Sandblasting

[Wayne Hicks]

Please add me to the list of sandblasting converts!

 

I've known for years that some builders have used sandblasting as a way to prepare their surfaces for the fill-n-sand process. They claim that it saves time, results in much better prepared surfaces, and causes no damage to the fiberglass structure. I have a humongous compressor in the hangar (thanx to my hangarmate, Steve) and a portable suction-feed sandblaster. So I thought I'd give it a try. I sandblasted my winglets as test cases and was immediately impressed with the results.

 

I have pictures on my website that show the obvious benefits of sandblasting versus hand sanding. What took me one hour to sand by hand took all of 5 MINUTES with the sandblaster, with much better distribution. The whole winglet was prepped in 20 MINUTES. http://www.maddyhome.com/canardpages/pages/waynehicks/chapter_25_1.htm

 

The naysayers always preach about the potential for disaster. They'll scream about blasting a hole through and through. I'm here to tell you that's a bunch of patooty. What are they using? 12,000 psi and rocks???

 

You just gotta be smart about it. I had my (Steve's) compressor set on 120 psi and I used extra fine black oxide media. I held the gun about 4 inches from the surface and used a gentle back and forth sweeping motion just as one does when spray-painting. It was very easy and very intuitive to know when the surface was roughed up enough. You could literally watch the surface gradually change from shiny to dull. For purposes of testing, I grabbed a scrap piece of fiberglass and intentionally tried to blast a hole through it. I literally had to hold the gun right up to the surface and hold it still before the fiberglass eroded enough to begin forming a hole. The extra fine media and the low pressure provided plenty of margin for error.

 

Had I known the sandblasting was going to be this EZ, I wouldn't have used so much peel ply!!

 

Be sure to wear a high-quality particle respirator and eye protection at a minimum. It's also a good idea to wear a disposable painter's suit with a hood. The media GOES EVERYWHERE and GETS INTO EVERYTHING! You definitely DO NOT want to breathe in any of that oxide dust.

 

Sandblasting is well worth it. I'm a happy camper.

 

====================

Wayne Hicks

Cozy IV Plans #678 http://www.maddyhome.com/canardpages/pages/waynehicks/index.html

[Spodman]

I like this idea. The concept of sanding to mate parts and leaving little shiny bits between the weave or grinding off lovingly applied fg seems a bit half-baked in comparison. So does including extra weight by peel-plying everything also. This beats all these things, and its another reason for me to buy a compressor .

[cncdoc]

Top o' the day to ya,

 

Do they have Outback Steak houses there?

 

Oh well.....

 

I have had a compressor for years and I wouldn't do without, even if I wasn't building a Cozy.

 

Besides, that gives you an excuse to buy all those cool airtools! (like you need an excuse... )

 

Ah, what would my life be like now without my 3/8 inch drive air rachet?

 

Anyway, make sure you get a compressor that handles at least 6 SCFM (they measure it in the air that goes IN to the compressor, not out.) or you will be waiting on tools. 9 SCFM is perfect and don't go less than 5 gallons or you will be working the pump off and on. A good setup is a 20 gallon main tank 10 HP motor and a 100 gallon reservoir tank with moisture removal.....OH yeah......is the drool apparent?

 

If you get a sandblaster get extra tips and face and hand protection. The sand WILL end up in your knickers, so plan accordingly....

[Jon Matcho]

Had I known the sandblasting was going to be this EZ, I wouldn't have used so much peel ply!!

Yikes... just when I thought I knew how I was going to do my layups. Are we now saying to NOT peel ply everything, but just the transitions, and sandblast everything instead?

 

I've used a self-contained sandblasting system before, but can't imagine the mess an open system would make. Will the EPA mark my house as a clean-up site once I'm halfway through chapter 13?

[Hennie Engelbrecht]

I. So does including extra weight by peel-plying everything also.

 

Spodman , do I understand correctly that you want to leave the peel-ply on the part? This item gets "peeled" off after cure to provide bonding surface. so you in fact reduce weight when using peelply

 

Hennie E

[Jon Matcho]

[Peel ply] gets "peeled" off after cure to provide bonding surface. so you in fact reduce weight when using peelply

Hennie, I'm sure Mark didn't mean that, but from what I understand, peel ply does add a small amount of weight when compared to layups without (and then sanding).

 

If that is true, then sandblasting may help save several pounds on the total airframe. Combine this with the Pressure Bagging technique and you might have the lightest parts possible.

 

This all sounds very appealing to me as a time saver PLUS potential the benefit to produce a lighter airframe. I can rationalize costs over the duration of the build by making the analogy of paying low-cost laborers to sand my parts for hours while I sip my beverage of choice.

[Rob Wright]

so would you say that peel ply is not needed? just sand blasting where the peel ply should have gone?

[Spodman]

When I say "peel-ply" something I mean the whole process, layup, apply peel-ply, cure, when ready to put on next bit remove peel-ply. I understand its used to:

 

1 - Create clean surface for next layup/joint (sanding required),

 

2- Create clean surface at edges of plies (particularly taped joints) and floxed corners,

 

These are as presented in the plans. Then you have two options:

 

1 - Peel ply final layup, filling voids between fg weave with (heavy) neat resin, or

 

2 - Just leave it and fill up the voids later with (lighter) dry micro, at the expense of much buggaring about and extra work.

 

I've read #1 could cost about 16lb for the whole airframe. Don't know how reliable (or significant) that figure is.

 

Haven't heard of an Outback Steakhouse, but I used to live in the outback, (Central and Northern Western Australia) where they run one cow per square kilometer. Recipe for outback steak: Place steak in pot with brick and boil until brick is soft. Throw away steak and eat brick.

 

Such animals are actually not eaten by Australians (except for pet food) and are exported to Europe and the US. WE eat King Island beef when we want a treat. YUMMMMMM!

[Spodman]

Thort some more about this. Others have said accidents have happened from peel-ply not removed and I can see why, in my one and only layup the peel-ply (from ASS) just dissappeared when the resin went on. Other others have said you can use anything that looks like the genuine peel-ply, but other other others hint darkly at fg eating sizing. Still other other other others draw on the peel-ply with a marker pen.

 

I'll go to my local fabric shop and buy something yellow. I won't forget its there, but should still be able to see any voids below.

 

Burt Rutan was very vocal against "peel-ply everything", but if you read the relevant CP articles he was mostly worried about resin being soaked up from lower plies. Just pile on more resin.

 

Sorry about all the "others" but I'm drinking Bundy on my birthday.

[noodles]

I was wonder what type of weight reduction there is when you sand blast?

 

I've thought of doing the same and was curious as to the amount of resin that is removed.

[Jon Matcho]

I was wonder what type of weight reduction there is when you sand blast?

That's a good question, but not sure this could be easily answered in the context of an entire plane. For example, the same question applies to vacuum bagging and the extensive use or non-use of peel ply.

 

Reading Wayne's Web page on the topic, he doesn't mention weight at all. He does point out a significant time savings of sandblasting over hand-sanding, suggesting its use for large areas such as the fuselage, strakes, and wings.