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Sanding composites



 
 
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  #1  
Old January 27th 05, 09:04 AM
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Default Sanding composites

How do you know when you're beginning to sand into the glass cloth? Do
you simply sand until you
have a smooth finish, then stop? Ot do you keep going?
thanks,

joe mcguckin

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  #2  
Old January 27th 05, 09:39 AM
......... :-\)\)
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You will know it trust me !!!

You will see the weave start to appear. Depending on the composite the
fibres will have a dull appearance and the resin a more shiny look ... there
is a contract that allows you to see the weave of the fabric. If you go into
the fabrix it will need to be repaied so go slow.


wrote in message
ps.com...
How do you know when you're beginning to sand into the glass cloth? Do
you simply sand until you
have a smooth finish, then stop? Ot do you keep going?
thanks,

joe mcguckin



  #4  
Old January 28th 05, 03:59 PM
[email protected]
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Roger wrote:
On 27 Jan 2005 01:04:49 -0800, wrote:

How do you know when you're beginning to sand into the glass cloth?

Do
you simply sand until you
have a smooth finish, then stop? Ot do you keep going?
thanks,


Are you sanding to get a smooth finish or to prepare for the next
lay-up?

If you are getting ready for the next lay-up you are sanding to

"rough
up" the surface to get a good bond to the next layer, not smooth it.

With Vinyl Ester Resin I use 60 or 80 grit (hard to get a smooth
finish with thatG) and just rough up the area. I then vacuum the
area clean and follow up with an Acetone wash. With the area dry or
just barely tacky I do the next lay-up.


For smoothing, as opposed to scuffing, has anyone tried scraping
instead of sanding? Using a scraper like this:

http://www.leevalley.com/wood/page.a...=1,310&p=32669

one can get a finish on wood roughly equivalient to sanding down
to 320 or 400 grit. Scrapers are especially good for removing
bumps and runs in film finishes like shellac and varnish so
I'd imagine that they'd do a good job on hardened epoxies and
resins too.

The cabinet scraper is not a paint scraper, it is a much more
versatile tool. Proper tuning of the scraper is a bit of an
art form but with an understanding of the process and a little
experience one can remove a large amount of material, or only a
small amount with each pass. It is much cleaner and faster than
sanding because it raises shavings instead of making dust.

--

FF

  #5  
Old January 28th 05, 09:00 PM
Cy Galley
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Why sand at all. Steve Beert's prize winning Long was sandblasted, then
micro was squeegee over the top , then a little sanding and paint prep.


wrote in message
oups.com...

Roger wrote:
On 27 Jan 2005 01:04:49 -0800, wrote:

How do you know when you're beginning to sand into the glass cloth?

Do
you simply sand until you
have a smooth finish, then stop? Ot do you keep going?
thanks,


Are you sanding to get a smooth finish or to prepare for the next
lay-up?

If you are getting ready for the next lay-up you are sanding to

"rough
up" the surface to get a good bond to the next layer, not smooth it.

With Vinyl Ester Resin I use 60 or 80 grit (hard to get a smooth
finish with thatG) and just rough up the area. I then vacuum the
area clean and follow up with an Acetone wash. With the area dry or
just barely tacky I do the next lay-up.


For smoothing, as opposed to scuffing, has anyone tried scraping
instead of sanding? Using a scraper like this:

http://www.leevalley.com/wood/page.a...=1,310&p=32669

one can get a finish on wood roughly equivalient to sanding down
to 320 or 400 grit. Scrapers are especially good for removing
bumps and runs in film finishes like shellac and varnish so
I'd imagine that they'd do a good job on hardened epoxies and
resins too.

The cabinet scraper is not a paint scraper, it is a much more
versatile tool. Proper tuning of the scraper is a bit of an
art form but with an understanding of the process and a little
experience one can remove a large amount of material, or only a
small amount with each pass. It is much cleaner and faster than
sanding because it raises shavings instead of making dust.

--

FF



  #6  
Old January 28th 05, 09:16 PM
Corky Scott
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On Fri, 28 Jan 2005 21:00:17 GMT, "Cy Galley"
wrote:

Why sand at all. Steve Beert's prize winning Long was sandblasted, then
micro was squeegee over the top , then a little sanding and paint prep.


Wow, now there is an inovative guy with a lot of courage. But Cy, a
lot of the Long's need the sanding to make the surfaces **REALLY**
smooth, y'know, laminar. So they use long pieces of 1x4's with
sandpaper glued to it to make sure they don't sand a crater into the
surface. The purpose of this type of sanding is to remove any
irregularities, not just rough up the surface.

Corky Scott
  #7  
Old January 28th 05, 10:46 PM
Tim Ward
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"Cy Galley" wrote in message
news:[email protected]_s53...
Why sand at all. Steve Beert's prize winning Long was sandblasted, then
micro was squeegee over the top , then a little sanding and paint prep.


Well, on sailplanes, anyway, you sand to make sure the airfoil is the right
shape, (shrinkage can occur over the spars after some time out of the
molds), and to make sure that any waves in the contour are less than .004
inches.

Tim Ward


  #8  
Old January 30th 05, 03:25 PM
Peter Dohm
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I have to presume that he was both quick and gentle with the sandblasting;
as the most common theme that I have heard, over many years, from experts in
composites is: "the less you sand, the better you sand."

That is very much in keeping with Burt Rutan's remarks, back when he was
actively selling plans for the Vari-Eze and Long-Eze.

The one I remember best was: 'The more time you spend on your cores, the
less time you will spend on your airplane.' The reason for the single
quotation marks is that I believe the statement to be a very close
paraphrase, but probably not exact, as more than twenty years has elapsed.

The other was that a very slightly dry top layer was regarded as less
detrimental than a too wet top layer. Both reduce strength, and the too wet
surface also adds weight and additional finishing requirements. As I recall
it, the primary control of the wetness of the layup was the angle of the
squeegee when removing the excess resin which had been stippled in... Keep
in mind that Burt was quite emphatic regarding the need for the entire
lay-up to be fully wetted out.

Therefore, I really like the idea of a light pass of sandblasting (or bead
blasting) to prepare the surface for the last micro application. I plan to
use the advice!

"Cy Galley" wrote in message
news:[email protected]_s53...
Why sand at all. Steve Beert's prize winning Long was sandblasted, then
micro was squeegee over the top , then a little sanding and paint prep.


wrote in message
oups.com...

Roger wrote:
On 27 Jan 2005 01:04:49 -0800, wrote:

How do you know when you're beginning to sand into the glass cloth?

Do
you simply sand until you
have a smooth finish, then stop? Ot do you keep going?
thanks,

Are you sanding to get a smooth finish or to prepare for the next
lay-up?

If you are getting ready for the next lay-up you are sanding to

"rough
up" the surface to get a good bond to the next layer, not smooth it.

With Vinyl Ester Resin I use 60 or 80 grit (hard to get a smooth
finish with thatG) and just rough up the area. I then vacuum the
area clean and follow up with an Acetone wash. With the area dry or
just barely tacky I do the next lay-up.


For smoothing, as opposed to scuffing, has anyone tried scraping
instead of sanding? Using a scraper like this:

http://www.leevalley.com/wood/page.a...=1,310&p=32669

one can get a finish on wood roughly equivalient to sanding down
to 320 or 400 grit. Scrapers are especially good for removing
bumps and runs in film finishes like shellac and varnish so
I'd imagine that they'd do a good job on hardened epoxies and
resins too.

The cabinet scraper is not a paint scraper, it is a much more
versatile tool. Proper tuning of the scraper is a bit of an
art form but with an understanding of the process and a little
experience one can remove a large amount of material, or only a
small amount with each pass. It is much cleaner and faster than
sanding because it raises shavings instead of making dust.

--

FF





  #9  
Old January 30th 05, 06:46 PM
[email protected]
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Posts: n/a
Default


Tim Ward wrote:


Well, on sailplanes, anyway, you sand to make sure the airfoil is the

right
shape, (shrinkage can occur over the spars after some time out of the
molds), and to make sure that any waves in the contour are less than

..004
inches.


That's another reason to try scraping. Scrapers can be filed to a
particular curve for just that sort of work.

--

FF

  #10  
Old January 30th 05, 07:21 PM
Tim Ward
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Posts: n/a
Default


wrote in message
oups.com...

Tim Ward wrote:


Well, on sailplanes, anyway, you sand to make sure the airfoil is the

right
shape, (shrinkage can occur over the spars after some time out of the
molds), and to make sure that any waves in the contour are less than

.004
inches.


That's another reason to try scraping. Scrapers can be filed to a
particular curve for just that sort of work.

--

FF


The curvature changes continuously chordwise, and most sailplane wings have
taper, so the curvature will change with the spanwise station as well. So
it's difficult for me to see how you could cut a single curve that would
match.
Now, for a constant chord wing, that might make an interesting production
technique:
Build your wing, then build up an extra layer of filler, then "extrude" the
whole wing panel through a CNC cut scraper, getting exact, smooth
coordinates on the way.

Tim Ward



 




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