Filament Maker: Preparing the Bottle
A complete guide on preparing a PET bottle ready for use with our Filament Maker.
Introduction
Recycling PET bottles into usable filament starts with proper bottle preparation. A well-prepared bottle ensures smooth, consistent strips that can be fed into the filament-making process without jams or inconsistencies.
This guide walks you through step-by-step instructions for preparing a plastic bottle, from drilling the cap and pressurizing the bottle to heating, cutting, and measuring. By following these steps carefully, you’ll create evenly processed PET strips, leading to higher-quality filament and better final prints.
Whether you're using boiling water or a heat gun to shrink the bottle, the key is to achieve a smooth, uniform surface before cutting. Consistency at this stage will make a huge difference in the reliability of your filament. Let's get started! 🚀♻️
Getting Started
You will need:
Protective Gloves & Safety Goggles – Essential for handling heat and pressure safely.
Bottle Cutter & TR525 Tire Valve - Included with the Filament Winder
Drill – For creating a hole in the bottle cap.
10mm Drill Bit – For accurately sizing the hole for the tire valve.
Bike Pump or Air Compressor – To inflate the bottle (max 25 PSI).
Sharp Scissors or Craft Knife – For cutting the bottle.
Calipers – To measure bottle thickness accurately.
Heat Source:
Option 1: Boiling water (for the water immersion method).
Option 2: Heat gun (for direct heating).
Optional Extras:
Rubbing Alcohol or Acetone – Helps remove label residue and glue from bottles.
Paper Towels or Cloth – Useful for cleaning bottles before cutting.
A clean, label-free bottle with a uniform cut is essential for high-quality filament. Inconsistent prep leads to weak spots and print issues.
FAQs
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Recycled PET is a versatile material, but it has some unique properties that affect what you can successfully print. While it offers good durability and resistance to moisture, it is not ideal for very thin or highly detailed parts that require strong layer bonding.
What works well:
✅ Functional parts – Brackets, tool holders, storage containers, and similar items that don’t rely on extreme thinness.
✅ Structural components – PET has good stiffness, so larger, solid parts perform well.
✅ Water-resistant objects – PET’s low moisture absorption makes it ideal for outdoor items, bottle adapters, and utility clips.
✅ Experimentation & prototyping – PET is a great material for testing designs that don’t need extreme strength across the layer lines.What to avoid:
❌ Thin-walled or intricate models – PET does not bond as strongly between layers as some other materials (e.g., ABS or nylon), making slim parts prone to splitting under stress.
❌ High-detail miniatures – Fine details may not print well, and small unsupported sections can be fragile.
❌ Load-bearing parts under bending force – PET is strong when printed flat, but parts that rely on strength across the layer lines can be weak.Tips for Success:
Increase infill – A higher infill percentage can improve part strength.
Use rounded, thicker designs – Avoid sharp corners and extremely thin features to reduce weak points.
Print orientation matters – Try to orient parts so that forces act along the printed layers, not across them.
The best way to learn what works is to experiment! PET is a fantastic material when used correctly, so test different designs and print settings to find what works best for your needs.
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If you’re experiencing issues with print quality or filament not extruding properly, follow this checklist to troubleshoot:
Correct strip size: Ensure the PET bottle strips are the right width for your bottle thickness. As a general guide:
10mm strip for 0.1mm bottle thickness
9mm strip for 0.2mm bottle thickness
8mm strip for 0.3mm bottle thickness
Filament shape: The extruded filament should form a consistent tube shape, not a “C” shape. Adjusting strip width or extrusion settings can help correct this.
Filament diameter: Measure the filament near the spool (after cooling) to ensure it is within 1.65mm–1.85mm (ideally as close to 1.75mm as possible). Fine-tuning the strip size will improve consistency.
Print settings: Default PETG settings may not work well with recycled PET. Ensure you're using our recommended print settings for optimal results.
Cleanliness: Any residue from bottle labels or adhesives can cause blockages and poor extrusion. Make sure bottles are fully cleaned before processing.
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This is usually caused by moisture absorption, as PET is highly hygroscopic (absorbs water from the air). To ensure high-quality prints:
Dry your filament before printing: We recommend using a dehydrator or filament dryer.
Drying time and temperature: Minimum of 2 hours at 65°C, though longer drying times may be required depending on humidity levels and filament quantity.
Proper storage: Keep filament in an airtight container with desiccant when not in use to prevent reabsorption of moisture.
Step 3 - Insert Tire Valve
Step 1 - Remove Labels & Clean the Bottle
Peel off any labels and rinse the bottle thoroughly to remove any leftover liquid or residue.
Step 2 - Drill Hole in Bottle Cap
Using a 10mm drill bit, create a hole in the top of the bottle cap.
Push the TR525 tire valve into the drilled hole and tighten it securely.
Step 4 - Attach Cap to Bottle
Screw the modified cap back onto the bottle.
Step 5 - Pressurize the Bottle
Use a bike pump or air compressor to inflate the bottle to a maximum of 25 PSI (for a 2L bottle).
Step 6A - Heat the Bottle (Boiling Water Method)
Slowly pour boiling water over the bottle while rotating it for even heating. A drill with a spinning jig can help.
Step 6B - Heat the Bottle (Heat Gun Method)
Set the heat gun to high, point it upwards, and rotate the bottle evenly over the heat source.
Step 7 - Ensure a Smooth Surface
Continue heating until the bottle shrinks evenly and has a smooth, wrinkle-free surface.
Step 9 - Remove Glue Residue
After heating, check for any leftover glue from labels. Use rubbing alcohol or acetone with a cloth to remove any sticky residue before continuing.
Step 10 - Depressurise the Bottle
Slowly remove the cap to release the pressure inside.
Step 11 - Cut the Bottom Off
Use scissors or a craft knife to remove the bottom of the bottle, ensuring a clean, straight cut.
Step 12 - Measure Bottle Thickness
Use calipers to measure the bottle’s thickness—it should be between 0.1mm and 0.3mm.
Step 13 - Adjust Cutter Settings
Insert the appropriate spacers into the bottle cutter based on the measured thickness and tighten them.
Step 14 - Cut Tail for Cutter
Cut a small angled tail at the bottom edge of the bottle to help guide it into the cutter.
Step 15 - Feed Bottle into Cutter
Place the bottle over the threaded rod and feed the tail into the bottle cutter.
Step 16 - Pull Tail Through Cutter
Pull the PET strip gently but firmly through the cutter to start cutting the bottle into a continuous strip.
Step 17 - Spool the Strip
Wind the cut PET strip onto the Strip Spool, following the direction of the arrows.