Here is another possible solution. I wanted an ER collet system for my metal lathe and my milling machine. An R8 ER40 chuck for my mill was not so expensive second hand, but for my metal lathe (Colchester with L0 fitting) the chuck was way out of my price range, considering the amount of expected use.
OK, so, back to woodturning. I bought an ER40 chuck second hand off ebay, the cheapest I could find and it happens to be a BT40 fitting which doesn't match anything I have, BUT I can mount it in a metal chuck on my wood lathe (and my Colchester, which was the main reason for buying).
So it is a case of fit a 3 jaw self centring metalworking chuck to my Viceroy lathe, which as it happens, came with the lathe (lucky me) Use the chuck to hold the collet chuck. Now while the job is being done, the collet chuck stays in the 3 jaw chuck, and the work is removed and replaced as necessary only from the collet. Therefore the built in inaccuracy of the 3 jaw chuck for removal and replacement of the work is bypassed. The 3 jaw chuck is not touched until the work is complete.
ER40 collets go up to 26mm I think, so a decent size there. Of course you need more of the collets to complete the range, and I don't have a complete set yet, but for clamping wood, I just turn to the size of collet I have where possible. Otherwise it's a case of buy another collet.
In terms of metal work, the drawback is I don't have a hole through the collet chuck for longer work, but I am thinking of modifying the BT40 to allow for this. Trouble is the chuck is pretty hard.
K