Anneal PLA

Overview

3D-printed PLA parts can be annealed at low temperatures (60-80°C) to crystallize the PLA. Crystallized PLA has a higher HDT (Heat Deflection Temperature), which is important for use with, for example, hot stepper motors. Standard uncrystallized 3DP PLA parts will deform at HDT temperatures as low as 135°F/57°C when subjected to stress. Raising the HDT prevents deformation and ensures that the 3DP part functions properly in use.

Typically, 3DP parts come in contact with hot stepper motors in the following situations:

• 3DP stepper mount
• 3DP pinion gear

IMPORTANT: Verify your stepper temperature using an infrared heat gun. Adjust the stepper driver VREF to decrease the stepper temperature--power and heat dissipation increase as the square of the current, so this adjustment is significant. Surprisingly, stepper motors can get really hot in spots when idle if all the current happens to run through a single coil.

3DP PLA Stepper Mounts

A 3DP stepper mount can easily be protected from high stepper heat by simply adding 1mm thick 3DP PLA washers to the stepper mount. The 3DP PLA washers can be incorporated directly into the stepper mount design or printed separately. In either case, the washers effectively become annealed in use and protect the PLA mount itself from the stepper heat. The 1mm air gap from the stepper is usually enough to afford about 20°F/7°C drop in temperature between the stepper and its 3DP mount. You can also add insulating fiber washers as needed and/or reduce stepper temperature by lowering the VREF on your stepper driver.

3DP PLA Pinion Gears

3DP PLA pinion gears have a tough job to do. They need to grab the stepper shaft tightly and transmit angular force in hot environments. The traditional way to attach a pinion gear to a stepper shaft is with a set screw and many 3DP pinion gear designs such as the Wade extruder have slots for set screws. Unfortunately, a tight set screw on a hot stepper shaft will often deform and slip, resulting in much unhappiness.

• One solution is to use a high HDT PLA. High temperature PLA includes nucleating agents that partially crystallize the PLA during extrusion. Even so, manufacturers of high HDT PLA do recommend additional annealing for a short time.
• Another solution, and the one recommended for FireGear PLA pinion gears, is to anneal the 3DP pinion gear directly onto the slotted stepper shaft. Attach your pinion gear to the stepper shaft with a loose set screw and anneal it for 50 minutes at 160°F/71°C water using double air-evacuated plastic bags (e.g., Ziploc). In this case, we are making use of the shrinkage associated with annealing. Part shrinkage is normally a bad thing, but here we are using it to good effect to obtain a solid and tight joint with a slotted stepper shaft. Be sure to use high-infill (80% or greater) for annealed pinion gears. Shaft-annealed pinion gears require little or no set screw tension to stay in place on a slotted drive shaft.