If you have a shaped 1 lb EPS blank and are about to throw it in your vac bag with some wood skins and your rocker bed, how do you keep your bottom contours from flattening out?
I have seen where some have built contour beds to put in the bag to achieve the desired bottom contour. But what about custom one-offs - can you shape some double barrels concaves with a spiral V out the back of a keel fin fish and at least keep the V (and possibly the concaves inside the V too?) Wedges of foam stratically placed? EPS, foam rubber, etc?
I just shaped up my first 1 lb EPS blank. I am going to put 1/8" balsa skins on it. I have vacuumed bamboo skins on decks of boards, but all of them already had a stringer or a bottom layer of glass - so no need for the rocker bed. Using a rocker bed is a first for me. Any tips on keeping the bottom contours true?
Mike Daniel - do you have anything - you hand shape all your board and also use the vac bag (for stringerless boards - so you must need a rocker bed). do you have some tricks for one-off bottom contours to eliminate the need for a contour bed?
pic - center rocker matches rocker bed but rail line does not (spiral v)
outline looks good.....some foam wedges under nose (added a little bit of lift from the rocker profile)
balsa skins in the bag - i decided to laminate the skins before placing sticking them to the blank. Most of the stuff I saw on here shows people just taping them up and throwing them on the blank. So I am adding an extra step - I was worried about the joints migrating away from each other under vacuum........hopefully i dont ruin the process by doing this..... i fear i am adding a lot of unncessary work ..... i will let you know how it turns out. Anyone else tried doing it this way? Any advise?
on a side note - my buddy has a bunch of these surplus vac pumps from a local hospital. some (if not all) were never used or only used a couple times - the hospital has vac lines throughout - maybe these were for backup or for offices that got turned into patient rooms? anyways they work good - run continously all night. bleeder valve to regulate vac pressure. you could hook one up to a regulation system (a la joe woodworker) if you didnt want to run it continously but it seems to work fine that way. they are for sale cheap on the 'swaybay'
There’s a whole load of different solutions to this problem on compsand.com
Having tried a few of them, I decided contour mats were the best way (for me) as they avoid a lot of fiddling around. I also shape the countours into the blank to avoid the deck distortion you get when the foam bends around the contour mat. You can make contour mats pretty easily out of dcell or even eps. You don’t need to do the whole fibreglass moulding thing.
If you really don’t want to touch contour mats, you can just free bag your blank with the skins on and then weight or strap it (with webbing) onto your rocker bed to get the rocker. Try to strap it in places where your bottom shape is actually flat, and use wedges around the vee. I’ve had some success with this method but it can still allow for the blank to move in unexpected ways under vac.
People like Paul and Lemat have some different methods which they have shared in the past. All in the archives on compsand.com
Grasshopper, no problem with premade skin, if you put the fiberglass on the outside you can really bend the skin on short radius without crack. For your problem why not lam a layer of fiber on the bottom + rails first then bag the top then bag bottom just with glue. This layer on bottom can help to keep shape when bag.
I can't tell you how Coil does it, but it can be done! What Dave references is actually a take-off on an old trick from the early days of modern wakeboards, when guys were shaping flat pieces of foam and doing the rocker in the lam.
Bagging without a mold or variable element form (3D rocker table)? Both are investments so one-offs from either? Yeah, not so much.
For one-offs you may want to work patiently - invest a little more time in the layup than the forms. Work from a multi-layer development approach starting from the bottom and working your way inwards to the top…
Yes, I said inwards.
The bottom of your board is the longest element or the outside of your curve (imagine concentric circles) so shape a bottom layer from a uniform flat sheet to your desired contour then wrap this face out progressivly around a a strong inner brace (the topside or inner face of the circle) with enough layers (the glue line count is the key) till the desired thickness of the blank is sturdy enough to stand alone, shape and finish glass within your bag.
Takes a few more bagging steps but it’s a precise, solid tested approach.
On the down side, most people are simply to impatient to do multi-layer layups.
Split the wood for vees. Concaves you should be OK on. Generally 1/16th balsa is what’s used … 1/8th is kinda overkill. The problem with 1# is that you can reasonably only pull 7 in. You can use a hard roller once it’s in the bag to press the wood edges into the blank. Also laminating the wood first makes the wood stiff which keeps it from bending.
Tape the top of the wood together with 2 in. masking first and then spray glue the fabric on the backside (Super 77) and cut your template. Then when your ready to bag wet the cloth and foam, then place the wood in position on the blank and tape that so it doesn’t move. Put that in the bag and pull. After you get a good pull going roll those edges and lastly set it on the rocker table and put some bricks on to hold the thing down. Pretty much all there is.
thanks for all the responses guys - some good ideas here. a million ways to skin a cat. i really like the rocker stick method a la nelson - will have to give that a try in the future.
i think my skins are a bit stiff now with 1/8 balsa laminated with 4oz and no breather cloth to wick out excess resin…break out the sander…
right now i am torn between:
1.bagging the board outside of the rocker bed and placing it on top of the rocker bed with weights (and maybe some shims too)
putting the rocker bed in the bag with some short of plastic covered eps shims.
I will have to dial in my skins and do some dry runs to see what works best. again - thanks for all the advise - I will post some more pics of the process as it moves along.
This may be a stupid suggestion since I have never vac bagged a board. Still trying to wrap my head around the whole process.
If you have the rocker shaped in the blank either in place with a glue line or hotwired in couldn't you just slip the board in the bag and not worry about your bottom contours getting flattened out?
Since the rocker is already in place the rocker bed is not needed the bag will just conform to the shaped blank. Not sure if you can get the wood veneer in place with the rocker already existing.
Any feedback would be great since this has me wondering now as well
If you have a stringer that does work. Without a stringer you’ll only get consistent results with a rocker bed. Surfboards have lots of curves … the bag doesn’t pull the same everywhere.
Would a glue line be enough to hold? This seems like it would simplify things for a one off process. Or what about a glue line combined with a rocker bed that is not in the bag. Just some weights on top of the vac bagged board pressing it down into the rocker bed? I need to do some more reading obviously. These are just ideas that seem most logical.
I guess a stringer seems to be overkill if you are adding a skin as well.
moonee - yeah that seems like a really good way to do it.
i was trying to shape the core by itself, then bag top and bottom skins on at same time, then trim the rails and add wood rails. i wanted to shape my rails before bagging and add wood rails last to make sure that i had enough material to get the rail shape right but not any more than i needed. i may have to take a couple extra steps that i wasn’t planning on doing…it all may have worked right if i didn’t laminate the skins first…doh
greg - i did a dry fit of both skins in the bag with the core last night - the bottom contours seemed to hold fairly true, but the skins straightened the rocker out a good bit through the middle of the board - i could not force the board to fit down into the foam rocker bed. skins may be too stiff. i may need to make a wooden rocker stick as Dave mentioned earlier or do one skin at a time. also i am planning to take the sander to the laminated side of the skins to thin it out a little and maybe take down some of the wood thickness at the perimeter to get it to wrap down the rails a little more.
My next experimental will be a combination of 1lb EPS , PU rails , Kauri Pine veneers done in the bag with a rocker stick.
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That is going to look SICK. I went to the local San Diego Fine Woodworkers meeting several months ago, and saw a presentation on the ancient Kauri Pine wood that is currently being dug up out of the ground in NZ. The guy that runs the milling operation was speaking and he brought a bunch of samples, and some finished pieces. The chatoyance of that wood, when finished, is incredible. It is expense, though. Please post some pictures when you start your project.
I vacced the skins on over the past couple nights. I did the deck skin in the bag weighed down onto the rocker bed with resin cans (It was interesting to see that the nose and tail tips did not bend too much, but the board would have been flattened out through the middle if it was not weighed down) Took it out of the bag, trimmed the edges and touched up the bottom contours on the tail tips.
Then vacced the bottom skin on in the bag resting on the rocker bed - no need to weigh it down, the deck skin held the rocker. Took it out and trimmed the edges. Ready to square up the perimeter to glue on the wooden rails....
Weights:
Finished blank - 0.8 lbs
Blank with deck skin - 2.8 lbs
Blank with both skins (trimmed flush to blank) - 4.5 lbs
The skins were made with 1/8" balsa and 4oz glass. The deck was vacced on with a 3/4 length 4oz patch with extra heel/toes patches on the tail. The bottom was vacced on with just resin and no additional cloth except for 4oz patches in the fin area (the 4oz integral to the skin was etched with 30 grit). I put this bottom up on the floor to see how it flexes - it doesnt.... at all......1/16" balsa vacced right to the blank with tape holding it together next time.....thanks for all the advise on this one guys!
PICS:
deck skin being vacced on
balsa fish ... coming along
foil profile - i shaped the core super thin anticipating 1/4" of skins - i still could have gone thinner!
bottom contours - altered slightly but still intact!
