algale wrote:When you are taking readings with the table mounted to the trunnions and trunnions mounted on their axles/pins, I assume you have the table lock engaged (otherwise the table would be flopping around).
When the table lock is engaged, a wedge is applied to the bottom beveled edge of the trunnion (510/520) forcing the the trunnions inward toward the center of the table until they contact the table bar/tube assembly.
If the top of the trunnion were not fixed to the table, the top and bottom of the trunnion would move the same distance toward the center of the table until contacting the table bar tube assembly. But because the top of the trunnions are bolted to the table bottom, which is a fixed distance, the table is trying to keep the trunnions at a fixed distance. Since the trunnions do move inwards (otherwise the table lock wouldn't work) something has got to give. Either the trunnion or the table. I assume that given the robustness of the trunnion casting, what gives is the table. As the trunnions are pressed inwards, the table flexes slightly and the bottom of the table is put in compression and the top of the table in tension. And your flatness readings change as compared to when the table is on the bench, with or without the trunnions attached to the table (but not mounted and locked).
Disclaimer: I'm a lawyer, not an engineer. But that's how I see it.
You make a very valid point.
When this first began, I was testing the tables' flatness with the tables mounted and the trunnion bolts loosened.
As time went on, it became obvious to me that there were other forces involved so I removed the entire table assembles from the carriages, removed the trunnions from the tables and even removed the table inserts.
I rested the tables on blocks of wood on my work bench. The only items still attached to the table were the front and rear rails.
This is how the tables were configured when I took the readings that Shopsmith had requested. It was these readings that Shopsmith used to declare my tables to be flat to within their manufacturing specifications.
They did not share with me what those specific specifications were but they told me that none of my tables were out-of-spec.
As I reassembled the tables, I tested them as Shopsmith had instructed and while the various numbers changed (as I bolted in the trunnions, etc) none of them increased to anything greater than the numbers Shopsmith had previously told me were in spec.
