hi Derek
I have been piddling with some gantry loads as I see it . Again I have not fooled around with this stuff for a very long time . so feel free to correct me .
I have tried to minimize the gantry moment loads on the black pipe/skate bearing trucks and have included a hand sketch of how I think the loads are distributed .
I do not think it is a good idea notching the side rails so that the bed crossbeams carry through it virtually halves the beam depth and as all loads end up in the side rails it will severly reduce their bending strength [varies with the depth cubed if I recall. The loads from the gantry result in outward bending load on the gantry side arms which could be strengthened if necessary with and outer web .
The vertical loads on the truck should result in a differential loads on the front and rear bearings respectively ,the sidewall will experience a reactionary load to the gantry side load as an inward force on the sidewall. The black pipe will try and deflect downward at one end of the truck and upward the other trying to force into a shallow "s" form locally. This possibility could be reduced effectively in my opinion by nesting the pipe between top and bottom angle irons bolted into the sde rails along the length of the pipe and if required each tack welded at intervals along its length [belt and braces if you get my drift.
So in short I think if the moment is minimized by making the drive axis coplaner with the cutter axis, or as near as can be [obviously the cutter plane varies with the X axis position .The deflections in the bed and tracks I feel could be improved by the suggested mods .
I mean this in a constructive way ,and heavens knows I have been wrong many times ,this thread and Joes efforts have been a great inspiration to me and I do not in anyway want to his efforts .....mjh |