Tuesday, June 10, 2014

Painting The Floor Clips

I've tried epoxy paint and find it scratches off too easily.  In general I favor Zinc Chromate primer, with Enamel paint baked to harden it.  Epoxy is plastic so you can't bake it or it just melts.  Epoxy or aluminum tape are the only good solutions to protect parts where fabric will be attached or where Dope or Poly Fiber products will contact the painted surface.  The solvents in them attack Zinc Chromate.
 The original floor clips were Cadmium plated by WACO.  Plating is a good solution if you have a reliable plating shop that will properly bake the parts immediately after plating to prevent Hydrogen Embrittlement.
My choice is to paint parts.
I still wanted these to look as close to plated parts as possible.

I wash parts with MEK (available at Lowes and hardware stores) to remove any oils.

If you don't have Zinc Chromate, Dupli-Color Self-Etching Primer (from Advance Auto) works well.  You want 2 or 3 very light coats about 10 minutes apart so the metal is covered with very little buildup and let it dry 30 minutes.  I hang parts from coat hanger wire, and I wear latex gloves (from the farm co-op) to save cleaning my hands. The gloves also keep MEK out of you and your hand oils off the parts.

For the color I used Dupli-Color Engine Enamel, Aluminum, again 2 light coats 10 minutes apart, with a final slightly heavier coat and then dry 20-30 minutes.

To get the the satin finish of Cadmium plated parts I used 1 light coat of Rust-Oleum Painters Touch 2X Matte Clear (from the hardware store, Lowe's probably has it).

I then let the parts dry in the sun for a couple hours before baking them.

To bake the enamel I used our kitchen oven with one rack at the top.  I heated the oven to 325 degrees, then turned it off so it was less likely to explode.  I quickly hung the parts from the rack so they wouldn't touch, closed the door and left them until the oven cooled.

I've got some 100 watt bulbs to build a parts drying oven.  Hopefully a better solution than the kitchen oven.

The parts came out great.  Now I need to make the ones for the NINE before I forget all this.

Sunday, June 8, 2014

Floor Clips for WACO TEN

This post will be a little long because I never got around to writing as I was working on this.

As part of the trade with John LeBlanc for his radiator, I agreed to make new clips for mounting the floor in his WACO TEN.  The 3/16" plywood floor is screwed to cross pieces of spruce.  These cross pieces are attached to the fuselage lower longerons with steel clips which wrap around the longeron and and are screwed to the spruce.
The clips are made from strips of 0.050" sheet steel 3/4" wide.

At first I thought the floor was done the same in the NINE and the TEN.  The concept is similar but the details are not the same.  In the TEN and possibly later NINEs the cross supports set on top of the longerons (see the picture below of Bob Howie's NINE).  In my NINE the cross members are between the longerons, not on top.  I believe having the supports rest on the longerons makes the floor more stable then trying to hold them from moving at the ends with just the clips.  With the supports between the longerons the floor sets on the cross tubes where as in the TEN it sets only on the wooden cross supports.  Another difference is that in the NINE the floor board stops before the clips.  In the TEN it extends to the middle of the longeron tubes so it's under the top end of the clips.

On the TEN there are 2 style clips, P/N F-016 is a short one which holds the 3/16" plywood floor and the 1/2" spruce support.  There are 10 of these.  The blank for this part is 6 3/8" long.

The angled corner for the plywood was not on the factory part.  Someone had made a part for John with this bend and he liked the idea so I included it on these.  I think the person made a part and realized they forgot the space for the plywood and re-bent the part to allow for it/

The other style P/N F-017 is taller to hold the support which screws to the top of the floor so the front seat can screw to it.  The blank for this is 8" long.

While the details differ between the two the methods of making the parts are the same.
The shear I use won't cut .050" 4130 steel so I cut the blank strips with the band saw and smoothed the edges with the belt sander.  I didn't know how long the strips needed to be and wasn't confident in my calculations because of all the bends.  Instead I made the first of each part with a strip that was longer than needed.  I punched the hole in the first end and then measured the length.  Once the parts were formed I measured the excess and made blanks which allowed about 1/8" extra.
The way I made these was to work from one end to the other.  I started with the end under the floor and worked to the top end.  We'll get back to making the start end later.
The first bend is 90 degrees with a 1/16" inside radius.  It requires a form block and a backing block.  The backing block holds the metal tight to the form block to get a better bend.  For the form block I cut off a 3" piece of 1" x 1/2" steel.  I wanted the bottom to set on the vice with the top end a little above the jaws of the vice.  That way I could pound on it without it slipping down in the jaws and the strip wouldn't hit the vice while making the bend.

I started the hole with a center drill deep enough for the 3/16" drill to enter the hole.  Next I drilled the pilot hole through from the pilot hole of the center drill.  The hole was then finished with a #11 drill to provide a small clearance for the bolt used to position the strip end.

The backing block was done in the same manner.

I then carefully ground and filed a 1/16" radius on the corner and checked it with a radius gauge.

The end of the block was ground next, with the belt sander, with a 3 degree angle to allow for the spring back of the steel.  To set the angle on on the belt sander table I made a gauge board with a piece of plywood.

With the miter set square to the belt the end of the block was ground by sliding the miter back and forth with a gentile pressure against the belt.
By marking the end with a felt marker, or blue die ink, the end can be slowly ground until it is just blended with the radius.

The blocks are assembled with the strip between them and a 3/16" bolt in the hole to hold the end in position while making the bend.

The strip was squared to the top face of the block by aligning the edge of the strip with the edge of the square.

A hardwood block and mallet were used to form a nice 90 degree bend.

The next piece is a hardwood block to make the bend around the 1 1/8" tube for the taller F-017.  It's an "L" shaped piece.  To make the 2 sides of the leg of the "L" parallel, I rough cut it with the band saw and used the drum sander on the ShopSmith to grind the cut side parallel to the back side.  Just push against the drum, so it doesn't snatch it, then raise the table a small increment, and repeat until the surface is even and to the correct depth.
The round end was cut with the band saw and the belt sander used to smooth it to the lines on the side.
I used the bolt again with this block  to hold the bent end in position so I needed to drill a 3/16" hole for the bolt.  The hole center was punched using the 3/16" punch from the Whitney Punch through the hole in the clip.

I worried a lot about how I would bend the steel without breaking off the end of the block.  It bent around it just fine by hand.

Here you can see the spring back in the steel.  I did some experiments by bending pieces of steel around various pieces of tubing to determine the radius formed vs the tube radius and plotted the results.  From the graph I determined I needed a 1/2" form block radius to make the 9/16" radius to fit the 1 1/8" tube.

The next question was how far do I have to bend the piece around a 1/2" radius to make a 180 degree bend when it springs back.  The inside circumference of the finished bend is (½ π D) 1/2 x 3.1416 x 1 1/8" = 1.767".  The outside circumference of a 1" circle is  (π D) 3.1416". We need to bend the strip 22.5 degrees past 180 degrees around the 1/2" radius to make our 180 degree bend, (360º x (1.767" / 3.1416")) - 180º =  22.5º.  That's the angle which is cut on the top of the block tangent to the radius.
The formed clip goes into the vice with a block of wood under it to prevent it slipping down in the jaws and our piece of 1/2" steel behind it to back up the bend.

I needed a clamp to hold everything tight while forming the bend with the wood block and mallet.
That Completes the bends on F-017.  The blocks are slightly different but the idea is the same for F-016.
Back to making all those blanks.  I made a template out of some scrap steel 3/4" wide with a 3/16" hole punched 3/8" form the end.
This template was held centered on each strip and the 3/16" hole punched using the Whitney Punch and a punch with the center nib ground off so it can drop in the guide hole before punching.

All the blanks made.

To allow the bolt to fit easily in the hole I drilled them out with a number 11 drill.  This gives a couple thousandths clearance without the hole being too loose.

To round the ends I snip off a little of the corners and then grind them on the belt sander with a bolt through a scrap piece of wood.  Just swing the strip from here to the left, flip it over and do the other half of the end.
You clamp one end of the wood to the table and little by little move it closer to the belt so you only take off a little at a time.  That way you don't overheat the part or wear out the belt.
I do all the parts then move it a little and do all again, etc.  It goes quick enough.

Then you lightly grind edge wise from the flat pulling the part down to the center of the radius to just remove the grinding marks.  A light filing of the edge will remove the remaining burr.
The block was made for the shorter F-016 and the round end was formed by the same process.

Because of the joggle for the plywood on this part the bend angle isn't 90 degrees but it's close enough that I used the same 3 degree overbend for the spring back.  If I were making these again I would just make the corner square at the right height like on the F-017 clip.

Another block was made for the remaining bend. and the hardwood block and mallet used to form it.

With all the bends made I added a piece of aluminum angle to my hole template to punch the hole at the other end of the clip.  This stop is located so the hole is 1 1/2" from the outside of the tube and aligns with the first hole.  I riveted the stop on to the template with flush rivets so I can still use the other side to punch the starting holes in my clips for the NINE.

To hold the clip while punching the hole I used a small c-clamp.

The Whitney Punch was used like on the first end to punch this hole.

I ground a round end on my template and clecoed it to the clips so I could mark the the end with a felt marker.  I did this so I could see where to trim off most of the excess before grinding this end round.

To hold the first end nicely clear of the belt while grinding this end I made a "U" shaped clamp from a piece of 1/16" welding rod.  This pulled the end back about 1/8".  The end was ground like the first end.
By moving the bolt near the left edge of the belt and putting the clamp on the left side I was able to swing the clip 180 degrees.

Grind all the parts, nudge it in a little and repeat until done.

I smoothed the edge and deburred it like the first end.

To make assembling the floor easier the bolt holes were then drilled 1/64" oversize, as the factory did for most bolt holes, using a 13/64" drill.

All done, ready for paint.