Shopsmith Forums

I bought into the idea that maybe, just maybe having the bench tubes inserted too far could cause the problem. The problem being that in vertical the tubes go 7° past vertical. I'm still sceptical so I mocked up my spare parts just to see what I might see.
OKAY. Assumptions and Speculations.

edma194 wrote: ↑Wed Nov 25, 2020 3:10 pm I'm wonder if the base casting and the base arm casting are matched. The service parts list identifies them as the 'Base for older units' and the 'Base Arm for older units', so there are at least two different versions.

There are at least three versions at the assembly level, plus Double Tilt. 1) Compatible with large diameter bench tubes. 2) Revised for compatibility with the smaller diameter bench tubes, has a 3/4 inch diameter hinge pin. 3)Has the smaller diameter 1/2" hinge pin and setscrews for the way tubes are moved to the top. Most 520's that are originally built as 520's seem to have the third version, though I don't know when it was introduced into production. I think I mentioned the hinge pin fit in an earlier post, but to restate it needs to fit well into both the Base and Base Arm castings. A 1/2" hinge pin combined with either casting being made for 3/4" would cause a significant deviation from vertical, but there would be other symptoms.

- David

Off hand I can only think of three versions and i doubt SS sells the earlier one made for 1 7/8" bench tubes.

That leaves the older with the 3/4" hinge pin(albeit with left/right retaining pin holes) and the newer dual tilt version.

I am unsure if there is another with different hinge pin size.

FWIW I mocked this up with a spare base and a short piece of tube. I could only get about 5° from correct and the entry hole was the limiting detail. The early greenies had larger holes so maybe he has one of them????? But he said 520.

Dusty go the other direction(shallow insertion so the tube misses the second bearing rib.

I got about 5° off the other direction(drill press mode would be over rotated).

I have done a similar set up involving under inserted way tubes. The results substantiate your observation. I get 4.6° past vertical. However, as I envision what this would produce, the headrest would be out of position at the other end AND the exposed bench tubes would measure something over 48".

I believe I am through with this unless the OP comes back with more info and hopefully some pictures.

I am still skeptical.

As an after thought, while I had the parts on my desk, I measured the depth of tube insertion into the castings. The two of them insert a total of 4 5/8" into the casting.

Fifty two inches minus the 4 5/8" insertion loss leaves 48 1/8" of exposed tubes.

JPG wrote: ↑Wed Nov 25, 2020 5:06 pm Dusty go the other direction(shallow insertion so the tube misses the second bearing rib.

I got about 5° off the other direction(drill press mode would be over rotated).

I mocked that up using the newer version Base (1/2" hinge pin, setscrews on top) and got 6.7 degrees over-rotation, pretty dang close to what the OP reports. BUT the Base Lock screw lines up perfectly in this configuration despite the over-rotation. Oops! That seems contradictory to what the OP said about his in an earlier post. Suggesting??? I think it is suggesting that the problem is not related to how the Base is mounted to the Bench Tubes. Which is the opposite of what I thought an hour ago.

Back to basics - The upper and lower casting hinge around a pin. There is a hard stop in the rotation when the upper casting meets the stationary lower casting. For the described symptoms, one or both of the casting surfaces that form the stop must be in the wrong place in space, and/or the center of rotation must be wrong. Or???

- David

Initially I thought the base lock screw 'above' made sense. No longer does that make any sense. The base/bench tube misalignment would NOT affect the lock screw/dimple alignment.

I think you nailed it!

Until the OP posts pictures we will never know. If in fact the lock screw is above the dimple it has to be a problem with the end casting. Hard to believe SS would let something that far off out of the factory.

I am wondering what the OP meant by 'above'? Above when in horizontal position?

P.S. I think we know!