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Clay Alternatives

DanH

Legacy Member
Mentor
Another thread asked if your mind wanders while you work. Well, I've been shaping clay for upper gear leg fairings and what comes to my mind is "gotta to be a better way".

I've done the clay thing previously. I've also used male forms made from foam and coated with tape or a filler, but usually they have been larger components, often incorporating a lot of straight lines. I can sand foam much closer to a desired contour as compared to working with clay; a fairing made over a close-contoured shape needs much less filler and finish time (example below). Trouble is that foam blocks would be kinda hard to fit for gear leg intersections.

Anybody found a spray can or 2-component mixed foam that when cured has small cell size and good shaping properties? Foam might work well if you could spray it or blob it into place.

Cabane%20Fairing%201.JPG


Cabane%20Fairing%204.JPG


Cabane%20Fairing%20Finished.jpg
 
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<<What airplane is in those pictures?>>

Skybolt, top wing center section, upside down.

The red is thin plastic tape over shaped block foam. Center photo is after the part has been popped off the form (the tape is a no-stick surface), trimmed, microed, and sanded. In the bottom photo you can see how little filler (white, micro and epoxy) it took to finish shaping the part.

<<What about Instafoam, available from Wicks.>>

Ever tried any? What sort of cell size and texture? Does it shape and sand well?
 
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I use this pour foam:

http://www.shopmaninc.com/foam.html

but I generally build some kind of dam to pour inside. If you really need to blob it on "against gravity" it might be tricky. I guess you could let it react until it was thick enough and then quickly blob it on. It is very sticky stuff...

The cured foam - especially in higher densities - is very easy to work with common bodywork tools. Works great for forms and such.
-Karl
 
DanH said:
<<What about Instafoam, available from Wicks.>>

Ever tried any? What sort of cell size and texture? Does it shape and sand well?

Small rigid cell, easy to cut, shape and sand. Sometimes too easy. You mix 2 parts and pour on the area. It then expands 20-30 to 1. Used it alot on a past project.
 
I have built a Vari-Eze but I could not think of any better method than the clay :confused:. The clay (plasticine) is a bit fiddly but with patience it works and it has the advantage that you can reshape/add more until you get it right. It works easier if the temp is hot. The worst part for me with the upper intersection fairings was laying the glass on upside down. You don’t have to strive for perfection with the glass work. I applied a fairly thick layer of dry micro over the whole fairing (applied with gloved fingers) and was able to get the fairing to an acceptably smooth surface and contour in the one sanding.

Fin 9A
 
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I like the density selection at Shopman so I think I'll order some 4lb. A quick cardboard dam should keep the stuff in the right place for some small lower fairings integral with the pant parts. Good example, as it would be nice to shape the fairing parts and glass over them with no need to remove the clay after cure. The foam core is a plus and I can go shape to bond in one step. I'll report back.
 
Dan,

Use 3M shipping tape under the area you will be using the pour foam. Go at least one strip wide of all dimensions of the area. Once the pour foam has cured, it will pop right off. You can also cover the shaped foam with the tape when you glass it and the glass shape will easily separate from the foam.
This stuff is REALLY STICKY. Be Warned.
 
<<The worst part for me with the upper intersection fairings was laying the glass on upside down.>>

Yessir Fin, I think that is everybody's worst part. I'm doing a straight 8 with Grove gear this time, so I can do the upper fairings right now, in the shop, while the fuselage is upside down....instead of me.

<<Use 3M shipping tape under the area you will be using the pour foam.>>

Thanks Greg. In this case I think I'll let it stick to the pant parts and retain the foam as a core in the finished part. The leg will get tape of course.
 
Fast forward one month. Here's the rest of the story.

I ordered some 4 lb density 2-part urethane foam to try as a replacement for clay in shaping intersection fairings.

Bottom line? Using expandable foam as a replacement for clay is great.. I had good foam cores in about 1/4 as much time as shaping clay, and they were much closer to final contour. I declare the experiment an unqualified success.

Some paper and tape form a temporary dam. Mix and pour; the stuff is cured and ready to work in about 15 minutes. Initial shaping was with a bare hacksaw blade to slice off excess foam. Primary shaping was with a length of 1-1/2" alumunum tube covered with stick-on 60 grit sandpaper. Final touch up was with some handheld 120 grit.

Try it, you'll like it <g>
 
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