Hey Crew,
I've been looking and looking throughout the forum and could not find anyone mention this. Quite often we get epoxy under the base which is not squashed into a thin layer all over the base, but is gathered into sort of round epoxy pocket. Sometimes these can be pushed quite deep into the base, so that grinding them off exposes fiberglass in other parts of the base.
Any ideas why this might be happening? This happens regardless of whether we use a cassette or not.
Cheers!
Anyone experienced epoxy pockets under base?
Moderators: Head Monkey, kelvin, bigKam, skidesmond, chrismp
Hey Damon,
Yep, its a heated press, bottom and top. The resin is quite thick coz it has a toughening agent added to it so by no means is it free flowing. Having said that, it gets quite liquid around 65 deg.
It may be the case that we are taking too long to lay up. Because the resin is quite thick, it takes a while to wet out fiber properly, which slowes us down heaps.
Cheers!
Yep, its a heated press, bottom and top. The resin is quite thick coz it has a toughening agent added to it so by no means is it free flowing. Having said that, it gets quite liquid around 65 deg.
It may be the case that we are taking too long to lay up. Because the resin is quite thick, it takes a while to wet out fiber properly, which slowes us down heaps.
Cheers!
Hey Shopvac,
We get quite a bit of epoxy on the base and most of it is nicely and thinly spread over the base. But quite often along with this thin layer, which as you pointed out, grinds off easily, we get these epoxy dimples. They dont always happen in the same spot, so its not the mold. I had them in the tip and tail, along the running length in different spots, so in the end it all got way too confusing.
The only sure thing is that when they appear, they will be slightly beyond the edge towards the center of the base.
We get quite a bit of epoxy on the base and most of it is nicely and thinly spread over the base. But quite often along with this thin layer, which as you pointed out, grinds off easily, we get these epoxy dimples. They dont always happen in the same spot, so its not the mold. I had them in the tip and tail, along the running length in different spots, so in the end it all got way too confusing.
The only sure thing is that when they appear, they will be slightly beyond the edge towards the center of the base.
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MontuckyMadman
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Hey Rockaukum,
The base is held with clips. And when we used a routed out cassette, it was sitting in the cavity held by the walls of the cassette. I thought the same thing, that the bubbles are just epoxy puddles that have set off prior to pressing. Gotta try flattening the base properly before layup.
Hey MontuckyMadman,
I thought exactly the same thing - prewetting. We've always laid a sandwich layer by layer in the cassette. The results have been ok, apart from the base dimples and air bubble type voids under transparent top sheets. Will try to give the prewetting a go asap.
The base is held with clips. And when we used a routed out cassette, it was sitting in the cavity held by the walls of the cassette. I thought the same thing, that the bubbles are just epoxy puddles that have set off prior to pressing. Gotta try flattening the base properly before layup.
Hey MontuckyMadman,
I thought exactly the same thing - prewetting. We've always laid a sandwich layer by layer in the cassette. The results have been ok, apart from the base dimples and air bubble type voids under transparent top sheets. Will try to give the prewetting a go asap.
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MontuckyMadman
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knightsofnii
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My thought, although this is just a guess, is voids in your layup.
If your core is solid all the way through, and your mold is flat, your cassette is clean, and your pressure is even, then the epoxy should be flattened out under your base.
(If any even migrates there)
but... if you have a soft spot or void in your core ...
Other than that you could be right and your epoxy is setting up in lumps (for want of a better word) under your base before you get it under pressure.
Does your epoxy have an exit strategy? (is there somewhere for it to get pushed to when pressing or is it trapped in your cassette?
I get some epoxy pooling at my tips and tails on occasion but I'm vacuuming and can't generate enough pressure to push it flat in those areas.
just thinking with my fingers here
sam
If your core is solid all the way through, and your mold is flat, your cassette is clean, and your pressure is even, then the epoxy should be flattened out under your base.
(If any even migrates there)
but... if you have a soft spot or void in your core ...
Other than that you could be right and your epoxy is setting up in lumps (for want of a better word) under your base before you get it under pressure.
Does your epoxy have an exit strategy? (is there somewhere for it to get pushed to when pressing or is it trapped in your cassette?
I get some epoxy pooling at my tips and tails on occasion but I'm vacuuming and can't generate enough pressure to push it flat in those areas.
just thinking with my fingers here
sam
You don't even have a legit signature, nothing to reveal who you are and what you do...
Best of luck to you. (uneva)
Best of luck to you. (uneva)
hey knightsofnii,
I do put it in cold, then apply pressure, then heat. But you may be right in terms of pressure - pressing at 40 psi, with a cattrack, but the hose is only 250 mil wide when flat, so once inflated, the contact area is probably only 20 mil or so. I see skibuilders recommend up to 80 psi...
Hi sammer,
lumps, thats what they are. yep, epoxy has exit strategy - it can just run off. However, when we use a routed cassette, then, no, I guess it can get stuck in the cavity. Been pressing without the routed cassette though and getting the same results.
On my next layup I will speed up my process, try to prewet the fibers before layp and ramp up the pressure to 60 - 70 psi. will keep you guys updated[/b]
I do put it in cold, then apply pressure, then heat. But you may be right in terms of pressure - pressing at 40 psi, with a cattrack, but the hose is only 250 mil wide when flat, so once inflated, the contact area is probably only 20 mil or so. I see skibuilders recommend up to 80 psi...
Hi sammer,
lumps, thats what they are. yep, epoxy has exit strategy - it can just run off. However, when we use a routed cassette, then, no, I guess it can get stuck in the cavity. Been pressing without the routed cassette though and getting the same results.
On my next layup I will speed up my process, try to prewet the fibers before layp and ramp up the pressure to 60 - 70 psi. will keep you guys updated[/b]
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doughboyshredder
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I don't think I understand your numbers. Are you saying that you have a 25cm wide lay flat hose and when you inflate it only 2cm is making contact?
You need to know what your pressure is at the laminate. Your psi of the hose is largely irrelevant. Figure out your actual contact area between the hose and your cat track. Multiply this area (in square inches) times the psi of the hose. Then divide this number by your actual area of the board or skis. This is your actual psi at the laminate.
Either your actual pressure at the laminate is really small and you aren't actually generating enough pressure to expel the wet epoxy, or you have voids in your core.
You need to know what your pressure is at the laminate. Your psi of the hose is largely irrelevant. Figure out your actual contact area between the hose and your cat track. Multiply this area (in square inches) times the psi of the hose. Then divide this number by your actual area of the board or skis. This is your actual psi at the laminate.
Either your actual pressure at the laminate is really small and you aren't actually generating enough pressure to expel the wet epoxy, or you have voids in your core.
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knightsofnii
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if your tip fill is different thickness than your core @ the ends, this can cause voids, we've experienced this mostly on the topsheet, where we'll get a dimple or 2 near the seam where the core meets the tip fill, because our core was planed too thick, or too thin. Then the pressure stops @ the highest point, and the thinner materials are then free to float a little.
We actually got one of these epoxy bubbles in a recent test board, pretty much just like you're saying, and I couldn't fully grind it out, and I'm pretty sure it was due to lack of full pressure thru the entire system because of mismatched thicknesses.
our new cores are on the way, and core, sidewall, and tip fill are expected to match perfectly this time, but seeing is believeing of course.
You got any photos of your setup? Or a photo of your press in action, with the board in it? How much space do you have between your cat tracks and bottom mold when the press is at rest?
We actually got one of these epoxy bubbles in a recent test board, pretty much just like you're saying, and I couldn't fully grind it out, and I'm pretty sure it was due to lack of full pressure thru the entire system because of mismatched thicknesses.
our new cores are on the way, and core, sidewall, and tip fill are expected to match perfectly this time, but seeing is believeing of course.
You got any photos of your setup? Or a photo of your press in action, with the board in it? How much space do you have between your cat tracks and bottom mold when the press is at rest?
Doug