When I first started experimenting with shells, I made them big and bold. I didn't worry about fitting them to the C clamps. They were robust. You could mame somebody with one of those early shells. In time, I got feedback from friends who said they'd like to see them scaled down a bit, so as to use them in the gimbals. As I did, I found the shells to become more fragile. It's tough because you have to clear 2" to slide them over the plastic inners but you have to stay within 2.5" to get them into the C clamps. Wood being more porous and spongey than either plastic or aluminum, I found the 1/8" shell walls unpleasantly thin. I suspect that one reason Grado put a thicker ring at the end of the SR2 and SR1 was to brace the emaciated walls for some shock resistance. The thicker 1/4" ring at the mouth of these headphones gives the impression that you're getting a thicker shell than you really are. It's certainly more pleasant to look at. It's really the seedling of the later hammerhead on the mushroom top of the GS1000. With the drill press, I've found that using a 2 3/8" hole saw (which actually produces an outer wall of 2 1/4") to be the best fit but I've also cut slightly thicker shells, using the 2 1/2" hole saw. These latter shells still fit within the C clamps because they cut an outer diameter of 2 3/8". One trick is to enlarge the holes for the lateral pins connecting the cups to the C clamps. Doing so allows greater ease as the clamps are brought closer in. This has allowed me, on some projects, to get away with larger shells, even if the clearance is, as you've noticed, a little more hairpin. On the other hand, such shells are thicker and a little more able to handle some knocks and bumps.
My mistake. Thank you for correcting that. I wondered, while I said it, whether Grado did something to lessen their resemblance to the more expensive RS1s. So far, I've made aluminum gimbals with 3" rings, but that was for the aluminum project, which is unapologetically big and brash. After comparing other aluminum shell designs, including the PS1 and the HP1000, I've decided that on my next aluminum project, I'll let the inners rest at 2", with rear chambers at 2 1/4" and with three points (the front lip, the middle ring and the end "hammerhead lite") at 2 1/2". This "middle ring" of which I speak is the gimbal that will replace the old plastic gimbal. Having already moved in that direction, I have ordered the materials to make 2 1/2" aluminum rings. Knock on wood. Such rings will be useful for both types of shells - aluminum and wood. I had previously envisioned using wood on wood Grado mods, but - as my son points out - aluminum has a structural strength that wood of that diameter simply doesn't have.
Ah I see, so the removal of the pin now isn't necessary? Thanks for your elaborate response. Fascinating to hear the perfection of such a great project