Doors

November 2016

 The old side windows were in Ok condition but only 3/32" thick, and of course 30+ years old.  Anyway I decided to use new .125" material.

 I used the old glass to experiment with forming.  This hotplate setup was unable to achieve the 325F temperature needed to form acrylic.

 I made an aluminium form, and took everything home for baking in the oven.

Timing is everything with this operation. With the oven preheated to 300-325F and the glass clecoed to the form, the whole thing is placed in the heat.  I spent three minutes starring through the oven window, then chickened out.

As luck would have it 3 minutes was about right.  Too much and contact forming occurs meaning that the surface picks up marks from whatever it touches.  Too little and of course the glass fails to take the desired shape.

The fixed widow is bonded in place.
I used 732 clear silicone after experimenting with various options.

As it happens I found the metal frame, screwed to the bench, which worked very well for clamping the lower edge.

Never one to make life easy,  I decided to make a spruce frame for the slider.  This allows the whole assembly to be physically held in place by the inner window frame, in addition to the adhesive.

 After urethane varnish, the frame is bonded in position.

 A felt-like synthetic is added to line the slider track.

 Recreating the slider leading edge.

 To get a better appearance, a small flange is formed in the 025" 2024 T3.

 Initial bend with the brake,

 and then I used a piece of acrylic and a slotted piece of maple to finish the bend and radius to 180 degres.

 result

 Holes drilled in the slider and countersunk,

 and the doubler drilled and dimpled.

 Ready for assembly.  Note the window is curved but the doubler is still straight.

 Glued and screwed.

Finally the doubler is formed by hand to take up the desired profile.

 The inside frame is lined with the felt-like fabric,

 as is the trailing edge of the slider.

Hold my breath and cut out the opening, and chamfer and polish the edges.

 The finished frame.

And successful test.

 I also glued tinnerman nuts along the lower door frame so I can use smaller screws to secure the door panel (although the factory used Pk screws into aluminium, it's not really an airccraft-quality solution imo). 

Last step before the doors are finally ready for top coat is grey urethane for the exposed interior frame.

August 2016

The interior panels are cleaned and primed, then the stiffeners and doublers are riveted in place.

 Right side.

The knee panels are now ready for upholstery (which means choosing and locating fabric).


Next up, I need to decide on how to do the sliding windows.

June 2016

While waiting for material for the top cowlings I went back to the doors to make interior panels and window frames.

The left interior panel was salvageable.

In addition to a couple of repair doublers,  I added a stiffener to make the panel a bit more knee-proof.

The right panel was toast, and made of 040" soft aluminium anyway so both over and under-kill as it were.

A new panel is fabricated from 025" material.

Again a 'Z' channel is fabricated and added to reduce drumming and provide some additional stiffness.

 Typically the old parts were not even adequate as templates so I laid out the window frames with craft paper.
















I used 2024 T3 032" at least in part because it's what I had on hand.

 Window opening is carefully cut.

 The forward and aft flanges need to be shrunk so that the frame takes up the curve of the door frame.

Final trimming and dressing out the marks left by the shrinker.

I have not yet decided what do do about the windows.... to slide or not to slide, that is the question.

July 2015

Given bringing the doors back into acceptable shape continues to be a project in and of itself, I felt they deserved their own section.

They both looked in reasonable shape... from a distance.  Closer inspection revealed many problems.

At some point the passenger side door had been damaged and "straightened" and I suspect as much damage was done in the straightening as in the original mishap.

the Pilot side was in better shape but still required a lot of work.

Dismantling without damaging the magnesium door handles was tricky











Reinforcing the structure by inserting a doubler.  This type of repair was done in several places.

Some of the spot welds had popped and significant oil-canning in the right skin.  I spent too much time trying to remove the oil-canning and should have made the election to re-skin sooner.

Both doors were repaired/reinforced in the latch area.

Cracks in the structure extended into the outer flange.  Repair doubler is inserted but it's necessary to stop drill the crack without touching the outer skin.

Start with a standard 1/8" bit but stop before penetrating the channel.  Grind the end off a 1/8 bit and finish the stop hole.  This bit will tend to stop cutting once its through the first layer but a little at a time caution gets the desired result.

A note on stripping paint.  Not a particularly enjoyable process which can be smelly, messy and frustrating, not to mention hazardous.

I'm no expert but I have developed a technique that yields satisfying results in what I believe is a reasonable time-frame.

First I buy the cheap rubber gloves, in Canada available from Canadian Tire usually for less than $2.  I wear cheap vinyl surgical gloves inside those and put barrier cream on my hands.  At the first sign of failure, I change out the gloves. Tried all the so-called chemical resistant gloves and they don't do much better at four times the price.

Next, when I was restoring my 172, I made the pictured scraper from and old laminate counter-top.  I guess its formica but the key is the stripper doesn't soften it and it won't damage aluminum.  I keep a 45 edge on each end by occasional running  a sanding disc over it.

  Of course a good extraction fan is a must.  A 10" diameter flex duct is connected to mine which puts the extraction airflow right where it does the most good.

 I use Klean Strip I think it's called, available from US hardware stores.  Applied with a natural fiber brush.  The brush goes hard after but then the stripper softens it up again.  My brush is just about completed its second aircraft!  Actually so is the paper cup I put the stripper in.

Lay down some paper (some stripper will seep through so make sure you're on a resistant surface or use more paper layers).

Apply lots of stripper and don't be tempted to move it around or work it with the brush.

Let the stripper do its thing.  Wait long enough but not too long and this is dependent on the type of paint. Test with the scraper.

Use the scraper to remove the lifted paint and move still-wet stripper over areas where the paint is still stuck.

apply a second coat of stripper and repeat the scraping process.

Step three is dabbing more stripper on any still stuck areas.

Finally scrape off all remaining stripper and immediately clean with lacquer thinner.  Use scotchbrite with thinner on tough areas of primer around rivet heads etc.

On larger surfaces work in sections about 2 sqft each, you can have two or three sections going at once, each at a different stage but don't try to do too much at once.

Roll up the paper and put it somewhere where it will dry out.  After a couple of days all the pain/stripper will be dry and hard and it can be disposed of safely.

Right Door Skin

As mentioned I should have bit the bullet and gone for re-skinning sooner but I think I was spooked by the spot welds.  Then I realized I could simply ignore the spot welds.

Door is traced and 2024 T3 is cut for the new skin

Clamped in place and hole pattern laid-out

The old skin is removed by cutting flush with the structure.  Spot welds and associate small sections of the old skin remain and provide extra thickness for countersink/flush rivets.

Holes drilled through door frame and new skin.

Found another repair to make

This time external doublers to replace the original internal splice.

Most of the holes are countersunk to accept 3/32 flush rivets

Leading edge is flanged per original.  and the other three edges receive just a hint of a flange for appearance.

A little primer on the mating surfaces,

and ready for riveting.

Leading edge flange.


















Skin is tacked then hung on the door frame to ensure the shape is still good

A few tense moments while the window opening is cut... please don't mess it up now! and rechecked on the door frame.

Flat snap is used on universal head rivets to emulate the original steel truss-head rivets














The left Door was in better shape except for the multitude of holes left by various window mods over the years.  The original Tcraft windows slide and the plan is to recreate that so I needed to find a way to plug the holes.

A doubler was cut to fit in the space between the door frame edge and the edge of the window opening.

After etching the doubler was bonded in place using proseal. and all my clamps.  Door had to be supported to prevent any twist.  Gallon of thinner is used for ballast :)

 doubler is trimmed

and vinyl ester filler is used to fill the holes and smooth the surface to some extent.

Doors get etched, alodined and epoxy primed.

Door mechanism was worn in several places.

We don't want floppy door handles so the old tubes are carefully cut out and new ones installed and reamed.

New crank arm fabricated and welded in place at the correct angle to make sure the door handles line up with airflow

other cranks made too

Test fitting

Primer

and assembly of the hinges

and door mechanisms.












Still to do are the interior panels and window sliders. Wow, a lot more work than I thought.  How many times have I said that!  Oshkosh 2016 may be not enough time.