Expreinces with coating / sealing blades

[Wes]

I am about to finish carving my first set of blades, about 6 ft diameter, and I didn't want to go simple with my design just because I'm green. I used the excel spreadsheet blade calculator from Hugh's site, and I ended up with blades that are veeeeeeery thin at the tips, about 350 thousandths inch at the thickest part of the tip.

I laminated strips of wood to save money and to add strength, however I am afraid the bending moment caused by the lift may break the blades in high wind. I am planing on furling design, however I want my wooden blades to be robust.

Dose anyone have experience with strengthening blades for bending? Anyone tried applying fiberglass to wood?

Also what are good coatings? I was thinking something that will dry hard and have some tensile strength to it. Possibly epoxy resin or polyurethane? Again, has anyone tried any of there or anything else that has worked well from your experiences?

 

[Flux]

That is nearly 3/8" and sounds better when expressed in a less toolroom way.

That will be ok it's normal enough. The bending moment is at the root, the tips aren't going to break.

Fibreglass and wood can be a tricky situation and you eventually end up with fibreglass blades with a wooden core before you reach a useful combination.

Flux

[elt]

My mill is about 15 months old. The plywood tail is painted "normally" with primer and three coats of paint. It is showing some warp and buckle

But my blades are still nice and smooth. I painted my blades with three coats of epoxy (not polyester resin.) Being a little worried about wear, I mixed some fused silica in with the first two coats that I put on the leading edge and tips. When dry, I sprayed two coats of Krylon Fusion (specifically formulated for plastics and resins.)

http://www.otherpower.com/images/scimages/6527/GreenDragon.jpg

That is as durable a finish as I know how to make (so far) and is probably overkill but it's stuff that I always have on hand so why not...

Hope that helps,

- Ed.

[Wes]

Thanks Flux...I'll remember to convert measurements into fractions for my board postings (I'm used to reading my dial caliper.)

The thickest part of the root is slightly under 1". I hope that is thick enough.

Maybe I will try making my next set of blades out of fiber glass...

[luckeydog]

using fiberglass over wood is done often in the boat industry.

I don't see any problems with glassing wood blades as long as you are

working with bare wood "No linseed oil on them" you will achieve

the best results using west systems epoxy and vacuum bagging them.

I have done this using 3 layers of 6 oz glass your blades will

be very robust.

  Glassing them gives you a great finish. the blades must be painted

after glassing, most epoxy dose not have any UV protection. and will degrade

fairly quickly in the sun.

Luckeydog

.

[zeusmorg]

 My coatings of choice would be first.. Fiberglas, then Imron (an epoxy paint) then probably a good latex (outdoor), polyurethane, and then linseed oil, from best to worst.

 It will depend on your particular weather conditions to determine just how much you're willing to spend in materials and maintenance of the protective layer.

 I WOULD however do a full balancing of the blades prior to any protective coating.

[pepa]

    Hi Wes. I carved three of these as combination fan and windmill blades for a project and fiber glassed them with good results and they are very strong. My test stand fell over with the blade turning because I mounted the unit before I weighed down the base after moving the stand. The blade hit into the edge of my gravel drive with our any sign of damage. pepa

[Wes]

Thanks all for the advice! Those pictures with the fiber glass are great too!

I ended up calling a manufacturer of wooden fixed pitch propeller blades for the aviation industry and asked one of the engineers what they used to coat their blades.

They said that they used "Spar Urethane", but that the finish had a shorter wear life than "Marine Spar Varnish." Apparently when a crack would develop in the hard urethane coat it would peel up and take off a good chunk of the finish, while the marine spar varnish adheres better, and isn't as brittle as the super hard drying urethane.

Since this is my first set of blades, I have decided to forgo the fiberglass route.

I've decided to stain and seal with a light Minwax wood finish, which claims to stain, penetrate, and seal. Then I intend to put on a few coats of Minwax Helmsman Spar Urethane. The Spar urethane claims that it can expand and contrast better than regular urethane. I got all of this from my local Lowe's hardware store. I want the blades to look good since they are my first.

[Wes]

I have two questions, or rather points that I would like you to elaborate on.

1. Why outdoor latex paint over polyurethane? Wouldn't polyurethane have a much better wear resistance?
   
2. I was planing on coating my blades, then assembling them into a rotor, and then balancing. Do you think it is advantageous to assemble the rotor, balance it, then paint/seal?
   
   

Just as a reminder I have never done this before so I just want to understand why you ol' pros do the things you do.

-wes

[zeusmorg]

 In my experience, a good quality outdoor latex paint will outlast polyurethane. As far as color goes, white would also be my preference, no heat buildup from the sun making the blades warp. A light blue would also be a decent choice.

 Personally I'd balance the blades before the last coat. That way the weights are also sealed in.

 Of course my method of balancing is probably more time consuming than most people's I like getting the blades both statically  and dynamically balanced, and the tips aligned.

 If you look in my files you'll see a post of how I balance blades.