how about this foamcore-ish design

[gh0stsignal]

so i got this idea from that shortboard in the board buildoff contest. was just wondering if it would be a worthwhile weight/strength compromise to do cutouts like this and replace em with foam.
although i did this design from scratch, it ended up looking similar to a firefly but i like the flowing lines more in mine

this is just a quick render of the veneer layers that i did this morning before work.

[gricco]

lol your first post and you've been here for a year

[jspats40]

that would be sweet.

[gh0stsignal]

lol your first post and you've been here for a year

yeah well i've always used the fish as more of a reference site. lotta good information, so much that i've never really had the need to post... haha.

but anyhow, back to the point at hand, would this design be feasible with only a few ply's and glassing w/o reinforcement? planning on using airex c70 foam tho i'd like to find a supplier of the c90.

this was the layup i was thinking:
glass
u/d cf (running length)
u/d cf (running width)
veneer/foam
... (however many layers i might need to achieve proper strength/thickness ratio, hopefully a total thickness of around 1/2")
veneer/foam
u/d cf (running width)
u/d cf (length)
finish cf (prolly twill weave or something to look good)
clear coats

a friend said it would be cool to add some hand rails runnin the length of the platform (like those old-school pool board plastic rails) n i was wondering: if i did them in foam n coated em with the glass, would the angles created add extra strength?

kinda like this (a rough, early version, same deck design but wefunk stringer style):


anyhow, just lookin for some input on the structure/design

[gh0stsignal]

well, since i haven't gotten any useful response as of yet, here's a lil update:

looks like my airex supplier misunderstood me and only has 3/8" sheets (rather than 1/8") so i'm thinking of switching to core-cell, since its the cheapest of the following 3 options.
core-cell is heavier and weaker than airex or divinycell but ends up being almost half the price.

cause i'm bored, heres a comparision chart between core materials, for anyone who's interested. i tried to only include specs related to board building:

FOAM CORE MATERIAL COMPARISION CHART

.............................................Airex C70.75....Core-Cell A550.....Divinycell H-80.....Pink Insulation Foam

Density (lb/ft3).......................5.0...................6.4.. ....................5.0........................2.2
Compressive Strength (psi)...190..................161......................1 90.......................40
Tensile Strength (psi)............290..................225.............. .......363.......................180-240?
Shear Strength (psi)..............175..................157............ .........167........................?
Shear Modulus (psi)..............4350................4350............ ........3915......................?

[EDIT]
oh yeah, from the suppliers i've found, airex is almost twice as much as core-cell or divinycell (although its strikingly similar to divinycell in structure). just found some divinycell for the same price as the core-cell but its scored so i'm gonna stay away from it, i'll keep looking.
[/EDIT]

[brainfartalerts]

That idea works pretty well.
Search around a bit - that method was shown here on the 'feesh as long as 3 - 4 years ago.
The image above shows an updated version I'm using for rapid composite construction.
As you were describing above, instead of a larger frame with a thicker core, several 1/8" wood/foam layers are pressed using more widely accepted standard horizontal lay-up press methods.
From practical personal experience, Core Cell in differing densities is a very good alternative - especially for the price - that works better than in some ways than the others.
More importantly, the recovery characteristics are as good - if not better - than some of the others when bonded.

[.pete]

[gh0stsignal]

[brainfartalerts]

So far, it's working great. The biggest concern I've had to date was just how cheap the wood can be.
BB holds up well enough, bamboo better still. Solid 1/8" veneers of oak (heavy), walnut (can splinter but tough and lighter), cherry (next best thing to maple and the red color), teak (woah!), mahoganies (some of the denser rain forest varietals are pretty good, many others splinter to easily) may be made to work but severe articulations cause problems if the foam wraps while the wood moves around.
Try a dry press to make sure any alignment problems show up before pulling the trigger.
One thing that may or may not help, with everything flat, use 4oz plain weave glass and lightly bond the wood/foam layer together on one side.
Adds weight and best used in a solid press but the result is a 1/8" layer that goes down flat in the mold.

By all means, please share where you're getting the divinycell at corecell prices.

As for the rest, it got saved and will be posted to eHarmony the next time they have a free weekend.
Who knows, Tye Pennington might see your profile and like it.

[SteveC]

Had any problems with the seam down the middle?

[brainfartalerts]

Had any problems with the seam down the middle?

Nope, it doesn't run down the middle.
It laps by ~ 3/8" after the tangs are trimmed on one side then joined.
Also, you cannot see it in that photo but the material is fixed for shaping/routing by a series of mounting screws. That leaves a series of matching 1/8" holes around the rim/down the middle which are indexed with dowels during layup - keeps the layers aligned.

[geolemon]

I had a similar idea from an industrial subwoofer project I worked on years ago - a kevlar vane oscillated on a steel shaft between two servo motors:
(scroll down to where it says "Update 4/16/2003" - ignore everything else, it's not a skateboard per se)
Rotary Servo Subwoofer Project

I cut channels in the foam core, so that when vacuum bagged the kevlar on both surfaces would be drawn into the channel and bonded together.
The reason was to create rigidity and strength with less weight using the same physics you get with a steel I-beam.

With my rotary vane, the channels run from the steel center shaft to the outer sweep surfaces to resist the bending forces of the panel changing directions at such high speeds.
With a skateboard deck, you'd run them nose to tail, but I was concerned that you'd possibly inadvertently create torsional instability or diagonal flex. And I'd think if anything, you'd really want to have zero diagonal twist, with a nice responsive nose-to-tail flex characteristic - sort of the opposite of what this would yield, I would think.

I haven't built one, but what do you think of my concerns? It would be a fun project...

[brainfartalerts]

I like the way that /\ was put together.

I wound up building internalized vertical composite beams this way:



In a nutshell, slice your core length wise then weave material over and under. Builds several smaller internal box sections.

There's a little more detail here

[geolemon]

So you have basically a very thin woven material in and out between the foam/wood joints? That is very trick. How do those boards test out strength wise and flex wise? I imagine very good in terms of nose-tail flex - but Is there any of that twisting flex I was concerned about? Seems like your approach would be much more solid, since you'd have complete boxes, essentially.

[brainfartalerts]

So you have basically a very thin woven material in and out between the foam/wood joints? That is very trick. How do those boards test out strength wise and flex wise? I imagine very good in terms of nose-tail flex - but Is there any of that twisting flex I was concerned about? Seems like your approach would be much more solid, since you'd have complete boxes, essentially.

Straight biax (on the 45's) glass/foam boards, 40" board length at only 3/8" thick with a 31"+ inside wheel base @ ~ 3lbs

It is a very solid solution that can be done via hand layup or infusion.

[Ted]

I like the way that / was put together.

I wound up building internalized vertical composite beams this way:



In a nutshell, slice your core length wise then weave material over and under. Builds several smaller internal box sections.

There's a little more detail here

NI iice.... I think I just wet my pants Brian!

[brainfartalerts]

NI iice.... I think I just wet my pants Brian!

I thought I pointed that out to you back when we talked several months ago.
That is the core structure for the 40" Two Bolt Main GiVA track pins.

Talk about wetting your pants, I showed that to the marine supply guys in Norfolk.
They got it immediately.
I'm thinking of building the new hollow surfboard skins that way via infusion

[gh0stsignal]

By all means, please share where you're getting the divinycell at corecell prices.

well, i might just be finding overpriced core-cell, jamestowndistributors.com has a550 core-cell 1/8x46.5x96.5 for $72 a sheet but fiberglasssupply.com has h-80 divinycell 1/8x48x85.6 for $43.67 a sheet. been to that site dozens of times but never bothered lookin at their core materials page till recently. for comparision, how much do you pay per sheet for core-cell?

heres some other stuff i found along the way. maybe not for me but if it helps someone else, figure its worth posting:

1/8 inch AirLite PVC Foam Mat (haven't found the tech specs on this stuff yet):
3.5mm thickness x 24" x 42" Resilient cross-linked closed cell foam that is microscored & scrimmed for contourability.
$16.00
Core Materials & Pour Foam

H45 DIVINYCELL 1/8 X 32 X 48" (prolly not strong enough for my design but might be useful to others)
$14.75
Foam from Aircraft Spruce


i like that idea, with the v-lam board. especially the v-lamed edge ribs. lemme know how it rides
i've been a lil worried about overall strength/flex with my design and have been thinking about adding a spine/stringer down the length on the underside. maybe two 1/8" strips, the upper going the length of the board and the lower in between the trucks, to keep from adding another 1/8" to the riding height. kinda like this:

anyhow, just a thought

[gh0stsignal]

so ran into a lil snag with the foam cutter.
the laptop power supply has a built-in overheat circuit n died halfway through my first attempt at cutting the foam mold. duh, i shoulda knew that.. anyhow, went n picked up a 25v/2a ac transformer from radioshack n wired it up to a light dimmer knob. it cut great at first, started dragging pretty bad halfway through, guess it couldn't keep the wire constantly hot enough. i think i might be using too thick a wire.
so i tried slowing the cutting n now i have these low 'melt spots' on half of the mold, where the wire got too hot in one spot.

on to the question at hand: i was wondering if i could use wood filler or drywall spackle to fill these low spots, sand it all smooth n then wrap the mold in glass or if i should just start over on a new piece of foam?

[~Nick~]

Filling should work but get a second opinion haha.
Solid looking design though!