What I meant was that poly glue likes to bubble and expand. If it doesn't get to expand, in my experience (and I'm sure others will correct me if their experience is different) the poly glue doesn't hold as well. By contrast, CA, even thick CA, doesn't like big gaps. If you look at the spec's for thick CA, the "gap filling" ability is limited to only a few thousandths of an inch. So, if you're drilling a hole that's small enough for CA to get a good bond, it's probably too small for poly glue to get a good bond, and conversely, if you're drilling a hole that allows the poly glue to get a good bond, it's probably too big for CA to get a good bond.
That leads to my next point...blow-outs. One of the big problems that I experienced early on (and still do on occasion) is a blow-out. That's where I'm turning everything down, and all of a sudden part of the blank just goes flying off the lathe. In many cases, the break goes all the way down to the tube, and there's a very pretty, shiny piece of brass staring at me. The reason this happens, in my experience, is that I had a little catch, and not all of the blank was glued to the tube properly. So, I have this piece of material spinning at at least several hundred RPM's, and some of it is reinforced with a relatively strong piece of metal, while other parts of it are not. When the catch happens, the parts that don't have the metal reinforcement have to withstand the force of the catch all by themselves, and some times the catch hits the material with more force than the material can handle. And that's when...BAM...instant projectile.
Does this happen all the time? No. I've improved my glueing technique significantly since I started. I also keep my tools sharper, and I've learned to minimize the number of catches. Of all of these, though, for me the most important was getting a good glue-up. With good glue, the materials (woods, back then) that I turned could withstand the extra force of a catch on a dull tool.
If I only glued the outside edges of the blank to the tube, would that be sufficient? Maybe - it depends on whether I get a catch, how sharp my tools are, how bad the catch is, how brittle the material is, how much material is left when I get the catch, etc. But that's not a chance I'm willing to take, so I try to get really good glue coverage.
][V]. Ill teach him to use the skew next time he comes over.