Just remember, David, that the longer the curing time, the stronger the epoxy bond. 5 minute epoxy is fine for model rockets, but not strong enough for HPR, in some cases--especially with fins. That being said, West is among the best epoxies.

Just remember, David, that the longer the curing time, the stronger the epoxy bond. 5 minute epoxy is fine for model rockets, but not strong enough for HPR, in some cases--especially with fins. That being said, West is among the best epoxies.

I disagree. 5 minute is more than strong enough for the vast majority of bonding done in HPR, including fins. It's not ideal for all situations, but it does sound like a great product.

I've never used 5 minute for building, as I have always been a bit sketchy on it myself - and then one of the guys from PML told me that was all they had EVER used. Strange.

Does this stuff stink as bad as the basic HobbyTown stuff? Yikes, that stuff smells strong...

I didn't notice any smell. Sure made fin tacking alot easier, i mixed a small 24 grain batch for each fin, tacking all 3 in about 20 minutes with cofidence they were on straight. Seems to sand just like 205 and 206 too.

Having built boats and a fair number of all-composite rockets over the years, I feel I have a little background to make some comments.

Cure time has little to do with strength, although depending on the specific polymers involved, accelerated cure times can often result in poor-crosslinking and therefore a much weaker epoxy. All things being equal, the longer the cure time, the more fully cross-linked the polymer chains are and the stronger the epoxy bond.

As much of what I do is fabric layup, I prefer the longest cure time I can get. For much of the work I do with West Systems (my preferred epoxy for most things), I use the 209 hardener which gives 4-6 hours of working pot life in temps below 80 degrees. 206 hardener is my second choice with a pot life of from 20-40 minutes. 205 hardener kicks off much too fast for good layups unless you're working in cold temperatures (50 degrees or less) and in the 70's or 80's can kick off in 10 minutes.

The biggest problem with most epoxies when used in rocketry is the Td value - the temperature at which the polymers begin to soften from heat. I've seen black rockets soften just sitting in the sun at the North Site. Heatsoak from hot motor casings can temporarily weaken epoxies such as West Systems or Proline. For high temp applications I use JB Weld or Cotronics high temp varieties. Of standard epoxies, Aeropoxy has a higher Td value than most. However, the ease of use of West Systems (1 pump of each) means I will continue use it in preference to all others.

This new West Systems product uses a variation on their standard resin and a faster catalyst to promote cross-linking. However, it gets HOT fast.

Even for bonding, you can rarely go wrong with a longer cure time.

Professional epoxies typically won't cure at all without the application of heat - sometimes including a temperature ramping up/down protocol to ensure maximum strength.

Warren

as it flows well. Aeropoxy makes nice fillets. It does take a long time to cure.

But I build slowly, taking days to fillet a rocket as I can only do one set of fin fillets per night.

It takes about 6 hours to set up and 24 hours for a hard cure.

It does seem to do well, as I've had one rocket flat spin in without cracking the fillets. I actually did it twice. It was a GLR dynatube frame to boot. (Not my favorite -- I'm trying their Magnaframe at the moment...).

Aeropoxy is something I am used to. If you're a speed builder, try something else. Seems to remain hard in the heat too.

as it flows well. Aeropoxy makes nice fillets. It does take a long time to cure.

But I build slowly, taking days to fillet a rocket as I can only do one set of fin fillets per night.

It takes about 6 hours to set up and 24 hours for a hard cure.

It does seem to do well, as I've had one rocket flat spin in without cracking the fillets. I actually did it twice. It was a GLR dynatube frame to boot. (Not my favorite -- I'm trying their Magnaframe at the moment...).

Aeropoxy is something I am used to. If you're a speed builder, try something else. Seems to remain hard in the heat too.

I like Aeropoxy, too. I tend to be on the impatient side, so I almost always elevate the temperature one way or another to speed up the cure. In the winter, it's a space heater. In the summer I tend to build at night and then put the part on my dashboard the next day. A couple hours on the dashboard on a hot day and it's hard as a rock. Elevating the cure temperature also increases the high-temperature strength. From what I've gathered from the product literature, for best properties at high operating temperatures, you want to let the part soak with temperatures that are at least as high as your max operating temperature. For a black rocket in the sun, that can be 160F.

Hey guys,

West System 209 hardener I'll give that a try. I've been using 206 for my tubes and for fin fabric, seems to work great, and the pump set does come with a 209 pump which is doing nothing.

Warren, do you always use a vacuum method when doing the fins? I have not.

So far, I've just used the vacuum to make tubes and plate stock for fin material, which works fantastic. Idea stole from Adrian, I bought two slate tiles, then I lined them with Mylar, wet out fabric on Mylar, sandwich the two pieces together and wrap them in some breather material then the vacuum plastic.

I like Aeropoxy, too.

As do I, and it's all I've used. I have the patience, plus it doesn't smell. I've never had the bond loosen or get soft, even in extreme heat. Warren is definitely the West expert, hands down.

I should be out at the September launch - Oktoberfest most definitely. I'll show you some of my v-bagged layups. I typically vacuum bag everything I do. My specialty is v-bagged tip-to-tip reinforced fin cans integral with the airframe. My L3 project, The uprOar project of a couple years back, John Wilke's 30K plus North Site record flight, the bird John and Adrian flew at the July launch - all unitary, v-bagged layups. My L2 project 5 years ago was the first successful one and it landed without a chute (flat spin) from over 8000' and bounced. No damage to the fins whatsoever and so far no problems up over Mach 3+.

Making plate is easy, even without a vacuum bagging system. Just add weight - a LOT of weight - evenly distributed across the layup. Tubing is a bit different and depends on your mandrel material. Steel, aluminum or solid wood are all easy to v-bag. However, v-bagging around a paper or phenolic mandrel requires some fancy setup work to prevent collapsing the tube.

My plate layup system also works with v-bagging, but I generally don't bother. I have 2 laminated pieces of 3/4" furniture plywood that consist of a layer of 3/4" ply topped with another piece of 3/4" 90 degrees offset and then further topped with a layer of oak hardwood flooring. These were run through a furniture planer and a industrial belt sander to provide a completely flat surface. I have 2 of these blocks. I do the layup on top of a piece of 1/4" tempered glass with Mylar film between the glass and the layup, then top it with another piece of Mylar and another piece of 1/4" tempered glass. The glass-Mylar-layup-Mylar-glass sandwich goes between the wooden blocks and the whole thing gets screwed together at the corners to preserve alignment and then I just park my pickup truck on top of it. I figured the compression weight on the layup is about 50psi. V-bagging gives you at most about 14psi unless it is done in a pressurized autoclave.

I haven't done nose cones myself yet, but the technique is fully applicable to the standard parting-board method that Mick Kelly describes in the Composite Rockets Group on yahoo.

I have been known to teach classes in this technique. The key is pre-layup prep work, building the bag right and having enough hands to hold everything in it's proper place while the vacuum is pulled.

Warren

I wonder what the interest is in another class? I surely would like to participate, if one were available.

My main interest is in tip to tip reinforcing. I am also curious as to building carbon-fiber fin sets; though, machining/cutting them is a bitch.

Steve

I've had decent luck cutting G10 and CF with a jigsaw and a tungsten carbide blade. A dremel with a diamond cutoff wheel works too, but it's a lot harder to hold a straight edge with a dremel than it is with a jigsaw.

Hey everyone,

The principle behind vacuum bagging is that of using atmospheric pressure as a tool. At sea level, one atmosphere weighs 14.7 psi (pounds per square inch) or 29.92 inches of mercury. In the absence of a vacuum, a surface has atmospheric pressure exerted on all sides and is equal. When a vacuum is generated on one side only, the result is an increase of pressure on the other side equal to the amount of vacuum being generated. A one square foot area is receiving 2,116.8 pounds of pressure with a 29.92" Hg vacuum beneath it...

Since were in Colorado we can only achieve 25 Hg which equals 1768.71 pounds per square foot, I'd say its just a little heavier than the truck, its small truck, right? hehe 1768 x 4 wheels =7072lbs

I smashed a small metal can no problem when i was experimenting with a reservoir. I use glass now, Ball Aerospace canning jar which is really pointless, but makes me feel better, hate to ruin a free pump.

So yeah, gotta be careful how i word this, I'd love to see your rockets Warren. Yeah a class or watch you sometime working on your own stuff.

Yep, although you don't need anywhere near that level of vacuum to get decent compression. Even if you're left with a couple of PSI on the vacuum side, you'll still get quite a nice result.

(Oh, and it's definitely impressive how much force vacuum can generate. I'm working in the physics labs at CU this summer, and one of the things I'm working with has to do with high vacuum. The chambers we use are thick stainless steel, and they weigh an enormous amount)