Sanding Cured Fiberglass

[argoldman]

Have you been building?

 

 

 

How about this one?

 

Close, but no cigar.

 

That looks like a Craftsman flapper wheel. the flaps will just go over the high spots and miss the low. The one that I am talking about has nylon bristles, not flaps. I will try to get the name and publish it.

 

However looking more closely, that one might suffice. If they indeed are a collection of filaments, I would like to see the filaments longer so they are more flexible.

 

Memory says that the filaments on the device to which I refer are about 1"long and are held to the hub by a plastic center piece that has 6-8 fiber holders so that between each group of abrasive fibers there is a space which allows the oncoming fibers not to be bent by the previous as it rotates.

[Jon Matcho]

I've got the sandpaper, now I'm just trying to figure out how to get the gloss out of the valleys.... which sandpaper does just fine if you sand away the ridges and the corresponding glass fibers.

Stop worrying about those tiny depressions and do the layup already!

 

Your bond will be fine if you've roughed up the area "good enough". Check chapter 3 for a comment on this, as well as the Rutan 70s video if you have it to give you some more peace of mind. It doesn't need to be "perfect". Sandblasting is NOT necessary here.

[Jason Heath]

I also know that if I sandblasted the bond areas, the result would an area prepared better than if sanded, with less damage to the glass fibers. I would expect a stronger bond.

 

I would have to agree with Steve & Edge, the 36 grit will work fine, yes you'll damage the fibers some and is to be expected. If you use what Rich is talking about, it will still damge the fiber but with less elbow grease. Either way you'll be fine.

Don't expect sandblasting to create a stronger bond for additional layups, the finish you create with blasting MAY be equivelant to a much higher grit paper than needed, it will make it dull and thats better than shiny, but Waynes use was for finishing and theres nothing trying to pull the paint off the skin.

[macleodm3]

Well, I'm working on the other side while figuring this stuff out. It Was peelplied.

 

I had fun attaching the bottom longeron, its great to have nice easy small tasks after doing large layups!

 

Tonight is doubler and elec. channel type stuff.

[Edge 513]

Have you been building?

 

 

 

How about this one?

...For about 2-1/2 years.

Yea, I am building a cozy MarkIv- I am finished with my controls and starting to install my canopy and turtleback- so I've sanded a little bit.

[macleodm3]

...For about 2-1/2 years.

WOW! Good progress! You have done some sanding then. Thanks for the advice on figuring this out.

[Edge 513]

The sandblasting idea may be a good one. Good idea to use the spent media sand as shot bags. I use soft scuba weights.

Theres some bright minds here.

Theres also a lot of Hyperbola.

The gas tanks in the wheel pants were particularly special.

[Jon Matcho]

Theres also a lot of Hyperbola.

Hyperbole.

 

The gas tanks in the wheel pants were particularly special.

<sigh>

 

Anyone can post. Take you for example, Edge, my initial guesses for who you were included:

• A spammer
• A new and eager builder-to-be
• Owner of Edge aircraft #513 taking time off between Red Bull Air Race dates

Given the lack of background information, I take the position of a paranoid skeptic. Glad I was wrong, so... welcome!

[Wayne Hicks]

With reference to sand blasting as an acceptable method of surface preparation, I post Michael Hoke's response with his permission. (www.abaris.com)

 

Hi Wayne:

 

Good question. In my opinion, GENTLE grit blasting can be the most effective method of all for creating the high-energy surface needed for durable adhesive bonds. However, it's pretty easy to cause problems if one is not very careful doing this. One problem is the simple one of possibly breaking fibers on the surface ply. All you really want to do is to remove an extremely thin (a few microns) layer of the resin on the surface, to mechanically rupture the cross-links there, to give you the high-energy surface. If you break any filaments on the surface ply, then technically you have a damaged ply which needs to be repaired.

 

Obviously one can get too anal about all this; a few broken filaments on a large surface really won't matter, but I have seen people cut completely through the top ply without realizing it, since it's so hard to see what you're doing. 30 psi max, and don't get too close or too vertical with the nozzle; practice on some scrap first.

 

Another problem is that most people grit-blast using compressed air, which almost always has water and oil in it. This will very effectively contaminate the surface as the grit particles quickly get contaminated themselves and drive the contaminates into the surface. It's really hard to have truly clean compressed air; my shop certainly doesn't. Typical inexpensive filters aren't nearly enough. In my shop, when we are grit blasting for surface preparation for structural bonding, we use new, clean grit, and use compressed dry nitrogen from bottles, not air from our compressor, for the blasting. However, if one is confident that your air is really clean and dry, then that would be OK; it's just hard to know if it's really clean enough. Blowing some air for a few minutes through some clean white paper towels, and then holding them up to the light to see if there is anything showing is said to be a good check for compressed air cleanliness, although I have seen no formal testing to prove this.

 

Anyway, given a good job with an observant, careful operator and clean grit and air, this is an excellent method for surface prep for bonding, and it's what I would use if I was building my own airplane.

 

Best regards - Mike

[Edge 513]

Hyperbole.

 

<sigh>

 

 

Should've typed Hyperbowle [missing the acccent mark on my keyboard] Sorry to say, I am College educated as well. G'figure.

[mplafleur]

Hyperbole.

 

<sigh>

 

Anyone can post. Take you for example, Edge, my initial guesses for who you were included:

• A spammer
• A new and eager builder-to-be
• Owner of Edge aircraft #513 taking time off between Red Bull Air Race dates

Given the lack of background information, I take the position of a paranoid skeptic. Glad I was wrong, so... welcome!

The Edge be one cool dude. I can vouch for him.

 

Just be on the watch when he starts slinging the prose.

 

Edge,

 

Can you say 'blended winglets'? It's just only one more mod.