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Best way to sculpt convex body work?

4K views 19 replies 11 participants last post by  charchri4 
#1 · (Edited)
I may as well say up front yes I know I am insane, probably ruined the car and I know this is not how it's usually done.

The back story is I am putting huge tires on a tiny car.

I did not care for any of the off the shelf fender flares so I am making my own. I started with a basic vision for what I want,


did some mapping on the car



Made metal frames in the basic shape to support fiberglass






Glassed them up



Most of my fill work has been with fiberglass and matt but I am moving on to Duraglass now.


I read in the excellent thread titled "Trying to understand filler work" several experienced guys recommend a hard block for what he is doing there.

My question is what is the proper block to use for convex panels like I have here? It seems illogical to me that a flat block could create a round surface. On the other hand there is a whole lot of illogical going on here...:)
 
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#2 ·
Use your imagination... Pieces of radiator hose, plastic pop bottles, wood dowel, radiator hose... You name it, I have used it. I seem to get the most use out of a plastic pop bottle though. I use them all the time.
Mark
 
#3 ·
Yep, you should have posted earlier in this project. You were a few more welds away from doing this whole thing in metal and it would have been much longer lasting. But starting from here, as Mark said, go to the parts store and buy a an 8" long straight radiator hose, it is very good money spent, a few bucks and you have a great tool.

I do curved panels with an odd thought on my mind. I look at it as a "curved flat". I feel it just as if it were a flat panel, and block off the high spots and fill the low spots, just as if it were flat. I see it as no different in my mind, just because it's curved doesn't change what high and low spots are.

Just a thought for you.

Brian
 
#4 ·
fiberglass???

Hi,Having been in the fiberglass business (mostly repairs) I wish I had read where you used EPOXY to go onto the metal support structure, It has been my experience,that vibration,will cause the polyester resin to pull away from the metal.if you still have the other side to do,,, STOP, rough up the metal with 40 grit paper,go to EPOXY and 10 oz boat cloth,then finish with poly putty...:nono::nono:
 
#5 · (Edited)
Hi,Having been in the fiberglass business (mostly repairs) I wish I had read where you used EPOXY to go onto the metal support structure, It has been my experience,that vibration,will cause the polyester resin to pull away from the metal.if you still have the other side to do,,, STOP, rough up the metal with 40 grit paper,go to EPOXY and 10 oz boat cloth,then finish with poly putty...:nono::nono:
Oh boy I did not know that! Bummer yeah it is polyester. No question this thing sees a ton of vibration and stress. The suspension came out of a race car and even though there is a ton of bracing all over the chassis there is a 425 hp engine where there stock 130 hp was.

My thought was fiberglass pretty much becomes one with itself when it sets so the gaps between the metal strips would bond front to back and leave the metal no wiggle room. I was thinking the weak point is the bond to the car so by welding the strips to it, then encapsulating them in glass it would be pretty stable. I am using heavy boat cloth but not sure of the weight. It's left over from building a canoe years ago. I have some weave I am going to cover the edge with.

I kind of hate to switch to epoxy at the point because I have nearly a gallon of polyester left but I certianly respect your experience in this. Is there any ramifications to using the 2 different types of resin and having them work together?

Would there be a benefit to drilling holes in it through metal areas for plugs so the back layer fills all the way through to the front side?

Thank you for your thoughts in this I really appreciate the expert insight on my little disaster!
 
#6 ·
Another problem with fiberglass on steel is that the expansion rates are quite different. When the sun heats up the surface, the glass expands more than the steel. So it is pushing and pulling sideways on the bond every day.

It doesn't matter in this case, but the expansion rate for aluminum is more similar to fiberglass.
 
#7 · (Edited)
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I used this one and the round smaller one. Bought at a paint store. Hey are part of a durablock set. The filler problem I was having came from the longer flat clocks flexing. The curved ones hold shape much better. I also bough a soft sander set. It's like what you see here but more strange shapes. I laid the paper on the fender and then formed my block to it, otherwise you crease the paper when you bend it.

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#8 ·
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I used this one and the round smaller one. Bought at a paint store. THey are part of a durablock set. The filler problem I was having came from the longer flat blocks flexing. The curved ones hold shape much better. I also bough a 11" soft sander set. It's like what you see here but more strange shapes. I laid the paper on the fender and then formed my block to it, otherwise you crease the paper when you bend it.

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#9 ·
i save beer cartons to make templates with. a good template takes the guess work out of it. as for blocks they really dont work on curves. you just have to do it by feel and by hand .
 
#10 ·
I have to agree about the fiberglass... You were very close to having it all done with metal.... fiberglass seems to stick good to metal,,, BUT it will pop loose down the road.. Seen it happen many times,,,You were doing a great job with the metal.. I would hate to see you do all this nice work, And have these problems later... I build a lot of custom parts with fiberglass,, But won't ever stick it to metal..Like Jay said... The expansion rates are quite different And more so on a good hot day..Good luck..;)
 
#11 ·
You guys nailed it for sure. I've got a whole set of durablocks and was only using the biggest hard one. I used the long flexible one like glhx said and it worked like a dream. THANK YOU!!

Sounds like I really screwed the pooch on the glass over metal. I'll have to spend some time pondering on it for a solution. If there is one... The good news is I started with a $700 dead rusty Miata and I have enjoyed every minute of the project. So even if it falls apart in a year it's all good.
 
#14 ·
I know it is a little late now, but if you ever do any more of those, I have have good experiences using 1/8" rod to form the basic shape similar to what you did with the flat stock, then you can shape and cover it with sheet metal once the rod stock is formed to the correct shape and size.

Kelly
 
#16 ·
Just a note to all you guys that said this mess is going to crack sooner than later you were 100% correct. I picked up a crack on the passenger side rear after about 50 miles of normal driving and managed to crack the drivers side rear with a pressure washer last week. Yeah I'm not sure what I was thinking there either but was not happy with myself! Both fronts and the scoop are fine so far but it will be interesting to see what 20 below temps do to it in storage this winter.


I'll probably rip it all off there someday and do something different but for now I'll just put road kill stickers over the cracks and drive it!



Thanks again for all your help guys. I really appreciate it!
 
#17 ·
How 'bout this: Before it deterriorates any further. Make a mold from what you have, out of fiberglass. Then, using that mold, build yourself new panels out of epoxy/glass. (Fiberglass cloth, with epoxy resin) then remove all your old work, and install the new epoxy panels, and mold them in.

As to block sanding convex surfaces, I use a color sanding pad. the stiffness of which depends upon the shape of the surface.
 
#18 ·
I've had several people ask me to do that and sell them fenders so I just might. Most of the wide body kits simply cover the entire surface with a not very thick panel and they don't have problems. I need to do some reading on taking a mold off a vertical surface...

Thanks!
 
#19 · (Edited)
To Take a mold or lay glass off a vertical (or an overhead surface that faces down) you need to use an "Evercoat" or similar "laminating resin" not a "finish coat" resin ,(Laminating type, first coat resin). Remains tacky to hold fiberglass fabric in place on vertical surfaces ! Its sticky and holds each layer of fiber or cloth in place as its applied and weted down or mat can be weted for overhead and then applied Its great for vertical or overhead layering of glass and mat! Most parts stores don't carry it as a matter of fact most won't know what your talking about and will have to look it up LOL And this is surprising, If you ask a lot of fiberglass repair shops if they use it they will scratch their head and say they only use Finnish coat!!! LOL

Jester
 
#20 ·
UPDATE for anyone interested. 12 months and 10,000 miles after paint and... 2 cracks but both happened in the first 50 miles of driving. No changes after that even with hitting 25 below in a Minnesota winter.


I don't usually drive it in the winter but did get it out at Christmas for a road trip with my son and we managed to put her in the ditch but no real damage...


I've run a dozen autocrosses and lots of romps well over 100


And this is a shot taken today with the areo on for a track event.



I have to say I am as surprised as anyone it has not fallen apart and still sure it will someday but so far I am really happy with it.

I really appreciate all the advice and help guys. I truly could not have done it with out you!
 
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