15 min. epoxy vs. Elmer's ultimate glue
 

Hi,

I need to repair a model rocket fin that has been cracked at the intersection of the fin and body tube.

My friend told me to use 15 minute epoxy to repair it, but I have heard that Elmer's Ultimate glue is the stronger glue (beating Gorilla Glue by 40% (according to an ad)). What do you guys think? Which one is stronger?

Thanks

Re: 15 min. epoxy vs. Elmer's ultimate glue
 

I use Epoxy @ my work (mechanic) and I have not had a problem with it.

Never used the Elmer's Ultimate Glue though. I'd worry about the high temps - and agian, I love my epoxy.

I'd go for the epoxy.

Re: 15 min. epoxy vs. Elmer's ultimate glue
 

Two-part epoxies by far are a lot stronger, and I will also recommend you use the 15 minute epoxy. One thing that I have (unfortunately) learned from experience is that 15 minutes is not the curing time, but the setting time. The setting time is the amount of time for the epoxy to become rigid, but not reach full strength. The curing time is the time it takes for the epoxy chemical reaction to end (true epoxies are chemical reactions) and reach full strength, typically 24 hours.

Re: 15 min. epoxy vs. Elmer's ultimate glue
 

What's the fin made out of? Choosing the right adhesive has a lot more to do with matching the proper materials than in determing some absolute level of "good."

If the fins are HDPE, for example, neither of the adhesives you name would be a good choice.

Re: 15 min. epoxy vs. Elmer's ultimate glue
 

The fins are made from plywood and the body tube is cardboard.

Thanks

Re: 15 min. epoxy vs. Elmer's ultimate glue
 

According to the link you posted, the fins are precise cut plywood. I'd go with the epoxy. To reinforce the joint, you can embed some fiberglass window screen material into the epoxy on both sides of the fin similar to fiberglassing something.

Mix your epoxy and apply to the both sides of the break. Place the fin back on and then apply more epoxy to each side of the fin and body tube and press the window screen into the epoxy across the break so that its tight to the fin and body tube and the excess epoxy is forced out through the screen. Then use a piece of scrap 0.020 plastic sheet or index card as a squeegee to spread the epoxy out in a thin layer over the screen and remove extra epoxy.

Next, use masking tape or your favorite method of holding the fin in position until the epoxy cures (24 hours), but check it a few times before the epoxy sets to make sure the fin is still straight. After curing, trim any screen overhanging the fin, sand lightly and your repair should be good for launch. If you want really strong screen, Home Depot sells screening which is labeled (I think) "Dog Proof". It has extra fiberglass strands or Kevlar strands embedded in the product.

Also, if this fin broke off during a landing impact, you might want to consider applying a fillet of epoxy to each fin where it joins to the body tube to strengthen all the joints.

Re: 15 min. epoxy vs. Elmer's ultimate glue
 

Arthur's advice is excellent. If you can repair the fin off the rocket, you might lay the fin on a piece of polyethelene plastic (the plastic sheets sold in rolls in home centers are mostly poly) create your repair with epoxy and fiberglass stiffener, squeegee out the excess epoxy, and the cover it with another layer of poly. Place a large flat weight on top of this sandwich and you will end up with a smooth, no-sanding-required surface.

Alternately, you can replace the poly with release fabric, which would "suck up" the excess epoxy in your laminate. Since you probably don't have any release fabric, you can just forget this part. :)

Good luck.

Re: 15 min. epoxy vs. Elmer's ultimate glue
 

What kind of release fabrics are you talking about, because from what I have read I thought it was only used when it cures in a vacuum, or vacuum bag. Kinda like when they make huge carbon fiber parts.

Re: 15 min. epoxy vs. Elmer's ultimate glue
 

At first I thought release fabric was like glass mat or kyntex. However, I was wrong. I used this to help explain what release fabric is.