After surfing around instructables for a couple of years, I finally decided to make some contributions of my own. The impetus for this instructable was to share with the community an alternative to dishing out lots of money for professionally made flat conveyor belts. With these DIY flat conveyor belts, conveyance is a breeze.

These belts were constructed as part of a low budget senior design project. After getting the process down, it took about 15 minutes of work amongst three people to make each 4' length x 1" width belt at about 50 cents per belt.

Step 1: Bill of Materials

You will need the following materials to make these belts. We spent under $50 on bulk materials, but the belts can be made with a much smaller investment than this using scrapped materials. By my estimation, each belt of about 4' length cost less than 50 cents each. Additionally, these supplies were sufficient to make hundreds of belts.

Some method of rubberizing the belts for grip
- We used Black Flex Seal: Flex Seal on Amazon
  - If you use rubber paint, you will need a paint brush as well
  - Wax paper is useful to prevent paint from drying on other surfaces
- Cost us $17
1X Duct Tape - the wider the better
- We used 4" wide duct tape: Duct Tape on Amazon
- Cost us $9
1X Twine - the longer the better
- We used twine like this: Twine on Amazon
- Cost us $10 for about 300' of twine
4X 10-32 x 1.75" length screws
- Flat head screws look the best
2X 3D Printed String Aligner Assembly
- CAD models attached
  - The diameter and slot spacing of the string aligners will need to be configured to match your pulley's ID
  - Modeled in Solidworks 2016 - 2017 in MMGS. STEP files are also attached.
- PLA filament cost under $5
  - We used makerbot PLA white (configure settings for high stiffness)
- These could be dremeled from wood as a stronger and cheaper (but less user friendly) alternative to 3D printing
4X C Clamps
- Used to mount the string aligners to the table
1X Measuring Tape
- To space the string aligners to your desired separation
OPTIONAL
- Wood plank to hold the string aligners spaced apart
  - Cut to length = (desired belt length) - pi * (pulley diameter)
  - Prevents the string aligners from deforming (ruining belt length standardization) when the twine is wrapped around them tightly
  - We used a 1" x 4" plank, cut to length

Step 2: Assemble and Mount the String Aligners

Pretty simple, see the attached images for a visual guide.

Assemble the 3D printed string aligners using 10-32 screws
1. I recommend quick clamps for their ease of use
Using two C clamps, mount one string aligner to the table
1. Do not squeeze them too hard as the print will crack
Measure out the desired separation of the string aligners
1. Desired separation = (desired belt length) - pi * (pulley diameter)
2. OPTIONAL: enforce this separation using the cut-to-length wood plank
Mount the second string aligner using the last two C clamps

Step 3: Wrap the Twine

This takes a little bit of precision but it goes fast after the first belt. We targeted 1" width belts, so we used 5 grooves. To speed this process, putting the twine on a screwdriver (shown in attached image) makes dispensing twine easier.

Wrap the twine around the string aligners in one long pass
1. We used two loops per groove, meaning there were ten loops per belt. This provided plenty of strength to our belts
2. Use one pass of string (a.k.a. one giant loop) for optimal strength in the belts
At the start and end of the twine, twist the strings in a spiral to ensure that the twine stays put
1. The grooves were tight enough that the twine did not come loose
2. This doesn't need to hold a load in the long run as the duct tape will aid with this

Step 4: Cover in Duct Tape

The next step is covering the belts in duct tape. This should be done carefully, as wrinkles in the tape will make applying the rubber coating harder

Wrap 4" duct tape around top half and then the bottom half of the belts
1. Take your time as this is pretty easy to mess up. Make sure to crease the tape's edges so it forms a crisp flat belt
Remove the belt from the string aligners by removing one side's C clamps
Finish by taping up the ends, connecting the duct tape into one long belt. It should look like the last image above

Step 5: Apply Grip

This last step is tedious and messy. However, it gives the belts a good amount of grip and makes them much more reliable.

Paint rubber sealant onto one side of the belts
1. Note that if you use flex seal, the paint will expand slightly as it dries
2. Try to apply an even coat for a uniform belt
3. Try to avoid wrinkling the duct tape as much as possible for high quality belts
4. Immediately wash your paint brush when done otherwise the brushes will become a solid rubber block when it dries
Hang the belt on something while the rubber paint dries (this was about 10 hours for us)
1. Put wax paper under the belt to prevent the paint from drying onto the hanging surface
2. Put wax paper on the floor below the belt in case the paint drips
OPTIONAL: Paint the other side of the belt
1. We chose not to do this because the tension on the belts created enough friction that they did not slip
2. If you choose to paint both sides, 'finger painting' both sides simultaneously may be easier
  1. The attached image shows our attempt at painting both sides by covering our fingers in electrical tape. That method was a failure :(

Step 6: Test the Finished Product

Test out your belts. If you were able to standardize the process enough, the belts should all have the same ID. Ours did, and you can see them in operation in the attached video. Best of luck to you if you attempt this, it was fun!

Advantages:

Low cost
Functional
Highly customizable width and length

Disadvantages

Hard to keep belts centered without adding walls to the pulleys
- Using a crowned pulley did not help in this case
Belts can slip if not properly standardized and tensioned
Fabrication can be tedious
Rubber paint fell off duct tape after lots of use
- Painting both sides might mitigate this

Alternatives: