Introduction: Solder Feed System

I made those feeders (yes, there are two versions: V1.01 and V2.0) because of my recent job in completting PCB kits for modular synths. It is a dull job but it's paid for pieces, so I wandered, how to make it more effective and give my time more worth. At last, you don't want to touch lead solder with bare hands for 4hous a day.
After building V1.01 I noticed, there already are instructables about it:
-uncanny simillar Solder Buddy
-and some purely mechanical systems

You can buy those systems from HAKKO or Weller for fairly high prices or under 100$ fom Aliexpress.

V1.01 costs me about 2$ for bowden, some nuts, FET and V2.0 about the same.
As you will see, my philosophy is to salvage and any time I have to go out, buy some parts and deal with general public, I take it as personal failure.

Step 1: V1.0 Whatcha Need

This version is Q&D and I will make it short.

Some necessary parts:
-DC printer motor
-microswitch from old PC mouse (they are high quality and easy to mount, right one is obviously better)
-1.3 intravenose needle (for 0.5mm solder wire)
-sheet metal
-nuts and bolts
-bike bowden
-sheet plastics
-metal ballpoint pen
-optional electronic parts for Q&D pwm

Tools needed:
-circular grinder (optional)
-DC source 12-18V
-creativity and history of hoarding dead and obsolete electronics
-hot glue gun

Step 2: V1.0 How It Works and How You Can Build It

There are some critical aspects, that you have to get right.

Torque of the motor is sufficient, but it is just with higher voltages (6-16V), so it is speed of feed then.
At first i powered it with simple LM317 1.2-14V 1A DIY supply, but:
If you want to feed solder just by pressing the trigger, not moving your hand, you will have to add PWM.
I used this guys circuit
Just with IRF510, because it is cheaper and original FET is overkill.
Now it runs from 16V laptop power supply witch is enough to move motor with good torque and low revolutions.
This is 12v motor, but it doesn't run continuously on 16V and it does not go even warm...
16V is good even for 555 witch has its maximum voltage 18V.
On the side, where wire is exiting gears you want to have bowden tubing as close as possible, so solder will not curl and make you angry.
Pressure of the bearing should be adjusted precisely, so motor bearings could spin freely and there will be enough of pressure to move solder.
On the tip of extruder pen i found no easy way to transit from larger diameter bowden tubing to the needle, so while you want to do a first feed, you have to disassemble tip and guide solder into the needle manually.

Now please look at the picture descriptions and:

Step1: look around you and think what is close to your application.
Step2: gather those things in one place
Step3: Proceed until you think, it is complete
Step4: Take your hack-saw and drill and mod those objects in the box in to the parts of the desired device
Step5: Assemble the device
Step6: Curse loudly why it doesn't work properly
Step7: Debug it, learn something.

I use it every day, ant it makes PCB soldering about 20% more effective, it took about 5 hours to build it.

Step 3: Intro to V2.0

Principle is the same, but it is possible to mount it on the iron in matter of seconds.
This one took far longer to build, then I could ever admit. And it still needs some tweaks. It is great tool for tons of wiring and big pads on the boards but not enough for precise work.

Step 4: V 2.0 Circuitry

Idea is to controll motor speed and feed time to achieve exact quantity of solder to be extruded after one trigger press. It leaves same looking joints as you can do small pads with one click, and bigger ones with more.
Circuitry is not on the PCB, it is just really dirty P2P ratnest. This is why I did not bother with EAGLE. It is just breadboard->paper->abomination.
I put here LM7805 which is not in the schematic to run 555s so I could later power it from anything between 7-20V (I guess 20V is the limit of motor). Also monostable 555s high-time is voltage sensitive.
It is not the most stable circuit in the world, PIC would be a better solution, because I noticed that reverse function would be nice (after each feed it would retract solder away from tip)

Step 5: V 2.0 Drive

I modded microwave gears to be driven from printer motor, all I had to do was to drill some new holes in to the case and and attach original gear to printer motor. I found out, that most effective way to remove original printer gear from motor is to crush it in the vice. Motor is attached to the gearbox with 2 M2 laptop screws. Be aware not to put too long screws in to the motor because you can damage winding this way.
On the second picture you can see solution of releaving stress from mw gears by scizoring it between two longboard bearings.

Step 6: Handle and Appendix

Handle is the most tricky and critical part of this build. As solder travels through it, it can only pass from smaller diameter to larger or there has to be a conic shape transition to avoid jamming. In ideal situation there would be constant diameter of 0.6mm for 0.5mm soldering wire.
Handle is made of two metal plates screwed together. I Q&D designed them in CAD, printed, glued on sheet metal from CD-ROM and grinded around. You can download pdf with sheets designed for WECP-20 handle.
Metal sheets got two of magnets glued inbetween with corresponding polarity to iron handle magnets.
Tip is the worst part, after struggle with finding the right material for it: metal tube with 0.6mm inner >4mm outer diameter and 10cm long. I've surrendered and chose non ideal solution- telescopic anthena segment with teflon tubing inside. It has its limits, it is soft so it bends easily and rapidly decreases accuracy of solder extrusion.

With present tip it is ideal for wiring and big pcb joints. If you have an idea about tip improvement, don't be shy!