Anyone know what to use, as Bert used, to copy the concave bottom? Looked like some pourable rubber stuff. Bert, I respect your keeping the wraps on your technology. Just wondering if you could divulge this item. Thx
Greg,
Google “mold-making” and you’ll come up with all kinds of materials.
dcell
you’ll need mold making stuff if the concave is gemini deep
overlaying various “contour maps” work too
Greg,
Are you making a wood lam composite? If so I have a few shots how to make a complex bottom on a flat surface in a wood lam situation. I made my contour with d-cell as oneula said per bert’s advice. It’s a great idea but you need a light foam to make it work. My way is pretty simple, but have only used it on wood lams. You can do it on any weight foam though. Can be used in single build or mass production situations.
cp
Yep, I’m gearing up for a balsa composite vac board. I’ve read and reread everything here and watched the vac video a couple of times and I am ready. Maybe. I’ll be using 1 lb foam.
Any tips would be appreciated on how to do the bottom. thanks
Greg,
With this technique the sky is the limit on design and botttoms. I happened to use divinycell 1/8" patches to make this on. You could use core-cell, thicker balsa, or even some thin 2 lb psf or denser foam. I haven’t researched swaylocks about this technique so it could be old hat. Oneula and his bro pretty much made me think this up or I possibly stole the idea from them. Anywhoo here it is.
I have a floppy 1 lb psf, stringerless foam blank, slight rocker molded in but bottom totally flat. All the pencil markings are my center line then some 2 inch off center lines, my fin placement marks and then the markings for the bottom contour. The plan is single scoop to venturi to double concave.
ugly huh?
Now I cut my d-cell 1/8" foam which consists 2 side pieces and one small piece in the tail to make a double concave. I used a template. You can free hand this. After you make one side use that for your template for the next one. Place them together, mirroring each other and sand to make them match up perfectly.
Not shown, I used a 3/4 length from tail to nose fiberglass patch using 1.4oz e glass. enough epoxy to wet out the fiberglass.
Add d-cell patches to my marked out spot on the wet out glass. The skin has also has a full length 1.4oz e glass on it’s down side wet out which is placed on top of the d-cell patches. Of special note, the skin is 1/16" balsa with the lateral outside pieces on each side being a 3/32". this is to help exaggerate my my shape. After you plop this skin on top of the sandwich a few pieces of tape go on the skin to hold it in place until its vacuumed. Release film applied and into the bag it goes.
My rocker was set during vacuum.
the nose is closest to the bottom. Still ugly huh?
out the bag it comes. the few pieces of tape come off. And here it is , ready to be sanded and tapered. A complex bottom on a flat floopy piece of foam.
Like I said Greg, this could be acheived with many materials, d-cell, wood, other scrape denser foam pieces. The contour mat is also a great idea if you are using light density stringerless foam and making lots of similar baords. I like my way because it’s easy , adds to the composite design and function, can use on one off customs or 20 of the same design without adding precious time to the constrution after only a few trys.
For your first trys flat bottoms are cool also until you get a nice comfort level with vacuum bagging. I look forward to check out you project when it’s done!!!
Greg,
I’m not sure but what you might be talking about is RTV Silicone. That’s used for flexible mold making.
CMP … VERY COOL!
Greg,
RV silicones, urethane rubbers, polyesters, epoxies. Depends on many factors. One prime factor is Shore spec. Another is durability. I mean you could probably use alginate. But it’s not very durable.
check out Smoothon.com or Polytech. Mann makes my favorite release agents.
These are all fairly expensive products.
But now CMPs work has really got my interest.
Quote:
Greg,
With this technique the sky is the limit on design and botttoms. I happened to use divinycell 1/8" patches to make this on. You could use core-cell, thicker balsa, or even some thin 2 lb psf or denser foam. I haven’t researched swaylocks about this technique so it could be old hat. Oneula and his bro pretty much made me think this up or I possibly stole the idea from them. Anywhoo here it is.
I have a floppy 1 lb psf, stringerless foam blank, slight rocker molded in but bottom totally flat. All the pencil markings are my center line then some 2 inch off center lines, my fin placement marks and then the markings for the bottom contour. The plan is single scoop to venturi to double concave.
ugly huh?
Now I cut my d-cell 1/8" foam which consists 2 side pieces and one small piece in the tail to make a double concave. I used a template. You can free hand this. After you make one side use that for your template for the next one. Place them together, mirroring each other and sand to make them match up perfectly.
Not shown, I used a 3/4 length from tail to nose fiberglass patch using 1.4oz e glass. enough epoxy to wet out the fiberglass.
Add d-cell patches to my marked out spot on the wet out glass. The skin has also has a full length 1.4oz e glass on it’s down side wet out which is placed on top of the d-cell patches. Of special note, the skin is 1/16" balsa with the lateral outside pieces on each side being a 3/32". this is to help exaggerate my my shape. After you plop this skin on top of the sandwich a few pieces of tape go on the skin to hold it in place until its vacuumed. Release film applied and into the bag it goes.
My rocker was set during vacuum.
the nose is closest to the bottom. Still ugly huh?
out the bag it comes. the few pieces of tape come off. And here it is , ready to be sanded and tapered. A complex bottom on a flat floopy piece of foam.
Like I said Greg, this could be acheived with many materials, d-cell, wood, other scrape denser foam pieces. The contour mat is also a great idea if you are using light density stringerless foam and making lots of similar baords. I like my way because it’s easy , adds to the composite design and function, can use on one off customs or 20 of the same design without adding precious time to the constrution after only a few trys.
For your first trys flat bottoms are cool also until you get a nice comfort level with vacuum bagging. I look forward to check out you project when it’s done!!!
Thats really cool stuff there. It would be really cool to check out your constuction methods.
Greg
As Greg sez, silicone rubber. I have just bought some to play with, quite costly though (in the UK £32.00 for a 1.1kg pack (2.42 lb)), I hope this will be enough for one bottom shape on a short board. Got it through my polyester resin supplier. I do like CMP’s method although don’t think it will work for me with a rocker table.
Come over anytime Jason.
Surfgear Hawaii Institute of Technology is open most weekdays.
We all have diplomas in Composite Research Analysis Principles and are happy to share ideas that we didn’t have to sign a non disclosure form on.
Greg…the technique I posted will work best on a rocker table.
regarding contour mats
When I made my contour mat with divinylcell I copied a bottom of a whole board by putting release film on the board to be copied. Vacuum bagged a double glassed d cell piece on the concave. Then fill the concave indent with something dense to keep the exact shape of the concave. With the d-cell still in the board to be copied. Adjust your rack to make the concave level and fill it in with 1:1 polyurethan foam mix or whatever will work to stiffen the shape so you keep the exact concave and the bottom is level for your rocker table.
You might want to check with Bert on what is the most dense foam you can use it on. His example was .75lb PSF foam core.
sounds like it will be a pretty cool board.
Quote:
Come over anytime Jason.
Surfgear Hawaii Institute of Technology is open most weekdays.
We all have diplomas in Composite Research Analysis Principles and are happy to share ideas that we didn’t have to sign a non disclosure form on.
Thanks CMP! ill send you a PM
Hey. Thanks to all for the great advice. I’ll be sure and post pictures. I’ll also throw in some pic’s of my wife screaming at me to clean up my board building mess in the garage.
Does anybody have an update to this information?
Thanks
For my part, I did google silicone rubber molds and found a couple of sources, called them and found the stuff was very very expensive. I ended up using a shaped bottom and flipping the board up on the deck off cut so the vac would pull the veneer down. No mold used. It worked.
It could be worth re-visiting. If you can find low cost material.
My day job keeps getting in the way of my personal life.
Bert did mention something about snagging bottom contours off various boards and how he went about procurring them.
If you used a couple coats of Johnson’s Paste Wax on a buffed out surfboard you could take a mold using plain old resin and scraps of fiberglass. This could easily be trimmed and feathered for a smooth transition on your vacuum molded bottom.
Bert’s contours were simply pressed into the blank as the skin cured under vacuum pressure.