Lathe

Part 2: an ER40 Chuck Adapter

by “JimSchroed”

Material: Steel
Units: (in)

This is Part 2 of 2. Part 1 can be found here.

If you do much turning using smaller round stock then you will find the ER40 chuck a very handy addition to your chuck collection.  The chuck is not hardened but for hobbyist work it should last many years.  The collet nut is purchased, probably from the same vendor that you purchased your collets from.  I purchased mine from

The material I used for the ER40 collet holder was a piece of 2.750” diameter 12L14 steel.  When you are step drilling you should drill to a depth of 3.200 inches, later when we mount the blank on the spindle we will cut it off at this length and then open the bore an additional amount to match the collet base.

Perform the same operations on the base as outlined in the four-jaw chuck adapter; all of the relevant dimensions are the same.  When that step is finished mount the piece on the spindle and if needed cut it off at 3.200”, this dimension is not critical.  Next take a finish cut over the outer side and face the end.  Open up the bore to 1.200”, and then turn the diameter for the threaded nose.  These are metric threads, 50 x 1.5 mm (1.9685”), notice the groove at the end of the threads this is 0.125” x 0.040” deep.  This is the landing area for threading.

(click drawings once to open in a new page, and then click AGAIN to enlarge).

Once you have finished threading and are satisfied with the fit of the collet nut we can move on to the taper.  The taper must be accurate or else the collet will not hold the work parallel to the spindle axis.  To set the taper on the compound you can use the protractor to get close but then we need to measure the slope of the compound slide with a dial indicator.  The following picture will give you the idea.

The slope for 8.000 degrees is 0.1405” for each inch of travel on the spindle axis.  I used a DRO to measure the travel; a dial indicator can also be used.  When the mouth opening approaches the finished dimension (1.610”) use a collet and some high point paste or fluid to test the fit.  If the fit is not uniform from end to end then a small adjustment to the compound angle is needed.  Use a dial indicator when making the adjustment so that you don’t get too far off.  A very small move will have a very large effect on the high point marking.  When the high point test shows uniform contact for the length of the taper then take your finish cut and polish with some Scotchbrite or fine emery paper.

One of the benefits of turning the taper while the holder is mounted on your spindle is that the taper will be in the best alignment relative the spindle axis that is possible.

One remaining step is to drill spanner wrench recesses in the body.  You can see in the picture above how mine are arranged.  If you have trouble removing the body from the spindle try a strap wrench.

Enjoy the ease of using collets and do not forget the safety warning in the first segment.  And finally do not forget to store your spindle copy in a secure place; it will no doubt be very useful at some point in the future.

Jim About the Author


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About Jim Schroeder