Why our first CF-Nylon bracket warped, and what fixed it

Carbon-filled nylon is stiff, light and takes vibration better than anything else we print. It is also the least forgiving material on our shelf, and our first production bracket taught us that the hard way.

What happened

The part was a drone arm mount — 96 mm long, 8 mm walls at the boss, printed flat on the plate in CF-Nylon at 0.2 mm. It came off the printer with a visible lift at one corner: about 2 mm at the far end of the longest flat face. Dimensionally the boss was fine. The mounting holes were not coplanar any more, which for this part is the whole job.

What we thought it was

Bed adhesion. It usually is. We went at it the obvious way first — more glue stick, a brim, a hotter plate — and the lift got slightly better and never went away. That was the clue: if adhesion were the problem, the fixes would have solved it outright rather than shaving a millimetre off.

What it actually was

Differential cooling. Nylon shrinks appreciably as it drops through its glass transition, and a long flat face cools unevenly across its length. The corner that lifts is the corner that cooled first. No amount of stickiness at the interface beats a part that is actively contracting.

The four changes

1. Dry the filament properly. Nylon picks up water from the air in Chandigarh in a matter of hours. Six hours at 70°C before every print, not once a week.
2. Chamber temperature, not bed temperature. Getting the enclosure to a stable 45°C did more than another 10°C on the plate.
3. Slow the first two layers to 15 mm/s. A first layer laid down slowly bonds along its whole length instead of dragging.
4. Reorient the part. Standing it up cost us support material and about 40 minutes, and removed the long flat face entirely.

The reoriented, dried, slow-first-layer version came out within 0.1 mm across the mounting face. We have printed the same part nineteen times since with no failures.

The part we would tell a client

If you send us a long flat part in an engineering material and you need the flat face true, expect us to suggest standing it up and charging for supports. It is cheaper than printing it twice.