John
how big is your table?
or is it just the offcuts?
and what size tube did you order from ACP?
Anybody think of buying (or has anyone used) one of Joewoodworker’s heavy duty bags?
Oneula, its just the thick green screening you can attach to a fence or an overhead trellis for shade from the sun. It works well as a breather to get air from your bag into the vac tube. Its not for letting resin through.
Its the center strip in this one, on top of the absorbent…
Thanks
I think we have some scrap old stuff…
out here our shade cloth is blue or grey vinyl tarp strung up on aluminum tubes with bungees…
Hardly ever see anyone use that screen stuff with holes in it outside of the construction sites where they block the dust from the home construction sites with these huge panels on 15-20 foot posts of black barrier to hold back the red dirt dust while they buils anothe 2000-3000 homes on the ewa plain…
wouldn’t metal door screen mesh do the same?
I got a bunch of that as well…
I used metal screen once and also the gray screen stuff once that I think is fiberglass. They both stuck in the epoxy pretty bad & took sanding & patching to remove completely. The green/black plastic shade cloth doesn’t stick to epoxy.
I’d go by one of those construction sites with a good pair of scissors & find a loose corner. All you really need is about 6" x 36"… 
wash the dust out & you’re in business.
Trent
I think that Bert uses heavy duty pvc bags, he has mentioned a bag holding system before, so I presume that his bags could be strung up by the ends (by his bag seals). Because these bags are pretty heavy gauge pvc, they don’t wrinkle like thinner films, he probably arranges the excess bag so that it follows the apex of the rail line from nose to tail. Hope I have explained this clearly enough.
Bert though suggests that he is infusing his skins and uses the cloth as a flow medium, negating any consumables.
When I vac my skins, I use a thin and stretchy perf/rel that has fewer holes than the ‘bread wrap’ type. It does leave a tiny resin ‘nipple’ on each hole, but I strip my bag down whilst resin is hard but tacky and brush on a sanding coat, so this is not a problem.
The thicker the perf/rel, the less creases you have on the flats, but the more hassle you have on the rails!
Tissue paper works fine for a breather, or j cloths.
Don’t bother with peel ply, If you use it, you have to wait until resin is fully hard before you can de bag, also the rails are a mare and if you are doing a clear board, you will spend forever removing all the tiny threads from your laminate on the frayed peel ply edges.
I have tried jjp’s method and didn’t likme the number of pinholes in the outer skin, but he reckons they fill with the sanding coat, so may give it another try.
i built some 30ml bags via joewood instructions and they sucked ass… they are so heavy and hard to work with, i could not get my rocker table into them by myself… i have been using the 36" tube from acp… i have used one bag for all the steps of about 8 boards and a number of experiments… i am very careful not to get resin on it and store it in a plastic bin when not in use.
my rocker table is 7ft and i use cardboard to change the curve for different boards, all my boards have been made on it so far (6’4" to 7’0") on thursday i am going to buld a perment one for 6’4"s and one for sub 6ft fish boards… i’ll post some photos when done…
pretty fun lanaikai reef today…
I tried an infusion experiemnt last week on a 6" long test laminate. No breather or peel ply in the bag, except to keep some resin flow channels from sticking to the flash on the edges of the laminate.
With a pum that only pulls 20"Hg, the experiment came very close to a perfect surface finish except for some tiny bubbles which are only visible on close inspection. Perhaps these could be removed by degassing the resin in a vacuum chamber prior to infusion. The test laminae was a scrap of corecell with somewhat haphazardly aranged scraps of biaxial glass, plain weave, carbon fiber, and some cotton print inlay - just to see what might happen with different materials in different combinations. At room temp it took 30 min. for the resin front to travel through the laminate, I need some heat and possible lower viscosity resin. I think heating up the baged laminate prior to infusing the resin would be a tremendous help, not to mention using a very slow hardener.
Markyv, you mentioned Bert is doing infusion and looking back through some old posts I am certian that is the case.
Also, I had sort of an ephiphany regarding a possible way to infuse resin at full vacuum onto an eps sandwich without crushing the eps:
Somewhere I have a woodworking book I bought a couple years ago which is titled “vacuum wood veneering” or something like that (I cant find the book right now). The book details process and methods for building veneer furinture. Sometimes in furinture making the whole mould is placed inside the vacuum bag and this requires a very strongly built mould to resist the vacuum pressure forces
However, one method detailed in the book is a “bag inside of a bag” where a second bag is placed inside of the vacuum bag with a tube that exits the vacuum bag and is open to atmosheric pressure. The second bag is place on the inside of the mould, opposite the actual mould surface. This allows the use of a relatively flimisy mould, because the atmospheric pressure inside of the second bag pushes back against the vacuum pressure.
So my idea is sort of an extension of the method above:
-
seal eps core (with resin+filler) so it is completely airtight.
-
install the board vent onto the eps core and test core for airtightness.
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connect a tube to the board vent
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apply sandwich and laminate dry, tacked down with spray adhesive
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Place board in vacuum bag making sure the vent tube exits the bag and is open to atmospheric pressure
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Apply full vacuum and be amazed as (hopefully) the board does not get crushed!
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infuse resin (note that this part is so easy it is just one step in my process, uh… right!
)
Below is a quote from Bert Berger, taken from a thread titled “Good intro to RTM article”
Quote:
i have no consumables …
except the tape to seal the bag …
also choice of fabric , becomes essential with infusion , or else you get the problems you highlighted …
if you think of the worst fabrics you ever laminated a board with …
chances are they are still good for something …
all my boards have been infused since 97 …
they went from being light and strong to lighter and stronger …
you are right about problems …
its keeps getting refined all the time …
viscosity , pot life , flow and pressure regulation , combined with technique …
Quote:
Just wondering if you ever did try the “Bag-in-bag” method and how it worked out for you?
Also, what tapes are you guys all using to seal your bags with? or do you use silicone or other similar products?