Welding Plastics: Instructables Robot Nightlight




About: Hi there, my name is Katarina and I've been an IT technician at Rapid PC Rescue for over 10 years. Apart from being an IT technician I'm also a DIY and crafts enthusiast. I love to learn new things and tech...

I decided to write a small series of Instructables to show that there are a lot of things that can be made out of plastic bottles and how easy the plastic welding process is.

This Instructable is the fourth and final installment of my milk bottles creations (at least for now :D), if you would like to see the previous ones, here is the Drill Bit Case, LED Flower and Cat Toy

So after completing the cat toy I found out that it's more than possible to use a papercraft template and the process is very similar except instead of using glue one would use a soldering iron. And so I remembered the super cute Halloween Instructables Robot and I just had to try to make one out of a milk bottle. First of all I adjusted the template, since I wanted my robot to be a little less square, then I made a paper prototype and the rest follows . . .

Step 1: Tools, Materials & Preparing the Bottle

Tools & Materials:

  • plastic bilk bottle
  • two small magnets with central hole
  • clear tape
  • couple of wires
  • battery
  • LED
  • small ON/OFF switch
  • soldering iron
  • solder
  • scissors
  • sharpies
  • hobby knife
  • marker
  • ruler

Start by cutting the bottle in half and then cut off the curvy bits so that it's easier to draw on later. Clean the bottle halves if necessary.

Step 2: Cutting

Print out the template. Cut the bottle half into smaller more manageable pieces, but make sure they are still big enough for the template elements. Place a bottle piece over the template and hold in place with a bit of a tape. Score all of the lines that will be folded later with a hobby knife and trace the rest of them with a marker. Repeat for all of the shapes and cut out. Bend the body and head parts just like you see in the photo.

Step 3: Legs

Take the leg piece and curl into a cylinder shape. Hold it in place with a bit of a tape and weld the tab from inside. Bend the spikes outwards and slide the leg into the body piece. Weld the spikes to the body on the inside and repeat for the second leg.

Step 4: Body

Tape the front of the body to the side with the spikes inside and weld together. Repeat for the other side. At this point I decided that I would quite like some guide lines for the face and buttons so I placed the body and the head onto the template and traced the features on the insides.

Step 5: Arms

Bend the side of the arm at the second and fourth spike and fold the spikes inwards. Attach the side to the front with tape and weld from inside. Place the back of the arm onto the side piece and weld from the top. Repeat for the second arm. Hold the arm against the body, use tape if necessary and weld from the inside of the body. Repeat for the second arm.

Step 6: Head

Tape the head piece and weld the tabs from the inside. Weld the head onto the body piece. Close the back of the head and weld the tabs from outside at the bottom and the sides.

At this point I still didn't know this was going to become a nightlight and so I welded the back shut, which I had to cut open later. I guess you never know where the project will take you :D

Step 7: Wheels

Take the wheel side piece and curl into a cylinder. Hold in place with tape and weld from the inside. Bend the spikes inwards, place onto the front of the wheel and weld in place. Repeat for the second wheel.

Cut two thin strips out of the bottle and fold in the middle. Pinch about 1cm of the fold, open and place onto the back of the wheel. Weld the strip from both sides and slide the magnet onto the fold. Flatten the folded strip inside of the magnet and weld the outsides of the stripe onto it.

Fold in every second spike on the back side of the wheel. Place the back of the wheel onto the bended spikes, fold over the rest of spikes and weld them on. Repeat for the second wheel.

Stand the robot on its head and place the wheels onto the legs. Spot weld the wheel in the places where it touches the legs. Cut two small pieces of the bottle, place and weld them on the back of the legs to make them sturdier.

Step 8: Antennas

Cut two very thin bottle strips for the antennas. Take the antenna circle, overlap the cut and weld from inside. Make a small hole on top of the cone, slide the antenna through and weld on the inside. Repeat for the second antenna.

Hold the antenna cone against the head and weld on by sliding the tip of the iron over the edge of the cone onto the head. This should make a neater mark than the spot welding.

Step 9: Battery Holder and LED

Take the square for the battery holder and tape the battery onto it. Place on the top piece of the battery holder and tape again. Push down each of the tabs with a small flat headed screwdriver and weld in place. Cut off the tab remains.

Poke a hole through the top and bottom of the holder and slide in wires that have been stripped on both ends. Cut two bottle strips, place them over the wires and weld in place to secure the wires. Bend the edges of the rectangle bottle cutout for the width of the battery, place over the battery and weld in place.

Cut another two bottle strips and weld them to the center of the battery square with enough space for the LED in between. Bend the LED legs, place them under the strips, weld in place and cut off the leftovers. Solder the wires to the LED and to the switch. Place the battery square into the body and weld inside and out.

Cut out an opening for the switch and the battery on the back of the body and weld on two bottle stripes from inside to hold the switch in position. Slide in the switch, place the strips over and weld in place.

Check the balance of your robot and if needed weld on tiny bottle pieces to the wheels as necessary.

Step 10: Colour In

Take out your sharpies and colour your robot. Don't forget the antennas ;)

Step 11: Result

This project was the most challenging one out of the four of my milk bottle creations, but still quite easy to replicate I think. It took about 4 hours to finish and was well worth it in my opinion. He can be used as a nightlight, or as a decoration and can even hang upside down from metal surfaces :D

Step 12: Bonus Tip

Like me, do you have one of those touchless soap dispensers that you are fed up of buying the expensive refills for? Here's a tip :-)

To rid yourself of this inconvenient problem, all you need to do is find yourself a bottle with suitable screwy top, cut a hole in an empty refill container and weld the screwy top onto it. Optionally you can also apply hot glue around the weld to make it spill poof like I did. Or you could just use hot glue for the whole thing instead.

Now your hand soap dispenser can enjoy cheaper refills as often as you like :D



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    31 Discussions


    1 year ago

    Thank you, IMO this is great in (at least) *two* ways:

    #1, excellent robot, I'll be nudging a friend to read your Instructable.

    #2, I've often re-used HDPE container plastic, but have had difficulty welding the sheets together because I've previously tried to use a hot-air pen or equivalent -- which has caused the surrounding material to deform. Contact spot-welding the sheets completely avoids that deformation, of course -- and afterwards, I can probably still melt-to-seal the edges of the joined sheets, if it still seems necessary :-)
    Oops forgot, voted, of course :-)

    1 reply

    1 year ago

    Nice idea but remember you might cause your soldering tip to corrode so clean the tip afterwords so what about a Dermal Multi and use a plastic knitting needle which you run against the two edges to be joined and the friction will cause the knitting needle to melt and make the join, this is similar to a modelling kit which used friction welding to fix the parts together.

    2 replies

    Reply 1 year ago

    AliExpress has replacement soldering iron tips / bits for around 50c each, so keeping one tip (or repurposing any one for which the iron cladding has worn through, so the copper is exposed and the solder dissolves it) for welding is no great expense.

    And while friction welding is ingenious (thanks for the suggestion!), I'm certain I can follow nerdyKat's spot-welding steps; I'm skeptical that I can get a good result with my Dremel-equivalent Proxxon :-)


    Reply 1 year ago

    Sounds like an interesting idea, I just wonder if it would work due to the different plastics being used. I tried to weld together a milk bottle with a clear water bottle and the joint was very weak, but I would love to know if it works if anyone decides to try this ;)


    1 year ago on Step 11

    Wow! I am really impressed. I have often used milk bottle polypropylene material for projects but never thought to weld it. DUH! This project is awesomely well-done. And now I can use old milk jugs to build protective covers and bellows for tools in my shop, add opaque windows in 3D prints, etc. I really like the battery holder also. A deep bow and thank you. (Has anyone tried cutting this material on a Cricut type cutter? You may be able to go into the GlowBot business... of course I know a lot of the charm is in the hand work. But then building a PP spot welder would be cool also.)

    2 replies

    Reply 1 year ago

    The possibilities really are endless. I also made myself a little battery holder and was even able to fix the back windscreen wiper holder (even though for that I needed to crank the temperature to 350 degrees due to different plastic) I would love to see what projects you come up with and thank you very much for your lovely comment ;)


    1 year ago

    The PP welding is such a great idea and your execution was really awesome. I'm really happy that you made it into a night light as it looks like such a benevolent entity to protect sleep. Keep up the great work and thank you!

    1 reply

    Reply 1 year ago

    Thank you very much for your kind comment ;)


    1 year ago

    Must have been fun "welding" the plastic! Really well done!

    1 reply

    Reply 1 year ago

    Thank you, it really was a lot of fun ;)