11/2000
The WR42, 24 Ghz, 4 port transfer switch is made
up of several machined parts. The parts in figure 1
from left to right are: knob, tfe spacer, top plate,
bearing cover plate, main body, rotation stop pin,
rotor assembly, and bottom cover. The rotor consists
of an upper section with shaft and rotation stop pin
and a lower section. Both upper and lower sections
are fitted with ball bearing races. The upper section
contains the arched waveguide slots on its bottom
surface. The
lower surface of the waveguide slots are formed by
the addition of the lower section. Slots in the
control knob, similar to those in the rotor, indicate
the passages through the 4 ports of the switch.
PROCEEDURE:
Make facing cuts on both ends of the 1-1/4"
OD aluminum bar and a 0.005 cut across the outside
diameter to clean up and smooth the outer surface.
This is cut into three pieces using a cutoff tool
in the lathe. Cut off pieces to be finished to 3/4"
long, 5/8" long and the remaining section
approximately 1- 7/16" long. Make facing cuts on
each rough end and finish to size with the exception
of the 1-7/16" long piece which will be left long
for now. This will be the rotor and will receive
the waveguide cuts and upper bearing. The remaining
length will become the rotor shaft. The 3/4" section
will be the bottom of the rotor, forming the bottom
of the waveguide slots and holding the lower bearing
race. The remaining 5/8" piece will be used for the
control knob.
Machine the 3/4" thick piece of 6061T6 aluminum
to 1.5" square. It is important that it be exactly
1.5" on each side, and square. Waveguide slots will
be cut in the exact center of all four sides after
machining for the rotor and upper bearing. Cut the
0.060, 1/4", and 1/2" aluminum 6061T6 pieces to1.510"
square. Make a cleanup cut on the top and bottom
faces of the 1/2" and 3/4" blocks. Usually a couple
of thousandths cut with the flycutter will clean and
smooth the surfaces really well. The 1/4" block will
be done later after machining the rotor stop cutout.
The 0.060 bearing cover plate I used was as anodized
piece and did not require further finishing.
On all of the squared up pieces, find, and using
a center drill, mark the exact center of each. Drill
a pilot hole thru each with the exception of the 1/2"
block. On this piece locate the center and drill the
pilot hole only to a depth of 1/4" on one surface only.
SELECTING THE BEARINGS:
An old defunct 100 MB computer hard drive contained
two bearings with the following dimensions:
ID 0.198, OD 0.512, Thickness 0.156. If you use
bearings of different dimensions appropriate changes
will have to be made in the bearing seats, shaft
diameter, etc.
MAIN BODY:
Open the center of the 3/4" block with a 1/2" drill.
Chuck block in lathe, center up and enlarge the 1/2"hole
with a boring bar to except the bearing with a push in fit.
It should be snug but removable with moderate pressure.
On one face of this block enlarge the hole to except the
1.240" rotor to a depth of 0.594". (The block thickness
minus the bearing thickness 0.750 - 0.156 = 0.594) If
your bearings are different change both of the above
operations accordingly. Open the rotor hole in the main
body until the rotor just fits. It should turn easily
with no binding.
Mount the block in the milling machine with the
large rotor opening at the top. Cut the waveguide slots,
0.420" deep and 0.170" wide, centered on each of the four
sides. Clean up the edges after machining.
ROTOR:
Insert the rotor into the main body cavity and mark
where the rotor is flush with the top of the block.
On the opposite end drill a center hole in the rotor
and tap for 4-40 screw approximately 1/4" deep. This
area of the rotor will be cut down to the ID of the
bearing and shaft after the waveguide slots are cut.
Using the piece of 1/4" X 1-1/4" X 1-3/4" aluminum
plate make a jig for machining the rotor slots. Machine
the 1-1/4" dimension to the exact diameter of the rotor
body. (~1.240") Mark off a square area at the end of the
plate 1.240" by 1.240" and locate its center. Put the
plate in the milling machine and using a center drill
locate the center hole and two other holes 0.425" in
line with and on opposite sides of the center. Drill a
pilot hole with a #55 drill at these three locations.
Open the center hole to just clear a 4-40 screw and
countersink one side so screw head will be just under
flush with surface. Mount rotor to this plate with a
4-40 FH screw. The outside edges of the rotor should
be flush with the plate edge on three sides. With the
#55 drill locate the other two holes in the rotor.
Remove from plate and drill and tap both holes for 4-40
screws. Drill out and countersink the two remaining
holes in plate. Mount the rotor to the plate securely
with three 4-40 flat head screws.
Mount the rotary table, set at "0" degrees, on
the milling machine and locate the headstock to the
center of the table. My rotary table has two "T"
slots on it that divides the top into 4 equal segments.
The slots are 0.248" wide. One half of the slot is 0.124".
Set the jig, with rotor attached, in the lower right
corner of the upper left quadrant of the table. Align
to leave 0.124" on the "X" and "Y" axis of the "T"
slots showing. The lower right corner of the jig
should be at the table center. Clamp the corners
of the jig securely to the table and set the cutter
well above the rotor. Dial in 1/2 the rotor diameter
on the "Y" axis. This puts the cutter in the center
of and to the right side of the rotor. Back the
cutter off a few degrees by turning the rotary table
and bring the cutter down to the material. Cut the 90
degree arc in the surface of the switch rotor to a
depth of 0.420". Check width and cut each side equally
to a width of 0.170" maintaining the 0.420" depth.
Remove the jig with rotor attached from the milling
machine and rotate the rotor 180 degrees on the jig.
Align as before and repeat for the slot on the other
side of the rotor.
Remove jig and rotor from rotary table and
remove the three screws holding the rotor to the jig.
Insert the rotor into the main body block and
recheck the depth line on the rotor previously made.
Chuck the rotor in the lathe with the waveguide slots
facing toward the chuck. Reduce the diameter of the
exposed end to the depth line to 0.250". Leave a
0.002 segment next to the rotor and reduce the
remaining shaft for a tight fit to the ID of the
bearing. As before, if using different bearings,
adjust dimensions accordingly. See rotor drawing.
Clean up rotor slot edges and insert the rotor
shaft up thru the bearing seat hole in the main body.
The lower edge of the rotor should be flush with the
bottom of the main body and when rotated the rotor
waveguide cuts should line up with those on the four
sides of the main body. If problems occur with upper
bearing alignment the bearing seat can be opened and
a tolerance ring installed. 1 This will
adjust for minor misalignments in rotor and bearing seats.
Make sure "no drag rotation" is possible to at least
two slots. If complete rotation is possible so much
the better, however only 90 degrees of rotation will
be necessary on final assembly.
TOP PLATE AND BEARING COVER PLATE:
Open center holes in the top plate and bearing
cover plate with a #7 drill. Locate and drill pilot
holes in the top plate, bearing cover plate and the
top corners of the main body. These are to be 0.125"
in from each edge in all four corners. Drill the top
plate first and use as a template for the other two.
Open the top plate corner holes for clearance of 2-56
screws and countersink the cap screw heads using a
larger drill to 0.125". Drill and tap the corner
holes in the top of the main body for 2-56 screws
to a depth of 0.250".
BOTTOM COVER:
Locate and drill pilot holes in the four corners
of the 1/2" block 0.125" in from each side. Drill
all the way thru the block. Chuck block into lathe
with the previously located center drilled side
facing away from the chuck. Extend the center hole
with a pilot drill to a depth of 0.400". Open hole
with a 1/2" drill to this same depth, 0.400". Use the
boring bar and open hole to ~0.510 for the lower
bearing seat. This should be a snug fit. Leave 0.165"
for the bearing seat and clearance and open outer 0.235"
of hole to rotor diameter, 1.240". See pictures.
LOWER ROTOR:
Fit lower rotor section into the bottom cover,
mark and turn to bearing ID. Leave 0.002" X 0.250"
diameter shoulder for clearance. Cut shaft to 0.152"
long and press bearing onto shaft. Drill two pilot
holes with #55 drill for mounting to the upper rotor
section. Place lower rotor section on bottom of upper
rotor and locate holes. Drill and tap for 2-56 screws.
Countersink heads in lower rotor at just below flush
with rotor bottom. Using previously drilled pilot
holes in bottom cover, align, locate, drill and tap
2-56 corner holes in bottom of main body to a depth of ~ 0.300".
PREASSEMBLY AND CLEANUP:
Assemble rotor into main body and attach bottom
cover and both top and bearing cover plates. Assure
no drag rotation of rotor and snug up top and bottom
mounting screws. Mount assembly in milling machine
and with the fly cutter take a cut of 0.006 to 0.010"
to get all plates and main body flat and even on all
four sides. Using a prick punch make a witness mark
on the upper corner of each plate on one side for
future alignment. Flycut the bottom of the bottom
cover for a clean smooth surface. Disassemble and
remove top plate. Clean off top surface of top
plate with fly cutter. On the bearing cover plate
cut a 0.0625" slot centered on the center hole the
length of the stop pin. This enables removal of the
plate when the stop pin is installed in the rotor
shaft. Once the stop pin is installed the rotor
cannot be removed from the body without removing
the pin. Locate the pin location on the shaft to
fall in center of the thickness of the 1/4" top
plate. Drill hole in shaft. The pin I used would
just go thru a drill gage #59 hole. The shaft hole
was made a #60 and the pin was pressed in. If you
have trouble locating a pin a #59 drill shank will
fill the bill nicely .
Locate a 90 degree segment, plus one half the
diameter of the stop pin on the bottom side of the
top plate for removal. Make sure of its location
relative to rotor rotation if rotor only turns
freely through a 90 degree segment. You don't want
the 90 degree area to be where the rotor binds when
the witness marks are aligned on assembly. Mill out
this area to a depth of 0.215 to 0.220". See picture.
Locate holes for end of rotation stops and drill #43
hole for taping with a 4-40 tap. Open clearance hole
for the tap body to a depth of 0.500" with a #27
drill. Tap holes and insert 4-40 Allen head set
screws flush with the 90 degree cutout edge. They
will be adjusted later on final assembly.
WAVEGUIDE MOUNTING HOLES:
Remove the rotor assembly from the switch.
Put the bottom cover back on and snug up the screws.
Using a piece of hardwood (maple) shape a rectangular
piece to the size of the internal dimensions of WR42
waveguide and about 2" long. Insert this through two
opposite holes in the switch body. Lay the body on
the workbench with one side down and the hardwood
protruding through the waveguide slot on the top.
Place a waveguide spacer (this is a block of metal
with waveguide cutout and 4 mounting holes bored
through it) on the exposed hardwood flush to the
side of the switch body. Using a #32 drill bit
with the shank end ground to a point insert the
drill shank end into each of the 4 holes in the
waveguide spacer and tap lightly with a piece of
wood. Repeat this process until all four sides
of the switch body have mounting hole locations
around its waveguide slots. Prick punch these
16 holes and drill to a depth of 0.200" with a
#50 drill. Do Not penetrate the rotor cavity
wall - use caution. Tap all holes with a starter
tap followed by a bottoming tap.
KNOB:
With the remaining 5/8" piece of 1-1/4"
diameter aluminum make the knob. Locate and
drill the hole for the rotor shaft. Drill
and tap the side of the knob for a 4-40 Allen
set screw. Mount knob on rotary table and
make two 90 degree cuts about 0.010 deep on
the knob top. These are used to indicate
connecting ports on the switch. See picture.
Cut a small 1/2" doughnut from 0.005" teflon
sheet to be used as a spacer under the knob.
ROTOR ATTENUATION SLOTS AND FINAL ASSEMBLY:
Mount rotor onto milling machine and with
a slitting saw cut 0.010 slots in the rotor
parallel to the long dimension of the waveguide
openings. These are located 0.125" on each side
of the waveguide openings and are 0.125" deep.
They are cut the entire length of the rotor.
In the bottom cover drill a center hole
with a number 43 drill. Tap this hole using a
4-40 tap and install the nylon hex head bolt
with nut attached up thru the bottom hole.
The nylon bolt is used to put friction on the
rotor to prevent accidental movement when
switching from one position to the other.
The nut is used to lock the bolt in position.
This bolt assembly is not shown in any of the
drawings as it was added when it was noted that
the switch could get offset from the desired
position too easily!
Clean all pieces thoroughly and wipe down
with a solvent such as lacquer thinner. Assembly
rotor into main body and press stop pin into shaft.
Install bottom, bearing, and top covers and secure
mounting screws. Place spacer and knob on shaft.
Adjust indicator slots to the switch position and
tighten the knob set screw. Check rotation and
adjust set screws for proper rotational stops.
Adjust the nylon bolt in the bottom cover for
slight frictional binding of the rotor movement
and tighten the lock nut.
FINAL COMMENTS:
If you are a machinist by trade this probably
took you much less than the 60 hours that it
took me. The end results are however well
worth the time and effort.
NOTES:
Cross-talk between the two circuits is less than -45 dB (which was just
at the limit of the test equipment setup).
The information contained on this page is provided for amateur radio interests.
It may be copied for those purposes only. If copied and reproduced for this
purpose, this statement must also be copied and reproduced. This material was
authored by W1RIL and presented at http://www.wa1mba.org/
1 Pc 6061T6 Aluminum plate 3/4" X >1.5" square 1 Pc 6061T6 Aluminum plate 1/2" X >1.5" square 1 Pc 6061T6 Aluminum plate 0.060" X >1.5" square 1 Pc 6061T6 Aluminum plate 1/4" X ~1-1/4" X ~ 1-3/4" (for jig) 1 Pc 6061T6 Aluminum rod 1-1/4" dia X 3-1/4 long 2 Ea Bearings (from defunct computer hard drive)
ID ~ 0.193", OD ~ 0.512,
Thickness 0.156"8 Ea Socket head cap screws, SS, 2-56 X 3/8" long 2 Ea Pan head screws, SS, 2-56 X 3/8" long 3 Ea 4-40 allen head set screws 3 Ea Flat head screws, 4-40 X 3/8" long (for jig) 1 Ea Pin 0.040" dia X 0.665" long 1 Ea Tolerance ring (may or may not be needed - see text) 1 Ea 4-40 hex head nylon nut & bolt 3/8" long
Tolerance rings are available from Small Parts Inc. Miami Lakes, FL 33014-0650