Aaron's Progress (chapter 4)

[Air-Ron]

Hey All -

 

After a hiatus, I'm back on track. I completed the seatback before getting lazy, but I'm not sure about the quality of the part. I tried the Plastic Pressure ply, but I think I may have left too much epoxy on the front. It was hard to tell, so I was more aggressive on the backside. Way too aggressive. I'm torn between remaking the part and sanding off 75% of the backside and doing the proper repair. (probably the latter)

 

Anyway, my question here is concerning F22, which I layed up last night. I started with the forward face instead of the aft face so I could weight it down with a large piece of MDF.

 

I tried to trim the part with the Fein tool, and as it cut, gummy stuff got all over the blade. okay, NOT fully cured. I did the scratch test with the cup. The scratch came out white, but the epoxy was sticky as well. I tested the epoxy ratio, and it came out to .379. It is cool here in tulsa right now, even with the insulated shop, so I figure I'll be building a heat tent before more cure.

 

I'm also pretty sure I didn't squegee enough through the plastic, but I'm not exactly sure how to identify this on a layup that was peelplied and plasticplied. I'll post pictures tomorrow.

 

I'm starting to wonder now whether i should investigate the LoVac technique. I imagine that this would make it easier to avoid overly wet layups (without the vast expanses of white I found on the seatback), but it could be that I just need more practice. There aren't a lot of composite builders in my area, so it's hard to get good feedback.

 

okay, enough rambling... Pictures to come tomorrow.

 

Aaron

[rickh]

It is cool here in tulsa right now, even with the insulated shop, so I figure I'll be building a heat tent before more cure.

I'm working in a cool shop too, I double my cure times. As in 'bubblegum' stage is in the AM whenever, not exactly two hours later. 48 hours and the parts are rock hard (a bit brittle actually), then I bring them upstairs near the wood stove for a week or more. I did for the bulkheads anyway. Maybe I'll post cure in the summer, bag the parts in black plastic, and out in the sun...

I'm also pretty sure I didn't squegee enough through the plastic, but I'm not exactly sure how to identify this on a layup that was peelplied and plasticplied.

The times I did this, I got a little air that sucked back in at the edges. It looks kinda spider vein like. With plastic on top, you can squeegee the beejeebies out of the layup, but go lighter near the edges. The epoxy will flow back to a point, avoiding the air suck-back-in at the edges. IMHO.

 

Squeegee lightly in a warm shop, a bit heavier in a cooler one. Depends on the viscosity of the epoxy from what I've found. A hair dryer (not a heat gun) helps a bunch! It also shortens the cure time.

 

I've been told that the micro slurry in the foam may bleed back into the glass-epoxy layup with excessive squeegeeing, making parts look a mottled white deep down. Further reading, I think my slurry is too thick, it's not fully flowing into the pores of the foam. Even though I squeegee the beejebies outta it before laying the glass on.

I'm starting to wonder now whether i should investigate the LoVac technique.

I tried this in demo mode much earlier, as well as for the electrical channel plug(s) I made today. It works, but takes up a metric boatload of time to setup for a borderline better part (IMHO). It does have it's place, but I'd recommend getting a stronger suck machine for production work.

 

Rick

[Kraig]

My recomendation at this stage of the game is to just build parts like the plans say. Forget about the vacumn bag stuff until later, it really won't make 5 lbs. of differance later on. Most people won't be bagging the big parts anyway, and that is the only place I could see saving any major weight.

 

The plastic technique is good, and easy to learn, but wait a bit till you get parts coming out right the first time. I have said many times before that we all get so worried about over-wet layups early on that we end up with a bunch of dry layups to do over and waist time and material. Just make the layups as best you can and error on the side of too wet. The part will be correct the first time with no bubbles or dry spots, you will move on to the next part, and so on. Before you know it, your parts are coming out just right, not dry or heavy, and the chapter's will go by quicker.

 

Now this advice comes from someone who bought my little Medo pump with my first order of foam. I dinked around with it in chapter 4, some with and some w/out success, I even got good at it. Do these parts look any better than my fuselage sides, my hoop layups, my my entire canard, or the main spar? Absolutely not. By staying with the good technique I have developed early on, my layups all look great now and I have not wasted any time. And none of them are epoxy heavy now, it all comes with practice, ie... lots of parts.

 

I still bag some small stuff, and will more as the plane progresses, but I would call these advanced techniques, and to concentrate on the fundamentals in chapter 4.

 

Good luck,

 

Kraig

[macleodm3]

Do not use any lo-vac techniques now. You need to learn plans layup method NOW, and the Lo-vac will only cause trouble at this stage.

 

Leave your initial layups (bulkheads) a little wet... its better than dry. You will quickly learn what just right is.

 

Plastic peel ply is fine, or regular peel ply. Don't trash seatback unless its totally junk. Post pictures if you're not comfortable with it.

[TMann]

Counter Point:

I vacuum bag everything I can. The motivation isn't so much about saving weight (although that is a wonderful benefit) but instead it is about producing quality parts. I really don't think it takes any additional time to speak of.

 

Get the setup right and the rest is simple.

 

Vacuum bagging does not cost you time on your project. There are tons of thing that do cost you time ....... but in order to blame it on vacuum bagging, you would have to actually be working on your project.

[Lynn Erickson]

Do not use any lo-vac techniques now. You need to learn plans layup method NOW, and the Lo-vac will only cause trouble at this stage.

 

Leave your initial layups (bulkheads) a little wet... its better than dry. You will quickly learn what just right is.

 

Plastic peel ply is fine, or regular peel ply. Don't trash seatback unless its totally junk. Post pictures if you're not comfortable with it.

I agree, Go back to the basics and do your layups by the plans at first. do some flat layups on the table covered with release tape if you want to practice. the layup won't be wasted as you will find many uses for the flat glass as tabs and supports as you build. wet is better then dry. even if you made all the layups wet I doubt you could add 1 gallon of resin to the entire plane but if you did it would only be 10 lbs. heavier. likewise if you vacuum bag everthing the most you will save is about 10 lbs. vacuum bagging does add time and money to the project, especially if you are hard shelling first before you do a layup, this is one unneeded step and if done on all the layups is a lot of extra time spent.

[Air-Ron]

Fair enough! I'll hold off on the fancy stuff for now. I will be picking up some heat tent supplies on the way home, though. While I was writing last night's post, I had my shop heater on next to the table, with a fan pointed over the layup. I turned off the heater before going to bed, but the layup seemed dryer in the morning. The residue in the cups still seemed a little sticky, which makes me nervous. Even with nearly all slow hardener and a somewhat chilly shop, (the shop heater gets things up to 80 or so while I'm working, and then it cools off overnight) MGS 335 shouldn't be sticky after 30 hours, should it?

 

aaron

[Big Steve]

If your temperature is below 40* It might never get hard. Take it in the house put it on the table where it is flat and make sure your house is at least 70* If it does not get hard over night you have a problem with your resin ratio or something to that effect. Get yourself a Little heater and some plastic or carboard cover your layups over night my shop gets in the 30's all the time. I use a heater in a box or something to that effect. My parts are always hard when I come out the next moring. Get a Black and Decker heat gun at Lowes for about $30.00. Use it to wet out your epoxy in a cold shop. I went through 3 chineze heat guns before the black and decker it works great and has variable heat. If you cant make a part the plans way I doubt if you can have succes vacum bagging. Learn how to do it the Rutan way and when you get good at that then learn how to vacum bag. You have to walk before you can run. Here is a picture of how I cured a part I was working on behind the front seat.

 

[Kraig]

Dang Steve,

 

Did you clean your shop too?

 

Kraig

[Lynn Erickson]

Fair enough! I'll hold off on the fancy stuff for now. I will be picking up some heat tent supplies on the way home, though. While I was writing last night's post, I had my shop heater on next to the table, with a fan pointed over the layup. I turned off the heater before going to bed, but the layup seemed dryer in the morning. The residue in the cups still seemed a little sticky, which makes me nervous. Even with nearly all slow hardener and a somewhat chilly shop, (the shop heater gets things up to 80 or so while I'm working, and then it cools off overnight) MGS 335 shouldn't be sticky after 30 hours, should it?

 

aaron

It will set hard, it may take several days in cold weather. the resin will harden even in the freezer. many of my layup were done with the hanger door open and the sun shining on the part as I did the layup. and the shop would cool to 40 at night but in a few days it would set hard. do some of those practice layups and get use to the way the resin system works. the time spent learning now will save you time later

[Marc Zeitlin]

It will set hard, it may take several days in cold weather....

You need to be careful with letting curing epoxy get cold, though. SOME will cure OK as Lynn says, even when cold, but just take a lot longer to do so. But others will merely go into "B" stage, feel hard, but not be strong - they'll be brittle and weak.

 

To be safe, unless you're absolutely sure that the epoxy you're using won't just go "B" stage on you, but will still truly "cure" when cold, you should keep your layups warm (above 60F, really) until they're cured.

[argoldman]

You need to be careful with letting curing epoxy get cold, though. SOME will cure OK as Lynn says, even when cold, but just take a lot longer to do so. But others will merely go into "B" stage, feel hard, but not be strong - they'll be brittle and weak.

 

To be safe, unless you're absolutely sure that the epoxy you're using won't just go "B" stage on you, but will still truly "cure" when cold, you should keep your layups warm (above 60F, really) until they're cured.

One way to find out is to call the manufacturer of the epoxy. They will have the real sticky.

 

The chilling of epoxy is not a subject to go into blindly:cool2:

[WileEZ]

Looking at Air-Ron's icon, I get the feeling he's building his canard the hard way!

[Air-Ron]

You need to be careful with letting curing epoxy get cold, though. SOME will cure OK as Lynn says, even when cold, but just take a lot longer to do so. But others will merely go into "B" stage, feel hard, but not be strong - they'll be brittle and weak.

 

If it goes into the "B" stage, can raising the temperature (post curing) pull it out? Does anyone have experience with cold curing MGS 335? If I have to scrap this part, I should do it before I glass the other side. :eek:

 

I will be sure to cure everything else in nice warm weather (or the heat tent)

 

Looking at Air-Ron's icon, I get the feeling he's building his canard the hard way!

One of my jobs is as the owner and chief instructor of a flying trapeze school. The pic is from my days teaching and performing full time. If anyone happens to be coming by Tulsa, OK in the summer, I'd be happy to give them a lesson!!!

 

Aaron

[rickh]

If it goes into the "B" stage, can raising the temperature (post curing) pull it out? Does anyone have experience with cold curing MGS 335?

I can't speak for MGS, I use Pro-Set in a 60-65F environment. Cures are 'bout twice as long, and somewhat brittle for several days.

 

The motorcycle bits I make from drug store epoxy can be forced the next day by placing in an oven @ 120-140.

 

Assuming your epoxy ratio was correct, might try placing an electric blanket over your part and turning the heat up. I made a heat tent (as have others) out of poly sheeting and a small electric space heater. Kent Hoit 2 try.

One of my jobs is as the owner and chief instructor of a flying trapeze school. The pic is from my days teaching and performing full time.

Hmmm, could be a unique way to tape the bulkheads in... avoiding epoxy drips on your head...

 

Rick

[Marc Zeitlin]

If it goes into the "B" stage, can raising the temperature (post curing) pull it out?

Sometimes. It depends on the epoxy. Some will require a substantial temperature raise for a long time, and some won't do it at all, while some just require coming back to regular curing temp (room temp). Depends on the epoxy.

 

Search the COZY mailing list archives - there might be something about this in there - can't remember.

[Air-Ron]

After searching the archives, I found an email from a MGS representative. To Paraphrase:

 

1) 16 Celsius (61 fahrenheit) is very low for cure

2) try for at least 20 celsius (68 fahrenheit)

3) Don't worry about cold cured parts - they will continue cure as temperature heats up

4) try to post cure everything

 

heat tent it is - at least until the 100 degree summers set in!

 

Aaron

[TMann]

heat tent it is - at least until the 100 degree summers set in!

.....or just get yourself an electric blanket.