How much glass

[TheJoe]

I just finished my first board. Just curious how much glass people are using. I did12oz on top 18oz on the btm. Thinking of using more for my next board since my rocker did not hold up as much as I wanted. Had my table with all most 3" and came out with less than an 1" rocker which is fine since I was making a light wind board.

[plummet]

Depends on many factors.

What core is used
how thick the core is
the amount of flex you want
The weave of glass used.
The direction the glass is layed up in.
length
width
rocker

plus weight of rider.....


So you really have asked how long is a piece of string!... .... . . .. ..

Going buy the fact you got 66% springback I assume you are using a solid or ply wood core.

[rynhardt]

What plummet said.

I'm curious about one thing though. Since you had 66% spring back, I assume the core is exerting some tension on the laminate, which means it is already under some load.

Now if you put a rider on the board, I expect the rocker will change again. So your static 1" rocker may be 3" at the rear tip under load and may even be cambered (negative rocker) in the centre.

[TheJoe]

1/2 Plywood with the tips 1/4 inch. 143/43 I'm 185lbs. 6oz plain weave glass http://www.acpsales.com/6-oz.-Fabric-38 ... Weave.html . I'm using West Systems resin.

[zfennell]

structurally, you don't need any glass as reinforcement for a light wind board with 1/2" wood core.
i'm sure the plywood will hold up for quite some time.

if the function of the glass is only to set the rocker, 18 oz is overkill.
one layer of anything should be enough. (no more than 1 ply of 4 oz on top and bottom )
By the time your top/bottom skins approach 18oz of laminate, I doubt you'll need any tensile or compressive contributions from the core. if increased rocker is your goal, (negating flex, stiffness) , 18 oz glass skins would allow you to consider much thinner wood cores or multiple ply wood cores or cheap home depot foam cores.

its not likely that any of the spring-back you have experienced is because you are challenging the tensile or compressive limits of the glass. this is more or a shear problem between the 3 layers you are trying to keep from sliding past each other (IMO)

perhaps:
-let the board cure on the rocker table for a few days ( or weeks) before you take it off. Epoxy continues to cure for a long time after it becomes a solid. check your mixing cups to be sure the resin is rock hard. I'm sure it does most of the deforming as your board returns to 'flat'

-during layup use your squeegee/spreader to 'stretch' the glass fibers in the lengthwise direction.
only straight fibers can effectively resist bending loads.

-the top/bottom veneers in plywood are pretty good at holding curved shapes.
soak/steam the top surface , prop it up on some bricks and leave it in the sun for a few hours to see how fast it will take a set. (...before any glassing)

overall, with plywood, flat and flexible work well together. you could save the glass for cores that need it.

no worries,
-bill

[plummet]

Cut your ply thickness in half. 3mm at the tips 6mm in the centre.

Ditch the woven glass in favour of some uni, double bias or triaxle.

[downunder]

I just finished my first board. Just curious how much glass people are using. I did12oz on top 18oz on the btm. Thinking of using more for my next board since my rocker did not hold up as much as I wanted. Had my table with all most 3" and came out with less than an 1" rocker which is fine since I was making a light wind board.

3" to 1" sounds right. In reality it is very very difficult to get the rocker and concave if not using 2 layers board (even 3mm top layer ply will do more than any glass, saving epoxy and glass).

If u look at how big boys are doing it, they use tiny wood strips. I managed to do the same with minimum glass and using two carbon strips on top (see New Year build). The trick was to loosely glue this strips so they don't form one big sheet (like your ply), which is difficult to bend.

So, with a ply I would go with 2 layers, build it first with no glass. Use a PU (fast, cheap, strong) glue and vacuum. If happy with a shape and flex, glass it all in one go if u want (not my cuppa of tea).
Use minimum glass first like 200g UNI for bottom and 150-180 biax for top. Test flex. Do more if needed.
Change WS epoxy for Entropy CLR (heaps better results, as bill says, rock solid in 6 hrs).

Or, ditch plywood and use cedar or similar light wood (143/43 cm ply is heavyyyyy).

Report back

D.

[TheJoe]

Thanks for this advice guys. The only reason I'm using the plywood right not is to get all kinks out of my process before I move on to more expensive core materials. As far as the triax goes I have only been able to find it in 20oz so far. Anyone know where a good place to get that stuff in the US?

[zfennell]

Thanks for this advice guys. The only reason I'm using the plywood right not is to get all kinks out of my process before I move on to more expensive core materials. As far as the triax goes I have only been able to find it in 20oz so far. Anyone know where a good place to get that stuff in the US?

there is a saying that is common where I work.
"good, fast, cheap....pick any two."

once you have chosen plywood as your core material, you've definitely placed yourself in the "fast & cheap" category

wood has good flexural and compressive strength but is relatively heavy.
perhaps a better way to improve you current build approach is the use of lighter density solid wood like cedar or pawlonia or balsa

the folks that buy 'triax' are looking to maximize flexural and torsional strength on relatively light cores that have virtually no flexural strength of their own... so 20 oz is more appropriate for those applications. the combination is a pretty effective way for home builders to make high strength-to-weight composite sandwich.
in your case, I believe the triax is over-kill for a plywood core.

wood can be used effectively in sandwich layups. typically, highly loaded areas like the decks and bulkheads in moderate sized boats.
For kiting or surfing, a wood core is often found in the top and bottom skin, sandwiched over a very light Styrofoam core. Here, the wood skin is less than .1" thick and the glass schedule is very light ( 2-4oz).
take a peek at the comp-sand site for a better description
http://www.compsand.com/forum/index.php

once you get your head around it. you may see that it is a pretty easy way to make a fancy composite with cheap materials...and make use of the skills you are currently developing
.
just some thoughts from someone who is still a fan of wood.
but you still get to choose for yourself. there are lots of ways to make this stuff work

have fun.
-bill

[mthboards1]

1/2 inch core is way to thick to fiberglass for a mold, you would need a lot of fiberglass to get it to stay to the mold, then it would just be way to heavy and not flex at all.
I use at least 18 ounces and up for cores that are 3/8 inch in the middle down to almost nothing at the tips. If I use anything less than 18 on the cores I make, over time they will lose the rocker and twist. Another thing is if heat is not added to the board while curing you will have to leave it in the mold for several days depending on the epoxy, Lot of them say it only take 6 or 8 hours to cure but that's only to the touch, it will strengthen over 70% over the next few days and you dont want that to happen out of the mold.
All kiteboards, snowboards, skis that use a mold will have at least 18 ounces of glass on top and bottom.
The kiteboards that use less fiberglass are usually preformed and really thick like a surfboard or use a thicker foam core and they flex a lot less if any.
Strips of vertically laminated wood is the cheapest way to go and the strongest if you fiberglass it, but you need all the machines to thin it down or do it by hand which can be done but it takes a while.