About this project
One print that tells you how much clearance a printed thread actually needs on your machine, in your material, at your layer height — and how much that answer changes with print orientation.
The bar carries a row of through-threaded holes. Every hole is the same thread, cut with a different diametral clearance, and the number engraved beside each one is that clearance in millimetres. Two male test pieces come with it, both at zero clearance: an upright bolt with a knurled head, printed standing on its head, and a side bolt printed lying down with the thread flattened top and bottom. Run each into the holes. The first hole that turns freely without wobble is the clearance that orientation needs.
Why two bolts
A thread printed standing up is turned from stacked rings and comes out close to its modelled size. The same thread printed lying down has its crests flattened, sags on the underside and usually needs more clearance. The two bolts normally land on different holes, and that difference is the number worth knowing before you commit a threaded part to a print orientation.
The side bolt's flats sit where the thread surface reaches 45 degrees, so it lies flat, prints without supports and keeps as much thread as the orientation allows. Its paddle tab is the same thickness as the flats, so nothing on the part stands above them.
Defaults
| Setting | Value |
|---|---|
| Thread | 14 x 2.5 |
| Holes | 6, from 0.2 mm to 0.7 mm clearance |
| Step between holes | 0.1 mm |
| Bar | 192 x 37 x 12 mm |
| Engagement | 12 mm of bar, about 5 mm of it full-height thread |
| Upright bolt | 22 mm knurled head, 20 mm of thread |
| Side bolt | 40 x 22 x 9.9 mm, flats top and bottom |
Reading the result
- Binds or will not start — too tight, move one hole along.
- Turns with firm resistance the whole way — a good fit for a joint that stays put.
- Turns freely, no side-to-side play — the usual choice for a threaded assembly.
- Rattles — too loose; back up one hole.
The answer moves with the printer, the nozzle, the material and the layer height, so it is worth re-running when any of those change. Larger threads and coarser pitches usually tolerate less clearance than the numbers suggest, because the same gap is a smaller fraction of the thread depth.
Printing
- All three parts are already in their print orientation: the bar lies flat, the upright bolt stands on its knurled head, the side bolt lies on its flat. No supports anywhere.
- Print them together in one go, in the same material and profile you will use for the real part.
- Do not iron the top surface or add a horizontal expansion offset for the test, or you will be measuring the slicer instead of the thread.
- Every hole has a tapered lead-in and lead-out. The thread fades out over that taper instead of stopping dead at the face, so the first turn on the underside prints without an overhang and a slight elephant foot does not decide the result.
- All markings are cut into the material rather than raised, so a 0.4 mm nozzle resolves them cleanly. The one on the upright bolt head is mirrored in the model and sits on the first layer, so it reads the right way round on the printed part.
What you can change
- Thread — major diameter, pitch, and the facet count per thread. The facet count ships at 64; set it to 0 to hand the choice to the kernel.
- Test range — number of holes, the clearance of the first hole, and the step between holes.
- Bar — thickness, which is the engagement depth, the wall around each hole, the size and depth of the engraved numbers, and the angle of the lead taper at both ends of every hole. A shallower angle runs the lead deeper into the bar and leaves fewer full turns.
- Test bolts — whether each bolt is included, the side bolt's across-flats height and whether that height is engraved on it, and the size and depth of the bolt markings.