Neil
Supporter
Even low pressure expanding foam can create serious distortion over such a wide area. Be very cautious.
Classic HorsePower Scratch GT40
- Thread starter Wolfman
- Start date
I was thinking about that as well. You have me thinking I may spray it open faced upside down and shave off what expands above the height of the skeleton before I bond the inner skin. That way it doesn’t add any pressure inside a cavity but yet does most of what I need it to do.
Lots of work done to make it fit and look the part. Lots more work to perfect it. It has really stiffened up with the bonding and am happy that it will be more structurally sound than an all fiberglass spider. Even though I don’t plan on anyone using the roof/A-pillar to support someone entering or existing the car, I think this will be able to give me peace of mind to avoid the possibility of it stress cracking the windshield.
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Work continues on the scratch spider. Inner skin bonded, insulated (albeit some voids), A-pillar weather seal flange installed.
Some lessons for those challenged with part or all of these steps. 1) bonding mix of the epoxy resin with the silica powder with various ratios seems to be working well for filling voids, thickening to stay in place and added strength during/after curing. 2) clamping is obviously super important but clamping it in the installed position is paramount. During the inner skin bonding it was necessary to lay out the epoxy while I had it dismounted and upside down to line up and clamp together by myself, however looking back I should have had another set of hands to help me remount the spider back onto the chassis and readjust the clamping prior to it curing. This was evident as I lighted the spider by removing some of my MANY clamps and remounted the spider before the final curing had occurred. When remounted, the inner skin had a slight buckle at the rear bulkhead flange to which I had to correct (just a couple hours into the cure) with a heat gun and releasing the outer edges of the bulkhead inner/outer skin door/weather seal flanges. Later I had to come in to re-bond those area I separated to take out the misaligned areas. 3) Insulation… I toiled over how to tackle this and settled on getting a can of “door & window” minimal expanding foam. Made extra long straw extension to reach the deeper recesses of the open spider cavities and sprayed a “layer” of the foam from inside out, due to the length of straw and how it flowed, the product only approximately doubled in size so I ended up having a few voids next to the inner skin (had it upside down while spraying) but best I can tell it covered 90% or better of the cavity between the two skins. Those considering doing this, it is important to visually see where it is being sprayed and with how much product/the expansion rate to avoid over filling and possibly warping the skins. I am glad I did do it as it sounds so much more solid, added strength and am sure will help a little with heat transfer. THE MINUS for using it. It doesn’t appear to be as hard or solid at the normal version of the expanding foam. I am attempting to use it as the shaping layer for my inner A-pillar fiberglass skin…yet to see how that will work but a grinder appears to be the best shaping tool so far since it tears easier being softer. 4) Welded the weatherstripping flange on the A-pillar. Not only did this add the ability to secure the same pinch weld seal but since it is welded steel, it has also added strength to the corners too.
The great news is that with what is complete on the spider so far and without the windshield in place, this thing is now strong enough to support almost my entire body weight on the center of the spider (at least 150lbs+)! Frankly I never thought it would be this strong so it gives me confidence that my windshield will be safe from people grabbing the corners of the A-pillar as a support getting in/out of the car.
Some lessons for those challenged with part or all of these steps. 1) bonding mix of the epoxy resin with the silica powder with various ratios seems to be working well for filling voids, thickening to stay in place and added strength during/after curing. 2) clamping is obviously super important but clamping it in the installed position is paramount. During the inner skin bonding it was necessary to lay out the epoxy while I had it dismounted and upside down to line up and clamp together by myself, however looking back I should have had another set of hands to help me remount the spider back onto the chassis and readjust the clamping prior to it curing. This was evident as I lighted the spider by removing some of my MANY clamps and remounted the spider before the final curing had occurred. When remounted, the inner skin had a slight buckle at the rear bulkhead flange to which I had to correct (just a couple hours into the cure) with a heat gun and releasing the outer edges of the bulkhead inner/outer skin door/weather seal flanges. Later I had to come in to re-bond those area I separated to take out the misaligned areas. 3) Insulation… I toiled over how to tackle this and settled on getting a can of “door & window” minimal expanding foam. Made extra long straw extension to reach the deeper recesses of the open spider cavities and sprayed a “layer” of the foam from inside out, due to the length of straw and how it flowed, the product only approximately doubled in size so I ended up having a few voids next to the inner skin (had it upside down while spraying) but best I can tell it covered 90% or better of the cavity between the two skins. Those considering doing this, it is important to visually see where it is being sprayed and with how much product/the expansion rate to avoid over filling and possibly warping the skins. I am glad I did do it as it sounds so much more solid, added strength and am sure will help a little with heat transfer. THE MINUS for using it. It doesn’t appear to be as hard or solid at the normal version of the expanding foam. I am attempting to use it as the shaping layer for my inner A-pillar fiberglass skin…yet to see how that will work but a grinder appears to be the best shaping tool so far since it tears easier being softer. 4) Welded the weatherstripping flange on the A-pillar. Not only did this add the ability to secure the same pinch weld seal but since it is welded steel, it has also added strength to the corners too.
The great news is that with what is complete on the spider so far and without the windshield in place, this thing is now strong enough to support almost my entire body weight on the center of the spider (at least 150lbs+)! Frankly I never thought it would be this strong so it gives me confidence that my windshield will be safe from people grabbing the corners of the A-pillar as a support getting in/out of the car.
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More fiberglass work…be gentle, this is some of my first attempts at free form molding and layup. I know there are a few voids due to air pockets in the shaped expanding foam. It was ok to shape and found the grinder made quick work and a smooth surface and followed up with 80 grit sandpaper to smooth and round to the shape I wanted. Although I need to add one more layer of glass for added strength, I want to make sure it is as smooth as possible, cut out & fill the voids and sand the entire added areas before this final layer.
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Started working the door hinges using rod ends, bronze bushings, removable hinge pin, and steel reinforcement plates. Next will be tacking the adjustable mount plate.
Also have started the refinement of the windshield mounting channel. I decided to source and use a 1/4” thick rubber as the spacer on the back of the windshield to replicate the urethane/butyl sealant thickness as well as an 1/8” thick rubber for the surround spacer. Once secured with painters tape, I laid the windshield in place and are only using fiberglass stranded filler on one side of the windshield surround at a time to enable an easier & safer extraction of it once dried. This is a multiple step process as once removed there is lots of trimming, sanding and filling of voids to perfect the channel for a smooth and form fitting spider.
Also have started the refinement of the windshield mounting channel. I decided to source and use a 1/4” thick rubber as the spacer on the back of the windshield to replicate the urethane/butyl sealant thickness as well as an 1/8” thick rubber for the surround spacer. Once secured with painters tape, I laid the windshield in place and are only using fiberglass stranded filler on one side of the windshield surround at a time to enable an easier & safer extraction of it once dried. This is a multiple step process as once removed there is lots of trimming, sanding and filling of voids to perfect the channel for a smooth and form fitting spider.
Attachments
Mark Turner
Supporter
Looks good with the windshield sitting in there. very interested to see more of your door hinges.
I knew from my windy west Texas experience that the doors need to be as robust as possible when the 35+mph winds catch them unexpectedly to avoid future damage. I may be “over engineering” many things for a mostly street “race car” but IMO I hate to go back and redo things that should have been made to last more than a few years.
Well they may be true, but unfortunately that’s not what I had the opportunity to start with…just some pieces of splash molds taken off of an unknown car. For me it was better than nothing but requiring more work and an opportunity to “make” my own spider to match my clams, windshield & doors from various other sources as well as a mild 2” stretch to the wheelbase.
