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Old Mar 10, 2007, 07:45 PM
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London, UK
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Tips for sanding a square LE to shape

Hello

I am building a Paragon glider and need to sand a square LE to shape as indicated on the plans...any tips before I start?...I understand one should make a plywood template of the LE shape and use this as a guide...but wanted further tips and tricks.

Thanks for the suggestions.

Arun
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Old Mar 10, 2007, 07:48 PM
the-plumber
Joined Feb 2003
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Quote:
Originally Posted by arukum17
Hello

I am building a Paragon glider and need to sand a square LE to shape as indicated on the plans...any tips before I start?...I understand one should make a plywood template of the LE shape and use this as a guide...but wanted further tips and tricks.

Thanks for the suggestions.

Arun
I find it useful to have a straight-edge at least as long as the L/E, and check frequently.

A plane helps knock the corners down quickly.

After that I use the longest sanding bar that fits, at least half as long as the L/E and preferrably the same length as the L/E.
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Old Mar 10, 2007, 10:19 PM
B for Bruce
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The 'Wack, BC, Canada
Joined Oct 2002
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Start with planing or sanding the top and bottom so they are tangental to the rib nose curves (no sheeting on this one). A long strip of masking tape layed over the rib noses just back of the rear of the leading edge will help you see when the block is just barely touching the tape.

Once the two tangents are sanded or cut then you can run some flats at increasing agles to come to a rough shape. It helps if you lay all this out on the airfoil on the plans first. That way you can get a feel for the angles of these bevels and their widths. Adding pen lines as sanding guides helps a lot. Once you've got the original tangets and one more each top and bottom a light sanding with folded hand held paper should round the leading edge nicely to the right shape or close enough at least.

Like this.....
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Old Mar 11, 2007, 06:11 AM
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I'm with the above..a razor plane first, followed by a block sander..or even one of those concave sanders like Permagrit do, is ideal..

Its not necessary to be perfect in section so much as even all the way along. No one will ever know if it's slightly the wrong section.
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Old Mar 11, 2007, 10:05 AM
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United States, WA, Richland
Joined Mar 2006
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I ran across this in the Tower Hobbies catalog the other day and thought it might come in handy for leading edge sanding. Here's what it says:

"The Duplicator Mk1 is Designed Especially for Sanding Edges That Are Round, Semi-Round or Angle-Shaped. Great For Trailing Edges, Fuselage Corners and Inside Rounds Such As Fillets."

Anybody tried one?

Mike
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Old Mar 11, 2007, 01:34 PM
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Space Coast
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Use PVC pipe- choose the pipe with the radius you need and cut the pipe in 1/2 lengthwise. You can tack glue the sandpaper to the inside.

If you really wanted to get fancy, you could heat the PVC and form it to the exact shape needed.
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Old Mar 11, 2007, 10:06 PM
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I use the facet method described in post #3 and hand sand only after getting it as good as I can with an assortment of 'T' bar sanders.[80-140-220 grits.]
Buy two in the 30+ inch length and cut one in half. Cut one of these halves in half again. The full length one gets the 220. Next longest gets the 80. The remaining shorter sections get 140 and 220.
Attach the sandpaper with the thin double stick carpet tape.
Another thing that helps is to shape both the leading edges in the same time frame...while the process is in an identical current thinking mode.
art
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Old Mar 11, 2007, 10:57 PM
Zor
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Two pennies worth

The idea of using two sided sticking tape is good because you would like the abrasive to be as straight as the sanding bar (metal or wood). You should not have loose abrasive paper (or cloth).

Most people recommend to sand along the wood fibres.
Using a slight angle with the fibres hasten the sanding considerably to produce the desired shape. You can then finish the sanding in line with the fibres with the finer grit abrasive (320 is fine enough considering that a leading edge should be made of semi hard balsa).
Check and make sure that if your sanding bar is home made that it is really straight for a straight leading edge.
If the leading edge is not straight (like an elliptical wing) you can use a much shorter bar but use long strokes varying the angle (that the bar makes with the airfoil chord) slightly each stroke. Of course you have to do that with a straight bar as well.
There is no problem with slightly including the very front of the ribs to assure a smooth transition from LE to ribs. The atmosphere will not complainwhen flying, HeeHee.
Dust off often or vacuum so that sanded particules do not accumulate on the surface.
Wear some breathing protection. Your lungs do not appreciate sanding dust. Ventilate your work area.
Use a good "eye ball" technique. So called guages or pattern are not useful and are more a pain "you know where".
Good luck
Zor
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Old Mar 12, 2007, 12:03 AM
B for Bruce
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The 'Wack, BC, Canada
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Quote:
Originally Posted by hoppy
Use PVC pipe- choose the pipe with the radius you need and cut the pipe in 1/2 lengthwise. You can tack glue the sandpaper to the inside.

If you really wanted to get fancy, you could heat the PVC and form it to the exact shape needed.
Hoppy, if you're looking to properly shape the leading edge then this won't work. No airfoil uses a truly circular shaped leading edge. It's more of a parabolic shape with only the very nose approximating a circular shape over maybe 40 to 60 degrees worth of angle.

I don't recomend heating the plastic of the PVC pipe unless you want to make yourself sick. The fumes it gives off are terrible even when it's only just getting soft.
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Old Mar 12, 2007, 01:55 AM
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FWIW, I also agree with post #3 and it's how I do it as well. I never sand (balsa dust make me start sneezing if I'm not careful) so I always use a razor plane using full length strokes, when the plane is set right you should be getting nice long curls of balsa coming off.

Grab a scrap piece of wood and practice first. It's much easier and quicker to do than it looks but you need to master the technique.

FYI, you can also make your own trailing edge stock this way.
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Old Mar 12, 2007, 02:47 AM
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