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PostPosted: July 20, 2012, 3:10 pm 
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You've gone pretty far down your path so some of this may not help. For others though I would not recommend the pink stuff for this use. I may have missed something though. THe big box stores sell Masonite that has a white side that should take wax and mold release compounds well. This has a surface that doesn't need sanding and it can be bought in 1/8" thick section that would curve well onto plywood ribs with common glue.

For stiffening on this type of thing, thin plywood layed face against the fiberglass and then covered with another layer will add a lot of strength. 1/4" would be plenty thick.

When leaving the pink stuff in the part the heat from sun will be a problem. The foam is not strong enough to prevent delaminating and bubbling. The foam makes this worse because since it's a good insulator the surface can become very hot. Maybe 150 degrees or more if it is not white. The proper structural foams (divinycell) are similar in cost to marine plywood and are roughly 10 times stronger then the pink stuff.

For a dash board I think wood is hard to beat. You can get all kinds of marine plywood. It's so easy to glue and work with compared to composite. You can use a thin plywood and cut out reinforcement ribs and doublers for the edges and instrument holes etc. Then just glue the parts. It will be hard to beat the weight, it will look good and take much less work. Actually that's true of the roof too, just would look rather unusual...

One last thought. You might want the front edge of the roof to be above the front windshield by a couple of inches? For headroom.

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PostPosted: July 20, 2012, 3:59 pm 
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Horizon, thanks for stopping in and adding your comments. They are much appreciated.

As stated earlier, adequate (?) headroom will be made by making the top horizontal from the top of the rollbar forward ~18 inches, then drop down to the top of the windshield, not a straight line as shown in the the buck photos. My currrent plan is to follow the roof line from the roll bar forward as shown from my earlier topic in the Exterior forum, but not the full top though, just a sunroof with similar side wraps: Image
Are you thinking I need more headroom further forward than shown? I'm listening. I still have time to rethink that part....

1st, let me restate, the the pink foam you see is just being used as part of the buck. It allowed me to slit and form the continuously changing radius curve. The final roof layup will (fingers crossed) release from the buck and have no foam. The foam is a use once and throwaway material. I may use the foam to form stiffening ribs that will be fiberglassed over but not as structural members itself. Your suggestion of ply being used as rib forms is well taken. I had planned on using oak in the front and rear and still plan on it. Using the ply on the sides makes sense.

That melamine faced masonite is great stuff and I have used it in the past for making flat fiberglass sections. However, it will not form anything close to resembling a curve, let alone a complex curve. For a slightly tighter single curve, some thin plastic shower wall sheets "might" work a bit better.

And yes, thin ply with some glued on edges or doublers will work very good for a flat surface like a dash. I have built similar constructions for indoor use using cheap luan ply. I wouldn't use that in an weather-exposed car though. Jack uses Fir or Birch (I believe?) ply for his bonnet reinforcements in his Lalo body.

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PostPosted: July 20, 2012, 5:43 pm 
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Try using PVA release on the buck when finished. That should allow an easy release from the foam. Brush on or spray a few coats (spray at 50 psi to the gun!! for atomization). The PVA is water soluble.

JMR

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PostPosted: July 20, 2012, 9:21 pm 
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You've done a super job on everything else, and in the end, I expect your top will go the same way, Chuck. I'll be very interested to see how it turns out. You're definitely a trail blazer with this part.

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PostPosted: July 21, 2012, 3:55 am 
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What your saying about the masonite sounds right, I was thinking it was flexible, but it really isn't, even the thin stuff. I know your just making a buck but made the other comments for other folks. That's not a big help in your build log though. :)

You would need to use marine ply for the dash. Something from a specialty supplier, not fir plywood.

I was basically just sympathizing with how much work it takes to do this. Look forward to seeing this on your car!

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PostPosted: July 21, 2012, 1:49 pm 
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Chuck
For the entire top like you I used 1/2" and 1/4" pink foam that was 5 min epoxied it to the roll bars and other body parts . The foam was bent by hand and held in place with packing tape rubber straps. The roll bars, frame and body had 2 coats of PVA over them so i could get the epoxy off. 1/2" foam can be bent over a roll bar or for that matter over just about anything without breaking it if you tape the outside at 90 degrees to the bend with clear packaging tape/duct tape first.

Lowes has a tac spray that can b used on pink foam, 3M #72 i think. just don't put it on to thick or it will eat the foam also I used it to increase the thickness ( bulges in the top over each occupant). It worked marginally but it did work. Lamination allows you to easily change the shape with a little sanding.

The outside of my top had to flow evenly into the bottom body part so the foam had to b sanded back 1/8 " so 2 layers of glass would build to match the bottom part of body.
PVA is great stuff if you get enough on. I used it and wax on all parts that were going to come in contact with resin. You can then glass right over an existing part for a perfect fit. Another product that works when glassing over finished painted parts is a white plastic sheet that they use to protect new cars while they are being shipped. It can b stretched over a curved part and it sticks well.

I only used 2 layers of 2oz. chop mat for the shell ( no flat surfaces). After the foam was removed and the inside cleaned up and sanded, 2 or 3 more layers of 6"wide strips were added inside where needed to stiffen the areas where the doors and hatch glass cuts were going to b made. These cuts showed roughly 1/4" thick glass on the edges yet the parts were light and stiff.
Building the flanges was the most challenging part of the job and took more work than all the rest. See photos, very difficult to describe.
The finished parts look like they were built by someone who knew what he was doing.
Well they were. My wife did most of the sanding and all the painting. Amazing what she can do with a rough ass part i give her.

Gale

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PostPosted: July 21, 2012, 2:00 pm 
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Building the flanges was the most challenging part of the job and took more work than all the rest.


This is true. I tried to make body molds for the car in my avatar. I got shells off the body but gave up when I couldn't figure out how to do a good job on the flanges...

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PostPosted: July 22, 2012, 11:29 am 
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Where do I begin......?

All this talk about PVA. I understand it is great stuff. But, with a semi-flexible buck, and no intention of keeping the buck in one piece after its use, do you guys with experience think PVA is really necessary? I've never done large pieces. I've repaired 12" holes in a hull using nothing more that the previously mentioned melamine/masonite as a form with no issues at all. I'm just wondering...... I would think that the more flexible the buck/form, the easier it is to separate from the cured fiberglass.

I am under no illusions that the flanges and reinforcements will be a large part of the job. Much like getting a locost frame together, I'm thinking that getting the 1st fiberglass pieces off the buck is <10% of the total job.

2 layers of 2oz? WOW that is a thin layup. I was doing some web searching and thinking I'll need 4-6 layers of 6-10 oz cloth. But that is just a guess. I really have no concept of what is needed at all. I may be over estimating. i will have to think a bit more about that.

The poor man's reinforcement of cheesecloth and drywall compound on the inside seems the have worked well to make the buck a bit more stiff. It is sort of like putting a cast on a broken arm without the plaster of paris. I have decided not to add it to the outside surfaces. I got a coat of waterbased poly and then 2 coats of latex paint on it so far. Once dried real well, I'll then sand and give it one more coat of poly.

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PostPosted: July 22, 2012, 12:34 pm 
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You don't need the PVA if you don't want it. I think one use mentioned above was to protect the rest of the car for taking a mold of of it. If you have it it's easy for that. It's a lot less work then even waxing a part. SOunds like you have a good handle on what your doing...

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PostPosted: July 22, 2012, 11:31 pm 
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Chuck
horizenjob is correct. You do not need PVA for what you are doing unless you are going to use it to protect a finished part of the car from getting resin on it, and there other ways to do that. I first tried to use PVA directly on sanded foam to protect it from the resin. After 4 coats of PVA some resin would still get into the foam and melt it. I finally resorted to a thin coat of epoxy resin over the sanded foam, let it harden and then add the fiberglass lay up on top of that. Later i started using this new polyester resin that doesn't attack pink foam at all.
Did you find an inexpensive paint that poly resin won't destroy?
Are you attaching the buck directly to the car so that after the part sets up it will b an exact fit to your car or are you doing it by some other method?
Gale

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PostPosted: July 23, 2012, 12:47 pm 
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Did you find an inexpensive paint that poly resin won't destroy?
Ummmm. I have 3 coats so far, of latex paint over 1 coat of waterbased polyurethane. I've done some sanding so it is not 4 layers thick. Also, the curved part has drywall compund surfacing. I expect that should be well enough after a good coat of good ol' Johnson's Paste Wax. I will report how well this works.

Quote:
Are you attaching the buck directly to the car so that after the part sets up it will b an exact fit to your car or are you doing it by some other method?
. The buck was made to match the radius of the windshield and at the roll bar. But the buck is free from the car as shown in the earlier photos. I will be laying up the top off the car in 2 halfs, split down the middle. Then I'll glass them together and cut at 90 degrees to get the bow shape I'm wanting. In essence, it will end up being 4 quadrants bonded together. I did this for fitting at the corners of the windshield. It eliminates a lot of initial buck complexity (mostly mess). Plus, I'll not risk sticking anything to my car in the process. Maybe I'll be braver the 2nd time around but for now, I'm chicken. The last time I played with any real amount fiberglassing was over 30 years ago. I did some small stuff last year patching a friend's FV nosecone back together. That is still holding together :cheers:

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PostPosted: July 23, 2012, 3:16 pm 
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It's likely to shrink just a bit during cure. That varies, but cheap resin doesn't have "don't shrink" high on the list of things it is made for. Nothing wrong with that and it's probably a slight plus in a female mold. When you put together the pieces you might land up with gaps to fill though. Sounds like you will be able to deal just fine with that. The curves might land up just a bit different too, where they line up to the windshield for instance.

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PostPosted: July 23, 2012, 4:07 pm 
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Yep. When them resin molecules crosslink during the cure, the end result becomes a bit smaller. Not a problem with my process. I've planned the 2 sides to be about 1" oversize in the bonding-seam area. That should allow enough for a trim and a tight fit. But even a small gap (say< 5 inches :wink: ) should still be workable with a bit o' glass and resin. The front and rear are over-long and will be trimmed to fit before I add any support along the edges. I plan on a small amount of clearance at the ends of the windshield radius. This will hwlp self-center the top as it is closed. At the same time, I plan on raising the front edge across the top of the windshield ~ 1/2 inch for an added gasket/weather stripping/cushion. I will trim that piece to match the ever-increasing gap. So yeah, I sort of planned this whole ass'y process according to my skills or lack thereof. How well I can put it into practice according to plan..... that remains to be seen.

Thanks for pointing out some of the issues. It helps keep me on my toes and may be of help to other fools who follow this process. :cheers:

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PostPosted: July 24, 2012, 11:40 am 
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Have you thought about using epoxy resin instead of polyester. It is more expensive but sure smells better.


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PostPosted: July 25, 2012, 11:03 am 
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I can easily get hooked on the aroma of polyester. I considered quitting a job some 40 years ago to work at a boat building company just for the "benefits" :roll:

Hello, My name is Chuck I am a polyester-holic. It has been 327 days since I have sniffed polyester resin........ But it won't be long now :cheers:

No Epoxy on this job. I'll be using the polyester, not because of the smell or the properties, but simply because I can get it by the qt locally at a great price and I won't have to over-purchase just to be sure I have enough. It seems that determining the "correct" amount of resin for a hand-layup seems to be an art rather than science. I have the final 2 coats of water-based Rustoleum on the bucks (just leftovers from what I have in the paint cabinet). I have light-sanded them and have 2 coats of paste wax on them so far. As it turned out, I have only enough glass for 1 layer. I need to purchase some more glass before I can do the layup.

Come back next week when we will find out: Will our hero get the materials in time? Did the layup release from the buck? Will Chuck have a relapse from fume inhalations? And what about little Suzy? Dum-Dum-Dum (a little musical interlude/finale?)

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Visit my ongoing MGB Rustoration log: over HERE

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