Saturday, December 24, 2011

Latches Finished

 The latches are finished and work great.  I painted the steel parts an aluminum color over epoxy primer.  Originally I worried about using clevis pins for the 2 pivots.  By carefully folding the ends of the cotter pins tight to the clevis pins I don't think you could snag yourself very easily.  I'm eager to finish the doors now.

Friday, December 23, 2011

The Fun is in the Doin'

If you've read my postings for a while you've probably noticed I'm not very orderly in working through the project from start to finish.   I tend to work on what ever I have parts, materials, tools ,or ideas for at the time.   When I helped my dad build the Fly Baby back in the 60s we were very methodical.  Pete Bowers wrote the plans/manual as a set of step by step instructions.  You start on page one of a chapter and just check off each task as you go.  When every item is checked off you have an airplane, actually a very cool airplane.

As much fun as it was working with my dad on the magic of building that plane you would think I would be more orderly in my current projects.  I'm not because what I learned from that process was that each little item was a project in and of it's self.  Each had it's own knowledge required, it's own materials, tools and methods.  To some extent it didn't matter so much the order things were done as it did that each was done.

By focusing on each small task, enjoying it, and taking pride and satisfaction in it's completion building an airplane is very easy, a lot of fun, and rewarding.  Finishing and flying the airplane was great but just one more little task or adventure just as each flight in it has been since.

By enjoying each saw cut, each hole drilled, each tool made, each little assembly, each flight for all the joy it contains, the Fun really is in the Doin' Not Just in Being Done.

Merry Christmas and a Fun New Year!

Tuesday, December 20, 2011

Window Latch Pivot Pin (Cessna 0413148)

The trick to this latch mechanism is that it folds up like a jack knife when the window is closed.  To do that, the steel link folds inside the aluminum link.  It sounds simple but the pivot at the door end of the link, which moves in and out of the aluminum link, includes the brackets and the pin holding them all together.  The parts manual calls this pin a rivet. It needs to be something with very thin heads on the ends.  The inside of the aluminum link is 3/4" (0.750") and the inside of the steel link is 7/16" (0.438").  The brackets are each 0.040" thick and the link is made of 0.050" thick steel.  Allowing a little (0.010") for clearance for the brackets and link to move, and about the same for the links to move in and out doesn't leave much to form the heads on this rivet. (.750-.438-(.050x2)-(.040x2)-.010-.010)/2=.056" for the rivet head height.  They can call it a rivet all they want I have no way to form a head on a 3/16" rivet and still have all these parts move.  As an alternative I looked at using an aluminum book binder screw (male and female parts which screw together).  They are readily available but the shaft diameter is more like 7/32" than 3/16" and the aluminum seemed very soft and would wear out to quickly.  I decided to make the same type connector with a piece of 3/16" x .035" 4130 steel tubing and an AN526C-632R6 in each end.  The screws will be held secure with Loctite.  The 6-32 version of the AN526C screw has a head height of  0.860" so it will need to be ground down to clear when folding.  After grinding there is still enough of the Phillips slots left to easily install and remove the screws.  The 6-32 screw is perfect since the inside diameter of the tubing is almost exactly the correct hole size for tapping the threads.  The head on these screws are a large enough diameter that they will hold the parts securely even as the holes in the brackets wear out larger.  Because of their size they can also be tapered nicely to more easily slide into the link during folding.
The process for making these parts is easy, thread a piece of tubing about 5/8" long and modify 2 screws.  I have no easy way to hold this small piece of tubing while threading it.  A collet would work nice but I don't have one.  I chose to use my metal bending pliers with a piece of Scotchbrite to get a good grip without scratching or distorting the tubing, it worked well.  Threading works best with some cutting oil.  After the first couple threads are cut, small moves turning the tap in a little and back a little with very light force will prevent breaking the tap.  They are very brittle.  Because of the small size and fine threads I only went about 3/6" in and then removed the tap and washed off the chips in MEK, and then re-oiled the tap.  This made it a little slow but the threads came out nice.
The piece was then cut off on the band saw and the end ground square with the belt sander.  The trick to getting a nice clean square end is to roll the tube holding it against the miter fence as you move the fence across the face of the belt.  By using a light pressure against the belt you can take off as little as .0005" in a pass.  I ground the end down to make the length about .005" longer than the desired finished length.  I counter bored the ends of the tube and this extra length left some metal for cleaning up the ends after drilling.
The counter bore is done for 2 reasons. First it assures the screws will seat completely when tightened.  The other reason is because the tap is not long enough to cut threads all the way to the end of piece of tubing.  The first few threads on the tap are not full treads to make it easy starting the tap.  The other end of the tap has a bit of a shoulder which limits the depth the tap can go.  The counter bore allowed the tap to be run in just deep enough to run the tap in from both ends to clean up the threads at the far end.
The counter bore was only done about .020"-.030" deep so there would be as many good threads as possible.
Now the tap is just enough deeper.
The 3/8" long screws had to be shortened slightly so they would both bottom out against the tube ends.  I probably could have used 1/4" screws but I used what I had.  The heads were ground down by chucking the tube in the drill and spinning the screw while grinding it.  You have to work on the side of the head which holds the screw tight or exciting things happen as the screw comes out at high speed.  That's probably why I wear safety glasses at all times, not just when doing something dangerous.
After grinding I finished the screw heads with a fine mill file to smooth them up a little more.  I don't want them to wear a notch in the sides of the aluminum link.
Except for painting the steel parts I've run out of things to do on this.  Now I can install them and put the new glass in the doors.  I didn't want to install the side glass until I was sure all this would fit and work correctly.

Friday, December 16, 2011

Aluminum Window Latch Bracket (Cessna 0411360)

 This part was originally made from an extrusion, cut to 5/8" wide and the holes added.  I don't have any way to get the extrusion or to cut the shape from bar stock with a milling machine.  Instead the plan is to use the hole saw to cut the concave curve at the rivet end and the belt sander to shape the rest of the pivot end.  I decided to make 4 pieces to make it easier.  The first step was to band saw 2 blocks 1-5/16" long from a bar of 1/2" x 1-1/4" 2024-T3 aluminum and square them up with the belt sander.
 I'm going to clamp the 2 blocks together and use the hole saw to cut down the split between them 1/4" from the edge.  Since the 3/4" hole saw will cut past the edge I need a pilot hole to assure it goes straight through the blocks.  The easy way to assure the hole is straight and square is to cut it with the table saw with half the width into each block.  The fence is set to center the cut 1/4" from the edge and the blade is set 1/16" deep.
 The 2 blocks are clamped together with the bottom and side faces lined up.  The square cut hole is drilled out to 7/32" diameter.  The drill on the cutter is 1/4" so this will leave a little for the drill to assure it fits tight as the cutter saws down through the block.  The teeth on the saw have set, so the body of the saw won't help pilot it through the hole.

 The cut is started with the block setting on the metal table to assure it is as square as possible.  Half way down a piece of smooth plywood is set under it to allow the drill and cutter to clear the end of the block.  The adjustable wrench is there as a stop to prevent the block spinning, which would be a major disaster.  This all worked perfect and turned out to be quicker than I dreamed possible.  The gap helped clear the chips.

 The points at the open end need to be removed to leave a flat area for the rivets which is also parallel to the bottom surface. Back to the table saw.  I should have made a holding block for this cut.  It didn't look this unsafe when I did it.  The blade is 1/8" from the fence and 1/4" deep.  it worked great.

 The blocks were then band sawed in half and and squared up with the belt sander.
 A piece of 1/16" aluminum angle was cut off to use as a jig for locating the rivet holes and the pivot hole.  By clamping the block against the side, and with the end lined up with the edge both rivet holes can be center punched with the 1/8" punch.

 The center punched holes are then punched with the 1/8" Whitney punch.
 By clecoing the part back in the fixture, the center of the pivot hole can be punched with the 3/16" punch.  Because this hole will be drilled I center punched the mark to improve the drill centering.  We tend to call a spring loaded punch a center punch but they really are prick punches.  The center punch has an included angle the same as a drill.  The prick punch is a much sharper angle so it will make a more accurate mark. Because the center punch angle is the same as the drill it will keep the drill from wandering better than a prick punch.

 Another help to an accurate hole is to use the center drill until the hole edge is about 1/16" deep.  Then the standard twist drill can be used to drill through withe a good hole.  Once the part is finished this hole will be drill out from 3/16" to 13/64" to give the pin some clearance to pivot easily.

To finish the shape the same method of pivoting on a bolt is used as in making the false rib tool for the Waco Nine project.  The parts are all done. Clevis pins will be used for the outboard and center pivots.  The inboard pivot was a rivet.  The clevis pin won't fit so I still need to solve that and paint the steel parts.  It all the parts fit and work as planned.  I could have bought these assemblies from Univair for $286 each.  Clearly this was more fun and may have even been cheaper even allowing for my labor because I Built 4 latches.

Thursday, December 15, 2011

Window Latch Knob (Cessna 0413169)

 I don't have an actual knob so the best I can do is work from pictures.  There are pictures on pages 21 & 24 of the owners manual and the drawing in figure 30 of the IPC.  I'm making these from aluminum which will be riveted to the aluminum link and have holes for the center pivot pin to hold it securely. There are 2 parts to make this knob (handle seems more correct). One is a folded piece of .025" 5052-H32 aluminum sheet and the other is a piece of the .040" I used for the aluminum link.
 The folded piece is 1" x 3-1/4" and the flat piece 1" x 1-3/8".  The flat piece is just a stiffener to distribute the loads into the bent piece without it cracking from fatigue to quickly.  The bend lines are 5/8" from the center and 5/8" from the ends.  I used 5052 because I need to bend a tighter radius than 2024-T3 could handle without cracking.
 For small parts like this the easiest tool to use is a pair of Vise-grip sheet metal pliers.  I put as much radius on the blade edges as I could (+1/32"), they come with a sharp corner.  It took a couple pieces to work out the dimensions to form the parts.  I just line up the bend line with the edge of the blade and bend it over by hand, pushing the aluminum right at the bend to keep the radius tight.
 There are 2 bends to make so I just bent them to about 45 degrees.  The ends are close to forming a triangle.

 Then the pliers are used to make the reverse bends.  Line it up and bend while pushing the pliers in to finish each of the first bends.  The bend angle isn't critical at this point because the stiffener needs to be inserted and the end bends squeezed tight.  At that point the tab bends can be squared up.

 With the stiffener inserted,The link is positioned to leave the knob overhanging the link about 1/16".  There isn't room to get the Whitney punch in the channel so the stiffener need to be center punched and the removed and the hole punched.  Then that hole enter punch is transferred to the knob.  Again the punch won't fit in so in this case the hole must be drilled.  Before riveting these 3 parts together the hole will need to be reamed with a #30 drill to get the rivet to fit.

 To make the holes in the sides, the center of the hole on the inside part needs to be transferred to the outside of the knob sides.  They sell a tool for this but it's such a simple tool to make I've never bought one.  First I cut 2 strips of the scarp .040" aluminum about 1/2" wide and about 4" long.  Three holes were laid out on one piece 1/4" from each end and 3/4" from one end along the center line.  The holes were punched and then transferred to the second part.

 An AN470-4-3 rivet will be squeezed in one of the ends with only one hole, but first the 2 strips need to be clecoed together and the edges at that end filed to the same width.  I did this to assure the 2 holes, the with the rivet and the one without are lined up after riveting the other end together.  The 2 holes at the other end are close enough together that the 2 strips can be misaligned while riveting. We're going to plug one of the holes at the other end so the only way to easily keep them aligned is just to make them the same width.  The hole locator rivet needs to be squeezed so the worked end just snugly fits in the 3/16" holes in the link. The worked end of the rivet needs to be on the inside of the 2 strips.

 With the handle end riveted together the 1/8" punch can be used to mark the center of the new hole.  The holes that get riveted need to be reamed with a #30 drill.  Don't drill the hole for the punch and it will fit so nice and snug you won't need extra hands to use this tool.  With the knob clecoed to the link the locator rivet is fit into the pivot hole in the link and the punch lightly tapped to make a center mark.  You need some kind of backing block to hammer against but you don't need much of a mark.  You can re-punch it with a spring loaded punch if it helps to find the hole when punching the 3/16" holes.

 The holes are perfectly aligned on both sides.
 The last step is to round the corners on the knob.  I soften all corners and edged.  Sharp corners do not add any strength.  They do add weight, I know it's not much but it all adds up.  They also add safety hazards.  I carry band-aids with me at all times but they are a pain to use when you are bouncing around the sky because some slacker didn't soften all edges and corners.
 Ready to rivet and it all aligns perfectly.  An AN470-4-4.5 rivet and the job is done.  One more part and it will be ready to install.