wild_musk wrote:So I can shorten the rear register of the backplate as long as it still does in fact register on the face of the spindle?
Correct. It's important that it makes intimate contact when the chuck is installed, as that is what guarantees perpendicularity of the chuck with the spindle.
And it should have some room between the ID of the faceplate and OD of the spindle to allow their respective faces to register against each other, ideally parallel to the bore?
Again, correct, but try to observe the rule of thumb of a thou of clearance per inch of diameter, and no more. Even better would be to present ONLY the amount of clearance that permits the chuck to be mounted to the spindle. If a half thou allows installation, that's all you should provide. Any more and you offer the opportunity for the chuck to misalign, although that may or may not be an issue. The point being that once the metal is gone, it's gone, so remove only what you must, as wear is going to happen, too.
I'll get the ID cut first, then see what I've got when it's mounted - if it's good, I'll leave the length alone.
That, in my opinion, is the correct approach, but unless you have the means to
properly measure the bore as you machine, you're risking going oversized, and the amount may not be to your liking.
DO NOT MEASURE WITH A CALIPER, VERNIER, DIAL OR DIGITAL. None of them have the degree of precision required to permit successful results, although you can achieve your goal by chance, and some do. Use a telescoping gauge, and measure with a micrometer, the same micrometer you use to measure the register of the spindle. That way, even if the mic is not properly calibrated, you'll be working to the same dimension, real or not.
Last question, If the backplate is concentric after I get it mounted, should I still check concentricity of the chuck itself?
There is nothing to check,
because that feature is adjustable. So long as the chuck is capable of being corrected so it runs true at any given diameter, that's all that is necessary. Because the thread is quite coarse, once it seats, it's highly unlikely that it would seat deeper yet, and that's what it would take to make the chuck run out once it was properly adjusted.
Be aware, there is most likely some error in the scroll, so the chuck will likely require adjustment for each diameter that you choose to grip. That, of course, depends on the degree of concentricity you desire to hold. The chuck may surprise you and repeat within less than a couple thou, regardless of diameter.
Harold
