West Systems question for the experts

[ge9a]

I have a few fiberglass divots/dings to repair prior to painting - oil door edge on the cowl, plus a couple other locations on the plane. The attached pic shows three small divots on the cowl at the bottom edge of the oil door. They're small, but I'd like to fix them.

I'm thinking some epoxy and 406 mixed together to fill these. Or is 407 better for this or something else altogether? These are pretty small 'divots' - maybe 3/16" x 1/16" in size, on the edge. I'm planning to use something to "block" whatever I use from spreading too far, like a piece of aluminum angle with wax clamped to the oil door edge (when the oil door is open) so it doesn't stick where I don't want it.

These are just my thoughts on what and how. I'd really appreciate some advice on this.

Thanks!

 

[scsmith]

I have a few fiberglass divots/dings to repair prior to painting - oil door edge on the cowl, plus a couple other locations on the plane. The attached pic shows three small divots on the cowl at the bottom edge of the oil door. They're small, but I'd like to fix them.

I'm thinking some epoxy and 406 mixed together to fill these. Or is 407 better for this or something else altogether? These are pretty small 'divots' - maybe 3/16" x 1/16" in size, on the edge. I'm planning to use something to "block" whatever I use from spreading too far, like a piece of aluminum angle with wax clamped to the oil door edge (when the oil door is open) so it doesn't stick where I don't want it.

These are just my thoughts on what and how. I'd really appreciate some advice on this.

Thanks!

I would make a little dam from electrician's tape (epoxy doesn't stick to it) to hold in the filler where you want it and keep it from running down into the gap between the cowl and the door. Filler should be epoxy thickened with microballoons to a pretty dry paste, and a small amount of cabosil to keep it from sagging. An alternative is to use the ready-to-use epoxy+filler from Poly Fiber. I think its called Super Fill. It is already blended to give a good consistency and sandability if you haven't done much of this before.

I've ranted about this before, you can read why in other posts, but I think the best place to put West epoxy is in the garbage can. Use a GOOD epoxy like Jeffco 1307 LV or MGS 285.

 

[Ralph Inkster]

It looks like you made a pretty tight recess fitting for the door. You might consider block sanding the edges open for a bit more of gap to allow for the paint thickness.
As for the small divots, a bit of bondo or glazing compound would easily fill them in.

 

[rockyfatcat]

It looks like you made a pretty tight recess fitting for the door. You might consider block sanding the edges open for a bit more of gap to allow for the paint thickness.
As for the small divots, a bit of bondo or glazing compound would easily fill them in.

+1 for filling in. I did full time fiberglass work at Robinson Helicopter while I was going through A&P school.

If it is not structural it is decorative. Structural requires proper technique and materials for strength. This is surface preparation for paint.

 

[Larry DeCamp]

No micro for these tiny spots, you will make a bigger job than you are fixing. Auto paint stores sell 2 component fillers (creamy paste and hardener) for this job. Bondo is cheap and OK but old school.
Get some POLYETHYLENE tape for masking drivet coatings on commercial buildings. Cover the cowl opening surface and as much of door as you care. This stuff DOES NOT LEAVE ADHESIVE FILM LIKE BOX TAPE , and does not stick to epoxy and good fillers like vinyl tape can.

 

[rockyfatcat]

Back in the day (25 years ago). When I was doing pre-paint filling. I developed a mix of the stuff available at RHC that I could whip up into a paintable and easily sand-able liquid I could brush on.

I would make a witches brew of stuff in a paper mixing cup I’d put a small blob of our fiberglass resin, a drop of the hardener, about a 1/4 cup of micro-balloons, and a spoonful of a product called final-fil that was mostly chalk.

I do not know if this product is available. I would google body filler that sands like chalk.

The next thing is that any small bondo like repair has a tendency to grow into a much larger repair.

To keep things from getting bigger. Before you start mixing get your favorite tape. I used plain old masking tape. Mask off as much of the area that you don’t want to f*ck with, and brush the mix on the area with an acid brush.

Let it start to harden up and while it is still setting up. Peel off the masking tape with all the extra filler on it.

Put it off to the side and let it harden. If everything worked as advertised. You should be able to use a hand held sanding block to knock off the high spots and be ready for your pre-paint finish work

 

[71459]

I'd just leave them and go flying. Your airplane will be picking up hundreds of these (and much larger) imperfections as time goes on. You will eventually find that trying to keep it perfect becomes a never-ending quest for the Holy Grail.

 

[ge9a]

Thank you for all the replies so far. I know I can always count on VAF for decent advice and varied (good) ideas. Not sure what I'll do yet - I obviously don't want to make a bigger issue than I have - I have lots of practice doing that already with this project. But overall, I'm really happy with the plane and my workmanship, even though I'm a bit of a perfectionist when it comes to projects. So I want to get the dings addressed before it goes to the paint shop.

Regarding Post 7, yeah, I have definitely considered that, too. I try to make everything perfect which sometimes gets ridiculous and is generally unnecessary. But I try hard to get everything right.

 

[Toobuilder]

Id apply standard auto body filler AKA “Bondo” and then while sanding, open that gap to account for paint thickness, hinge wear, vibration and expansion. You might find after opening the gap that the chips have disappeared and are now in the pile of dust on the floor.

 

[srothert]

West Epoxy is the BEST!!! I have used the 105 Resin and the 206 hardner for over 20 years, repairing wing tips, wheel pants, various fairings. For filling, get some micro balloons. Once the resin/hardner is mixed thoroughly, using a tongue depressor (about 2-3 minutes of mixing), start adding the micro balloons until you get the consistency of cake frosting. Sanding can commence in about 18-24 hours. I start with 80 grit sand paper and finish up with about 220 grit.

A quart kit from Spruce will last a while. Make sure to get the mini pumps as well. They help dispense the correct ratio of resin and hardner.

Prep the surface with sand paper and then a cleaning with alcohol. At about the 12-18 hour mark after filling, you can take a razor blade, or Olfa knife, or Xacto knive and cut around the perimeter of the door, leaving a narrow and clean gap. Thus, making it easy to pop open the door, after a full cure of the epoxy. Sand and paint.

It is not hard. It just takes some patience.

 

[jrs14855]

The Dan Horton mix of 1/3 epoxy, 1/3 micro and 1/3 flox. The flox gives it structural strength that is much stronger than plain filler.

 

[penguin]

I agree with those who class West resin as a poor substitute for other products, I use MGS H285 mmostly. If the lip has cracked off in few hours and it is repaired with any kind of filler the chance is it will crack off again. Glass cloth has to be used to provide strength, but that is a much more involved repair. By all means first try epoxy thickened with chopped cotton and cabosil, and rough the ding up well with 60 grit, to find out how long it lasts.

 

[Laird]

+1 for MGS. Never had great luck with West. ProSet was a little better (same manuf) but MGS is hands down the best to work with, but BOY is it expensive now.

As Steve's suggested, I'm going to try Jeffco after my bottle of MGS is empty. Canopy and cowling are near in the future so it shouldn't be too long now.

 

[DanH]

The door opening in the first photo needs work to clean up the gaps and edges. The best long term result (No paint chipping) requires rounded edges, and gaps about 1/16" wide.

Rounding the corners of the door and filling the cowl opening to match will largely eliminate the small cracks commonly seen in the corners after time in service. Reinforce the door with additional thickness (or ribs) while you're at it. Thin doors bow outward when subjected to Internal air pressure.

How good is good enough? I've some very expensive paint on glasswork with poorly finished edges and seams. It's enough to make a grown man cry.





Polyester filler is a classic Chinese Menu choice....fast, cheap, good, pick any two. Little dings and divots, ok.

Let's not discount West too much. It's good to excellent for any kind of surfacing, and works fine in low strength structure. The hardeners allow use in a shop with poor temperature control. The User Manual is an excellent guide for epoxy novices. The pumps are popular, although I only use them to dispense into cups proportioned by weight.

Jeffco is much better for structure; compare the values below. Its higher heat deflection temperature is a particular plus for cowling structure.

 

[Larry DeCamp]

The door opening in the first photo needs work to clean up the gaps and edges. The best long term result (No paint chipping) requires rounded edges, and gaps about 1/16" wide.

Rounding the corners of the door and filling the cowl opening to match will largely eliminate the small cracks commonly seen in the corners after time in service. Reinforce the door with additional thickness (or ribs) while you're at it. Thin doors bow outward when subjected to Internal air pressure.

How good is good enough? I've some very expensive paint on glasswork with poorly finished edges and seams. It's enough to make a grown man cry.

View attachment 65010

View attachment 65011

Polyester filler is a classic Chinese Menu choice....fast, cheap, good, pick any two. Little dings and divots, ok.

Let's not discount West too much. It's good to excellent for any kind of surfacing, and works fine in low strength structure. The hardeners allow use in a shop with poor temperature control. The User Manual is an excellent guide for epoxy novices. The pumps are popular, although I only use them to dispense into cups proportioned by weight.

Jeffco is much better for structure; compare the values below. Its higher heat deflection temperature is a particular plus for cowling structure.

View attachment 65008

View attachment 65009

My reaction to some of the original posts on resin selection was “ bet the expensive stuff is best suited for sophisticated infusion practices”. Dan IS the expert and lots of folks get great results with West, Glass and Carbon from ACS. Fixing chips and pimples is not aerospace fabrication.

 

[DanH]

My reaction to some of the original posts on resin selection was “ bet the expensive stuff is best suited for sophisticated infusion practices”. Dan IS the expert and lots of folks get great results with West, Glass and Carbon from ACS. Fixing chips and pimples is not aerospace fabrication.

Small side note...thank you for the compliment, but it deep knowledge depends on what sort of work is being done. Guys like Steve Smith, Bob Kuykendall, Craig Catto, and Ken Kruger know things I don't. They're turning out production stuff. My game is tuned to best practices in the home shop.

The composites world is huge. At the low end we have Bubbas slapping polyester on old Corvette bodies. At the other end we have manufacturers like GKN making Sikorsky rotor blades, carbon satellite frames for Sirius, and prototype HondaJet fuselages. And let's not forget the people making yacht hulls and wind turbine blades, mostly with resin infusion and materials largely unknown in EAB. Every application requires significant niche knowledge.

Me? I've just been lucky enough to meet some experts, and tried to pay attention