YES, the entire weight of the two rollers (about 250 lbs.) is carried by the 10 foot long top rails supported only at the ends, and no matter how huge and stiff the beam, there will always be SOME deflection — that’s just physics!

The manufacturer of the extruded aluminum parts BWC.compublishesformulae and a chart in order to allow customers to calculate deflection of the various extrusion products in application.

There are three sets of formulae and graphic representations — one for each of three simple beam configurations:
1) “cantilevered” where one end of the beam is rigidly fixed and the load applied at the free end,
2) “simply supported”, which is the situation where the beam is simply laid across two pivot points and a load applied in the middle, and
3) “rigidly fixed both ends” in which both ends of the beam are ‘rigidly fixed’…

This stuff was critical to me in designing the press, because I obviously didn’t want the press to ‘fold up’ under the weight of the rollers. Because the rollers are supported on the outboard side of the rails, the height of the rail dictates the roller dimension, so the rails had to be a first decision, the dimensioning of the rollers dependent on the height of the rails!

see BWC chart — the red line represents actual values for the press and indicates a bit over 1mm (1/24 inch) deflection of the rail under 125lb (600 Newton) load.

Yesterday, with my 200 lb. body sitting on the center of the assembled press rail, I measured actual deflection at about 1/16 inch, so it really is pretty stiff as the chart indicates — much less deflection than I’d imagined! Even though it’s not ‘rock solid’, it’s plenty rigid for my purposes, and I won’t accidentally bend the frame by sitting or standing on it even while the rollers sit in the center of the press.

– Mike

Question: can those rails sustain the weight of the roller assembly across the breadth of that log span without bowing slightly? It didn’t seem to me that there was any kind of supplementary support mid span, so I’m just curious.