Sandwich Construction questions

Hey guys, I usually like to work stuff out on my own but I am officially stumped. I am trying to work my way through a sandwich board with eps core, balsa rails, and an H-80 divinycell shell(3/8"). I just have a few questions.

  1. I acquiried some eps insulation panel from lowes, not real sure of the density, could not find a number on the package. I used West System Epoxy with fast hardner. I had a fair amount of melting (not so much melting, more re-molding?) while under vacuum. Is this fairly normal, I`ve never used eps before. It didnt seem to be that big of a deal since most of it stayed within the balsa frame. Was this the incorrect stuff or what?

  2. While under the vacum (-.8) it actually pulled the edges up making a what is best described as a rocker going the along the width. Not being able to control the vacuum on my machine, I quickly stacked paint cans around the edge of the board. Not the best solution, but it worked for now. What can I do to help prevent this next time.

  3. Alittle off topic, but is 6oz cloth weaker then 4oz in any way? Sounds like common sense, but I`m talking about tensile or impact strength.

Thanks, Ryan

It sounds like you’re using too much resin and pulling too much vacuum. If the resin is penetrating the foam while under vacuum it will have a kind of molding effect. If you’re using a rocker table, stick the whole thing in the bag, or use double sided tape to tape the bag to the rocker table, that will help you keep the rocker you want.

If you have a rocker table and extra bag material, try putting the whole thing in the bag, vacuuming the whole board to the table. I saw it done that way in another thread.

Hi Ryan

classic over vacuume by the sound of it

add a t piece to your vac hose put a valve on it

this valve allows you to let known amounts of air into the system to reduce the amount of vacuume

also install a vac guage so you can see the results

same deal just add a t and hang the gauge off the t

you must know what pressure you are pulling

once squashed to that degree the eps will most likely not ever fully recover

which will effect the shear quality of the eps

this relates directly to riding perfrmance of the board

you only need enough vac to hold it all down

about -6 psi

you do need to vac on to some thing either a table ie eps block that the foam was cut out of

or a rocker table

either can be made simply or much more detailed depends on what you want

with out either the shape will be hard to control while in the bag not impossiable just hard

6 oz vs 4 oz the higher weight should be stronger

beware thu if there is more of a excess of resin used filling the weave with the 6 oz the surface will be more prone to cracking from impacts this is a function of the resin not the glass