Hollow boards require a vent to be able to equalize internal pressures from changes in temperatures. If you surface mount a plastic vent or make your own brass vent you do not need to install blocking and you can simply drill a hole. For a more professional look you can countersink the flange and have the vent sit flush or just proud of the surface.
This 1/8″ rabbit allows the vent to sit just a little proud of the board but requires internal blocking of some sort. Vent blocking does not to be overly structural as it doesn’t get the pulling forces that leash blocking gets and its main function is make sure the vent isn’t a weak spot. There are 3 main ways to install plastic screw vents:
Method 1 – Drill a cross hole through a piece of wood blocking in one or both directions before the top skin is added. This method is simple and works well if you are using solid wood blocking and want a strong light weight support for a recessed vent. The disadvantage with this method is you need to be very accurate when you locate the internal blocking or there is the possibility to break/blow-out a corner and create loose bits of wood to potentially rattle inside your board.Method 2 – Add an extra piece of the skin material to the vent area. The best way to accomplish this is to drill a small pilot hole where you want you vent located before you attach the top panel. Use this hole to locate the support blocking on the inside of the top panel and add as small as piece as is practical with a bit of epoxy. The disadvantages with this method is the top skin with have a stiff area where the blocking is and it can potentially be harder to flex this area. Be careful the blocking won’t interfere with the fishbone frame.
Method 3 Use a 2″ x 2″ piece of foam. Not really the coolest thing in your wood board but it is my current favourite method as it has no potential to rattle and I have a friend giving me bags of foam chucks from construction sites. After the vent is installed you can press a wire through the foam block to create the air channel.
The most stylish venting option is to make you own mechanical vent out of some common brass hardware. Depending how you do this you can probably skip internal vent blocking all together. Epoxy a hollow brass insert like the one pictured above into a hole in the top panel. A pan-head bolt and an O-ring is then used to seal the board.
The 3 basic parts to making a vent are an O-ring, a slotted pan-head bolt and a threaded insert. This bolt will be cut to length and cross drilled like the banjo bolt below or filed. The cross drilling or filing a channel in one side of the threads allows the board to vent in just 1 or 2 turns. A bit overkill maybe but you will never lose you bolt!
No matter what option you pick make sure you leave some marks to locate the blocking. I drill a 1/8″ hole to locate my blocking before I shape the top panel. It really sucks to peal off your location marks before you locate the internal blocking!