Only if the bottom clamp is squeezing too.
Actually the glue up is being squeezed between two clamp bars that are trying to each bend in opposite directions thus counteracting the bends in both bars. Loosen either clamp and the other will bend along with the piece being clamped.
Not in my world. Not even with pipe clamps which don't flex like bar clamps.
IF...
the work pieces may wind up flat.
That doesn't happen in my world. I tweak flatness by loosening/tightening top and bottom clamps while checking the glue up surface with a straight edge. Even with that it is normal for me to wind up with a slight (1/64 -
1/32+-) bow, not to mention lippage, neither of which bother me because eventually the glue up will be flattened on a drum sander.On 10/15/2016 7:55 AM, Leon wrote: ...
The fella' in the video has the work being clamped supported on heavy flat cauls underneath, not the clamp bars so the top tapered clamp is pressing against them, not the other clamp bar. I didn't watch it again, don't recall if he'd use another caul on top or just the bar but his scale demo illustrated a pretty decent vertical force being exerted; a couple hundred pounds.
Of course, holding the panel flat forcibly while it's being glued doesn't mean it'll stay there when the clamps are removed...that'll mostly depend on how well the edges were milled square w/ the faces or that were alternated to compensate. :)
The act of simply putting a clamp on top and bottom counteracts the clamps tendency to bend.
As you may have been referring to, if the glue up is warped to begin with, flattening it during glue up will not change anything.
His downward pressure is simply to counteract improperly placed and applied force. If he would learn how to clamp panels correctly he would not need this crutch.
Just make it a moot point. Since not all clamps apply forces in the same plane, especially on wide glue ups where your clamp selection is mixed/limited and the "you can't have too many clamps" theory fails you, you can always force the issue if need be, easily and cheaply, thusly:
Where there's a will, there's a way, even it include bags of cement, bricks and/or other heavy implements/tools:
On 10/15/2016 11:26 AM, Leon wrote: ...
...
The problem generally isn't the clamp itself bending but getting the force _directly_ normal to the edge...
If the edges are milled correctly, his technique possibly will speed up things a little by not requiring such finicky placement as otherwise.
But, agreed, it _can_ be done without the "crutch"...
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