Two - part foam questions

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AfterBurners

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Just finished my PML Bull Puppy and putting on the final finishing construction touches. I would like to use two-part foam epoxy in the fin can to strengthen the fins. I figure it would a lot easier than trying to do internal fillets.

A few questions

How much weight does the foam add?

I was told to put external fin fillets on first before using the two part foam because it will expand through whatever openings you may have.

What is the work time?

Do you mix it up without water and then pour and add a couple drops or do you mix the parts with water and then pour?

I never used it before so that's why I'm asking? I don't want to make a mess.

I'm also going to build it per instructions with the piston ejection. Has anyone ever built one of these kits with the piston? Did you CA the piston and sand smooth or just leave it as is? I noticed the nose cones fit really tight so I ended up sanding it with 100, 150 and smoothed it out with 220. Fits much better now but it took the better part of a couple hours to get it right. When I pick up the rocket from the nose cone the tube will slide out so I'll need some tape for a slightly snug fit. When I sanded the nose cone I didn't have the rest of the rocket together so that why I may have slightly over sanded it.
 
Are you using the PML foam? The weight it adds depends on how much water you add (to make it expand or not). More water= less dense overall.

If you haven't used the foam before, try doing it into a cup first to test to see how fast it moves, before pouring it into a rocket and making a mess. You'll waste some foam this way, but trust me, it's a good idea.

If it's the PML foam, the work time is probably 30-45 seconds. Once you mix it, you have to move fast. I added water to one of the parts (part A) first before mixing. Afterwards, you don't really have the time to mess around.
 
When I do it I use a helper who holds the rocket. I measure the 2 parts in individual cup and then I put one in the other, mix few seconds and then poor right away in the tube. Do try to clean the overflow, do it when it dry after, it's easy to cut when dry.
 
When I do it I use a helper who holds the rocket. I measure the 2 parts in individual cup and then I put one in the other, mix few seconds and then poor right away in the tube. Do try to clean the overflow, do it when it dry after, it's easy to cut when dry.

My concern is making a mess and adding too much weight to the aft section. Maybe this is something I should try on a scratch built rocket just to get an idea for how much weight it will add etc...
 
A few questions

How much weight does the foam add?

Not much, depends on density, which is determined by how many drops of water you add.

I was told to put external fin fillets on first before using the two part foam because it will expand through whatever openings you may have.

Good idea.

What is the work time?

Pretty quick, if it starts foaming in your mixing cup, it's too late!

Do you mix it up without water and then pour and add a couple drops or do you mix the parts with water and then pour?

Mix a couple of drops of water into part "A", then mix them together.

I never used it before so that's why I'm asking? I don't want to make a mess.

Good luck with that, I have never done it without a mess... Tape off anything you don't want it to get on or into.

I'm also going to build it per instructions with the piston ejection. Has anyone ever built one of these kits with the piston? Did you CA the piston and sand smooth or just leave it as is? I noticed the nose cones fit really tight so I ended up sanding it with 100, 150 and smoothed it out with 220. Fits much better now but it took the better part of a couple hours to get it right. When I pick up the rocket from the nose cone the tube will slide out so I'll need some tape for a slightly snug fit. When I sanded the nose cone I didn't have the rest of the rocket together so that why I may have slightly over sanded it.

Don't add tape until you're at the launch. Temperature will affect the fit.
 
My concern is making a mess and adding too much weight to the aft section. Maybe this is something I should try on a scratch built rocket just to get an idea for how much weight it will add etc...

it will add the weight of the 2 parts. The more drop of water you add the more light it will be but it will be less strong also.
 
Hint:
Put foam bottles in the frig. for 20-30 minutes before using. This will increase your pot life dramatically!
This stuff is extremely temperature sensitive...above 70 degrees it's pot life is only 30-40 seconds.....above 80, you better be quick.

Cooling it before mixing will get you 1 minute or more pot life!

When finished, squeeze all excess air from bottles, then replace caps. Turn upside down to coat/seal lids, briefly then store right side up. This will greatly increase shelf life.
Since it's moisture cure, removing as much air as possible helps greatly......especially in humid climates or on humid days.
You guys living out West where it's dry need not bother.
 
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Wow the rocket is looking great, you are gong to love flying this one.

I have the same rocket and used the PML two part foam, here are some tips:

- No issues on the weight, I do have a nosecone alt bay so some additional weight forward but I have never had any stability issues, can't recall the caliber right now.
- Don't try to change the to save weight density, I have had mixed results with this and you could end up with a mess inside that you now hove to scrape out, and if you do only add a drop or two drops etc.
- When foaming, make sure you have everything prepped and dry run it in your head first, tape everything off and don't try to pour it in one go, mix a small amount until you get a feel for the expansion then do the other layers.
- The boat tail on the PML will want to expand with the foam so having your external fillets on first will help keep things in-line.
- When I mix foam I pour one amount first on a scale set to 0, close and move that part away, then mark down the weight reset the scale and pour to match it. Organized is the key
 
The website says it has a 6lb per cubic foot density. That means a cubic inch weighs 0.0555555 ounces (96oz/1,728 cubic inches). Assuming straight BT(Tailcone changes this) of 3.0" ID and MMT of 1.6" OD, you have a cross sectional area of ~5 square inches. That means that for every linear inch of space you fill with foam, you add .2777777 oz of weight. Their website says that adding 4 drops to a mixture of 20ml of each component makes it increase from 10x to 25x expansion. If you did that, you would have a weight gain of 0.1111 oz per linear inch. But it would not be as strong as if you added no water. Does this help?
 
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