Plastic stick (friction) welding is a fun and relatively easy way to assemble 3d prints. My students always enjoy it and get pretty good at it. A few key points:

- Plastic types must match, or at least have similar melting points. We only use this technique with PLA. In the past, we have used a heat gun with other plastic types (polyethylene and ABS) with mixed results… it works but is often sloppy and only functional on pretty large parts.

- This is friction welding, but just like stick welding metal, one has to ensure that both pieces are being melted into by the “puddle” for the best connection.

- Also like metal, spot welding works great to tack things together quickly but for the best connection all contact points need to be welded.

- Buying straight filament sticks is well worth it.

Step 1: Supplies

Rotary tool – we use a Dremel

Rotary tool chuck – quickest way to hold filament

Straight filament – must be very straight. Store with desiccant pack so it doesn’t become brittle.

Sharp cutter – cut filament to break into useable sticks

Eye Protection

Step 2: Technique

0. Put on eye protection.

1. Cut a piece of filament about 5-6 cm long.

2. Insert short filament piece into chuck until 2-3 cm sticks out and tighten chuck snugly. (see video - Filament Insert)

3. Turn on rotary tool and verify that the tip of the plastic filament is stationary while spinning - not wobbling.

4. Set RPMs on rotary tool to 15,000-20,000. See Tips section for more detail.

5. The goal is to create and “walk” a puddle of molten plastic along the joint being welded(see video - Welding Example).

a. Prep plastic surfaces to ensure the two pieces are in close contact (sanding, scraping, etc.)

b. Secure pieces so the joint being welded is as tight as possible.

c. Plan motion so you don’t have unexpected problems like power cord getting caught.

d. Turn on the rotary tool and gently touch the tip of the spinning filament to the joint, ensuring equal contact (melting) with both pieces.

e. Feed (gently push into the joint) the filament in while also moving laterally along the joint. If you push too hard the filament will bend and quickly fail, flying into the nearest unprotected eye, sharp side first. Gentle is the key. The rotary tool spins the filament so fast its motion will generate all the heat needed.

f. When the filament gets too short, stop the rotary tool and adjust length of filament, getting a new piece as needed.

Step 3: Tips

Cut several pieces of filament for quick reloads.

Keep old prints to practice with. We have a bin of failed prints that often live many lives over multiple class-years.

If a gap is too big to join together you can fill in the gap by building up layers of plastic on each piece until they meet.

Decrease the rotary tool's RPMs if the filament seems to melt before the joint melts (it will blob up on the filament tip and not stick to the pieces) and increase the RPMs if the plastic is not melting after 1-2 seconds of gentle contact.

If you intend to weld printed pieces, print the parts with thicker walls so the weld bead doesn't melt through the wall.