From the Loftsmith Workshop

Two-material joint pull test for PLA, PETG and TPU

Tells you whether two materials really hold onto each other before you commit to a big multi-material print. Each strip is half one colour and half the other, locked by tiny keys that get smaller down the set, with a loop at each end for a scale hook. Set it to your nozzle.

5 parts · 37 g · 131 × 174 × 3 mm

by Loftsmith Workshop

Five flat strips, white on one half and orange on the other, each with a round hole at both ends
Loading the 3D view
Loading the 3D view
No adjustable sizes

Ask for the sizes you want to tweak, e.g. “make the width adjustable”.

Change it in the Studio

Parts

  • butt-A · PLA (filament A, slot 1) · Flat, top up as modelled

    Joint 1, plain butt: one dimple. Measures the bond alone.

  • butt-B · TPU by default (filament B, slot 2) · Prints inside butt-A as one object

    Second material of joint 1.

  • teeth-A · PLA (filament A, slot 1) · Flat, top up as modelled

    Joint 2, square teeth: two dimples. More bond area, still slides apart with no bond.

  • teeth-B · TPU by default (filament B, slot 2) · Prints inside teeth-A as one object
  • dovetail-A · PLA (filament A, slot 1) · Flat, top up as modelled

    Joint 3, single dovetail: three dimples. Locked along the pull; can slide out vertically.

  • dovetail-B · TPU by default (filament B, slot 2) · Prints inside dovetail-A as one object
  • ckey-A · PLA (filament A, slot 1) · Flat, top up as modelled

    Joint 4, C-key: four dimples. Two C-shaped hooks grip each other; locked along the pull.

  • ckey-B · TPU by default (filament B, slot 2) · Prints inside ckey-A as one object
  • comb-A · PLA (filament A, slot 1) · Flat, top up as modelled

    Joint 5, captured comb: five dimples. Two headed fingers sealed under and over by 0.8 mm B skins; blocked in every straight direction.

  • comb-B · TPU by default (filament B, slot 2) · Prints inside comb-A as one object

Print settings

Layer height
0.2 mm
Walls
2 (page figures); use the same settings for every coupon so the results compare
Infill
15% (page figures)
Supports
None. Every coupon prints flat and the build report shows 0% overhang
Notes
Slot 1 = filament A (light, PLA by default), slot 2 = filament B (orange, TPU by default; switch with the Material pair choice). Both materials sit on every layer, so expect a filament change on each layer and a prime tower. Engine estimate at 2 walls/15%: about 81 g and 2 h 55 min. That counts abou

Hardware

  • Luggage scale or hanging spring scale with a hook · Reads the peak pull. The default 8 mm loop hole takes a hook wire up to about 7 mm; use the Loop hole slider for thicker hooks.
  • Fixed hook, carabiner or screw eye · Holds the other loop while you pull.

Assembly

  1. Pick the Material pair and the nozzle you print with, then load filament A in slot 1 and filament B in slot 2.
  2. Print all coupons flat on one plate. They come off as finished parts and need no assembly.
  3. Read the dimples on the light half: 1 = butt, 2 = teeth, 3 = dovetail, 4 = C-key, 5 = captured comb.
  4. Hang one loop on a fixed hook, hook the scale into the other loop and pull slowly in a straight line along the strip. Note the peak reading and where it broke.
  5. Repeat for each coupon and compare. Butt and teeth measure the bond itself; dovetail, C-key and comb measure the interlock.

Good to know

  • The engine checks geometry only: overlap, key width and whether the halves can come apart in a straight line. It does not predict bond strength. Results depend on materials, temperatures, print order and slicer settings, so please post your numbers with your settings.
  • Both filaments are on every layer, so you need an AMS/MMU, a toolchanger or a dual-nozzle printer. A manual pause-and-swap only works where the two materials meet on a horizontal plane, and every joint here has vertical faces, so it can't print these coupons.
  • TPU often can't be fed through an AMS-style unit; check yours, or use an external spool or a second nozzle. With TPU as filament B, the interlocks can stretch and slip out without breaking: the no-pull-out check assumes both halves are rigid.
  • Choosing PLA + PETG brings up the engine's warning that the two barely bond. That's expected, since it's the weakness this test measures.
  • The dovetail and C-key are locked only along the pull. They can still slide out vertically, so don't twist or bend them.
  • Your scale's range limits what you can measure. Check it before pulling the interlock coupons, and pull in line: a sideways pull breaks the loop or strip instead of the joint.
  • The loops-outlast-the-strip check compares cross-section areas (1.25 times the strip at the defaults). It is not a stress calculation for where the hook presses on the loop.
I printed this Remix

Comments