Molder/Dado Arbor

[judaspre1982]

After doing some research it appears the tongued washer plays a role in keeping the arbor nut in place. But the key word is "hardened "tongue washer. It looks like the tongue washer by design is prone to being deformed and damaged whether it be from over tightning, movement of items on shaft/arbor after nut has been locked down or just the process of repetative assembly and disssembly. If it is hardened enough it should have a reasonable life expectancy. If not then the tongue washer is nothing more than a glorified cotter pin. ----------Dave

[Nick]

And sometimes a glorified cotter pin is exactly what is needed. In case of a castrophic stop (i.e, a wrench falls into the lower sawguard), the tongue of the washer will deform before the threads on the shaft are damaged beyond repair. Which would you rather replace -- an inexpensive washer or the whole shaft?

As for Dennis' question, I need to expain a little engineering. There are two ways that you can keep a nut from turning off a revolving shaft. The first is to use a groove and tongued washer, as we have discussed. The second is to make sure that the nut tightens in the opposite direction in which the shaft is revolving looking from the direction of the nut. We employ both of those safety measures in Shopsmith designs.

Take a look at the saw arbor. The saw mounts on the quill and the nut is to the left of the blade (between the blade and the headstock). Looking at the blade from the left side, it turns to the right (clockwise). So the nut on the saw arbor is a left-hand nut that tightens by turning it to the left (counterclockwise). There's no groove or tongued washer because the arbor is designed to be mounted in this position only.

When mounted on the quill, the nut on the dado/molder arbor is to the right of the blades and knives. Looking at the molder or the dado from the position at which we find the nut, the blades and cutters revolve counterclockwise, so we've made the nut turn clockwise -- it's a right-hand thread. Theoretically, if you use the dado/molder arbor in this position, set up as I have described, you don't need the tongued washer. The nut will tighten as the shaft revolves.

However, unlike the saw arbor, the dado/molder arbor is sometimes mounted on the opposite side of the headstock and spins in the opposite direction. (I do this on the Academy's sharpening station, using the arbor to hold a buffing wheel.) Additionally, we have some tools out there such as the Mark VII and the Craftsman's Station that are reversible. Because of this, we add a groove and a tongue washer to the arbor just so all the bases are safely covered.

If you have an arbor without a groove, it wasn't made by us. Whether or not you can use it on you Shopsmith safely will depend entirely on how you mount it.

Aren't you sorry you asked?

With all good wishes,

[beeg]

I'm NOT sorry at all Nick, that someone "asked". Thanks for the lesson.

[judaspre1982]

Nick , thanks for all your input on the subject in this thread and also the many others you have responded to. Having someone representing SS who has the knowledge and resources to answer the many ? we ask on this forum is a great asset in being a SS owner. Thank you mostly for sharing the knowledge you have with us, and taking the time to do so.-----Dave----judaspre1982

[Nick]

Thanks for the kind words, Dave, but don't think I keep all this stuff in my head. Most of the time, I simply take your questions back to the folks in the factory. They are the experts and they're happy to share what they know.

With all good wishes,

[perryobear]

Nick,

I too thank you for your input.

I think the key to the 1-1/4" saw arbor that you describe is the fact that even if the nut loosens, the blade is held captive on the arbor by the nature of its design. Certainly there is nothing keeping someone from improperly mounting this arbor on the MK 5 or MK 7 such that it is spun the wrong way.

I must say for the record that all three of my tongue-less arbors were indeed supplied by Shopmith Inc.

Here are the Shopsmith p/n's for your information.
555619 - Molder/Dado Arbor
517118 -1-1/4" Saw Arbor
555608 - 5/8" Saw Arbor

You can see them here if you are interested:

http://picasaweb.google.com/PERRYOBEAR/SSARBORS

Thanks again for everyone's input, it seems to me that direction of rotation is indeed the key to safe operation of the arbor (and I will continue to use my tongue-less arbors as intended).:)

Dennis