As my friend finished to build the plastic injection machine ( https://preciousplastic.com ) for recycling plastic here in FabLab Moscow ( http://fablab77.ru/#/ ), I started to wonder what could be done with it. Of course it is not difficult to find examples of plastic objects because they are all around us but I still had some limitations:
- The part had to be relatively simple. (I had no previous experience with plastic recycling)
- The mold had to be done by hand (as a first test)
- The part had to be medium-sized (limited by the machine size) (small is more difficult)
- And finally I wanted the part to have a meaning as it is an ecological project
This last requirement brought me back to my obsession for biking. I did not want to make a fidget spinner because it would have counteract my effort to recycle plastic as it would ends, at best in a closet, at worst in the ocean. Also, having pedals made of old soda caps is kind of ironic.
This instructables contains three main parts:
- Make the grip mold
- Make the pedal mold
- Inject the parts
Step 1: Tools and Material
The main tool that you need is the precious plastic injection machine. Good news: this project has become internationally popular. Just check the community page to see if there is one around your place: https://preciousplastic.com/en/community.html . Nevertheless a lot of people are still deprived of recycling machines (and access to medication) but it is not difficult to make your own! There is a lot of documentation on the web about this subject and it is not the purpose of this instructables. For the rest of the tools, you need:
- angle grinder (cutting and grinding discs)
- flat file, round file (opional: small grinder rotary tool like Proxxon or Dremel)
- press drill
- clamps (at leaste 3)
- welding machine (only for pedals)
- radius scriber (a marker works well too)
- welding gloves, jacket and mask
- protection glasses
- respirator with A1 P1 filter (hot plastic fumes and particles filter)
- safety gloves
- hear protection
- sanding paper (grit size around 80) (optional: electric sander)
- measuring tape
- square edge
- M6, M8 thread tap
- drill bit 4.3; 6.4; 6.8; 8.4; 11; 20 ; 22.5 mm (if you don't have the 22.5, use your round file like I did)
- tweezers (optional, for ball bearings assembly)
plastic waste: I made experiments with polystyrene (PS) and polyethylene (PE). PS looks more strong but I had only black one so the presented objects are made of PE. The pedal volume is 145 cm^3 and the grip 84 cm^3.
For the grips
- metal tube (no matter which metal) (internal diameter = diameter you want for the grips, big ones are more comfortable. I chose 35mm. Lenght = lenght you want for the two grips - 3 mm. I have 2 x 130 mm so my grips are 127 leght)
- metal sheet (steel 4 mm thick; 180 x 60 mm)
- threaded rod (M6 x 450; M8 x 150 mm)
- 6 nuts M6
- metal cylinder (diameter 22.3 length 111 mm) (standard handlebar have diameter 22 mm so take just a little bit more if you want to assemble them easily. Keep in mind that the plastic retracts when cooling) (the length has to be equal to the tube length minus the bottom thickness)
- 1 bolt M8 x 20
- 1 washer (inner diameter 22.5, outer diameter 34.5) (it has to fit into the tube and around the cylinder) (you probably won't find such dimensions but M20 washers almost fit, you just have to remove 1.5 mm to the outside diameter with a file)
- 1 nut M8
For the pedals
- metal sheet (steel 4mm thick; 120 x 240; 26 x 700 mm)
- welding rod (2 or 3 mm)
- 3 bolts M6 x 10 (any size would works but you need the corresponding drill bits)
- 2 pedal axles with ball bearings, washers and nuts
- wood (for positioning during welding, optional) (pedal size)
- 4 bolts and nuts M4 x 40 (only length matter)
- 24 setscrews M6 x 8
Step 2: Make the Grip Mold: Cut the Parts
- cut the tube at the length you want for your grips (mine are 130 mm)
- cut four hexagones with side length 33 mm
- in each of them, drill three holes in the corners
- in the first one, drill another hexagone with 10 mm side length in the center
- in the second one, drill a 5 mm hole in the center
- in the third one, drill a 22.5 mm hole in the center
- in the fourth one, drill a 8 mm hole in the center
- cut three M5 and one M8 threaded rods at 150 mm
- cut the cylinder at the length you want (111 mm for me)
- make a M8 x 20 threaded hole at the center of one cylinder side
For each cut, I scribed my part with the radius scriber and a wooden template and then cut with the grinder. Sometimes I clamped the wooden part and used it as a guide for the grinder (cf. picture).
To drill a hole precisely where you want, you need to scribe a cross (work on a flat surface), then punch the cross center, then use a center drill bit (I skipped this last step, the result is less precise). Also instead of drilling directly the diameter you want, it is better to start with smaller diameter. Finally drill your hole with a free moving vise if diameter is less than 6mm. If you want to continue with a larger diameter, secure the vise before removing the small drill bit, then change for a bigger bit. I found this article about the subject http://www.micro-machine-shop.com/hole_drilling.h... )
To drill the small hexagon, you need to drill with a 18 mm bit and then use a flat file to make the corners. This shape is only for centering the injector nozzle with the mold hole (cf. picture). If you want to go faster, simply drilling a 22 mm hole should works too.
For large holes (more than 20 mm diameter), I drilled with the max I had (20) and finished with the round file. Having previously scribed the shape you want to make helps a lot.
To ensure a perfectly perpendicular thread in the cylinder, you can secure the thread tap in the press drill chuck and manually rotate the chuck with one hand (do not switch the drill on!). While with the other hand you softly press down the crank.
In the first picture, the fourth hexagone has six threaded holes. Do not drill them. I did them when I was trying different ways of extracting the grip from the mold but it failed.
Your grip mold is (already) ready!
Check the "injection part" of this instructables to know how to use it.
Step 3: Make the Pedal Mold: Cut the Parts
- cut two squares 120 x 120 mm in the metal sheet
- make holes in the four corners (4.3 mm in my case)
- scribe the pedal shape on one square face
- drill the injection hole where you want it(I chose diameter 5, in the center)
- cut a band of 26 mm height and at least 300 length and another of 26 (precisely) x 340 (at least)
- cut the 300 band in 15.6 (2x); 24 (2x); 18 (2x); 33 (2x); 25 (2x); 43.4 (1x)
- cut the 340 band in 40 (2x); 56 (4x); 27.7 (1x)
- cut also six small pieces in order to wedge the mold part together (5 x 10 mm)
- cut three more to make the triangle and trapeze center (25 x 7 (2x); 4 x 35 (1x))
To obtain these values, I modeled the pedal with a CAD software and extracted the dimensions of each face. The parts made from the 300 mm length band correspond to the pedal outside faces. The parts made from the 340 mm length band correspond to the pedal inside faces (the triangle and the two trapezes). These lengths are calculated for a 4 mm thick metal sheet. The drawing files of the faces are joined to this article in order to be used and modified if necessary. I used a laser cutter to quickly obtain the wooden templates but it is not necessary. I glued together several wooden layer to obtain the desired height.
After each cut I deburred the edges with the flat file. You can make a chamfer on the edges that will be welded.
Step 4: Make the Pedal Mold: Weld It
Before welding you need to add an angle (around 2 degrees) on each vertical face of the wooden parts (triangle, trapezes and pedal). This will ease the extracting process. I accomplished this with the sanding machine. After having designated the top faces and having written on them, I pressed the vertical faces against the sanding paper with more pressure on the side I wanted to remove the material (top for the triangle and bottom for the pedal sides). (cf. picture)
Weld the pedal perimeter: Clamp the wooden pedal on your welding surface and clamp the edges you want to weld (cf. picture). Continue with the other parts always ensuring that your parts are well against the ground.
Weld the triangle and the trapeze with the same technique. I used a small hammer to secure the smallest parts in position during welding.
It was my first arc welding job and you can notice the poor result but it doesn't matter, it just extend the grinding time. Even if arc welding is not the most appropriate technique for such small job I enjoyed to train my technique. (MIG would be better)
The last step before injecting is to file and grind the parts. Return to welding step if necessary to add some metal. Make sure that the top and bottom part are flat to avoid plastic leaks.
Weld the three positioning part on the first square and three positioning part on the second square. On the first square the function is to set the perimeter part relatively to the base. On the second square, the function is to position the injecting hole relatively to the injection nozzle. (cf. picture)
Finally scribe and carve the positioning part of the triangle and the trapezes using them as template. Drill and thread them and secure them to the base with bolts.
I think we are good to go for the Injection!
Step 5: Inject the Grips
- turn the heater on
- assemble the cylinder with the basis hexagon (Nbr. 4)
- add the three threaded rod
- add the washer around the cylinder
- add the tube
- add the top hexagon with the injecting hole (Nbr. 2)
- add the top hexagon with the hexagonal hole (Nbr. 1)
- secure it with the nuts
- start filling the machine with plastic
- compress with the piston
- repeat these two steps until the machine is full
- the machine heats up and the plastic start to flow. Plug the nozzle to avoid that. (almost ready)
- wait some more time (5 min). The plastic (PE) start to expand and try to escape from the top. (PS doesn't but you feel that it is like shewing gum) It is now ready to inject
- quickly remove the plug and place the mold under the nozzle. I use a jack to secure the mold.
- operate the injecting lever until you can not anymore
- turn the heater off
- remove the mold and the hot plastic with gloves
- cool down the mold (optional)
- drill in the injection hole until you reach the central cylinder
- disassemble the part except the central cylinder
- place the grip vertically and the hexagone with large hole on it. (Nbr. 3)
- add the cylinder
- add the basis hexagone (Nbr. 4)
- add the threaded rods and nuts
- screw the M8 threaded rod inside the cylinder
- add the M8 nut and screw it to extract the central cylinder
Done! Easy as pie :)
Step 6: Inject the Pedals
The process is very similar to the previous step. It is even simpler because I don't have an extracting screw for the pedal. I try to remove the central parts (triangle and trapezes) when the plastic is still a little bit soft. If it has already cooled down, I use the force: hammer and vise. I could resume the injection like this:
- heat the machine
- fill with old plastic
- open the mold
If the grips are ready to use after injection, the pedals require some deburring (it is certainly due to the poor quality of my mold).
Step 7: Finish and Assembly
After cleaning the pedal, you need to drill the central hole with a 11 mm bit. Then the last but critical operation is to drill the bearing cavities. It consist in enlarging the 11 mm central hole on both sides with a 20 mm bit. If you want proper functioning of your pedals, these two last drills have to be perfectly aligned with the central 11 mm hole. To ensure the alignment, I designed a jig (cf. picture). One part (left part on the picture) remains fixed to the press drill while the other can be opened to flip the pedal.
- secure the pedal in the jig
- mount the 11 mm drill bit and align it with the pedal center
- secure the jig to the drill
- drill through all the pedal
- mount the 20mm drill bit
- drill the bike side of the pedal 8 mm depth
- flip the pedal
- drill the outer part of the pedal 15 mm depth (measured from the flat face, not the top triangle)
Now you can push the metallic bearing surface inside its cavity. Then add the balls with grease to hold them in place. Finally secure the axle with the second bearing surface and the pined washer and the locknut.
To avoid your feet slipping on the pedals, I suggest you to add some M6 x 8 setscrews. Threads are not required, just drill 4 mm depth.
Now you can show off with your marble looking pedals and grips!
Enjoy recycling and enjoy riding!