[bmitchell82 (Brendan)]

Greg? Ive already gone though wall thickness and pier diameter do you want me to go though it again thickness is a major component of strength irrispective of diameter! I have analysed it along with section geometry a good 8 months ago now in a very long debate to which ACE's where present.

Im a 4th generation civil engineer (maj structural engineering) with my g grand father and grand father and uncle (structrual engineer) both infrastructure engineers I never heard my grandfather talk about the old maxim of 5 x as strong.... he designed to the materials strength with capacity factors of safety that gets upto 1.5 times the maximum loading. But im not going to go into load combinations and their realitive factors as thats nearly 2 years worth of uni and much more than this thread will accept. This doesn't mean that you have to take my opinion as Gospil but if you have facts/proof/expertise then bring them to the table and lets figure it out. I have supplied facts and the proof while my expertise is quite extensive over alot of different fields giving me logic im still learning loads in my choosen career path.

So back to topic. Irrispective of the angles that we hang these off i have just analysed for the worst that is using the smallest Second moment of inertia in the weak axis or Iyy or Geometric stiffness of the section at horizontal, anything over the side will start taking into account a deeper section to which the cube root really beefs up the Iyy tending towards Ixx which is the strong axis. Even at this a 10mm thick Aluminim plate will only flex 1 micron under 40kgs of weight if you want to tell me some specifics of your dovetail length i can tell you the simplified approximate deflection.

If you want to look at the basic analysis in the PDF its all there and if you would like to correct anything im not precious, if i have made a mistake say so.

As for the difference between the vixen and losmandy dovetails its not the actual dovetail section that makes a difference its the top plate that makes the difference eg the difference between 100mm width and 40mm width for lateral stability or torsion.

If you where to have a look at the Williams optics Vixen style dovetail you will see it has a massive top plate, Same with losmandy they have a big thick top plate and your PME has an extremely wide and if i remember quite a thick adaptor plate. Also this is the reason why they can honeycomb the plate because the depth of the section hasn't changed and the thickness still is the same more force is placed into the honeycomb ridges because they will attract more forces.

Overall this plate thickness is to take the moment couple created by torsion to the central axis of your mount to which your motors/adjustments take that moment and stop it hence your stability.. Big motors = lots of holding torque. aka your motors are the key point here and will be the limiting factor not material strength!

Thats what the point of my post is, people underestimate the strength of materials and go way over board without knowing what they are doing and then seem to sprout that they are knowledgeable or as i call these people ACE's or Arm Chair Expert s. Its extremely frustrating!

Brendan