Wood working question

[riorex2002]

Bug master brings up an interesting subject, Living in California our weather is just a wee bit different than North Carolina? at the moment our humidity is rather high and as i am building my wings in a hangar instead of in the house ,where i have built previous projects,i am having trouble with warped wood and humidity.One wing is complete but mostly unvarnished.Do i varnish this in this humid weather  or wait till it improves?I fear that i might be sealing moisture in.The completed wing is not warping  and the book says no more than 20%moisture content.i do not posses a moisture content meter what is the general feeling on this situation?
Rex

[Bugsmasher]

on moisture content....from what I have read it needs sealing to trap what moisture that is in the wood there....and keep it from traveling in and out as seasons and temps change....expansion and contraction. I am sure that's just a small part of the whole picture though...I am sure there is someone that can elaborate on this that is far more educated than me with wood. I would seek the counsel of AC 43.13-1B....lots of airplane related wood info there.

[riorex2002]

The -43 is not much help,it only gives the content of aircraft wood to be between 18 &20% if i remember correctly but as i have had this in my hangar for a while i think that the moisture content has increased,I am wondering if i now seal it i will have too high a reading..Have not come across this before.
Rex

[Dan_]

The -43 is not much help,it only gives the content of aircraft wood to be between 18 &20% if i remember correctly but as i have had this in my hangar for a while i think that the moisture content has increased,I am wondering if i now seal it i will have too high a reading..Have not come across this before. Rex

This is all I could find on it...  See the July 09 entry. ( page is from: http://www.eaa1279.org/oldwebsite/Pietenpol4.htm )

They seemed to have a way of dealing with humidity...

	-Chapter 1279 Home-
The Pietenpol Project 2009
2005-06    2007    2008
-two links for more information about the Pietenpol-

Sept '09
The basic structure is nearly complete after 4 and 1/2 years of part-time work by members of Experimental Aircraft Association Chapter 1279.  This photo was taken on Saturday, September 12 during a trial fit of the left wing.  The right wing is complete and varnished as is the fuselage.  The woodwork on the left wing is nearly complete, but unvarnished (notice the color difference as compared to the fuselage and right wing).  Originally designed to be powered by a liquid-cooled four-cylinder 1929 Ford Model A engine, we chose the air-cooled six-cylinder 1965 Corvair engine to power our airplane.  It will run smoother and provide twice the horsepower.

July '09

 It has been some time since my last report on the Pietenpol project and many of you are wondering what's happening.  Do not be alarmed.  We are making steady progress on the project.  I just have found precious little free time for communicating these days.  Eventually, that situation will change.  But for now I simply offer my apologies.

  

 In January I reported to you that our right wing was complete enough to hoist it into place to test fit it to the center section (and to take some inspiring photos).  At that time we were still working on the aileron structure.  Once the bracing was in place, the hinge locations were marked and the aileron was cut away.  What fun it was to attach the hinges and move the aileron!  The wing was done and ready for varnish.

  

 At this point I would like to share a few thoughts on what we have learned about varnishing using the Poly Fiber two-part epoxy varnish.  Two things are ABSOLUTELY CRITICAL to obtaining the best results.  The first is following the mixing instructions explicitly.  The second is making sure that the environmental conditions are right for proper curing.

  

 Southern California has the reputation for having great weather almost year round.  When the sun is out and the temperature is delightful, it is easy to ignore the humidity in the air.  We found ourselves having to do things over because we decided that "we were ready to varnish."  Be honest when evaluating the conditions.  The instructions give temperature guidelines and say allow additional induction time for high humidity conditions.  I say, unless you're on a production schedule, wait for a better day, if conditions are not right.  "Right" means warm and dry.  There are always other things you can work on.

  

 When mixing, DO NOT fudge on the induction time.  Mix Part A and Part B, then find something else to do for AT LEAST 30 minutes (45 minutes to an hour is even better).  Then, and only then, add in the proper amount of Reducer.  Again, do not fudge on the amount of reducer.  The Reducer is a key element in the proper curing of the varnish.  By the way, better use a coffee can or glass container for mixing.  The varnish will eat right through a Styrofoam or paper cup.

  

 The instructions also say to apply two coats - a third coat is optional.  We achieved the best finish by applying a first coat, allowing a couple of days curing time, then sanding with 150 grit sandpaper before applying a second coat.  The bare wood will soak up a lot of the first coat.  The sanding is necessary, because the first coat raises the grain in the wood.

  

 You can consider the second coat your finish coat, if you are the type that figures "it's all going to be covered anyway."  If that is your mindset, then adding a third coat would only add weight.  Forget it.

  

 However, if you are a craftsman and you want a silky smooth, glossy finish, then sand that second coat almost completely off.  Get a nice smooth surface to the touch.  Then carefully mix the final coat according to the instructions, but add in a little extra reducer.  The varnish will seem thin and runny, but it will cure up hard and glossy.  That's the ticket.  You will love the results.

  

 So, now we have our right wing in a rack and working on our left wing at this time.  All of the components are there.  It's just a matter of assembly.  In the meantime, Dave McPhee is working in the cockpit, locating the brake master cylinders and getting that system finished and working.

  

 I will let you know when we have reached another milestone.  Thank you for your continued interest.

  

 Steve Williamson, Pres.

Jan. '09

 A lot of saw dust was created shaping the leading edge, trailing edge, and tip bow.  The results are rewarding.  The contour looks great.  The wing is straight and square.  All of the fittings for the lift struts and jury struts are in place.  With a little finish sanding the wing will be ready for varnish.

  

     We will be fabricating and attaching the aileron hinges this week.  Once the hinges are located, the aileron can be cut away from the wing.  The control horn is finished and attached.  We need to fabricate one more fitting - for the control wire pulleys.

  

     On Saturday, January 17, the wing was finished enough to test fit it to the fuselage center section.  It was an exciting moment for all of us who were present.
 

[riorex2002]

thanks Dan.It must have been on their mind too.I think from reading this that i can leave it till the spring when the other wing is complete ,then varnish them both together.At least they will end up with the same moisture content and have more chance of being the same weight.Will not go to their lengths to varnish mine,To heavy.
Rex

[Vince Carucci]

I've been doing woodworking for years. One of the great historical innovations in furniture making was the frame and panel design. Solid wood pieces would eventually tear themselves apart. The reason for this is that wood will always continue to fluctuate in its humidity content at the last few percent. Articles written about such things say that you can never completely seal the wood 100%. As the fibers absorb and release moister they expand and contract. The fibers are shaped like drinking straws they get thicker but not longer. The thin wooden frame around a floating panel change size so little that they never stress themselves to failure. Another way to prevent the expansion and contraction with humidity is to lay thin layers alternating at 90 degrees like in plywood. This make it very strong and very stable.
So, regarding the wings. If the wood was properly dried before purchase, you probably do not need to worry about local fluctuating humidity. The .25 inch ribs will effectively not change size with humidity. The plywood used in the spars also probably won't react to the humidity. You can probably press on without consequence. But if you have ANY doubt about how wise it is to work the wood under these conditions, then for peace of mind wait for better weather. Hope that helps.


Vince

[Tom Stephens]

Hi Rex,

It's Tom in Arnold!

Just a thought...

I have no idea how accurate these meters are, but looking on the Net, I see there are inexpensive 'moisture content meters'.  You can just type that into Amazon, for example.  At least that way you will know for sure when the moisture content reaches "no more than 20%".

Great to see you progressing!

Tom

[riorex2002]

Thanks Vince.
My concerns started When i brought out my spars to start assembling the second wing.All spars had been built at the same time and were flat at that time,They now have a slight bow in them.This worried me re the condition of my completed wing as i have not varnished them.For peace of mind i will not complete my second wing at this time and give every thing a time to normalize.I have installed a fan in the hangar which should help.All wing material was purchased from A/S so should be OK,incidentally the ply they sent me is finnish and 6 ply,Have never used such a beautiful ply before,it makes you want to come out to the workshop just to use it.Will do some metal work in the mean time.Thank to you all for your input
Rex

[Vince Carucci]

I just received my pre-cut .250² inch spruce strips from ACS for the ribs and they look fantastic. But the whole lot of them measure .290² inches. That is 34% more material by volume than specified. I (foolishly or wisely) made my rib fixture so that it could fit up to .270² inch strips. I took 3 of them and ripped them down to .260² inch and assembled the rib. They fit in the fixture nicely but the process seems like it can be dangerous to fingers and wood. So before I take anymore action, I wonder about the experience of others. 

• Is .250² inch for the ribs merely nominal and anything close will do?
• Has anyone else used spruce measuring .290² inch?
• Should I find the safest method and continue ripping them down to .250² inch?

Vince

[leshoman]

Over the years i have ordered a bit of 1/4" spruce stock from ACS.  With the micrometer it  has varied between .230 and .280.  I believe it depends on who at ACS is cutting it, or where ever the get it.  I do not think they measure with micrometer, just use saw guide and cut.  The big problem, other than weight, is making sure parts that get gusseted are same thickness.  I went thru the order and culled out the thicker pieces and used for none rib parts, like cross braces on ailerons. My last order they varied between .230 and .280 in same batch.  In past generally all were the same width at least.  If there is a cabinet show around with large sander, or a planner, they can easily, and safely reduce them to .250.

[Vince Carucci]

Thanks Les. 

I think I will try the planer instead of the table saw. Should get a much smoother finish on the piece too. 

Vince

[CHARLES DEBOER]

Leonards' remark in the instructions for the XL stated that "sanded wood absorbs 70% less varnish"  Sooo.... I laid 10 or 12 of the 1/4"+ strips together on the workbench and hit them with a sanding block a couple times on each side.  That way I didn't have a lot of sanding when I finished my ribs and they came in close to 1/4" square.

[Will Weidner]

Charles, be careful with that.  Sanding also reduces epoxy penetration.  It might be best to wait till all your gluing is done before you sand.

[Vince Carucci]

My solution:
I ran the spruce strips through the planer and brought them down to .260² which will leave me .010 for safe sanding. If you orient the grain pattern correctly before feeding them through, the finish is very smooth with no tear-out.  I am using Titebond II ^(R) as an adhesive. It's an interior/exterior water-resistant glue with a quick setup time. I ran a sanding block over the joins where the gusset will sit for flattest glue surface. The gussets were held in place with spring loaded wood working clamps that I got from Harbor Freight for $1.39 each. They have a surprisingly strong clamping force. I still had to put a few staples at the ends of the gussets for full contact. Any glue that squeezes out can be easily cleaned with a wet or dry rag. Unlike epoxies, wood glues work best on sanded surfaces with high clamping force (read article).

There has been a lot of discussion about adhesives on this forum and I am definitely NOT advocating for any specific type. I'm just sharing my reasoning and my methods.

[Will Weidner]

Interesting article, especially when you read through the comments at the end.  There's a comment concerning aircraft that is contradictory (about 1/2 way down) to the article itself.