How do you clamp/secure lams?

[mmattockx]

No cupping is because of the way you apply the clamping force. If you are using thin lams you need to use a pressure strip.

Yep, learned that lesson. On the next one I will be using aluminum strips to keep everything flat and I'm using different glue.


Mark

[bownarra]

The amount of pressure really depends on the glue so you should look at the manufacturers recommendation. Clamps will help close gaps but if the mating surfaces are a good fit you don’t necessarily need a ton of pressure for PVA glues like Titebond. Not sure about epoxies, especially since some have good gap filling properties. I use plastic packing wrap for my bows and have gotten great results. I’d like to get my hands in some inner tubes.

Pat might be right about inner tubes never being able to clamp too tight - but I do know with epoxies in general laminations (eg wooden boat building) that you can make a joint too tight and squeeze out all the glue and have a resin starved joint. There are products such as glass spheres, or very thin copper wire filaments, or some people use monofilament line, to act as “bond-line spacers” to make sure that however much clamping pressure you exert there is space for the epoxy...
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Unless you are getting some super duper extra thick/wide tubes it isn't a problem. Normal tubes upto 2" you should pull till they bottom out. I've done a few hundred glue-ups using inner tubes with EA40 or Titebond 3. Even with my 2 piece forms I use 70 psi in the tubes. To get dry joints you pretty much need to use clamps and really cinch down on them.

[Digital Caveman]

O, I'm not planning to inflate the tube, it is a cast off flat.  Wrapping it really tight is what other people meant, right?

[mmattockx]

O, I'm not planning to inflate the tube, it is a cast off flat.  Wrapping it really tight is what other people meant, right?

bownarra is talking about using a firehose with a 2 piece form for fibreglass bows with the 70psi mention. Are you planning on cutting the tube(s) into strips before using them? Normally people cut them into strips 1/2"-3/4" wide and wrap with that, not a complete tube.


Mark

[Digital Caveman]

I was going to wrap a whole tube around each limb, you mean I can cut the thing in half length wise and wrap a whole bow with one tube?

[mmattockx]

I was going to wrap a whole tube around each limb, you mean I can cut the thing in half length wise and wrap a whole bow with one tube?

I think you will find a full inner tube pretty hard to handle for the wrapping. It is much easier to stretch and hold the strips while wrapping. Maybe someone here who uses an intact tube can comment on this.


Mark

[Digital Caveman]

Yea, I cut it into two strips and got the whole bow tied down with it.  Forgot to add the ceran wrap,    I may need to hunt down some more inner tubes.  This was way simpler than my bar clamps, I don't think it's nearly as tight, but this is epoxy, not TB.

[willie]

There are products such as glass spheres, or very thin copper wire filaments, or some people use monofilament line, to act as “bond-line spacers” to make sure that however much clamping pressure you exert there is space for the epoxy...

with epoxy, I prime the surfaces with a thin resin to prevent starved joints. maybe this is not practical with something like EA-40, but with any thin glue joint, I have always wondered if some failures attributed to starvation were in fact a joint that opened slightly when clamping, and having previously squished out most of the glue, leaving little in the joint to make up for shifting etc.


@tradcraftsman
here is another method. it allows closer clamping points and can hold it's shape without a form. very trad!
https://www.primitivearcher.com/smf/index.php/topic,61961.msg866940.html#msg866940

[bownarra]

I leave the tubes whole to get sufficent pressure. I generally pull them to bottom out then do a wrap. Yes it takes a bit of pulling but i've been a climber for neck end of 20 years! Pulling a wimpy innertube ain't nuffin! Haha!
One of the great points about EA40 is that you need to use clamps and really cinch down on them to starve a joint because it is so thick.

[Digital Caveman]

I had some glue sqeezeing out every where, but there is no way I starved it.  I hope that it's not to thick.