A picture of entire spray
machine during development. The wooden frame supports the spray tank and
all associated hardware. There is a hinged lid on the frame to convert
it into a table top when not in use. The whole machine has been designed to be
stored and operated permanently outdoors.
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| A picture when I was in the
middle of developing the control box firmware. The stepper motor drive, had taken quite some programming effort from me. |
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Early in construction. Here I
was gluing PVC strips to the tank wall. This is a ledge to support the
glass lids.
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Top view of whole machine. Next
to the spray tank is a 3 stage counterflow rinsing tank. This was added
because of the need to quickly rinse PCBs after etching. For the
alkaline ammonia copper chloride type etchant I am using, any residue etchant will dry
and cause thick film of copper hydroxide that is difficult to rinse. The gray strip in the center
is a cover for the PCB opening slot.
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The tank top shown with the slot cover laid up side down. The PCB is inserted in the slot between the
two glass lids. At one side of the PCB slot there is a stationary
rubber lip, while other other side has an opposing PVC hinged door than can open
and close. This shutter arrangement is located just below the two
glass lids and will prevent etchant
mist or spray from escaping out. This idea was based on about 4 previous
design attempts I had at trying to stop spray mist while also allowing PCBs to be inserted.
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The spray tank with both glass
lids
removed. The hinged shutter is still installed. You can see a titanium
pin at each end, which is feed through into the tank side walls.
A piece of 1.5mm thick rubber is glued to the shutter and
makes contact under the glass lid to seal against spray
mist. This piece of rubber also acts as a spring
to force the door shut. Two small leavers located at each end of
the shutter are to open the door by pressing down on them
with your finger.
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Front view of tank. You
can see
the stepper motor housing and external pulleys for driving the spray
arm. The front cover of the machine is resting beside the tank,
with a bundle of wires poking through a hole and into the control box
on the other side.
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View of the sealed shaft and
bushing for driving the spray arm. This is a packing type seal,
where PTFE tape is wrapped around a 3 mm titanium shaft and packed down
by a plunger. Two M3 screws force down the plunger and compress the
PTFE tightly around the shaft forming a liquid tight corrosion
resistant seal.
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The spray arm assembly. This
is the traveling spray arm which directs etchant onto either side of
the PCB. It moves at constant velocity back and forth over the
etching area. Three white polyethylene wheels are responsible
for guiding the spray arm. A 8 mm diameter plastic coated
steel shaft (not shown) feeds in between the three wheels with
neat fit into grooves machined in each wheel. The 8 mm shaft spans the
length of the tank and is fastened to the tank wall at a fixed height.
The opposite side to these wheels is a free running wheel that simply
runs on the tank bottom. All wheel shafts are of polished 3
mm titanium rod. The flat EPDM rubber belt is clamped down to the
spray arm is for driving back and forth by two opposing pulleys fixed to the tank wall.
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Nozzle close up view with flow
restrictor. The two lower nozzles required a slightly reduced flow rate
to match etching rate of the upper nozzles. I suspect the added etchant
contributed by solution run off from the upper nozzles causes increased
etching on the lower side. The upper 2 nozzles do not haveadded flow restriction.
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The hall effect sensor. This
sensors the mid point position of the spray arm. A magnet is embedded
in the spray arm to trip this hall effect sensor external to the tank.
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The control box close up view.
A simple interface. The knob is rotated to desired number of
spray sweeps and start button is pressed. The temperature is
also continuously displayed.
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Stepper motor and housing
for driving the spray arm. The stepper motor is a 55mm tin can type
with 7.5°/step and was salvaged from an old printer. It is mounted
in a end cap of 100mm PVC sewage pipe.
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Closeup view of pumps. The
mounting plate has four folded down sides to prevent falling liquid
from running onto the motor and electrics.
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Machine bottom front view.
This shows the two pumps, the pump mounting plate, the drain
valve, filter housing, and associated plumbing and wiring.
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Machine bottom view of from a side angle. Shown are the
three hoses connected to the tank bottom. The left two (clear hose) go
to pump inlets, the right hose (black) goes to the filter outlet.
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The pressure gauge and
diaphragm seal. The pressure shown is during normal etching. Pressure
is sensed at the pump outlets and prior to the the filter.
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