Earlier this year I purchased an ER40 collet chuck with integral D1-4 mounting from hhip.com (their part #3901-5042). I wasn't completely satisfied with the quality and it didn't have sufficient stick-out from the spindle nose to get cutting tools to it using my solid tool post. I also had inconsistent registration to the spindle with unacceptable TIR. This is that chuck. I decided to replace it with a better solution - one that was adjustable to the centerline of the spindle rotation, along the lines for an Adjust True or Set Tru scroll chuck. After some research I bought an ER40 plain back collet chuck from an eBay seller, did some checking of it when it arrived and concluded it was built to decent tolerances. Then I bought a Bison D1-4 camlock backing plate, some 1045 stock from McMaster and set about making a sleeve to join the Bison backing plate to the ER40 collet chuck. This is the result - it has four M8 set screws around the perimeter that can be used to precisely center the chuck. I'm very happy with the result. Here's a nose-on view - you can see the centering adjustment set screws if you look closely. Although a bit expensive, the Bison D1-4 backing plate is exactly what I expected - outstanding quality: I'm attaching the drawing for this implementation in case anyone wants to do the same. Also, there are more images and description of the build process here: https://flic.kr/s/aHsm1PtHsq Hopefully this will be useful to someone here. Enjoy.