Sanding Glass

[macleodm3]

Would anybody be able to post a picture of a fiberglass layup that has been properly sanded in preparation for additional layups or fill (layup that has not had peel ply)? Basically, I've got some areas on the outside bottom rounded corners of the fuselage where the peel ply did not touch the curing glass, and I'd like to have these areas sanded enough... but not too much, for the side layups. Thanks!

 

Andy

[TMann]

You should check out Wayne Hicks site for sanblasting.

If you use one of those home units from Harbour Frieght or Home Depot, they do a great job of roughing up the surface in a uniform fashion and actually do less damage than regular methods. Reason being, you don't damage the high level fibers trying to sand the low level fibers.

[Wayne Hicks]

Here's the link to my sandblasting diatribe. Although the page is about the benefits of sandblasting, the first few pictures will show you what the surface will look like when it's been prep sanded by hand. I'll leave it to others to judge if I did it correctly or not.

[macleodm3]

Sandblasting is fine for finishing, and I hope to give it a try. I am very familiar with Wayne's finishing sandblasting, but I never really considered it for use during the build. It seems like a lot of mess and setup for sanding small areas for a layup prep... but who knows?

[longezdave]

I'd suggest just sticking to the info in the education part of the plans. Page 3-12 says "To prepare a cured glass surface for layup, the cured surface must be sanded to a completely dull finish with 36 to 60 grit sandpaper. If any of the glossy surface remains, an incomplete bond results which is weak." Pardon me if you've recently read that and didn't need it re-stated. For the areas that Burt has designated as critical structure, you want to make sure to use peel ply well (no gaps where it doesn't touch) and avoid the sanding.

[argoldman]

One question that I have always had about sandblasting, and that is, --- is there any residue of the blasting medium remaining embedded in the epoxy substrate???

 

This would be important, less so in the finishing application since an ultra-strong bond is not critical, after all if the bond is not good, the worse that can happen is a flake or so chips off.

 

If, however a structural bond is weaker because of media inclusions, the result may be more catastrophic.

 

Has anybody looked into Dry-ice blasting. That stuff evaporates (actually the word is sublimate). I know that it is used for paint stripping, but will it etch composite?

[TMann]

One question that I have always had about sandblasting, and that is, --- is there any residue of the blasting medium remaining embedded in the epoxy substrate???

To my knowledge, that was not a problem when they used that method on the voyager.

 

I usually touch op the bonding areas with 60 grit .... even the areas that are peel plied.

 

I have sandblasted a few areas and it works great. I keep my sandblasting sand in large ziplock bags and use them as weights so the sand serves double duty.

[argoldman]

To the best of any body's knowledge, has anybody looked at the sandblasted surface with a binocular microscope or any high magnification glass?

 

I wold imagine, also that the type of medium, itself would have some effect.

 

In my microscopic mind's eye, I see millions of tiny stress concentrators (crack starters), each on a grain of sand or whaterver, where we might not want them.

[TMann]

Good point Rich. I would like to see a comparison of both techniques under a microscope as well as a comparison as to the strength of the bond created.

 

When I tried it, the sandblasted surface appears to be uniformly abraded whereas the hand or machine sanded part appeared to have more fiber damage on the high areas while the low areas were not abraded at all. The only way to create a uniformly abrated surface using the orbital or hand sanding technique would have been to continue sanding through more fibers resulting in additional damage.

 

As I recall, the voyager used peel ply followed by sandblasting prior to bonding to a structural surface.

 

That’s just what I had read/heard/experienced previously but I would suggest looking into making a couple sample coupons to see for yourself.

 

Most folks freak when you talk about sandblasting composites but the reality is those units sold at the local tool store are very managable.

[Wayne Hicks]

(1) The purpose of my sandblasting reply was just to provide the originator with a picture of what a prep-sanded area looks like when sanded by hand. Not to slight Burt or the plans, it is nearly impossible to sand the valleys completely dull. If you watch the Rutan composites video, you will see that not even Burt achieved a totally sheen-free prep sand. My picture looks alot like the one in the video.

 

(2) In my opinion, sandblasting is not practical for prep sanding for follow-on, structural layups. Too much mess for so little gain.

 

(3) Was said, "For the areas that Burt has designated as critical structure, you want to make sure to use peel ply well (no gaps where it doesn't touch) and avoid the sanding." I don't agree. The peel ply is to keep layups from delaminating from the edges. At least it says so in my Cozy Chapter 3 education chapter, that is as far as I know an exact duplicate of the Long-EZ plans with the exception that the "CP" bucaneer has been whited out and relabled as the "CZ" bucaneer. The Rutan video backs this up too. The education chapter says to prep sand with larger grit sandpaper. The video uses 36-grit to prep sand a non-peel-plied area. And no, peel ply doesn't mean "don't have to sand." There are alot of experts in the field that say you MUST prep sand peel-plied areas before applying the next structural layup. There is at least one presentation on Marc's website that tells the reasons why.

 

(4) Was said, "In my microscopic mind's eye, I see millions of tiny stress concentrators (crack starters), each on a grain of sand or whaterver, where we might not want them. If, however a structural bond is weaker because of media inclusions, the result may be more catastrophic." My answer--> Total BS. Don't knock it until you try it.

[Lynn Erickson]

(1) The purpose of my sandblasting reply was just to provide the originator with a picture of what a prep-sanded area looks like when sanded by hand. Not to slight Burt or the plans, it is nearly impossible to sand the valleys completely dull. If you watch the Rutan composites video, you will see that not even Burt achieved a totally sheen-free prep sand. My picture looks alot like the one in the video.

 

(2) In my opinion, sandblasting is not practical for prep sanding for follow-on, structural layups. Too much mess for so little gain.

 

(3) Was said, "For the areas that Burt has designated as critical structure, you want to make sure to use peel ply well (no gaps where it doesn't touch) and avoid the sanding." I don't agree. The peel ply is to keep layups from delaminating from the edges. At least it says so in my Cozy Chapter 3 education chapter, that is as far as I know an exact duplicate of the Long-EZ plans with the exception that the "CP" bucaneer has been whited out and relabled as the "CZ" bucaneer. The Rutan video backs this up too. The education chapter says to prep sand with larger grit sandpaper. The video uses 36-grit to prep sand a non-peel-plied area. And no, peel ply doesn't mean "don't have to sand." There are alot of experts in the field that say you MUST prep sand peel-plied areas before applying the next structural layup. There is at least one presentation on Marc's website that tells the reasons why.

 

(4) Was said, "In my microscopic mind's eye, I see millions of tiny stress concentrators (crack starters), each on a grain of sand or whaterver, where we might not want them. If, however a structural bond is weaker because of media inclusions, the result may be more catastrophic." My answer--> Total BS. Don't knock it until you try it.

why would sand blasting leave an inclusion and sanding with paper not? they are the same material except the sand paper has a binder (Glue) that does get on the surface. I used both and it doesn't seem to have an effect on the way mine flies.

[ZUCZZ]

Dear folks,

 

One tries one's best, is about the best you can get from preparation.

 

There are superb examples flying from those that followed the plans and just sanded.

 

Then there are equally superb examples flying from those that did the sandblast, just to get the last iota of grip on the matrix.

 

Now folks, the object is to fly, no matter what the object is!

 

Be carefull, there is a fine line between picking your nose and making it bleed!

 

I say this, because I had all the same questions and fears before mine got to fly ... hindsight, I'd worry less and get to fly more ... have you seen some of the gastly examples that fly into Osh? ... but they flew there!

[longezdave]

(3) Was said, "For the areas that Burt has designated as critical structure, you want to make sure to use peel ply well (no gaps where it doesn't touch) and avoid the sanding." I don't agree. The peel ply is to keep layups from delaminating from the edges. At least it says so in my Cozy Chapter 3 education chapter, that is as far as I know an exact duplicate of the Long-EZ plans with the exception that the "CP" bucaneer has been whited out and relabled as the "CZ" bucaneer. The Rutan video backs this up too. The education chapter says to prep sand with larger grit sandpaper. The video uses 36-grit to prep sand a non-peel-plied area. And no, peel ply doesn't mean "don't have to sand." There are alot of experts in the field that say you MUST prep sand peel-plied areas before applying the next structural layup. There is at least one presentation on Marc's website that tells the reasons why.

 

Wayne,

 

On page 3-14 of the Long EZ plans, Burt states "Once the dacron is peeled off, the surface is ready for another layup, without sanding."

 

I do agree that it is better to lightly sand the area after the peel ply is removed, so I'm not arguing with you.

 

I also believe that Chris has it right that we need to get on with the building and flying and less picking of nits.

[argoldman]

why would sand blasting leave an inclusion and sanding with paper not? they are the same material except the sand paper has a binder (Glue) that does get on the surface. I used both and it doesn't seem to have an effect on the way mine flies.

 

Lynn, it's great that the sanding doesn't seem to have an effect on the way your plane flies. My guess is that if one left out some of the suggested lay-ups your plane would not fly much differently. (my further guess is that this has been done in many flying glass craft, of course when there is a in-flight failure, the first thing that is mentioned is the non-standard layup schedule)

 

That's not the point. The point is the question of whether sandblasting increases or decreases the bond strength. If it increases the strength, it is of little consequence (other than ease(?). If it decreases the strength, that may be a different story.

 

Does anybody have the ability to make up coupons of each and test them.

 

I seem to remember, back in the days of yore, when Burt was trying to prove that his glass (rather than the Burlington, similar weave, he made coupons and tested them to destruction.

 

Lynn, your plane may fly great, but is it flying on the verge of destruction or well within the structural strength specifications?

 

Please don't interpret this statement to imply in any way that I think that your plane isn't as strong or stronger than most, but the fact that your plane is not effected by sanding/not sanding/ etc may mislead some on this list.

 

I am all for modifications, as those who have seen my project and my previous dragonfly project can attest to.

 

However when it comes to changes of structural matters, which differ from those specified in the plans, I am personally somewhat leery until some mechanical testing and/ or engineering work has been done.

 

How about some tests.

 

Virtually every aircraft that has met it's untimely end, has taken off with it's pilot fairly sure that he/she would come down safely. And indeed it did function/fly well, sometimes for multiple hundreds or thousands of hours ,until the problem (possibly built-in) reared its head.

 

I don't need a PHD thesis relating the benefits of a specific procedure, but I do need something more than "It works for me"

[Wayne Hicks]

Longezdave rebutted, "On page 3-14 of the Long EZ plans, Burt states "Once the dacron is peeled off, the surface is ready for another layup, without sanding."

 

---> I stand corrected, and you said it like a gentleman. Thanx!

[brainfart]

> How about some tests.

 

Can't hurt to do them, but what's the benefit of a limited sample made under possibly questionable circumstances tested with non-adequate equipment...

 

There are thousands of laminated aircraft flying. These tests have been done countless times before under controlled conditions by experts. Just do it the way the experts and commercial aircraft builders do it. Even if some of the information might collide with 30 year old videos or outdated books written in the seventies.

[Phil Kriley]

Longezdave rebutted, "On page 3-14 of the Long EZ plans, Burt states "Once the dacron is peeled off, the surface is ready for another layup, without sanding."

 

---> I stand corrected, and you said it like a gentleman. Thanx!

Thank God! I thought I was going to have to scrap the whole darned thing!

[Richard Schubert]

On my E-racer restoration, I am finding places where some genius laminated brackets and whatnot over Zolatone. Thank god for the Fein tool!