Air from under the bridge while vacuum clamping

[Herman]

I used to clamp bridges the traditional way, but for 3 guitars now, I use a vacuum clamp like a lot of others do.
I experience that during the initial clamping quite a lot of air sucks through the wood under the bridge and comes out with some glue.
Questions: Is this usual, have you seen this also and will it affect the amount of glue under the bridge?
Thanks
Herman

[Carl Dickinson]

Do you have holes through the bridge and top for pins to index the bridge in place? That would let air through if not a tight fit. What kind of wood are the tops? Would that be porous enough to have air come through? I have had squeeze out after the initial clamp time, glue only, no air and didn't loose vacuum.

[Herman]

No carl, I use pinless bridges and the tops are European Spuce and Red Cedar. The only way I see it, that the air comes through the wood.

[John Parchem]

It is actually possible to suck out the glue under the bridge. I have gotten in the habit of holding down the bridge for a minute or so as the vacuum forms. Most likely you are seeing squeeze out but it did happen to me once where I did not end up with enough glue. The bridge cleanly popped shortly after I strung up the guitar.

[Herman]

Thanks John for the tip. I glued a bridge on a parlor for my grandson. I pushed the bridge down for 2 minutes till the glue grabbed properly. After connecting the vacuum pump only little glue came out (and no air). For the moment it looks promising. Thanks
Herman