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Reinforcing Body Glue Joints

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I am trying to reinforce a body where I've made major changes. This will require heavy sanding after I make the joint. Suggestions how to make a REALLY strong joint. The joint will be hidden (it's on the underside of the body) so appearance is less important than strength.

Thanks,

Mike

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If it is a strong joint you need, and it won't show because it's on the inside of the body shell, here's the method I have employed on more than a few occasions: 5-minute epoxy and small strips of paper towel, laid up like fiberglass. Unfortunately, I have yet to photograph the process - mainly due to the short working time of the epoxy.

I get a bit of epoxy on the joint, then lay a few small strips of paper towel over it in varying directions; I then mat the paper down into the epoxy with a toothpick until it gets nearly transparent, and often add a little more epoxy over the top surface. One time I even wove very narrow strips of paper towel together before laying it up, but I feel the added work made little or no difference.

This method makes for a very strong glue joint, and I have even used it on 1:1 car parts. A co-worker bought a set of JDM turn signal assemblies for his WRX from an Ebay seller in Japan, and one arrived with a mounting tab cracked almost all the way through. I fixed the part with the epoxy/layup method, and used my Dremel to shape the repaired area so the mounting tab looked like new. That repair was done about 3-1/2 years ago, and the part is still on the car. ;)

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If it is a strong joint you need, and it won't show because it's on the inside of the body shell, here's the method I have employed on more than a few occasions: 5-minute epoxy and small strips of paper towel, laid up like fiberglass. Unfortunately, I have yet to photograph the process - mainly due to the short working time of the epoxy.

I get a bit of epoxy on the joint, then lay a few small strips of paper towel over it in varying directions; I then mat the paper down into the epoxy with a toothpick until it gets nearly transparent, and often add a little more epoxy over the top surface. One time I even wove very narrow strips of paper towel together before laying it up, but I feel the added work made little or no difference.

That sounds like a VERY good method, thanks for posting!!

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Ok, Dave, I'm going to have to comment on your method. Forgive me for being the structural engineer that I am. This is similar to many composite methods of repairs and even the main method of making a complete structure, like a carbon fiber body. The paper towels you use are the reinforcing material. Carbon fiber uses carbon sheets in a resin bath. Concrete uses steel bars in a concrete mix, fiberglass uses glass fibers. The reinforcement is usually required to take the tension (pulling apart) in the material. For your paper towel/epoxy composite the paper towels are required to be the reinforcement, so to speak. The towels may help to get a nice even thin layer of epoxy, which is highly desirable in this joint, but they add nothing to the strength ... it's all the epoxy alone. Epoxy is not as good in tension as materials such as steel, glass fibers and carbon fiber.

When I've done seam reinforcement like this I've used wire or some sheet metal embedded in the epoxy for strength.

Now if we could easily get some carbon fiber strips. !!! ;)

Edited by Foxer

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i used paper towel and super glue for this for a while, but i discovered that cyanoacrylate loses bond strength reacting to the paper. now , if i need to strengthen a joint, it's with epoxy and bits of paper clips or pieces of styrene and liquid cement.

on one of my models from a couple of years ago, i used business cards from my job for making a floor pan and side panels, used a LOT of ACC glue on that. i need to dig it out and see how well it's holding up.

i use ACC and sanding dust for backfilling joints i know will get severe stress being worked; i used this method to put Chrysler dual headlamps on one of my revell Merc's.

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VWDave's method sounds good, but if you're gonna go there, why not real fiberglass? Check in the R/C section of your LHS, they should have 3/4 oz. fiberglass cloth, and various tapes. It's easy to use, cuts with scissors, and if you use 30 minute epoxy, you can lay in a bunch of layers before the glue dries. The strongest is to lay in progressively bigger pieces, so that it's thickest right over the joint, and feathers out to the largest area you can easily cover. You can do all sorts of cool stuff with fiberglass, and IMHO, it should be in every modelers tool box.

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Now if we could easily get some carbon fiber strips. !!! ;)

My LHS has carbon fiber strips in a bunch of different sizes. The trick is to be able to afford them!

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I've had really good luck with file card and water thin CA.

First, cut and shape the card until it lays flat, and don't be afraid to try several until you get it laying flat and smooth

Tack the card down with the usual mid-cure (don't glue your fingers to it)CA. When all is snug, use the water thin blue-top CA to saturate the card (as you would with matte glass)

It will make the card very stiff and give the joint good backing that will not come loose easily. Dries quickly, and even sands pretty easily.

However, to repeat some of the comments from earlier, you have to sort out how the joint can fail.

Will it twist? Want to fold on iteself? Be in tension or compression? Each of those calls for a different solution.

Good luck!

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My LHS has carbon fiber strips in a bunch of different sizes. The trick is to be able to afford them!

That Is interesting. I wonder if they come from scraps from larger projects. Any idea what target buyer is?

Edited by Foxer

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If it is a strong joint you need, and it won't show because it's on the inside of the body shell, here's the method I have employed on more than a few occasions: 5-minute epoxy and small strips of paper towel, laid up like fiberglass. Unfortunately, I have yet to photograph the process - mainly due to the short working time of the epoxy.

I get a bit of epoxy on the joint, then lay a few small strips of paper towel over it in varying directions; I then mat the paper down into the epoxy with a toothpick until it gets nearly transparent, and often add a little more epoxy over the top surface. One time I even wove very narrow strips of paper towel together before laying it up, but I feel the added work made little or no difference.

This method makes for a very strong glue joint, and I have even used it on 1:1 car parts. A co-worker bought a set of JDM turn signal assemblies for his WRX from an Ebay seller in Japan, and one arrived with a mounting tab cracked almost all the way through. I fixed the part with the epoxy/layup method, and used my Dremel to shape the repaired area so the mounting tab looked like new. That repair was done about 3-1/2 years ago, and the part is still on the car. :angry:

A variation I've done on this is use Fiberglass Mesh Tape for drywall joints. It's thicker, but is quite strong and the epoxy fills the mesh.

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That Is interesting. I wonder if they come from scraps from larger projects. Any idea what target buyer is?

They are all a consistent length, (24"?), and lots of different sections, maybe even rounds. I know the R/C aircraft guys use them for reinforcements, like in wing spars. Super light, super strong. I'm not kidding about the price, tho! :angry:

To return to the point of this thread, I've had good luck laminating styrene sheet to the inside of a body with liquid cement. (Like Ambroid or Testors) I hold the pieces together on one edge, so they're open enough I can get a brush between them. Brush cement, squeeze, brush cement, squeeze, and work your way across the sheet that way. If you get enough cement in there and squeeze good enough, the whole works is one piece of plastic.

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A lot of good ideas...

I like the really thin plywood from the R/C plane section of the hobby shop, (1/64 of an inch I think), coupled with CA.

It cuts easily with scissors.

Scuff the plastic with very coarse sand paper (100 grit or rougher) and allow the plywood to be saturated with the CA.

I have found it works better than metal as far as adhesion, and stays bonded if any flexing is involved better than plastic.

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This worked so far for me but...I'll be watchin' this thread for more ideas...

I just modified a Deal's Wheels "Trans Um" hood and nose to look a bit less cartoony. Used a piece of .040" evergreen sheet for a hood with .020"x.100" evergreen strips under the seams with Tenax/Testors Liquid. I shaped and sanded the heck out of it and it's still OK.

Smokey

Edit below...

I don't want this to change or highjack this tread. If there are any ideas or comments about the glue idea lets start a different thread.

The Testors Liquid and Tenax 50/50 and it appears to be a strong bond with a bit more workin' time than just Tenax.

Edited by Yekoms

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Here's another tip, use used dryer sheets instead of paper. This stuff looks like fiberglass in scale. I've used it on a couple of builds and it works great and it's free after it comes out of the dryer. :lol: Dan

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This has been a great discussion. Please don't think any idea is a hijack or unworthy. I'll admit this has been great to watch. In fact I've read so many great ideas that a still borne project is going to get pulled out of the stack.

THANKS!

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Great ideas...but are you really gonna see it ? What scale is this ? Maybe I am wrong. Butt.....!?

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I'm working on a Studebaker hood now, the one that has the two holes in it for the two blowers. I don't have any pictures of that yet but here is a picture of a Datsun hood that I used the dryer sheets on.

DSC03618.jpg

What do you think? Dan

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I use .010 sheet styreen..its like paper. I brush Bondine on both surfaces press out ripples etc and let dry, Tenax and Pro Weld are to hot, and dry too quickly. I use this when chopping and sectioning hoods and bodies....because it is thin it will fit and be easy to hide.The solvent will bond all 3 parts together...let it dry overnight before working it.

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For your paper towel/epoxy composite the paper towels are required to be the reinforcement, so to speak. The towels may help to get a nice even thin layer of epoxy, which is highly desirable in this joint, but they add nothing to the strength ... it's all the epoxy alone. Epoxy is not as good in tension as materials such as steel, glass fibers and carbon fiber.

A thin, strong epoxy joint is exactly what I was after when I first heard of the 'layup' method, and I certainly agree with you about the minimal contribution the paper actually offers to the strength of the joint. However.....

...I've yet to have an issue with epoxy joints not being strong enough on a model car body, so I figured the method I outlined would be at least sufficient.

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I was wondering if you anyone could supply any more specific tips or pics of using fiberglass sheeting and epoxy for reinforcing joints or perhaps even to create contours.  I'm also wondering about the thickness of the fiberglass sheeting and where to purchase.  Hugh mentions some of this above, but I would like to maybe see some pics of different kinds.  I like the tip above too about using dryer sheets.  This thread is the only info I could find on this forum, but I could be mistaken.  Thanks in advance.

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I was wondering if you anyone could supply any more specific tips or pics of using fiberglass sheeting and epoxy for reinforcing joints or perhaps even to create contours.  I'm also wondering about the thickness of the fiberglass sheeting and where to purchase.  Hugh mentions some of this above, but I would like to maybe see some pics of different kinds.  I like the tip above too about using dryer sheets.  This thread is the only info I could find on this forum, but I could be mistaken.  Thanks in advance.

I've covered this in some depth on many threads, as I'm the one who pretty well pioneered the fiberglass process, and I've been developing and refining it for many years. I also make close to scale-thickness parts from the material. There's some info here...

http://www.modelcarsmag.com/forums/topic/65965-mickey-thompsons-challenger-one-still-alive-feb-8/

DSCN7947.jpg

There's also information on my old thread here, from 2010  http://cs.scaleautomag.com/sca/modeling_subjects/f/30/t/97991.aspx

DSCN2668.jpg

If you have questions, please post them under the "MODEL BUILDING QUESTIONS AND ANSWERS" heading, and I'll do my best to help you.

 

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I have used the dryer sheets with epoxy where I need the somewhat slower time, (less than instant), that it offers. When I want something strong and fast, I use .010 to .020 plastic sheet, (thickness determined by how flexible I have to bend it to fit the joint), get the joint set, spray it with ZIP Kicker, apply the CA cement to the reinforcement piece, and quickly and CAREFULLY put the reinforcement piece over the area to be strengthened. It is VERY quick, and so far has produced bullet proof joints. I have had occasion to take one apart once or twice, and they are stronger than the surrounding plastic by far.

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I've covered this in some depth on many threads, as I'm the one who pretty well pioneered the fiberglass process, and I've been developing and refining it for many years. I also make close to scale-thickness parts from the material. There's some info here...

http://www.modelcarsmag.com/forums/topic/65965-mickey-thompsons-challenger-one-still-alive-feb-8/

DSCN7947.jpg

There's also information on my old thread here, from 2010  http://cs.scaleautomag.com/sca/modeling_subjects/f/30/t/97991.aspx

DSCN2668.jpg

If you have questions, please post them under the "MODEL BUILDING QUESTIONS AND ANSWERS" heading, and I'll do my best to help you.

 

Bill, just checked out the links you posted. Absolutely wonderful work! I will be trying this method with a couple of projects that have been holding down one end of my bench for a few years, waiting for a solution I had no idea was about to be put forth. THANK YOU!

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.  Hugh mentions some of this above, but I would like to maybe see some pics of different kinds

Bill (Ace-Garageguy) is definitely the man when it comes to fiberglass. Any advice or instruction you get from him you can take to the bank. I'm not sure that pics would do you much good. I can tell you that 3/4 oz. cloth is pretty thin, about like silk. That may be the lightest, tho it seems like I saw some 1/2 oz. somewhere. 8 oz. cloth (that I have used for canoe repair) is about the thickness of denim. The lightweight cloth is available from places that sell R/C aircraft building supplies. The heavier weights might be easier to find (and cheaper) at auto body or marine suppliers. I have found that one layer of 3/4 oz. cloth works fine for reinforcing splices in plastic.

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