We
have decided to manufacture the WAFs (Wing Attachment Fittings)
ourselves as we have access to the necessary machinery and the know how
to operate it to make precise replicas that are accurate to 0.001mm.
The CNC machine had been moved to its current position and
left
dormant for a number of years. We volunteered our time to
perform
the maintenance needed to get it back up to running condition.
Naturally we needed to test the CNC and what better
way than
to make the WAFs.
Hardy
has written out the code in Microsoft Notepad and is transferring it
from the laptop via a data cable to the CNC controller.
The CNC
controller steps through the code and orchestrates everything including
moving the table about the X and Y axis and the mill about the Z axis.
It takes care of all the tool changes, turns the coolant
on and off as required and looks after the feed and spin
rates,
though these can be adjusted manually while the program runs.
It
is not just a matter of lining up the points you want to drill then
just drill them. A 0.8mm deep pilot hole is drilled with a
2mm
drill bit for every required hole in the 0.125mm 4130N steel.
A
tool change happens, the coolant is then turned on and the lightening
holes are started with the same size bit. The program tells
the
CNC to take five plunges to drill every hole. This adds to
the
machining time but allows the bit and steel to cool enough between
plunges and in the flow of the coolant.
Another
tool change and the lightening holes are then widened to their
final sizes as mill stays stationary and the table moves in
increasingly larger circles
The final
tool change is for all those holes that the AN3 bolts will pass through.
First
job is now done as every hole has been machined. We got every
WAF
to fit on the piece of 4130N steel but not enough room to machine them
out. We knew this as soon as the sheet arrived but that is OK
as
it gives us an excuse to use the guillotine at work. You may
see
some small pilot holes is this photo. These are for alignment
with the guillotine to accurately cut out the WAFs.
Here's
the reverse side of the "work of art" after it has been dried off.
A few of the holes need a very light debur which will be done
by
hand.
Here is a video of the process.
..and a video of the guillotine in action.
Find a
block of steel that no one will miss, and clean it up. Might
as
well make it look nice in the process. Then mount it on the
mill, hard
against two 12mm dowels inserted into the table slots. This
provides
the reference position needed to align the WAF edges with the table Y
axis. Then clamp it down using my nice new set of clamps I
got given
by the family for my birthday.
Using the
large WAF, set the position of the large hole, so that the
smaller holes are still inside the edge of the jig, and the WAF edge
sits over the edge and can be cut without cutting into the jig. (Mental
note - test the small ones too next time). Set the verniers
on the X
and Y axis to zero for future ref. Drill the holes, starting
with a center drill ( a long drill might
dance on the surface otherwise), and then add some depth with longer
drills. I did find that the 3/8" drill ate the steel better
without
the 4mm pilot hole - it didn't chatter as much. Finish each
hole
before repositioning - this wouldn't be required if I had digital
readouts on the axis, but when positioning by hand on a table with a
fair bit of backlash, its easier to position it once and lock it.
With the
holes drilled, I cleaned up the hole edges with a countersink,
and mounted some brackets. Bolts through the holes in the
WAFs fit
perfectly into the jig and provide the alignment to cut the
edges.
Just need to make sure that the jig is hard against the dowels before
tightening the clamps.
Whilst
in storage I coated the WAFs with linseed oil to prevent rust
beginning. This oil must be removed prior to applying a rust
inhibiting paint. Acetone does the job really well but care
needs
to be taken as it is extremely flammable. Gloves are a must
too.
This stuff has a low boiling point and thus evaporates
quickly
which leaves your hands feeling very cold.
Look at my
painting production line. WAFs are hung on nails and then
sprayed with rust inhibitor.
Finished
and ready to be bolted to the spar ends.
The holes
have been drilled through the spars using a simple jig and digital
alignment which is explained here. I have used some
T-88 epoxy as well as the AN3-27A bolts for some additional holding
power.
AN365-1024A
elastic stop nuts with washers underneath are tightened up but not so
much that the WAFs crush the plywood webbing.
