Build
T-nut grid spacing for a home wall
How to count an M10 T-nut grid, what 100 mm, 150 mm and 200 mm do to the numbers, and why a system board ignores your grid.
A T-nut is a threaded insert in the back of the plywood. The hold's bolt comes through from the front and clamps into it. The grid is the pattern of those holes. Get it wrong and you either drill the sheet into lace, or you cannot put a foothold where your sequence needs one.
The count
Decide three numbers.
- Panel width and panel length, from the planner or from a system-board drawing.
- Edge margin. This site's planner uses 50 mm, so the first nut is not on the very arris of the sheet.
- Spacing. A round millimetre figure you will actually mark, such as 100, 150 or 200 mm.
Columns are the number of positions across the width. Rows are the number along the panel. Each is "how many steps of the spacing fit between the two margins, plus one". A 2440 mm panel with a 50 mm margin and a 200 mm grid has 12 positions: the first at 50 mm, then every 200 mm, and the last still inside the far margin. A square 2440 mm panel at that grid is 12 by 12, 144 nuts. The same panel at 150 mm is denser. At 100 mm it is a lot of drilling.
ALPIDEX, on the M10 pack below, describes a 10 cm grid as about 95 nuts per square metre and a 15 cm grid as about 45, and suggests offsetting every other row so the holds are not in a rigid lattice. Those densities are theirs, for the grids they name. Offsetting is a setting choice. It does not change the fact that each hole is a 12 mm drill from the back, which is the hole that pack specifies, and that they tell you to keep adhesive out of the threads and to stop at 30 Nm.
A wider 200 mm grid is what many home walls use when the aim is a movable set of holds rather than a hold on every brick of a lattice. You can always add nuts later in the gaps. You cannot undrill a hole. Start wider if you are unsure, and add where the setting is obviously empty.
Marking the sheet
Mark on the back, where the nuts go. A dry line or a long straightedge beats a tape dragged twelve times. Drill from the back at the diameter the nut maker states, seat the prongs, and draw the nut in with a bolt so the prongs bite. The front of the hole should be clean enough for a hold to sit flat. A nut that spins in an oversized hole will not improve with a longer bolt.
Keep the grid off the line where two sheets meet unless there is timber behind that joint. A T-nut in a seam is a T-nut in mid-air.
When the grid is not yours
Moon, Kilter and Tension publish hole patterns because their apps assume a hold in a known place. A tidy 200 mm grid of your own will not run those problems, even if the panel happens to be 2440 mm wide. If the point of the wall is the MoonBoard app, build Moon's pattern from their drawing and use the metric M10 bolts they specify. If the point of the wall is your own setting, the grid above is the right tool, and the holds guide is the next decision.
Mixing both on one sheet, a system pattern plus a free grid, is how you drill through a future hold position. Pick one pattern for each panel.