METAL CASTING: Backyard metal foundry, introduction

Time to start a new project, which involves extreme temperatures, molten metal, sublimating foam and more like this. 

My propane burner


Backyard metal foundry will enable me to melt metal scrap into useful drafted objects that could be later machined with precision.
Temperature achievable at home (up to 1200°C) enable to melt aluminium, brass, copper, bronze. Iron requires higher temperature and different techniques.

The receipt involves few elements:
- a liquid propane tank. Liquid Propane has various advantages in respect to traditional charcoal foundry: requires less space, because energy density is higher, so mre energy. Here you could find in local stores 30 liters propane tanks with standard attachment.
source Own Work - author Hustvedt

- a propane burner
. There are various models you can build, with back air or with venturi effect. The one i decided to build is the simplest one. It attaches to propane tank with standard pressure reducer, then with a pipe attaches to a custom burner based on two elements, the burner itself which is a drilled steel water pipe of standard length and the gas diffuser, another steel pipe with tiny hole on the center. The gas flows from the tiny hole then mix with back air and blows a blue flame of high temperature. A possible add-on may be a back air blower to enhance the oxygen available to complete the combustion inside the foundry.

Note the burner itself has specific dimensions and more air holes to capture oxygen.



- a foundry. This is where the burned gas inside a refractory lining fuse the scrape metal. The construction of the foundry is more or less a metal barrel with refractory cement on the bottom and on the walls. A removable cement top hat with hole, to regulate the heat into the chamber, complete the foundry.
For my application i found a convenient olive oil barrel that I cutted with grinder. On the side, near the bottom, I will drill an hole with specific angle to introduce the burner.


- the crucible. for hobby metal needs simple steel barrel is sufficient. For more specific application sintered crucibles made from ceramic or oxide powder is required because molten metal (Specifically aluminium react with iron). And more could be easily replaced.


- a flask with sand and cavity or, in my case, foam. Foam metal casting is a recent technique in which a foam pattern remain inside the sand. The molten metal replaces instantaneous the foam sublimating it. After cooling the foam is no more present and the metal has the design of the foam pattern.
Find more information on this process on wikipedia.
Of course the best site around from 2000: http://www.backyardmetalcasting.com/

- the pattern, that could be easily machined with cnc or standard technology.


OUTSIDE: KUROKESU - how passion can drive your life

As I noticed KUROKESU range of product, i wanted to deep dive on the philosophy guiding this lithuanian guy and his team. What I learned so far is that your passion can lead your life to new dimension.

About KUROKESU you can read in his website
"What started as a great way to burn my free-time has evolved into a full-time occupation – but from the start Kurokesu has been my passion. Initially I made all the parts and assembled every product myself, from USB cameras and lenses through to precision tools and motion systems. [...] At the end of spring 2017 I was able to quit my day job."
While you can find a machine probe from aliexpress, I would prefer 100:1 to acquire it from this source, to support his business, and also because the quality of his products could be measured just by by design details.

In the E-store you can find a fine motorized rotary stage:


A sturdy Raspberry PI enclosure (note the actual revision is F):
A complete USB camera with C-Mount lens (for instance to assembly a soldering or inspection macro camera):
A logitech c920 rework case:


What I like so much, is the touch probe:

I will give a try to the touch probe soon.

Good luck KUROKESU.

All credits for the photos belongs to him.


IOT TUTORIAL: Esp8266 (NODEMCU): MICROPYTHON, DHT22, MQTT and INTERRUPT


I had a ESP8266 - NodeMCU - module laying around, so I decided to install inside an electrical panel, to gather also data from energy monitor. I used a DIN empty support to mount the ESP:

Flashing micropython to ESP8266

Micropython install on ESP8266 without pain: 
a. Download latest version from http://micropython.org/download#esp8266
b. Deploy the firmare, install with pip the esptool tool 
c. Erase flash with:
esptool.py --port /dev/ttyUSB0 erase_flash
d. Connect ESP8266
e. Check the connected serial port with
ls /dev
f. Change directory to the unzipped firmware directory
g. Flash the new firmware from bash with the following command.
esptool.py --port /dev/ttyUSB0 --baud 460800 write_flash --flash_size=detect 0 esp8266-20170108-v1.8.7.bin 
That's all, if not working, check USB port or reduce upload speed to 115200, or check micropython website tutorial.

Running a script

By default micropython at startup execute a main.py file. Write it in your favourite text editor and  upload it using WebREPL.

Connecting to ESP

There are two options to connect to ESP with micropython, serial REPL or WebREPL (OTA or On the air or via WIFI).

Serial prompt - REPL

If you connect to ESP via serial port, you'll be prompted with a python shell, import modules and execute commands. You can stop main.py from execution, and also you can soft or hard reset. This kind of interface is called REPL, and is always available.

Over the air - WebREPL

During startup, ESP will create an access point called MicroPython-xxxxxx to which you can connect directly. Download a local version of html file from Github and open the html inside the zip file. 
I prefer this way because with this interface you can upload main.py when needed.
You will be prompted to a web page like this.

On the bottom left corner the standard access point address, change after accordingly when the ESP is connected to your local network via WIFI.
Once uploaded a main.py file, after reset, inside WebREPL is possible to read output from print statements and stop main.py with CTRL-C if something went wrong.

ESP8266 + NODEMCU + MICROPYTHON PINOUT

Considering the following layout using micropython you have to refer to pin numbering used by GPIO naming. So for instance D0 pin is GPIO16, inside micropython is pin 16:

#import machine library
from machine import Pin

# create an output pin on pin #0
p0 = Pin(0, Pin.OUT)
# set the value to high
p0.value(1)

CONNECTING TO LOCAL WIFI NETWORK

To connect Nodemcu to Wifi:
#import libraryimport network 
#import sleep function from dedicated time libraryfrom utime import sleep
#defined function to check connection or reconnectdef do_connect():    sta_if = network.WLAN(network.STA_IF)    if not sta_if.isconnected():        print('Connecting to network Wireless...')        sta_if.active(True)        sta_if.connect('SSID', 'PASSWORD')        while not sta_if.isconnected():            pass
do_connect()
while True:
    #do your loop here
    ....
    do_connect()
    ...
    sleep(15) 
Once connected, every time you reset you have to change the IP number to the DHCP assigned one, without connecting to Access Point, or you can connect directly to access point and use the internal IP.
You can also disable AP on startup after do_connect() using:
ap_if.active(False)

SENDING MQTT MESSAGES TO BROKER

from umqtt.simple import MQTTClient
SERVER = b'192.168.1.xx' #put your broker addressCLIENT_ID = b'ESP_Epanel'TOPIC_T = b'HOME/EPANEL/TEMPERATURE'TOPIC_H = b'HOME/EPANEL/HUMIDITY'
#after connecting to WIFIclient = MQTTClient(CLIENT_ID, SERVER)client.connect()   #Connect to MQTT broker
while True:    client.publish(TOPIC_T, 22)    client.publish(TOPIC_H,45)

READING DHT22 SENSOR

DHT22 is an expensive and accurate sensor to monitor temperature and humidity. I used one with breakout board from Banggood.
Sometimes DHT22 fail to read and the simplest solution I found is to soft reset via code
from dht import DHT22
from machine import reset
sensor = DHT22(Pin(5))
while True:
    try:
        sensor.measure()
        t = sensor.temperature()
        h = sensor.humidity()
        if isinstance(t, float):
            msg = (b'{0:3.1f}'.format(t))
            client.publish(TOPIC_T, msg)
            print("Temperature: ", msg)
        if isinstance(h, float):
            msg = (b'{0:3.1f}'.format(h))
            client.publish(TOPIC_H, msg)
            print("Humidity: ", msg)
        else:
            print('Invalid sensor readings.')
    except OSError:
        print('Failed to read sensor.')
        reset()

PIN INTERRUPT HANDLING

Handling external interrupt in micropython is really simple:
from utime import time
from machine import reset  
#define a callback function where execute simple and short code 
def callback(pin_number):
    #refer to global variable
    global last_time
    last_lime = time()
 
#pin setup
p0 = Pin(12,mode=Pin.IN)
p1 = Pin(13,mode=Pin.IN)
 
#start interrupt
p0.irq(trigger=Pin.IRQ_FALLING, handler=callback)
p1.irq(trigger=Pin.IRQ_FALLING, handler=callback)

CONCLUSIONS

Put all together and you will have a connected MQTT node which read DHT22 sensor every 15 seconds, managing errors and as in my case count pulse input.

What I learned so far:
- Micropython is little tricky at the beginning, but stable, flexible and finally is Python.
- ESP8266 is not energy friendly, it produces a lot of heat, so is better to mount DHT22 far from ESP. In the near area surrounding the ESP the temperature reach a stable 26 degrees Celsius vs 20 degrees Celsius of surrounding.
- I hate pins, I would prefer to have screw connectors.


REVIEW: Telwin Bimax 132 MIG welder review (with tool cart)

After years of services, it's time to review my actual MIG welder: 

Telwin BIMAX 132


If you don't know Telwin, please head to their site (http://www.telwin.com/) and discover which kind of product they have in portfolio. Telwin is Italian based productor from more than 50 years of the finest welders, plasma and more. Their market is Automotive, Industrial, Professional and Consumer, and if you know some of their products, you know the high quality and reliability: especially in the automotive market (you know for sure some titled Italian brand, Ferrari, Maserati, Lamborghini), so you can imagine the high standard the Italian industry professional requires also from these products.

I own this model from lot of years (more than ten if I could remember), I could say I learned to weld with this machine, without external help. In fact this is the most remarkable feature I would like to highlight from this consumer-grade machine: forgive you for any error.
I never had any trouble, except the fact I had to learn how to setup correct polarity, speed of wire, current setting, in relation to the work. In these years I learned how to improve my skills with wire welders, improving also technical and cleanliness of results.

This little machine, i bought without any expectation from a big of the house improvement distribution chain, is capable to deliver 105 Ampere with duty cycle of 15% (this mean that you can weld with this current for the 15% of time) and 50 Ampere with duty cycle of 60%.
What can you expect with these characteristic? Lower range can solder 0.6 mm sheet metal without distorting so much, with upper range, I created a L shaped steel frame with thickness of 10mm!
I learned also you can fill fill easily holes or separations between pieces of metal.

Just to give you an idea, following a photo of a big steel frame (2.5 meters by 2.5 meters) welded with this little machine without pain and distortion:

You can solder with gas or without gas, I prefer without gas with animated wire, because I don't want to complicate my weldings with Gas refurbishment, and I found with NoGas the results are more than acceptable: simply fill with a spool ranging from 0.6mm to 1.0 mm and forgive it.
Another characteristic I would like to highlight is that this machine can accept 5kg spool of wire.

This beauty can solder Aluminium, Steel, Inox with GAS (mix of CO and Argon) and Steel without GAS (animated wire, or wire with flux inside). Plastics are durable, but most of the machine is made of well power painted metal.

What I could say is not really a portable welder (21 Kg) so I built a small cart, quite different from the ones you can find in the market, because is really simple and designed for earth work (the welding gun start from a lower height), but occasionally you can weld on a higher surface like on a table.

For sure you experimented the dross problem on the tip, especially if as me you are not so expert and use animated wire. Cleaning the drosses is really easy and every consumable tip last from my experience at least 2Kg of wire. Replacement is easy and cost nothing. I never had to change the guard of the tip, always cleaned with metal brush.

More photos:


Taking a low center of gravity, allowed me to pull it in the shop without worry to overturn it.
A big improvement a simple hook to roll over the cables.) Spot-welding can be carried out on overlapped metal sheet with a maximum thickness of 0.8 mm.

I found also after all these years is yet on the market, which is a meaning of lucky and reliable product, so you can find at very affordable price also on internet (actually less more than 350 euros). But I remember I bought ten years ago for lot less, so seems like this machine gained value in these years...

How can you read, I'm very satisfied of this product, despite I tried some modern eletronic chinese product, this welder for me is unsurpassed in quality and price.

Five Star!