let's talk clamping pressure..

[sonny]

I found a good ERC stave in my stash today and roughed out a flatbow that I'll sinew back, eventually....unfortunately it's not thick enough in the handle.
So I found a scrap piece and glued it in place (after the necessary prep work was done. )
When I first glued it up I cranked down on the clamps but decided I had likely squeezed out most of the glue, which I verified by pulling it apart.
I applied a bit more glue and re-clamped using much less pressure....which leads me to ask- how do you know when you've applied sufficient pressure ??
I know that cranking down 'til the joint "bottoms out" is way too much pressure.......   
comments and wise-cracks are welcome !
   

[Marc St Louis]

I'm assuming here you mean a modern glue such as titebond. I don't think clamp pressure is critical but you don't want to crank those clamps till you can't anymore, this would be desireable with hide glue.

[michbowguy]

try going to local bike store,and asking for a couple of bicycle tubes that are no good.
then cut long spiral pcs out of it about 3/4 in thick.
use this to wrap your glueups.
youll get great glue lines and not squeeze out too much and close to even clamp pressures.

hell if ya lived closer id give ya all my forms and stuff for bbo/and other jigs ive made thru years till i figured out that i like to make selfbows best of all.

mbg

[Badger]

Try to think about a clamp this way, if the handle on the clamp is about 4" long it will travel about a foot to make 1 revolution, if the clamp moves downward 1/8" in one revolution  that means you have about a 100 to 1 advantage, so 2# pressure on the handle of the clamp would equal about 200# pressure on the clamp surface. If you use a pressure strip it will spread that out a bit but you get the idea, just a couple of pounds pressure on the clamp is plenty for tightbond 3. If you want to know what 2# pressure feel like just take a 2# weight and hang it for the end of your clamp handle and let it pull tight, then feel how much pressure it takes for your hand to tighten it more, almost nothing you will find.  I often use the clicker on ball point pens kind of like torque wrenches, I push the pen down on my scale till it clicks, usually about 1# pressure will make it click, you can put a little extension on your clamp handle made of a small pipe 12' long and push down on the end of it with a ball point pen till it clicks, this will give you about 200# pressure per clamp if the clamp has 8 threads per inch. Steve

[tom sawyer]

Different types of glue call for different clamp pressure.  They also need different surface preps.  For epoxy/URAC/resorcinol, you can score or otherwise rough the surface and this will make pockets for glue to remain when you clamp so you won't starve the joint with a firm clamp.  I've always used plastic spring clamps for my backing glueups, and c-clamps for handles and stuff.  I don't screw them real tight.

Google up info on glueing and clamp pressure, there is stuiff to be learned on the web.