There has been a couple of good points made in this discussion but none of them has touched on the real reason we have a gap. An earlier poster stated that when he made a tenon that was in the gap he removed the safety pin and that he was then able to hold the piece. This is the very crux of the matter. When we first made the Stronghold we had overlap. The biggest problem we had with the chuck was that people would open it up to the maximum so that only one partial tooth was engaged between the scroll and the base jaw and then tighten down hard and snap that tooth off the base jaw. When we devised the safety pin we limited the range of the chuck so that not only would the base jaws always stay engaged but that the partial tooth on the one base jaws would never engage alone. This was not a foreseen circumstance because it is common knowlege in a machine shop that you should never work a scroll chuck hard at its maximum capacity because it gets weaker as you work more towards the outer range of the grip. Sometimes at Oneway we forgot that what is common knowledge here is not so common in the wood shops of the world. Once we had the jaw sizes made and were selling them it was very difficult to change them as people sometimes want single jaw replacements so it is necessary to keep the jaw sizes the same. As for making new size jaws the screw holes work out quite awkwardly. Decreasing the size of the number 3 jaws to make a worthwhile size number 2-1/2 jaws puts the screw holes right in what would be the chucking diameter. This would not be so bad for chucking on a tenon but would not be so great for going into a recess as that is right where the pressure point is. The number 4 jaws were not designed by us but that size was arrived at by one of our larger dealers that wanted that exact size. As far as we are concerned they are kind of silly, that extra little bit of size will not do you much good. To best use our chucks we feel that the base jaws should always be used inside the body of the chuck. Obviously the chucks have more range than that and when required go ahead and use it but the chuck will work better and you will have less danger of collision with a protruding jaw when the chucks are used toward the smaller part of the range. As for the smooth jaws versus the serrated jaws, we consider the smooth jaws as poor, again they were made at the insistance of customers. We feel that chucking marks and methods should be completely removed. If you think that smooth jaws leave no marks you are incorrect. Wood is compressible and when you compress it, you mark it. If all you ever work is very very hard exoctics maybe the marks are so small that you cannot see the marks, but I have never seen a foot where I could not see the chucking mark. As an amateur craftsman you owe it to yourself to do the very best job you can.
regards Kevin Clay Oneway Manufacturing