T+G Secret Nailing - Length of Nails?

[rarara]

I am planning to hire a nailer to fix some 20mm maple onto the subfloor of original 20mm floorboards. There seem to be 2 lengths of nail available - 38mm and 50mm.

If these things fire in at 45 degree angle at the top of the tongue, are the 50mm nails going to protrude through the subfloor in any way? I don't want to risk that any pipes or cables will be sitting close to the bottom of the board, but obviously i want the max holding power possible.

So, 38mm or 50mm???

 

[john4703]

If the top of the tongue was half way up the new 20mm board then at 45 degrees, it would take about 14mm to reach the board underneath.

So if you use 38mm nails they would go about 24mm into the original boards. At 45 degrees it takes about 28mm to go right through so with 38mm nails you would be fine. If you used 50mm nails they would stick out on the underside.

 

[big-all]

45 degrees would make the wood about 37percent thicker
if we assume the top off the tounge is 7mm down that leaves 33mm plus 40% =45mm
are you sure the origional is 20mm at 24mm you would be ok