Quote:
Originally Posted by ZeroID
I put washers at the junction of the Alum tubes and the ply. Tube sits on the washer giving a nice flat wide surface so no bite.
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That's about the worst thing you can do.
You actually want it to bite in a fraction. If you use a good quality hardwood plywood it will only bite in less than .5mm. This is just enough to give the spreader poles grip on the plywood so there is no lateral movement in the top end at all. You should use aluminium spreader poles with a wall thickness of .9mm.
Dave Kreige from Obsession Telescopes actually cuts a 1mm deep circular recess in the plywood to seat the spreader poles with a Forstner bit and stop any movement. Peter Read at SDM Telescopes just screws the spreader poles up tight to the plywood face and lets it bite in a fraction. The reason Peter Read does not cut a recess in the plywood is because once you varnish the plywood it fills in the edge of the recess and it's then very hard to seat the spreader poles properly.
Cheers,
John B