How to 3D print a custom hat block.

New to slicer setup? Follow Start Here: Printer & Slicer Setup for supported file types, project-saving steps and the final print checklist.

1. 01

   Choose the finished size and head oval

   Use the intended finished hat size or a dependable circumference. Then choose round, standard oval, or long oval instead of assuming circumference alone defines the fit.

2. 02

   Set the open-crown geometry

   Choose the crown height and one of the four profiles as a starting form with enough material for the crease and style you plan to shape later.

3. 03

   Generate the crown block STL

   Review the selections in Blocksmith Works, generate the full-size model, and keep the STL at 100% scale when it enters the slicer.

4. 04

   Verify dimensions and orientation

   Confirm the displayed size, the flat print base, the three open front, center, and back stand sockets, and the estimated material before starting a large print.

5. 05

   Print for the felt-contact surface

   Use a compatible material and printer setup, random seam placement, adaptive layers where helpful, and fuzzy skin off on working surfaces.

6. 06

   Inspect before workshop use

   Check the crown, base, sockets, and stand for roughness, cracks, warping, layer shifts, or anything damp felt could record.

Start with the fit, not an arbitrary STL

Use the free hat block STL generator to create a crown form for your measurements. For an overview of crown and brim tooling, read Hat Blocks Explained.

A downloaded model that is close to the labeled hat size can still distribute its circumference incorrectly. Blocksmith Works starts from the intended finished size and keeps the head oval visible as a separate choice. If the fit terminology is unfamiliar, read Hat Block Sizes and Head Ovals before generating the model.

Crown height and profile come next. They define the open form you will crease and shape later; they should not be used to compensate for the wrong base size or oval.

Treat the slicer as an inspection station

Before printing, look at the model from several angles and confirm the reported dimensions. Make sure the flat base is on the build plate, the three front, center, and back stand sockets remain open, and no repair warning has changed the geometry. Review material use and print time before committing a full spool and many hours to a crown.

Print for the surface that meets the felt

The working surface matters more than cosmetic details on the underside. Use enough walls and internal structure for the loads you expect, but do not assume that more infill fixes every problem. Reliable adhesion, accurate dimensions, and a smooth outer surface are the release gates that matter most.

Keep fuzzy skin and ironing off on crown blocks, sockets, stand pads, and pegs. After the print cools, inspect it in raking light and run your hands over the entire felt-contact surface. A defect you can feel may be transferred into damp felt.

Check the stand and identification

Clear loose material from the sockets without changing their geometry. Confirm the stand seats as intended and that the block is stable before adding a valuable felt. Read the underside identification directly from the bottom and verify that it matches the selected size, oval, height, and profile.

Use controlled heat, moisture, and tension

Hat making places moisture, heat, pull, and time into the same process. Warm and steam the hat material—not the printed tool—and never rest a hot iron on the plastic. Stop if the block softens, moves, cracks, delaminates, or produces an uncertain result.

Record the material, nozzle, walls, infill, seam strategy, layer settings, and measured outcome that worked. A repeatable record turns one successful print into dependable shop knowledge.