What to measure
Measure the bit across its cutting diameter, and measure what goes in the hole: an 8 mm dowel, a fitting or a bolt. Then find the offset from the edge to the hole centre on the part you are copying or on your drawing; 25 mm is used here. Last, measure the thickness of the board. The fence on this page is 14 mm high, which suits boards of 16 mm or more. On thinner stock, reduce the fence height to 2 mm less than the board, so the jig lies flat when the board is on the bench.
Hole clearance, thickness and material
The guide hole is 8.2 mm for an 8 mm bit. An 8 mm bit removes four times the material of a 4 mm bit and pulls harder on the jig when it breaks through, so the block is 15 mm thick and the jig is 90 by 55 mm to give a clamp plenty of room. Friction is also higher: a printed hole heats and wears quickly at this size. For anything beyond occasional use, buy a hardened drill bushing with an 8 mm bore, measure its outside diameter, often 12 mm, and type that diameter as the guide hole with no added clearance, so the bushing presses in. PETG takes a press fit without splitting; PLA can crack around a bushing unless the hole is opened by 0.05 to 0.1 mm.
Printing
Print as generated: block on the bed, fence up, no supports. Use a 0.2 mm layer height, five or six perimeters and 40 percent infill or more, since this jig is clamped hard. The part is 90 by 55 by 29 mm and uses noticeably more plastic than the smaller jigs; the generator shows the solid volume before you download.
Using it
Turn the jig over so the block lies on the face of the board and the fence hangs over the edge. Clamp across the block, not across the fence. Start the drill before the bit touches the wood, feed steadily, and back out once or twice to clear chips, because packed chips are what melt a plastic guide. Wear eye protection. The jig only guides the bit; it does not hold the workpiece.
Outline drawing
To scale. Left: top view as printed, fence along the top edge. Right: end view, block 15 mm thick with the fence rising 14 mm above it.
Parameters the generator will use
| Setting | Link parameter | Value |
|---|---|---|
| Model | model | drill_jig |
| Jig length along the edge (X) | length | 90 |
| Jig width including the fence (Y) | width | 55 |
| Block thickness | thickness | 15 |
| Guide hole diameter | hole_diameter | 8.2 |
| Hole centre to workpiece edge | offset | 25 |
| Hole position along the length (0 centres it) | hole_position | 0 |
| Fence thickness | fence_thickness | 6 |
| Fence height | fence_height | 14 |
All lengths are in millimetres. Outer size from these values: 90 x 55 x 29 mm.
Open the generator with these values
This model needs the $7 licence key: one payment, one key, and it opens all five paid models. Get a licence key on Gumroad ($7)
The drill guide jig needs a licence key: without one the generator shows the model locked, lists the values from this link and fills them in as soon as you unlock. The fitted drawer organiser bin is the free model and downloads with no key.