Here’s an alternative approach to take with ABS plastic cowlings
and wheel pants.

I know many people like to get the fiberglass replacements for the
ABS parts in many kits, but for those of us on a budget, this is an
easy and inexpensive way to make the most out of what comes in
the kit. I’ve had good results with this method on several planes.
My cowls and pants look good, and as long as they’re not handled
too severely, they last a good long time, also.

The first step is to trim the edges of the pieces that will be glued
together as carefully as possible. If you’ve ever built a plastic
display model kit using liquid cement, the assembly is a
piece-of-cake. Use dope thinner as a liquid cement to glue the
pieces together. You can hold, clamp, or tape the pieces together
dry, then using a fine paint brush or applicator, run some thinner
into the seam. The thinner actually dissolves a bit of the plastic and
causes the pieces to “Weld” together.

Allow the assemblies to dry overnight, or at least for a couple of
hours. Drying time depends on how much thinner you got into the
seams. For the next step, the assembly doesn’t have to be rock
solid, but you don’t want things falling apart as you work with
them.

While waiting for the parts to dry, you can begin to make the filler
cement. Cut some of the scrap plastic from the moldings into little
bits, and place them into an old baby food (or equivalent) jar. It’s
important that your jar has a lid that fits well. After you have an
eighth to a quarter inch deep of plastic bits covering the bottom of
your jar, pour just enough dope thinner into the jar to wet all of the
bits. Cover the jar and wait an hour or two.

When you come back to the jar, you should find the bits all
dissolved and you now have a creamy paste which can be used to
fill the seams and any other imperfections in the parts. It can also
be used as a cement to glue reinforcements into the parts, such as a
ring inside the front of the cowl around the hole you cut for the
prop shaft. I smoothed my filler into the seams with a palette knife.
A flat blade screwdriver would also work well, or even a small flat
piece of wood. I filled the inside of the seam on my cowl to add
extra strength, also. The goo will come off of your tool pretty
easily with a paper towel while it’s still wet, or it will peel off when
it’s dry, but it welds itself to the plastic parts... it actually becomes
“One” with them.

This filler will shrink slightly when it dries, so don’t be afraid to
leave it a little thick. You can also keep the stuff in the covered jar
for a while, so if you need to add more filler later, that is not a
problem.

After drying for at least a day, the filler will be the same color and
consistency as the original plastic part, and the seams can be
carved, sanded and shaped just as easily as the plastic parts (which
isn’t saying much, granted). Be careful sanding, or you’ll just melt
the plastic and make a mess. I use very coarse (60 grit) sanding
blocks to begin the shaping, and progress to finer grades as I go
along.

Eventually the parts will be ready for primer and paint.

Hi Philip,

Excellent thread!

Do you reinforce your ABS cowls by fiberglassing the inside?
If so, any tips?

Thanks

Ari

Very nice phlip, thats an GP RV cowl hehe, got that on too

Apalsson, I find it necesarry to reinforce the cowl because otherwise it will crack rapidly.
The most important thing is to roughen the inside with p.e. 60-80 gritt paper. Otherwise the epoxy wont stick to the abs. I have always used epoxy but you can do it with polyester too.

I have to say, that is very ingenious, to use the left over plastic to make a filler/cement. Never would've thought of that.

I always just tack the two halves together with thin CA, then run a thin strip of 2oz glass/epoxy inside along the seam. Then I fill the whole inside with a layer of 0.75oz glass/epoxy to stiffen and strengthen up the whole thing. if the epoxy is used very sparingly, this method adds very little weight and the glass provides a little heat insulation from the engine that it otherwise would not have.

I then use just a smidgen of Bondo on the outside of the seam and sand perfectly smooth. Then, prime and paint. Seems to work pretty good for me.

Patriot

I've never reinforced before, but frankly, this GP RV-4 cowl is thinner than the other stuff I've done before... all Sig kits, I think. I'm considering it this time. Haven't decided yet.

You don't see it in my photos, but I did reinforce around the prop shaft opening by cutting a circle out of a flat piece of scrap and cementing it to the inside of the cowl, so now it is double thickness around the hole.

Phil

I tried this,,,
On a pod for a Seamaster 40-

and it works GREAT!! it takes awhile to set completely on the thicker parts, but sanding is easy, you can control the 'thickness' by letting it stand or adding more acetone. I used "layers" to build up the gap formed by the seam and you can't tell where it joined!!

thanks for the tip!

Thank you. I'd say you made my day, but great weather and a good morning at the flying field already did that!

ahh hope mine turns out that nice... that is one sa-weet looking plane..excellent job my friend =D

~Matt

I agree that ABS parts need reinforcing. I use glass cloth on the inside with Oatey's All Purpose Cement as the adhesive. No need to roughen the inside surfaces to get the glass cloth to adhere. Easy to do and tough as fiberglass parts. PVC cement will also work.

I usually use 2 oz cloth, cut into strips, and thin CA. I apply a strip over the seam on the inside and any areas that need reenforcing, such as where the mounting screws go. Works very well and bonds well to the ABS also.

I reinforced some ABS part inside with a light layer of glass sucked with acetone. It made the glass sink into the ABS. That method worked quite good. Instead of actone I also used thin CA.

The only negative I have found to acetone is that if you use too much, it can "melt" through the ABS piece and/or warp it.

"Oatey's All Purpose Cement"

you guys crack me up !!!

[:-]

GOOD TIP all the way around.

I tried this technique last night with the following modifications that worked wonderfully. For the solvent, I didn't have "dope thinner", and Home Depot only had gallon cans of Acetone. Being a firm believer in less is better, and scrounging, I discovered that the PVC Pipe Cleaner (found in the plumbing section) comes is nice small cans, is inexpensive, and dissolves ABS plastic just fine. Its composed mostly of Acetone, but it also contains MEK, so use in a well ventilated space. Second, coffee "sipper" lids are molded from ABS plastic, so I added a few to the mix since I had thrown many of my scraps out. I'm now "recycling" them from work! They work fine.

Brad

Very Nice Tip! I'm going to try this on my Super Skybolt.

This is a great method. Fills the gap and bonds the two halves all at once.

Don't laugh about the Oaty's pvc cement. I have used this stuff with fiberglass cloth to repair aircraft parts and it has held together when others did not. I have used this method to reinforce the abs model parts for years. Great solution to buying the expensive fiberglass parts. The glass parts are worth the money thought on the more expensive larger models. One plane picture other picture is of quality control inspector.

JEB