Hi all
I’ve found an awesome supplier of XPS foam at 32kg/m3 but instead of gluing peices together and then hotwiring the rocker I’d like to bend the foam to a predefined rocker.
Now I’ve heard that you can just put some heavy stuff on it but I’m wanting to get a bit more accurate than that. What’s the best way to get a consistent rocker on bending XPS? Hot air?
Thanks!
Cameron
I think Sharkcountry has done exactly what you are talking about .
Yep, Sharkcountry is the member to consult.
Glad to see we’re safe again, and this is a question I am close to experimenting with…
So I’ll be excited to see what Sharkcountry has to say.
http://www.surfersteve.com/polystyrene.htm
Toward the bottom of the page in this link you will find some help. I’m not sure if this is how Sharkcountry does it or not.
If you didn’t want to use the drywall/plasterboard anchors weighted method on the underside of the blank as you laminate the topside you could also try the following. Take a length of fibreglass tape (1” wide) which will hang over the nose and tail by a foot or so at each end when aligned down your virtual centre/stringer line. Attach your required weights to each of the ends of the fibreglass tape to pull the blank down into the shape you want. You can then lay your cloth over the top and laminate it all. This will leave you with no anchor holes on your deck.
Sorry guys, I think this is the person who PM’d me on this. I explained that we’ve only bent the thinner XPS, 1" max. We do it when we make compsands and the rocker must be held with perimeter rails, or it will fatten out.
I think this person wants to sell rockered blanks, and I don’t know how you’d get XPS foam thick enough for a blank to stay bent enough for a surfboard rocker. I’ve added weight on the nose to get more rocker when glassing.
It doesn’t work. It springs back, even if held bent for weeks.
Also, the stress brings it closer to it’s breaking point
Challenge accepted!
I’ve got some long, narrow 3" and 2" strips I’ll experiment with.
To be sure, my end goal is to make a blank to use straight away, and the point of curving the blank is to save work down the line - plus I’ve never done it, and I love little more than an experiment.
I’ve thought some about, what I think I’ve taken to be a bit of the “coil” theory - preloaded stress to spring back from flex - but I’m not gonna give up my 16 - 20 oz glass jobs.
I have a rocker/vacuum table on which I can place a blank in whatever spot I want and tweak nose or tail rocker. It was actually a windsurfer rocker table at one time so it’s pretty long with accelerated rocker at each end. It also has a little vee built in. No matter… I’ve placed a shaped blank with the tail on the nose section of the rocker table (I was looking for an accelerated tail boost) and vacuumed a wooden core sandwich skin to the blank while it conformed to the curve I had in mind. With an inner and outer layer to the skin, it held the rocker decently and hasn’t sprung back in time. Once both sides of the blank were glassed, the rocker was pretty well ‘locked in.’ I believe that the additional layers of reinforcement in the overall sandwich - of which just the deck and bottom are a part, helped hold it all together. Just to be clear - starting at the bottom: single layer of reinforcement fabric, blank, inner layer of fabric reinforcement/wood strip skin core/outer layer of fabric reinforcement.
I’ve often wondered about the role of tweaked tail rocker (up or down?) and how it might affect flex/rebound…
delete (double post)
Rocker in pu blank can be customise when gluing stringer, it work but often with some tweak. Some compsand builder as josh dowling start with flat panel and give rocker when gluing skins, it’s light EPS chewing gum foam. I would not use a pre stressed blank.
I’ll be following closely 
I experimented with a rocker table and XPS but did 3 layers and it held its curve.
This was back when we were all using Gortex vents.
i had a 10 mm sheet, then a 30mm outline ‘ring’ and then another 10mm sheet. There was a central strip in the middle.
Can’t remember if I used glass or just resin between layers but I didn’t ride it and years later saw it outside a house still in it’s original curve.
Mountainboard decks have extreme (35-degree angle) curves bent/pressed into them. These decks take a lot of punishment for offroad use and air – all things considered they hold up very well.
These MB deck blanks are maded by glueing/laminating 8, 1/16" layers of maple veneer together and placing them in a press for bending before the glue begins to set. The decks are left in the press until the glue has cured. They hold their curved forms very well.
So, by laminating multiple thinner layers of foam together while being “bent,” they should hold their bent shape better as the number of layers of foam you use increases. Adding veneer skins as johnmellor suggested provides extra layers to hold the bent shape.
Laminating multiple foam layers will produce many glue lines that will be difficult to sand evenly. To minimize this problem, you would need to leave a glue-free zone inside the perimeter of the desired final planshape of your blank.
As Lemat has pointed out, you are “pre-stressing” the foam – foam top surfaces become partially compressed and bottom surfaces partially stretched.
As good a method as any. Reminds me a friend putting a rope around the nose and putting weights at the end of the rope. His method though compressed the foam where the rope was. Sometimes you don’t think about consequences until after the fact.
I was just in a shop and one board really caught my eye. I didn’t ask about the design, but it appeared as a three layered laminate. A layer of foam, a layer of wood, and another layer of foam. When you looked at the board from the side of the rail you would see the wood as a horizontal stringer forming the rocker. I would imagine that the rocker was formed on a rocker table and the wood in the laminate held the rocker shape. I didn’t notice the manufacturer, but it was the only board in the shop with this configuration. If I can get eps or XP’s in 1 1/2 to 2” slabs I may try experimenting with this method my self.
Surfifty, I think 3 is the minimum number of layers.
Bert Burger said in a post years ago that he found 3 layers would hold a vacced bend on a rocker table and it’s worked for me. Because the contact area between the layers is so large the forces are spread out and it’s not as critical as expected.
I’m just thinking of some general curve/kick tail and nose- one two inch think piece and some relief cuts. “Bottom up” - Prop up the ends how much I will experiment soon, and sand bag the middle down.
Probably go with a few rows of carbon fiber tow. I got other unusal things I’m after for ease of steps, like glass the deck first. Last time I used the flat deck to keep stiffness while shaping the bottom and rails and it worked great - then glassed the bottom and had at the deck, but love the least sanding…