nub on 500 saw arbor

[peterm]

Today I ran across something I have never seen before on a saw arbor. I bought an old greenie for $50 and brought it home in my GM Tracker by taking the legs and head off.
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I cleaned the rust off these two arbors, which appear nearly identical.
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except one has a small square protrusion on the end, about 0.082" x 0.080 by 0.080 high. It is on the one with a small broken grind stone on it in the picture.
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I have never seen any reference to this, so what is it for?
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[judaspre1982]

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[dusty]

Using first one arbor and then the other to mount a saw blade, does the position of the saw blade change (the vertical plane of the blade)?

[peterm]

Thanks for the thoughts so far.
I would not expect the plane of the saw blade to change since it is pressed to the back of the flange of the arbor by the nut and the flange is perpendicular to the bore, which is a nice snug fit on the spindle. I will physically check this question tomorrow though, and also setscrew versus the "sweet spot". It just occurred to me to look for a little square hole in the face of the knurled bearing cap as well.

[peterm]

Well, I took a look. No little square hole in the knurled bearing cap. The saw blade does not wobble or change position on the arbor but when installed, is held off the knurled cap by the nub as Dave said, and Dusty is right that the position relative to the head moves out by the height of the nub.
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The blade revolves perfectly perpendicular to the spindle, so the only effect I see the nub having, is to hold the blade off the head slightly (0.080") but this amount is so slight that I do not see any advantage vs the "sweetspot".
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In case it is significant, here is a shot of the 2 arbors with the (broken) tapered grind stone removed from the nubbed arbor.
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So the mystery continues.

[shipwright]

It looks to me like the nubbed arbor is shorter as in the entire back face of the arbor has been machined away except for the nub. This should make little or no difference to anything on the saw blade end but I suspect that it may have served to locate and lock some other bit also custom machined by the FO, a special purpose washer or something. Look in the "box-o-goodies" if you got one with the machine, for anything that would fit over the spindle that has a matching hole. There are some amazing adaptations that clever SS owners have created over the years, like my fine lathe duplicator, but our challenge is to figure out what the are for. This is the place to start. Only with the help of forum members did I discover the hidden treasures of my 10 ER.

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Paul M

[dusty]

If the distance from the inside (left) side of the blade to the knurled bearing cap is the same with both arbors then there are no significant differences in installation and operation. However, if the distance is different by an amount equal to the nub then this difference changes the location of the kerf. This must be kept in mind whenever changing arbors.

A very small thing until it goofs up an otherwise perfect set of pre-cut pieces.

[billmayo]

It looks to me like the nubbed arbor is shorter as in the entire back face of the arbor has been machined away except for the nub. This should make little or no difference to anything on the saw blade end but I suspect that it may have served to locate and lock some other bit also custom machined by the FO, a special purpose washer or something. Look in the "box-o-goodies" if you got one with the machine, for anything that would fit over the spindle that has a matching hole. There are some amazing adaptations that clever SS owners have created over the years, like my fine lathe duplicator, but our challenge is to figure out what the are for. This is the place to start. Only with the help of forum members did I discover the hidden treasures of my 10 ER.

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Paul M

I would believe this hub maybe from one of the clone machines. I have found a lot of small differences between the Shopsmith and the clone machine equipment. I have used a similar type of hub with an indexing wheel to make swapping a quick changeover.

[reible]

Hi,

I've never seen an arbor like this, so Bill might be correct on the clone idea but here is another thought.

When I purchased my shopsmith in 1976 it came with a metal guard system AND the quill was spaced by a thin metal washer. Right now I don't know if I have it stored somewhere or if I even have it anymore but I'm sure some one here does have one and can measure it for thickness.

This metal spacer/washer was replaced by a 501307 rubber spacer when the new plastic saw guard system came along. This I was able to measure at .120".

If one could subtract the metal washers thickness from the .120" it would be interesting to see how close that comes to the height of the "bit" of metal on the arbor.

Position of spacers is referenced as "A".

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Ed

[peterm]

Measuring with a digital micrometer and my shaky hands, the arbor {originally with a rusty Shopsmith 8 tooth saw blade on it;did you ever see a blade with so few teeth?}, with no nub measures 1.627" thick.

The other arbor with the nub measures 1.682" and 1.614" not including nub. Shipwright was right. So nub seems to be .068" tall........forgive my wrong earlier figure.

So the arbor with nub puts the blade .055" further from the headstock, assuming the flanges are the same thickness, which they do look to be.

I checked the stuff that came with the greenie but no items which might go with the nub arbor are there. Sorry, shipwright.
So, I suspect Bill is right and this nub arbor is off a clone machine. Dusty, I am tempted to file the nub down so the nub arbor is the same as the SS one, to avoid future troubles with knerfs. Reible, no guards were with this greenie.

Thanks guys for the discussion!