My Other Current Build

[jqavins]

[The 4" Iris] is the one that was going to be, and I considered reconsidering and sat on the fence. Then the kit arrived and I held a half heard up against a fin from the kit, and it looked at least a third smaller. So stock it is. I'll use the half hearts for something else. Stay tuned for another build thread starting tonight.

In December of 2022, I was gifted a kit for my birthday, something with a 54 mm airframe and a 38 mm MMT, made with phenolic tube, from LOC (PML). I've forgotten what the kit is. I began building right away. (I may have an unfinished build thread out there; sorry.) When I got to the point of glassing the tube, because that stuff has a reputation for being brittle, I stopped, because I've never done that and didn't want to mess it up, and didn't have the material. Of course, I should have just ordered the material, practiced on some scrap, then gone for it, but fear of failure held me back.

Later in December, I was gifted for Christmas with some fiberglass chopped fiber, polyester resin, and tools. But I needed cloth, not chopped fiber. Still I sat and did nothing.

Now, over a year later, I want to fly that rocket at NYPOWER, which is under a week away. I ordered some FG fabric along with the Iris kit, and tonight I'm going to try out the fabric and resin on some scrap tube, then (I hope) glass that kit's tube.

New problem: I have the partially built kit in hand, but I cant find the fins. solution: I have those half-hart fins that I'm now not using on the Iris, so I'll use them on this.

Expect an update tonight or tomorrow about how the glassing goes.

 

[jqavins]

My test sample is curing (I hope). I mixed up way too much resin per the instructions, though I had to look up the density of the hardener; they give a resin quantity by mass and a hardener fraction by volume. Who are these people?

So, I looked at the hardener bottle in order to look up the density. So, what is it? Methyl Ethyl Ketone Pero... EEK!


I've also realized that I may be missing some other parts from this kit, so I have to go and search a lot harder. Or figure out something I can do with the parts I have on hand. This one may not happen for this weekend.

 

[tsmith1315]

they give a resin quantity by mass and a hardener fraction by volume

I always mixed polyester resin by eyeball. It’s less critical than epoxy. About the same proportions as Bondo resin:hardener. For a faster cure, use more hardener. But too little and you won’t get a cure. The “partly sticky not quite ever cured” only happened to me once. A squirt of MEK in a small Dixie cup of resin was my ballpark.
Adjust your amounts accordingly after the test cure. One word of caution, as soon as you feel the resin consistency change, stop working it. It goes off quickly and you’ll make a mess trying to continue.

 

[jqavins]

After 20ish minutes (maybe I should have noted the time when I left it to cure? Y'think? Learning here.) I went and checked. The large excess had kicked nicely in the cup, and came closer to melting through it that I'd like (learning, right?) and had also had time to cool. So I took the tight cling wrap off the test piece (a BT-55 or so coupler) and it was at the leather stage. I trimmed the excess off the ends, and it looks pretty good. But it's tacky. Of course, I had the sense to wear gloves when I was mixing and laying up, but not when I checked and trimmed it, so there was some on my hands. Acetone took it right off, so I learned that too. I'll see how it is in another hour, and if it's still tacky then, I'll see how it is in the morning.

 

[jqavins]

I always mixed polyester resin by eyeball. It’s less critical than epoxy. About the same proportions as Bondo resin:hardener. For a faster cure, use more hardener. But too little and you won’t get a cure. The “partly sticky not quite ever cured” only happened to me once. A squirt of MEK in a small Dixie cup of resin was my ballpark.
Adjust your amounts accordingly after the test cure. One word of caution, as soon as you feel the resin consistency change, stop working it. It goes off quickly and you’ll make a mess trying to continue.

The instructions for 125 grams said 1% by volume, but there's a chart - pints to oz - for 3/4%, 1%, 1.5%, and 2%. I started the calculation with 1% by volume, the s.g. of MEKP is 1.17, so that's 1.17% by mass, and I rounded up a little. If it's still tacky in the morning then I'll shoot for 1.5% next time.

 

[jqavins]

Now it's only ever so slightly tacky, and not coming off on my hands.

 

[jqavins]

This morning it's good and hard. I'm not sure whether there's tackiness or I'm just feeling the roughness.

Tonight I'll turn the rocket desk area upside down looking for a bag with the missing parts.

 

[lakeroadster]

This morning it's good and hard.

​

 

[jqavins]

​

You are one dirty, dirty old man.

 

[jqavins]

I haven't updated in a while.

Tuesday: I found the bag with all the remaining parts, including the 1/8" fiberglass fins. The kit is a PML IO, now complete with instructions. I contemplated the remaining time until NYPOWER and decided to go stock, kicking the half hearts down the road to another build for the second time in less than a week. Oh well.

Next, I smoothed the edges of the fins with 120 grit sandpaper (yes, I wore a mask) then washed them and prepared to epoxy them in. Mixed up a little epoxy then noticed that one of the slots was partially blocked by epoxy that had smeared when I inserted the motor mount. Cut it out real quick with my pocket knife (a stiffer, tougher blade than an exacto) but a fin still wouldn't go in. Tried cutting more then remembered that I had seen my pack of needle files on the rocket desk recently (I have no idea why they were ever left there) so used one to get the slot fully open. Checked the other two, and one of them needed a little bit of help. All in all, no more than ten minutes. The 30 minutes epoxy was hard in the cup. It was a hot day for Spring time, low 80s, so I expected it to go quickly, but not that quick.

So, I mixed up some more and got the fins in. Then had dinner.

Remember a few years ago when I commented that I see virtually no use for original, foaming Gorilla Glue in rocketry? And remember a few months ago when I asked people how important they think foaming a fin can is, and most agreed that it's really not? Well, after dinner I used original Gorilla Glue to foam the fin can. I had wanted to do internal fillets, but doubted I could reach in well enough to make fillets that would be worth much. so, I dampened the spaces the drizzled in some Gorilla Glue and let it sit for a while. I didn't know how much to to drizzle in, so I probably only filled the cavities half way; it'll have to do. The external fillets will be good.

Once I was sure that the foam wasn't going to overflow the cavities, I mixed up another small epoxy batch and put in the aft centering ring and engine retainer as a unit. But (stupid! stupid! stupid!) I neglected to cover the threads. As I tried to add epoxy to the small space around the motor tube and on top of the base of the retainer, not five minutes after mixing that epoxy, it was already rubbery, sticking to the mixing stick that I used to get it into place, and made a mess. I put the bottles of epoxy resin and hardener in the fridge and called it a night.

Thursday: I was tired. Really tired. I went to pick up a couple of prescriptions and couldn't remember my phone number. The next step for the IO is glassing tube, a process I've only tried once and that on a little test piece. I decided that in my fatigued state I was much too likely to make mistakes, so did not proceed. I thought I would take one of those needle files and chip the epoxy out of the retainer threads, but crumped out and didn't even do that. I did pick some epoxy gobs off the fins and body tube (easy because it had gone rubbery before hitting).

Time is running short, but I still think I can make it. I have the day off from work tomorrow and, depending on how things go tonight, I might punt what I have planned and finish the IO instead.

 

[lakeroadster]

Joe, Pictures are worth a thousand words.

 

[jqavins]

Yeah, I've been negligent in that too. I'll try to get some tonight.

 

[lakeroadster]

Yeah, I've been negligent in that too. I'll try to get some tonight.

With all due respect, I'd suggest taking photos as the glue / epoxy is drying Wipe off your hand first though ​

 

[jqavins]

OK, here are pictures of the state of things before I start working tonight.





The first thing I'll do now is clean away the errant epoxy. Then, the plan is, I'll clean up the workspace enough to do the glassing of the tube, then I'll glass the tube.

After that, we'll see. I expect not to finish it tonight, but quite possibly tomorrow. And If I need Saturday, so be it; I'll launch it Sunday.

 

[jqavins]

Crumped out again. All I did was clean up the stray epoxy. Most of it was as easy as I'd hoped, and there was one difficulty that I more than half expected and was prepared for.

Everything on the tube and fins came off easily enough. I couldn't chip enough out of the threads to screw the retainer ring onto the base. So, what am I holding in my hand that I've been using as a pick? Well, by golly, it's a triangular needle file! So I chased the threads with that, and everything goes together just fine now.

Now I'm sure I won't be flying it tomorrow, but I still think I'll make it Sunday. And there's Monday, so I might even fly it twice.

 

[boatgeek]

I did a lot of work with polyester resins in college, mainly repairing boats. A few tips/comments:

They give you different catalyst percentages for different temperature/cure time/material thickness conditions. So you’ll use the bottom of the scale for thick layups where you want a long working time in warm weather and vice versa.

If you have the little blue medicine measuring cups, the DR scale works reasonably well as drops of catalyst for that quantity of resin.

Polyester resin doesn’t fully cure in contact with air. This is a feature for most boatbuilders since they can start laying up where they left off the day before without having to rough up the surface for a mechanical bond. 29 years ago, you could buy two kinds of resin: laminating and finishing. Laminating had no extra additives and wouldn’t cure on the surface. Finishing had some wax dissolved in that would rise and seal the surface. However, you would want to clean that wax off with acetone before gluing something else to it.

You know this already, but as I told my daughter when she was starting out with polyester resin, if methyl ethyl ketone peroxide doesn’t scare you, you need more chemistry classes.

MEKP will also decompose slowly, so your catalyst will get less effective over years. It may have an expiry date on it.

If you put enough catalyst in a solo cup sized batch of resin, it can catch fire. I have not done this, but I’m one degree of Kevin Bacon from someone who has. Recommend putting the mixing cup on a non flammable surface until it has gelled and is starting to cool off.

Epoxy resin, even cured, will prevent polyester resins from setting. Put epoxy on poly, but not poly on epoxy.

 

[jqavins]

Thanks, all good to know. Especially the polyester epoxy incompatibility.

For what it's worth, the MEKP has been in the refrigerator ever since I opened the box and saw the little bottle and read what's in it. The bottle is marked with a maximum storage temperature that I didn't know until Monday when I opened the box; dodged a bullet last summer, but it won't be coming close to the maximum anymore.

 

[jqavins]

Well, today I discovered (not for the first time) that I'm an over the hill fat guy. Helping set up for NYPOWER, I badly dehydrated an overheated myself. I have not touched the IO tonight, and I'm forced to admit that flying it this weekend was an overambitious goal, because I'm not 30 anymore. So it's on hold.

 

[loopy]

Well, today I discovered (not for the first time) that I'm an over the hill fat guy. Helping set up for NYPOWER, I badly dehydrated an overheated myself. I have not touched the IO tonight, and I'm forced to admit that flying it this weekend was an overambitious goal, because I'm not 30 anymore. So it's on hold.

Smart decision. It sucks to stand down, but it's better than making a bone-headed mistake because you can't focus, and end up crashing something.

 

[SolarYellow]

Acetone is absorbed through the skin with very little resistance and is pretty hard on the filter organs. It can also drag other chemicals with it, which I understand leads it to be used as a topical medication delivery system. Wear gloves.

 

[jqavins]

It can also drag other chemicals with it, which I understand leads it to be used as a topical medication delivery system. Wear gloves.

I've never heard that about acetone. Are you sure you're not thinking about DMSO?

 

[lakeroadster]

I've never heard that about acetone. Are you sure you're not thinking about DMSO?

Make-up artists use acetone to remove skin adhesive from the netting of wigs and mustaches by immersing the item in an acetone bath, then removing the softened glue residue with a stiff brush. Acetone is a main ingredient in many nail polish removers because it breaks down nail polish. It is used for all types of nail removal, like gel nail polish, dip powder and acrylic nails. https://en.wikipedia.org/wiki/Acetone​

 

[Back_at_it]

Liking the IO build so far. I recently rebuilt mine. If you haven't already done so, consider leaving out the piston ejection system and replacing it along with the unnecessarily heavy shock cord with something a lot more reliable. The piston system in these rockets are terrible.

 

[jqavins]

Great, now you tell me. No, the piston and heavy shock cord have been in place since I shelved it over a year ago.

 

[loopy]

As long as you make sure the piston slides freely when you load it up, it will be fine.

 

[Back_at_it]

As long as you make sure the piston slides freely when you load it up, it will be fine.

You'll need to make sure it's extremely clean every time. Also, don't let the rocket sit in the sun as the piston material expands faster than the body tube and it gets stuck.

 

[jqavins]

Clean it after every flight, keep it in shade, test the movement with every prep; got it. And maybe some dry lube (graphite powder). And maybe some dog barf under it to help with cleanliness, or do you think that might jam up the works?

 

[Back_at_it]

Clean it after every flight, keep it in shade, test the movement with every prep; got it. And maybe some dry lube (graphite powder). And maybe some dog barf under it to help with cleanliness, or do you think that might jam up the works?

I wouldn't put anything under or on top of it. It needs to move as freely as possible.

I've owned two of these rockets. Both came to me built from someone elses collection and ripped the piston out of both of them.

 

[loopy]

You'll need to make sure it's extremely clean every time. Also, don't let the rocket sit in the sun as the piston material expands faster than the body tube and it gets stuck.

In this case, I don't think the expansion rates are as big of an issue as it would be with a Quantum tube rocket since it's a phenolic body tube.

 

[boatgeek]

I've never heard that about acetone. Are you sure you're not thinking about DMSO?

This is one, though there are no doubt others.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7761092/