I would say 1/2" - 20 tpi... which is the same sized threads for a standard jacobs chuck.
That is also that same that is threaded as an auxillery on the Craftsman, PowerKraft and Dewalt... Which the Dewalt 7740 is the same animal. I heard that Black and Decker bought out Dewalt about the same time that model came out.
The auxillery shaft speeds on my PowerKraft RAS are 20,000 rpm and 1350 rpm. On The 1350 rpm shaft, I do sanding disks, grinding wheels, drill chuck with sanding drums, drill bits and a surface planer. My aux shafts and saw arbor are in a transmission, gear driven separate from the motor. The 20,000 rpm shaft, I do routing and shaper tooling.
On my Craftsman Electronic RAS, same sized thread. Like yours, that one is on the same shaft as the armature, which also is the opposite end from the blade arbor. Craftsman says you can do routing from that aux shaft... but I don't think the tooling quality is there at that low an rpm (1350 rpm). It's more like "carving" at that speed.
I keep finding more uses for my aux shafts. My PowerKraft RAS is probably the most versatile tool I have in my shop. I keep saying I'm going to sell it someday, but darn it, it keeps making itself indespensible. LOL.
Some of the oddity things for aux shaft use, there was a "saber saw" attachment... I didn't "get" the attraction nor see that as functional. Then there was a pulley attachment kind of "thing" that was used to belt-drive other tools.
"Don't worry, I saw this work in a cartoon once."
"Usually learning skills and tooling involves a progression of logical steps."
Last edited by MAFoElffen; 12-27-2012 at 03:17 AM.