Exercise 3. Building a board from a PCB DXF

Item	Detail
Input files	03-MYB-6ULX_2D.dxf, 03-MYS-6ULX_2D.dxf
Time	3 min (8 seconds to build both boards)
What you end up with	Two documents (pcb_MYB, pcb_MYS), each with one board Body (1.6 thick, Ø3.3 mounting holes as a parameter)
What you learn	How to have only the layers you need read out of a DXF, how a polyline’s rounded corners (bulge) become arcs, and how to split holes by type

To fit a PCB into an enclosure you need a 3D board with just the outline and the mounting holes. A DXF contains hundreds of things — silkscreen, dimensions, vias — so the heart of this exercise is getting only what you need read.

Original and finished

Original MYB-6ULX_2D.dxf imported into FreeCAD Draft as a flat view — outline, holes, silkscreen and dimension layers all in one file

Finished MYB_6ULX — outline Pad + 6 mounting holes + 115 pin holes, 70×55×1.6, DoF 0

	File	Description	Size
Original	03-MYB-6ULX_2D.dxf	DXF	479 KB
Original	03-MYS-6ULX_2D.dxf	DXF	461 KB
Finished	03-pcb_MYB-done.FCStd	MYB board	91 KB
Finished	03-pcb_MYS-done.FCStd	MYS board	79 KB
Finished	03-MYB_6ULX-done.step	STEP	200 KB
Finished	03-MYS_6ULX-done.step	STEP	173 KB

The finished files are real

They were produced by running this page’s steps on FreeCAD 1.1.3, and the images are actual screen captures of those files opened in the FreeCAD 1.1.3 GUI (isometric, white background). Download them and you can look at the tree, the sketches and the Params directly.

Setup

1. Launch FreeCAD 1.1.3. You want [CAD X-ray] 서버 시작 in the Report view.
2. Put both DXF files in C:\cad\.
3. In PowerShell, move to C:\cad and open claude.
4. Do not open the DXF in FreeCAD yourself (no File → Open). The reason is in step 1 below.

Steps

1. Have it read the DXF and give you a table first

Say this

Read C:\cad\03-MYB-6ULX_2D.dxf (directly from the file, not through FreeCAD) and show me a table of element counts per layer, the outline polyline, and circle counts per diameter.

What the AI does — reads the DXF directly (ezdxf or plain text parsing) and pulls the POLYLINE entries (layer, closed flag, vertices and bulge) and CIRCLE entries (layer, centre, radius) from the ENTITIES section. Through FreeCAD’s DXF import, hundreds of silkscreen and dimension polylines each become a Draft object, which took over two minutes on MYB-6ULX when measured — hence “not through FreeCAD”. Three things should appear in the table without being asked: whether OUTLINE is closed, whether the bulges are 90° arcs, and which circles look like mounting holes.

What the AI says back

Four layers: OUTLINE (1 polyline), TOP (121 circles, 442 polylines), SILKSCREEN_TOP, DIMENSION. OUTLINE is a closed polyline, 8 vertices, 70×55, bulge 0.4142 at the four corners (90° arcs, R1.27). Circles: six Ø3.3 (the four near the corners look like mounting holes), 78 Ø1.4 (pin headers), a few Ø1.5–2.5, none below 0.5. Use all six as mounting holes, or only the four at the corners?

How to check — if the OUTLINE polyline is “closed” and the bulge values are near 0.4142, the board has corners rounded by 90° arcs. Six Ø3.3 circles is correct: four are mounting holes near the board corners and two belong to the connector on the left.

2. Give it the rules and have it build both boards

Say this

Outline is the OUTLINE polyline as-is (bulges become arcs), holes are circles of radius 0.5 or more only, one per centre where they overlap, only the four corner Ø3.3 are mounting holes as Params.mount_d, thickness 1.6 as Params.thickness. Build both boards with those rules: Body MYB_6ULX (Label MYB-6ULX) in pcb_MYB, and 03-MYS-6ULX_2D.dxf as MYS_6ULX (Label MYS-6ULX) in pcb_MYS. Features PadBoard → PocketMount → PocketPins.

What the AI does — solves each bulge b into an angle θ = 4·atan(b), turning the span between two vertices into an arc (the arc centre lies to the left of the direction of travel), transfers the 4 lines + 4 arcs into a sketch at DoF 0, then stacks one Pad and two Pockets in order. Circles are filtered by radius and centre into mounting holes and component pin holes. Once the rules are set, a board in the same family only needs new names.

What the AI says back

MYB_6ULX done. PadBoard (8 elements, DoF 0) → PocketMount (4) → PocketPins (117). Shape valid, bbox 70 × 55 × 1.6, 131 faces. MYS_6ULX done. PadBoard (8) → PocketMount (4) → PocketPins (100). Valid, 114 faces. On MYS every circle sits on the SILKTOP layer, so the radius rule alone did the filtering.

How to check — in the tree, PadBoard, PocketMount and PocketPins should be in black text (no errors), and viewed from above (number key 2) the four corners should be rounded. The Params sheet holds thickness and mount_d (width, height and corner_r are there for reference — the outline itself uses the DXF elements directly). Put the two documents side by side (Windows → Tile) and see how the pin hole layouts differ.

3. Look, then save

Say this

Show me iso views, and if they look right save them to C:\cad\pcb_MYB.FCStd and C:\cad\pcb_MYS.FCStd.

How to check — you should see the board thickness in the screenshot and the holes going all the way through.

Checking your result

Criterion	Value
Outline sketch	8 elements (4 lines + 4 90° arcs), DoF 0
Mounting holes	Ø3.3 × 4, Params.mount_d
Thickness	1.6, Params.thickness
Shape validity	valid
Features	PadBoard → PocketMount → PocketPins

When it doesn’t work

• Nothing happens for over two minutes — the AI used FreeCAD’s DXF import after all. Wait for it to finish (it cannot be interrupted) and ask again with “don’t open the DXF in FreeCAD, read the file directly”.
• The outline doesn’t close and the Pad fails — the OUTLINE polyline may be in several pieces, or under a different layer name (Edge.Cuts, BOARD). Pick the layer with a closed polyline from the table in step 1 and name it.
• Too many holes — raise the 0.5 radius threshold. Redefine it: “only radius 1.0 and above”.
• The mounting holes aren’t Ø3.3 — boards vary (Ø3.2, Ø3.5). Look at the radii in the step 1 table and specify: “treat radius 1.6 as the mounting holes”.
• The arcs are inverted and the corners cut inward — a bulge sign interpretation problem. Say “check the OUTLINE arcs bulge outward and fix the inverted ones”.

Going further

1. Build a “with components” outline Body by adding 15 mm of component height clearance above the board, and use it for enclosure interference checks (see the interference check in Exercise 4).
2. Change Params.mount_d to 3.5 for looser mounting holes.
3. Export both boards as STEP for your enclosure designer. “Export MYB_6ULX to C:\cad\MYB.step” is enough.

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What runs behind the scenes
Reading the DXF	The AI tool itself (parsing POLYLINE and CIRCLE with stdlib, converting bulge to arcs)
Building the model	build_features (elements profile + circles, Params aliases)
Checking	inspect_object, get_screenshot, save_document

Original session log: https://github.com/WaveSimm/cadxray/blob/master/examples/pcb_from_dxf.py