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sanding after peel ply

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AP aroma

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Hi techniques forum,
I'm new to rolling my own airframes. I'm wondering how much sanding you folks who roll your own body tubes do. Peel ply leaves a textured finish. Do you sand the surface to clean it up, or do you fill the surface to smooth it?

Thanks in advance-

Jim
 

rharshberger

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Hi techniques forum,
I'm new to rolling my own airframes. I'm wondering how much sanding you folks who roll your own body tubes do. Peel ply leaves a textured finish. Do you sand the surface to clean it up, or do you fill the surface to smooth it?

Thanks in advance-

Jim
If not bonding another layer, sand then finish is my M.O.
 

G_T

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I'd recommend looking into the perf-sheet. I forget what it is called. Smooth plastic with lots of pinholes. Like Peel-ply, it will allow evacuation of some excess epoxy. Wrap with perf sheet. Wrap with paper towels. Apply a compression wrap. If your paper towels get soaked you used way too much epoxy. You get the picture.

Peel ply is generally not to be used in structural applications. When peel ply is removed, it leaves lots of surface micro-cracks that go down below the obvious surface and weaken the layup, as well as cause nucleation sites for future failure.

I wish rocketry people weren't so enamored with the stuff. It isn't good to use for many of the things it is being used for.

Gerald
 

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G_T

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https://www.cstsales.com/peel-plies.html Just a quick link I found in about a minute.

Note, proper layup work minimizes the excess epoxy that needs to be evacuated from the part. If you are sloppy in your layup practices, the perforated sheet is going to need lots of holes, somewhat larger!

I wrote in the sticky some suggestions on how to do a layup, from fabric orientations to techniques. But for the TL;DR crowd, changed slightly for those who might be trying to make tubes or do T-T:

1) Prepare all material beforehand. NEVER touch the fabrics with your hands. Clean all surfaces where you want a chemical bond with a non-oily cleaner. Denatured Alcohol is a good last step.

2) Have a checklist and rehearse the procedures. That way you'll find out that you wanted some item at hand before you actually need it!

3) Have spares of things like gloves, brushes or rollers, etc.

4) Mix a small batch of laminating resin and mix in enough cabosil to get it to start to thicken a bit. You are trying to make a thicker mixture but not a paste! You just want it less runny. If using an epoxy system with multiple choices of hardeners, use a hardener or blend of hardeners for this batch that cures a little faster but still gives a good working time.

5) Paint your layup surfaces with a thin layer of this stuff. Give it time to start to thicken up a bit more afterwards.

6) Put first layer of DRY fabric on your epoxy dampened surface. If you did it right and timed it right, it will sort of stick. Not stick well you understand, but enough to make it a LOT easier to work with!

7) Use a 2" wide section of paint roller on one of those short roller handles, where the FOAM is as thin as you can get it - 1/8" thick is great. I saw up wider rollers to make the short pieces. Cheaper that way. Starting with the roller dry, roll the fabric smoothly down onto the epoxy cabosil mix. Start from the middle of the fabric and roll out from there to the edges. Roll in the directions of the fibers not at an angle. This will get it stuck down and leveled out, without introducing distortion.

8) Second batch of epoxy, with longer cure hardener. Put on plastic picnic plate. It should make a SMALL pool. You are not working with large quantities here. Pick up some with the edge of the roller, roll it on a cleaner section of the plate to make it uniform (DON'T swim it in the pool!).

9) Now roll from center of fabric out towards the edges getting the fabric uniformly damp. Pick up more epoxy as needed during the process. You don't want the fabric wet usually, just damp. You can judge by color when working with glass. You can give the "finger" test when working with Kevlar and similar Aramid fabrics - Press glove fingertip on layup and pull away. If it leaves a damp ring you have it right. If it leaves a wet spot you are using too much epoxy. If it doesn't leave a ring you are not using enough. Carbon fabric is the kicker though. That is much harder to wet out uniformly and much harder to judge. If you don't have experience with other fabrics, I recommend avoiding until you have a little bit of experience.

10) Now take the next DRY layer of fabric and stick it down onto the layup using a fairly DRY roller. If your epoxy roller isn't pretty dry, use a fresh dry one. You don't want to trap bubbles! That's the whole point of putting dry fabric on damp layup.

Etc. Make up new small batches of epoxy on the fly as needed. You only need cabosil in the first batch. Multiple small batches are much better than making up a big batch and putting yourself under serious time constraints. Note it helps to have two people for some layup work. Things tend to go much smoother.

If you make a layup this way, then you don't have huge gobs of excess epoxy to squeeze out. The layup should look on the dry side before putting on your release film and compressing. I tend not to add additional epoxy on the last layer of fabric, but roll it out to uniform dampless with a fairly dry roller and a bit of pressure. If the material is something like Kevlar, then I roll with a lot of pressure using a hard rubber roller to squish down and spread the tows. Regardless of type of layup, typically I'll put a layer of paper towels down and roll them on with a dry roller. Then remove and discard. If they came out wet rather than slightly damp, do it again. Only after that do you put on your release film and apply whatever form of compression you'll be using.

Gerald
 

rocketcharlie

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Wow. I thought peel ply was the way to go but it sounds like I have been thinking wrong. It certainly does leave a surface that requires a lot less sanding. If anyone knows the name of the "perf sheet" Gerald mentioned please post.
 

Zertyme

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Wow. I thought peel ply was the way to go but it sounds like I have been thinking wrong. It certainly does leave a surface that requires a lot less sanding. If anyone knows the name of the "perf sheet" Gerald mentioned please post.
It is called "Perforated release film".
You can find the different types of perforated release film: P, P1, P2.... Each one of them has a different hole diameter and spacing.
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By using different kinds of release fim, you can control the amount of resin bleed.
 

SDramstad

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I have been using peel ply for years on airframes with no issues. I dont think the "weakening" is going to affect you unless you are really pushing it. Below mach 2 or so I dont see any problems using it.
 

rharshberger

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Wow. I thought peel ply was the way to go but it sounds like I have been thinking wrong. It certainly does leave a surface that requires a lot less sanding. If anyone knows the name of the "perf sheet" Gerald mentioned please post.
just make sure the perf film is shipped ROLLED not FOLDED, the wrinkle from folding is nearly impossible to remove. I use peel ply as its easier to work with and I am not pushing performance envelope with most of my rockets.
 

G_T

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Same rule on fabric really. Don't fold the maps! (quote from a movie if you didn't get it)

Gerald
 

REK

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I'd recommend looking into the perf-sheet. I forget what it is called. Smooth plastic with lots of pinholes. Like Peel-ply, it will allow evacuation of some excess epoxy. Wrap with perf sheet. Wrap with paper towels. Apply a compression wrap. If your paper towels get soaked you used way too much epoxy. You get the picture.

Peel ply is generally not to be used in structural applications. When peel ply is removed, it leaves lots of surface micro-cracks that go down below the obvious surface and weaken the layup, as well as cause nucleation sites for future failure.

I wish rocketry people weren't so enamored with the stuff. It isn't good to use for many of the things it is being used for.

Gerald
I have done research on peel plys a while back ago. There are different versions of peel ply that do cause bonding issues. Nylon with silicone of course is one of those peel plys as mentioned in the artical that another member posted on here. The other is the PTFE peel ply or the fiberglass teflon coated peel ply.

There are other peel plys that do not leave behind micro cracks on the surface as you have described and promotes better mechanical adhesion. Some are even nylon based, but are not treated with a chemical like silicone that causes these issues.

If all peel plys were bad, Jim Jarves’s carbon rocket fins would have ripped apart at Mach 2+. I believe though the one he uses is the polyester based peel ply, which is the better one to use.
 

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