Introduction: Arduino PID Controlled Lee 4-20 Metal Melting Pot

So, does anyone remember the bullet scare that happened not to long ago? Everywhere one went there weren't any bullets to be bought. Powder and primers were available but not to many had the equipment nor the experience to reload their own bullets. This was an eye opener for many. Looks like there is a way to legally circumvent the second amendment after all. In turn we adapt to the heads up that Obama was gracious enough to give us..... Yeah... anyhow, there are a lot of new re-loaders out there now. Time has gone by, Trump is now in office and people have become complacent. Well, sort of. Most can't let go of the fact that there is a loop hole waiting to be exploited. In turn the re-loaders guild has grown substantially. There have actually been new advances that make it easier to match factory loaded bullets tit for tat such as powder coating bullets to simulate jacketed bullets. Which has indirectly opened up re-loaders to duplicate if not improve on bullet velocities and precision. Hence, the reason for this instructional. I wanted to make a cheap alternative to lead casting that any joe schmo can replicate. Problem is that a lee pot for melting lead, all be it cheap but is also poorly designed when it comes to temperature control. There is a YouTuber out there that took a stab at this issue using a PID controller to regulate the temperature. ( You can look it up under "Johnny's Reload Bench, PID Controller"). Well i saw this vid and decided that i would spend the time to write this instructional and a YouTube video to help others miniaturize his approach to alleviating this issue of control using a Arduino Nano. It's small enough to cram inside of a lee 4-20 pot and can be accomplished for less than 60 bucks.

( You can use a Arduino UNO if you prefer)

If you get discouraged because there are not enough pictures in this instructional don't worry i made a companion video that i will link to at the end. So here we go.

Step 1: Material List

1 @ 10k Potentiometer w/ knob

1 @ 12v 1Amp Transformer

1 @ MAX6675 Thermocouple Module

1 @ Thermocouple Probe

1 @ 10 Amp SSR-10 or higher SSR-15, SSR-25, ect.

1 @ Thermo-Electric Grease

1 @ Arduino Nano

1 @ Nano Expansion Board

1 @ Jumper Wires (Female to Female & Female to Male)

1 @ USB B mount to 5 pin mini usb

1 @ USB B male to USB male

Thinks not shown in pictures and can be bought at your local hardware store:

1 @ 3/4" Metal Conduit Strap

1 @ 9 #4-40 Screws & 18 Nuts

2 @ Spade Terminal Connectors

2 @ Female Connector 1/4"

2 @ 1/4" self tapping screws (Speaker Wire Connector)

1 @ Small piece of galvanized flashing

1 @ 1-3/8" x 3-1/8" x 1/8" plexiglass or lexan

Amazon link : (Shop around for better deals)

Step 2: Tools You'll Need

-You'll need a drill and some drill bits.

-A hot glue gun high temp.

-Multi-Crimp tool

-Metal shears

- Dremel tool with cutting wheel.

-Needle nose Pliers

-1/4" nut driver

-Phillips head screw driver

-Lead Thermometer

-Soldering iron and electrical solder

-Heat shrink and/or electrical tape

-Computer with USB port

-Felt tip pen

-Measuring tape

Step 3: The Break Down

-Now it's time to get to work. Remove the 4 hex screws on top of the melter that hold the thermostat plate in place using a 1/4" nut driver.

-Remove the thermostat from the plate using your needle nose pliers to loosen the nut.

-Turn the pot on it's side and remove the hex screw furthest to the rear and center. Remove the two side hex screws leaving the remaining screws in place to keep the front shell with the element from moving. The case cover will now come off.

-Go ahead and unplug the wire from the element and set the cover aside.

- with your dremel tool you will want to cut slits into the bottom where they won't be seen when put back together. This will be your air vent that will let in the cool air. Cut the slits on the left side of the case bottom opposite of where the nano expansion board will mount.

Step 4: Soldering Components & Mounting to the Plate

-Insert the I2C board like the picture above and soldier the pins in place from the front of the LCD board.

-Using three Female to Male jumper wires, insert the male end thru the potentiometer and solder them in place. Then snip the excess pins off.

- Using the old Thermostat plate and a felt tip pen trace the shape and square hole onto a piece of sheet metal ,mark the holes as well then cut out with your snips.

-Using the square in the middle as a reference point measure and cut out the LCD screen with your dremel tool. Then dry fit and mark the holes with your felt tip. Before removing the LCD place the Potentiometer beside the LCD board and mark the hole for it and the location of the prong. (You want the Pot on the left because the element in exposed on the right side. This is were we will cut a vent to expel the heat.)

-Once you have all of your marks cut out, drill and mount your components to the plate.

(Don't forget the vent)

-After that go ahead and mount the plate to the case using the hex screw that is closest to the melting pot.

Step 5: Adding Components

-In the photo you will see the placement of the components. The only thing that i suggest is that you lift the nano expansion board up about 1/2" from the bottom. So that you won't have to extend the jumper wires from the potentiometer like i had to do.

- So place the board where you want it and with your felt tip pen mark the holes for drilling.

-Use your drill to drill the proper size hole to fit the #4 screws that you marked. Punch another hole to mount the thermocouple module. Then drill a hole below it to allow for the thermocouple wires

-Insert the screws and fasten with a nut to the case (This will keep the board soldier joints from touching the case).

-I like to take my hot glue gun and run a bead around the edges of the boards to keep soldier joints from touching the case then mount the devices fastening with another nut. Add a touch of hot glue to the nut to keep them from backing off.

-Using your dremel tool cut the square where the USB mount will go and once again mark the holes with a felt tip pen and drill, then mount.

-Place the heat sink and attach it to the cover using a couple of self tapping screws. Go ahead and cut off the excess of the screws with your dremel tool.

-Drill the holes next to the heat sink for the wires to go thru. Use the picture for reference points.

-From the picture you will notice where to mount the transformer, I use a glue gun to stick it to the case cover.

Step 6: Wiring It Up

-For the Jumper wires use whichever color you wish.

-All pins labeled GND are ground wires and should be connected to the G pin on the Nano inline with the driving pin you are using. Do the same with the pins labeled VCC to the V on the Nano

RELAY (+ = D2) (- = G)

- You might want to extend the relay wires using a female to male jumper wire so that it's easier to plug in.

LCD (SDA = A4) (SCL = A5)

POT (center pin = A2)

MAX6675 (SCK = D9) (CS = D12) (SO = D10)

As for the thermocouple, connect the red connector to the + and the blue connector to the -

It's probably best to shorten the transformers cord to allow more air space in the case.

Now plug in the power adapter to the expansion board and the mini usb connector to the nano.

Wait until the next step to close the case up.


Step 7: Programming & Final Touches

First goto this site and download and install the Arduino IDE program.

You'll need to goto this page to download the follow the instructions on how to install it.

After that download the PID_controller.ino file that is here. I have included 2 different files. The PID_controller.ino is a wide range setting. 450-1000 degrees in increments of 25 degrees. The PID_controller_625-880.ino is set to 625-880 degrees in increments of 5 degrees. Download whichever suits your needs.

Plug your melting pot to your laptop using the USB cable and open the Arduino IDE program. Open the ino file. Then under tools/board select Nano.

Under Tools/Port select the COM port that is listed.

Now just click the upload button (the Right Arrow)

After uploading Everything should be working.

The next thing to do is to adjust the potentiometer on the I2C you soldered to the LCD board. This will fine tune your contrast. Tune it to your liking.

Now that you know everything works, go ahead and unplug the USB cable from the melting pot and put the pot back together.

Before we continue, you will want to protect the terminals on the SSR from being contacted by you or any other thing that may happen by. To do this you will need some way to isolate the terminal screws somehow. You can use a shield of some sort or you can do like i did and fill the voids with hot glue. Either way you feel comfortable with.

Another topic to mention is the addition of a splash gaurd that should be added to the LCD so that lead doesn't splash onto the screen and burn it up. There are many ways you can accomplish this. I just hot glued a small piece of 1/8" plexi-glass over the top of it. i will show this in my video when i get it finished.

The last thing we want to do is to mount the thermocouple. To do this take a 3/4" conduit strap and flatten it out with a hammer or vice. Dry fit the strap to the rear screw on the pot and bend it to the shape like the picture above to the proper height needed for the thermocouple you use. I left mine about an 1/8" off the bottom. Use the needle nose to make straight bends. Drill it out using the proper size drill bit for the thermocouple. (Using a block of wood to support the strap will prevent the strap from spinning.) Attach it using the screw on top of the pot towards the back and use the needle nose to tighten then nut down on the thermocouple.

Finally, plug the wall plug in.

Voila! Your ready to melt some lead.

Step 8: Info & the Video & Updates

If you want to change the temperature setting on your melting pot then explore the ino file. I made notations that describe what to do.

The YouTube video is being recorded. Check back here to get the link when it is finished. In the meantime i have included a video that i made a few days ago that introduced this project.


Due to the high views i did this video when i was on cold medicine i'm a little forgetful at times but i wanted to get this video out. i will remake the video when i get better.

UPDATES: At the end of each video, i link to the next update. As of today i have made 3 minor updates to the design.