Fibre glassing techniques

[north boy]

Hi Everyone, I've bought my first glass kit and fancy making a N.C out of a 75mm pvc one I have. I'm going to follow Tfish tutorial on the sticky on High power thread. He meantioned using peel ply in the process but I was wondering if plain Baking grease proof paper would do the same thing ? I think maybe just a simple Body Tube would be the first place to start as its a simple straight tube and if I can successfully manage a tube the N.C is next on the table for a try. Im keen to try this but its something I've never done but Tfish makes it look soooo Bloody easy yea right bet its NOT!!!

[GregGleason]

The main purpose of peel ply is to have a re-bondable surface. It also can help the curing of the surface resin. Bacon grease paper might make a great release surface, but may be poor in creating a re-bondable surface.

Materials that have been used are nylon and dacron (polyester), but this paper from McDonnell Douglas Aerospace called "THE CURSE OF THE NYLON PEEL PLY" (from 1996) echews the use of nylon.

See also this thread.

The layup process can be pretty easy. You will get better each time you do it. Understand that it is a process and you just follow the steps. Just allow adequate time. When I am in a hurry, I make mistakes!

One tool that I have found helpful on airframes is the laminating roller tool, suggested by stantonjtroy. It is like a miniature rolling pin that helps to wick up the excess epoxy off of the cloth.

Greg

[north boy]

The purpose of the peel ply in my case was to have a finish that is as smooth as possible like Tfish stated in the tutorial it reduces sanding massively. The backing paper is of a similar material from what I see but was wondering if anyone had used it for this purpose to save me the mistake of finding out the hard way

The project if I manage to get to grips of the fibre glassing will be for a 54mm motor rocket in the future but for now its a practice makes perfect senario. Ill possibly follow it up with a carbonfibre fin setup but thats in the future

[Aksrockets]

Peel Ply CAN give you a nice finish. It leaves a fabric-y texture in the fiberglass. Just go over it with some 180 and 220 sandpaper to get down the texture and paint as desired. Another smoother option is teflon coated peel ply from aircraft spruce. The texture takes hardly any prep work before priming.

Good luck!


Alex

[Tominator 2]

Peel ply is porous in nature to let the excess epoxy seep out. I dont think the paper you are talking about will do that. It would hold all the excess in creating more weight and less strength. It also keeps the layup in place.

[G_T]

Usually with composites, if you want a nice finish, you use a surface that gives a nice finish. Peel ply has a different purpose as has been pointed out. I'll be glassing some removable fins soon for a big project for LDRS. I'll be using typical vacuum bagging composites techniques.

The fins are 3/8" plywood, beveled at the leading and trailing edges. I'll be using S-Glass on them. The method I'll be using is as follows:

Sand and remove dust from the fin cores.

Make a strip of glass perhaps an inch and a half wide, for the case of my fins. This strip is cut on a bias - that is, the fabric is oriented on a diagonal. To make this strip, I will take a section of wax paper and very lightly mist with 3M77 spray contact adhesive. By lightly mist, I mean aim the can a foot or two over the top of the wax paper. Just let some mist settle on the wax paper. Then immediately take the wax paper, flip it over, and lay it down on the fiberglass. Brush it down into contact; it will stick. But it won't stick hard. That is the key.

One can mark out the cut pattern on the wax paper and cut the fabric with scissors. What I am making with the inch and a half wide strip is a leading edge and a trailing edge strip. I take each of these strips, and spray with 3M77. This needs more direct application of 3M77 but do not saturate the strip in this case. Of course, spray the fabric side of the strip.

Take the strip, and lay the center along the leading edge of the fin. Press it down along this line. Get a corner of the wax paper separated from the glass, and then literally rip it off quickly. Done right, the glass stays behind. Now take thumb and finger, and fold the glass over at the leading edge, then work the glass down to contact with the fin core.

Do the same for the trailing edge strip.

The purpose of these strips is to make the glass skin completely wrap around the fin. It should reduce the ease of peeling the skin off unintentionally...

Now make some fabric patterns for the fins and cut out the pieces of glass (or carbon or fabric of choice... I'm using S-Glass for mine but use whatever you think is appropriate for your application). If you think your core needs the most reinforcement in the bending direction, orient your fabric 0-90. If you think your fins need the most reinforcement in the twisting direction, orient your fabric on a bias (45 degrees). Cut out all your fabric pieces.

Now make some mylar sheets (or similar glassy somewhat stiff but flexible plastic) that have the size and shape of your fins. Make these slightly oversize - perhaps an eighth of an inch on the leading and trailing edges.

Wax these sheets on one side. Some waxes do better than others. Mother's carnuba wax works pretty well. Apply wax, DO NOT WAIT FOR IT TO DRY (a perpetuated myth) buff it out. Use a soft cloth and do not press hard. You are not trying to buff the wax off just polish it on. The surface you produce here is the surface the fins will have when done.

Now get a narrow paint roller, perhaps 2" wide. You want foam rolls, with the thinnest layer of foam you can get. This is the tool for applying epoxy uniformly.

You can save some money by purchasing the normal width rolls and sawing them down to 2" wide.

Mix up your laminating resin, for at least twice as long as it takes for it to become glassy clear. Most people don't mix well enough and the final mechanical properties suffer because of it. So mix it well.

Pour the epoxy out on a paper or plastic plate. Epoxy working time is somewhat a function of how thick the layer. The plate spreads it out to a thinner layer so it doesn't cook itself off as quickly or as aggressively.

Use the foam roller to pick up some epoxy. Roll a coat onto one of the mylar pieces - waxed side of course! It will not flow out but will instead bead up. This is fine.

Take one of the fabric pieces and lay it down on the wet mylar. Use the roller to roll it down. Work from the center to the outside. Never roll from outside the fabric onto the fabric, as that may pick up fibers from the fabric or even pick up the piece of fabric and wrap it around the roller. You can roll along edges and anywhere you want inside the fabric sheet. Roll from wet to dry. Dry to wet may move the fabric.

Repeat for all layers of fabric for that side of the fin. When you are done, you want the fabric uniformly wet out but NOT swimming in epoxy. If there are puddles, you need to roll off some epoxy. The roller can be used to remove epoxy as well as to apply or spread it.

Do the same for a second piece of mylar, for the other side of the fin.

Now take the fin core, and wet out the leading and trailing edge fabric.

Lay the core on one of the mylars. Pick up the other one, flip it over, and lay it on the core. Now we have a sandwich - mylar, glass, core, glass, mylar. Use some little pieces of masking tape to tape up a few spots along the edges to hold the mylars together around the perimeter.

This sandwich goes into a vacuum bag system. The vacuum sucks everything down into very solid contact, and the mylars give a glassy final surface. Since the fabric was wet out against the mylars, there should be no bubbles in the surface finish.

I'll skip all the details on vacuum bagging itself. You can research it if it is of interest. But realize you don't have to have expensive equipment to do it - a food saver can be used. I have the equipment though, so I've never done it with the food saver method.

But in rough outline, you need a bag on the outside of everything to hold the vacuum. Then between the bag and the mylars you need something to provide a path for air to evacuate the bag. This something is called a breather. Layers of paper towels work ok, felt works better, etc. Then there would be a strip of felt or a rope or something which provides a path from the breather to where the vacuum connection would be. With a food saver, that means the breather would go right up to just short of the edge where one would seal the bag.

Apply vacuum, seal (if applicable), and leave under vacuum until the epoxy has fully cured. Then ideally put at elevated temperature for a post-cure cycle. Only after all this does one peel off the mylars. The result should be like nice sheets of glass. The only sanding required would be at the edges, and only light cleanup should be required there.

I apologize for the length of this post. Perhaps it will provide some ideas for those less used to working with composites.

Gerald

[north boy]

Hi Gerald , thanks very much for taking the time for your post. Dont appolagize for the length as describing something so in depth can require full description as you've done. I'm going to have a go at it next week hopefully. For just now I'm going to try and get a bit of knowledge and an idea for products required. Tfish did it without the need for bagging and I dont have the gadgets to do this at this point so Ill be sticking with the way I seen on his tutorial and try to avoid purchasing to many tools

[T-Rex]

North boy,
Let me say from the start that I am not a fiberglass rocketeer. I have not worked with FG before. This is just the thoughts that came to mind while reading your thread.....

Practice with small pieces, potentially something you plan to throw away. Granted that is throwing away money, but then you will know if your thoughts will work like you think they will. Another option is just start small, try making a motor tube for a future project. Again, it will be small enough that you wont have a large investment of material if it fails. If it works, but it isn't pretty, well it's a motor tube, it goes on the inside anyway. Basically what I am saying is make something that isn't important as a trial/learning/practice run....

I hope this helps, and mostly I hope your project is a success

Terry

[north boy]

North boy,
Let me say from the start that I am not a fiberglass rocketeer. I have not worked with FG before. This is just the thoughts that came to mind while reading your thread.....

Practice with small pieces, potentially something you plan to throw away. Granted that is throwing away money, but then you will know if your thoughts will work like you think they will. Another option is just start small, try making a motor tube for a future project. Again, it will be small enough that you wont have a large investment of material if it fails. If it works, but it isn't pretty, well it's a motor tube, it goes on the inside anyway. Basically what I am saying is make something that isn't important as a trial/learning/practice run....

I hope this helps, and mostly I hope your project is a success

Terry

Thanks, i fully intend to do little bits to start off with but I just ordered 10 sq meters of cloth lol. Ill have pleanty to practice

[north boy]

I also was thinking about the centring rings and bulkheads and was wondering how you guys do them. I was planning on cutting 1/16 ply and sandwiching that between fibreglass as my way of building them. Then the fibreglass on them would be a good bonding point to glass them to the inner walls of the glass tubes I form. Is this over kill or an ok route to be taking ???

[north boy]

Ok I thought I could give an update on my fibre glassing skills...

I got my mylar type plastic round my madrel and went for it. Im using chopped fibre glass strand sheets which may be my first mistake as a woven cloth may have been a better option anyway I did a 70mm Bt setup and did 3 wraps of a 300 gram glass. My first 3' 6" tube came out ok ish but there was small imperfections on the tube when I took the peel ply stuff off. Some were quite deep holes. My second tube was much better but still not right so I did a 29mm Motor tube and loaded it totally with epoxy and wrapped it with epoxy and it was far better. so Is this where Im going wrong ???? Is it the epoxy that is the key to filling the imperfections ??

[troj]

Chopped strand mat is held together with an adhesive that dissolves in polyurethane resins. When you use epoxy, the adhesive doesn't dissolve, which may be part of why you're having difficulties with big holes.

Mat is also very rough, and will take a lot of epoxy, or other filler, to smooth it out. A fine-weave cloth will be better.

You'd be a lot better off, and end up with a stronger result, if you used cloth, instead of mat.

-Kevin

[north boy]

Chopped strand mat is held together with an adhesive that dissolves in polyurethane resins. When you use epoxy, the adhesive doesn't dissolve, which may be part of why you're having difficulties with big holes.

Mat is also very rough, and will take a lot of epoxy, or other filler, to smooth it out. A fine-weave cloth will be better.

You'd be a lot better off, and end up with a stronger result, if you used cloth, instead of mat.

-Kevin

Hi Troj sorry it is polyurethane resin that I have....just checked it....my mistake. Yes I agree I think the cloth will be worth a try. I got all the cut strand mat for about £13 so no major loss there but I will use it for certain projects. I seen 80gram cloth for sale is that about the same that you guys all use or should I be using something a bit heavier and also is poly resin ok for this application or should I stick with the epoxy. The poly Im using is good for up to 90 deg temp and Its just fine for the type of rocket Im building as its not going to be a high speed rocket

[troj]

I seen 80gram cloth for sale is that about the same that you guys all use or should I be using something a bit heavier and also is poly resin ok for this application or should I stick with the epoxy. The poly Im using is good for up to 90 deg temp and Its just fine for the type of rocket Im building as its not going to be a high speed rocket

80 grams is about 3 ounces; I'd call that a light cloth. What size tubes are you trying to make with it? Early in the thread, you referenced 75mm -- 3oz cloth is awfully light for that size tube.

Are you talking 90 Celsius or 90 Fahrenheit? It's a huge difference -- 90 C is about 194 F, which is quite different from 90 F.

-Kevin

[north boy]

80 grams is about 3 ounces; I'd call that a light cloth. What size tubes are you trying to make with it? Early in the thread, you referenced 75mm -- 3oz cloth is awfully light for that size tube.

Are you talking 90 Celsius or 90 Fahrenheit? It's a huge difference -- 90 C is about 194 F, which is quite different from 90 F.

-Kevin

Its a 70mm dia tube 3" and I was referring to 90 deg c Troj. I have no idea clearly with the fibre glassing weights etc and this is the first attempts I've had at fabricating my own stuff so I have a lot to learn, thanks for all the help.