Compsand laminating schedule and flex - experiences?

General Discussion
1

Hi,

Does anyone have any experience with the flex characteristics (and longevity) of a compsand being altered when you prebuild skins with handlammed tails vs. handlam all of the outside glass vs. bag the outside glass. I would argue that a handlammed layer of glass would be stiffer as the glass lays flatter and the resin content is lower with vacuum but I wonder if it is noticable. With all the compsands being built lately and so many of you building similar boards over and over again with slight changes in techique there is hopefully a bit of experience out there. Theories are welcome too… :wink:

regards,

Håvard

2

Theories…you must be talking to me :wink: . You’re probably right that the handlam would be a little stiffer, but I doubt that it would amount to anything. I think you would be better off just sticking with whatever techniques works best for you and instead playing around with glass weight and skin core thickness. On my most current board I’m doing a little of both, but I prefer bagging (but thats just me).

3

I’d actually argue that the handlam would be more flexible.

Unreinforced (no glass) epoxy resin is very flexible. Pooling resin or resin ‘draining’ into unsealed EPS makes mushy spots, not hard spots. A thick hotcoat makes a softer (and heavier) board than a warm, thinned “cherry coat” put on just a couple hours after laminating. I’d bet dollars to donuts that, even though it produces a slightly thinner skin, a bagged outside glass job is stiffer than a hand laminated one.

I’ve tried all of the above and the pre-made skins were the stiffest of all. Now that was just one board…and its entirely possible that my QC isn’t factory-quality (in fact, that’s a lock)…but I made 2 boards with similar shapes, identical lengths & thicknesses, same core foam, same balsa thickness, same rail schedule, and same glassing inside & out. One had pre-made skins like Dan’s & I hand-laminated the other. The pre-made one was stiffer and maybe a little lighter. The hand-laminated one is more flexible. It is about 1" wider all the way through, so it could be that the shape pushes more water which causes it to flex more…but I don’t think that’s the whole story.

4

Just to be argumentative - and theoryfy things - I like to imagine things in the extremes so here goes. Lay a piece of fiberglass on a table and next to it pour a resin pool the same size and thickness (and let it cure). Now try to flex the flex test - first the glass without resin and then just the resin. The glass would be infinitely flexible and the resin would have very limited flex. I bet your vacced skin has more resin intruding into the skin core so …

5
Quote:

resin ‘draining’ into unsealed EPS makes mushy spots, not hard spots.

Hmmm, I have exactly the opposite experience with ‘regular’ EPS/epoxy board. Where the resin has impregnated the EPS the compression strength is enormous compared to unsealed or unlaminated.

regards,

Håvard

6

Might be differences in our epoxies, Haarvard. Mine is designed for high flex already.

Dan, I don’t really think that’s apples-to-apples. Glass cloth obviously will flex more without the epoxy :slight_smile: But its used to make a composite product, even when the “composite” is as simple as cloth & cured resin.

I’d test it like this - lay down 2 pieces of glass. Pour resin on both. Squeegee one of them to remove all but the resin required to wet out the cloth & leave the other one pooled (not like 1/4" pooled, but like a floating lam or an unsanded hotcoat). Like one ends up 1/16" thick and the other 3/32" or 1/8" but they each contain the same amount of cloth.

With less reinforcement - in a relative-to-volume way - I bet the unsqueegeed cloth is more flexible.

I could be wrong, it certainly wouldn’t be the first time, but I don’t think so on this one.

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Quote:

With less reinforcement - in a relative-to-volume way - I bet the unsqueegeed cloth is more flexible.

Bet not :slight_smile: Next time we meet up we’ll test this and the loser buys beers.

8

I peeled the 4 oz layer off the bottom of 2 broken boards, both done in RR, one bagged, (bagged, thin seal coat and sand job done by myself) one hand laminated (hand laminated, hotcoated, and sanded by our inhouse “Pro” shop) . The bagged glass was like tissue paper, very thin and extremely flexible. The hand laminated 4oz was much thicker, say 8-10 times as thick- pretty amazing actually. It was very flexible, but nothing even remotely close to the bagged lamination. It was almost ridiculous… -Carl

9

Surely things are a bit different when you seperate the skins with, say, a layer of foam? The stiffness of the structure is a function of the thickness and it is the tensile and compressive strengths of the skins which determine the overall stiffness, OK shear strength of core is important too. I think that the relative thickness of hand and vacced skins will make very little difference to the overall board stiffness, however the weight will differ.

Better get testing, will let you know…

10

Carl - don’t think you’re weaseling your way into getting the beer Ben owes me :wink: Just kidding, he’ll owe us both beer.

11

Heres my theory.

Hand lam and bagged can’t be compared unless the resin usage is the same.

They’ll be very different, if the resin ratios vary.

Lets assume 1:1 for ease of comparison, for arguments sake.

The difference between bagged and laid-up by hand, is of course pressure. (duh, this guy thinks we’re noobs… :slight_smile: )

So what happens to the cloth/resin when you apply pressure?

The resin can’t be compressed, at least not by the “low” pressures we use. (assuming no air in the mix).

So it must either stay the same, or be re-distributed.

The resin has got to be pushed around somewhere, or the laminate will be identical to the hand lam.

The two main ways I see it changing are:

-compressing the cloth, which means that the resin soaked strands must spread wider, like ribbons. This results in a substantially thinner layer than hand lam.

  • Pushing resin into the core (either sandwhich or EPS core). this may not happen if you prevent it.

Both of those ways that the resin moves can happen at the same time, and both have effects on flex.

But what does that mean, which one is more flexible?

Err, too many variables to say for sure, as to get a finished item, you may need hotcoats, 2pak sprays etc, which change flex again.

I think the important part is the advantages of a tight, void free lamination. flex is secondary.

The difference in flex between hand lam and bagged lam is small compared to other factors in board construction that influence flex.

I’d go for the most sound construction method, and vary other things to get flex.

For example, a bagged 3oz may be as strong overall as a hand lammed 4oz! simply because the resin ratios will be spot on, void free, super tight, great bond with the substrate, maybe even no hotcoat required. (hotcoats weaken flexible laminates).

So, for the same strength, you’ve used less materials, which will be more flexible.

If you can make it work with your construction process, use the superior method of lamming!

Then there’s infusion, which is superior again, but that definitely doesn’t fit into my board building schedule or budget at this stage!!!

Not worth it on my scale for the small gains you get.

Kit

P.S If I had a dollar for every time the words “flex” and “shear” were used on this website… Are we getting too caught up with these two things and missing something else?

I think I need the attention of a good woman…

12

P.S If I had a dollar for every time the words “flex” and “shear” were used on this website… Are we getting too caught up with these two things and missing something else?

Right on Kit.

Dont care for the “shear” thing (mostly worthless “buzzwording” IMO)…love the flex thing.

The something else is compression on one side of the panel, tension on the other.

There’s dynamic movement there, but its not “shear” (whatever that means). Of course Im speaking from my own experiences, yours may differ.

The resin stiffens the cloth while the cloth reinforces the resin.

Each has its own mechanical advantages - put them together and youve got multiple mechanical advantages in the part. The resin’s cured mechanicals (mostly compressive and flexural) stiffens the cloth. The cloth reinforces the resin, mostly in tension and some flexural. They work together, like steel reinforced concrete. Analyzing them seperately, while might be intuitively helpfull, is non consequential wrt FRPs.

HTH

13

I buy so much beer anyway, you guys could steal half and I probably wouldn’t notice.

erp

Well, Ok, I’d notice. But I’d consider it a good investment :slight_smile:

Interesting about the peeled skins, Carl. When I bagged a skin together, I thought it actually came out too dry. After bagging the skins onto the blank and adding the rail pieces, I was using a hand plane to shape the rails and accidentally caught a corner of the glassed skin. Peeled it right up and I kept pulling until it wanted to stop coming off on its own, as I thought it would be easier to treat it like a ding repair than to try to re-stick peeled-up glass.

I ended up pulling all the skin off the back 8-10" of the tail. I really didn’t like how easy it came off the balsa (which was totally dry underneath - it seems ALL excess resin went out through the peel ply into the absorbent and NONE went into the wood) but you’re right that the cloth itself was rediculously thin. Almost like it ended up half the original thickness of 4 oz cloth. I was kind of blown away. But it didn’t seem all that flexible to me. More like paper-thin and brittle. Kind of snappy. It was e cloth too, not even s. Might be the epoxy I was using too, although that’s the same stuff that gets mushy when it pools…

I should have hotcoated that chunk to see what it was like when filled.

14

First off, Kit I agree with everything you’ve said - in fact it was pretty much what I said in my first comment.

Quote:

If I had a dollar for every time the words “flex” and “shear” were used on this website… Are we getting too caught up with these two things and missing something else?

I agree with the sentiment, but I want to add why I think its necessary. It might surprise you that I never read posts made by some of the composites people. They go on and on about engineering concepts as if they should drive the development of the board. My approach is to try something and see if it works then see if their is a scientific reason behind it. If there is you’re more likely to be able to control it and design around it.

I’ll give you an example of what I mean. In longboarding people talk about the wonders of glide. Its a term specific to surfing and dependent on people having an mutual agreement on what “glide” is. It turns out the glide really means inertia. Anybody can look up what inertia means and have the exact same understanding. By calling it what it is opens up a bunch of avenues of understanding: for instance the board with glide/inertia wants to keep going straight, but its inertia discourages it from turning. You can’t use physics to design a board, but you and use its vocabulary to describe whats happening.

15
Quote:

it seems ALL excess resin went out through the peel ply into the absorbent and NONE went into the wood

Do you remember when Bert talked about saying he felt peel ply was a waste of money? This is probably why. With no ply when you pull a vacuum air gets drawn out through the foam. The excess resin also tries to get sucked into the foam (but doesn’t make it), but in the process makes a good bond. With peel ply the easiest route for the resin to travel is into the the absorbent.

16

I’m in complete agreement with you there!

I sort of woke up this morning at felt like throwing around an opinion… read my signature :slight_smile:

You said it a lot more concisely that I did!

These words everyone uses, a lot of the time i’m not sure what they are meaning when they talk about shear.

I know some about shear forces and the associated calculations (a very little!), but it still seems like people are just inserting these words into sentences to explain something in place of plain english!

I like to break down thinks into simple logic, it’s just my way.

So when Havaard asks the question about different layup techniques - I don’t have enough builds under my belt to speak from experience.

So I think about it… what does the bag actually do? It pushes on the cloth/resin. What does that do? it trys to compress it, but can’t, so it moves it. Where does it move it to? … and so on like that, until I think I know what is actually physically happening, without actually using much physics!

So then I look at what that resin it gunna do in it’s new location, and hopefully come up with a reason why it will/won’t allow it to flex.

What does the vacuum do? it sucks on the resin. So if thats not desirable, put your breather against a different surface, or put plastic between it and the surface.

Don’t want that resin to move? figure out some way to stop it moving. If you want it to move (penetrate, whatever) then find ways to encourage it. (thinner resin, more vacuum, etc etc).

Want the resin to stay in the cloth? Hand lam is one way of achieving that.

So my randon short answer to Havaards original question, is: Depends what is happening when you bag it!

Figure out what is happening to the resin (and cloth), and that may tell you what your ending up with, which hopefully matches what your finding in practice!!

Now, don’t for a second think that I have it all figured out for my own boards! FAR from it! But this is the way I like to rationalise things, a lot more fun than calculations, and cheaper than test panels!

Dan, as you rightly imply, there is no substitute for trying some something to see if it works.

From what i’ve read, you’ve tried many times more configurations and tricks than I have!

Good stuff!

Kit

17

Kit, I always read your post very carefully and think about what you’ve said. You seem to have gained a lot of understanding very quickly. Everything only came together very recently for me. Its not hard to understand, but it does take a lot of shuffling together of ideas till all the pieces come together.

18

hey Mo, you rock,

gee thanks Larry,

we love you too Curly.

19
Quote:

hey Mo, you rock,

gee thanks Larry,

we love you too Curly.

I’ve never quiet understood you,

edit: deleted part of the post. I guess theres really no need for me to get sarcastic.

20

I think that physics can be used to design a surfboard, but a surfboard is never going to be perfect, so using physics only works to a certain point.

I was thinking, since vac bagging allows you to get really good resin/glass ratios, couldn’t you add an extra layer of light cloth and still have the same weight?