In a recent woofer update in particle board boxes, I examined any and all options:
T-nuts, threaded fasteners, wood screws, sheet metal screws, clamps, etc. None of which offered an optimal solution due to the mounting circle diameter relative to the cutout.
T-nuts should be pressed in. Threaded fasteners require sufficient margin of which there was little. Wood screws waste a fair portion of their length. Clamps don't apply the full force to the driver. Which left sheet metal screws.
The particle board, of which I have zero expertise, is covered with a hard outer shell, seemed softish in the middle and harder on the inside. The original install used straight #8 Philips head screws. It appeared the holes were originally drilled at the recommended 80% root diameter as the surface was pulled up which is not ideal.
Countless hours perusing online fora didn't ring any chimes.
I came across this by chrisb wherein he suggests using Crazy Glue to harden the particle board fibres prior to insertion.
⚡
Cogitating a bit, I reasoned that a good wood glue in a root diameter hole might be just the ticket.
And lo and behold, it's perfect!!
Method:
T-nuts, threaded fasteners, wood screws, sheet metal screws, clamps, etc. None of which offered an optimal solution due to the mounting circle diameter relative to the cutout.
T-nuts should be pressed in. Threaded fasteners require sufficient margin of which there was little. Wood screws waste a fair portion of their length. Clamps don't apply the full force to the driver. Which left sheet metal screws.
The particle board, of which I have zero expertise, is covered with a hard outer shell, seemed softish in the middle and harder on the inside. The original install used straight #8 Philips head screws. It appeared the holes were originally drilled at the recommended 80% root diameter as the surface was pulled up which is not ideal.
Countless hours perusing online fora didn't ring any chimes.
I came across this by chrisb wherein he suggests using Crazy Glue to harden the particle board fibres prior to insertion.
⚡Cogitating a bit, I reasoned that a good wood glue in a root diameter hole might be just the ticket.
And lo and behold, it's perfect!!
Method:
- Accurately mark and double check driver mounting holes
- Accurately punch hole centres
- Drill root diameter with brad point drill
- Using a slightly smaller drill, fill the flutes with a good 24 hour wood glue and coat the holes thoroughly
- W a i t ... let the glue set
- Using a sharp metal drill slightly smaller than the root diameter in a tap t-handle, gently clean the excess glue from the hole
- Vacuum any detritus from the holes
- Wax the mounting screws [I used candle wax melted in a pan of hot, not boiling, water]
- Place driver
- Insert screws and tighten just shy of contact
- Follow flange bolt tightening sequence, preferably with a calibrated driver
I have modified t-nuts ( grinding a flat on them so they are left with three prongs ) where space was limited, I think if I was using particle board ( apparently it has good damping ) I'd be tempted to PVA small bits of mdf behind, so the screw passes through the particle board and screws into the mdf, however your method of using glue is a useful alternative. I'm nervous of the spikes of t-nuts splitting the wood when using them.
In addition to screws, on one project I used a thin layer of RTV silicone sealant on the mounting surfaces. This was for a driver that didn't have a gasket on the rear of the mounting flange and I wanted an air tight seal. Years later one driver needed replacement and I couldn't believe how strong the RTV was.... no need for screws after that stuff has cured.
Use Thin Super Glue "cyanoacrylate" let the glue soak into the wood for 2 or three minutes. Then spray on or apply " cyanoacrylate accelerator" The accelerator can be found in a hobby shop or craft store.
After the above treatment the "MDF" will be hard enough to tap threads into it. I have used this technique for many wood projects.
After the above treatment the "MDF" will be hard enough to tap threads into it. I have used this technique for many wood projects.
Hmm, sheet metal screws better overall than ones designed specifically for PB?! Not IME or any other woodworker specializing in hobby/commercial PB construction that I've known.
Right, as much as I espouse rigid/massive cabs for LF/mid bass to raise its Fs at least an octave above its intended BW, the mids-up should be as lossy as practical to 'push' its Fs at least an octave below it, which usually means the cheapest PB (not MDF) with no braces is plenty good enough, though often makes for more work/materials if a fine finish is desired/required.
Within reason, using the proper PB screws works fine for all but repeated install/remove, which requires at least the glue trick, though obviously a proper PB insert is the way to go if doing it regularly, such as a driver test box.
I kinda like those Hurricane nuts that parts express sells. I have used an angle grinder to lop off bits of the back when space is tight.
e.g. https://www.parts-express.com/8-32-Hurricane-Nuts-50-Pcs.-081-1080
e.g. https://www.parts-express.com/8-32-Hurricane-Nuts-50-Pcs.-081-1080
Without a link to your referenced work, went with what you posted here and from dim memory can't recall ever needing/knowing of any non-countersunk head PB hardware, so would need to use a finishing washer, but flat or not it's still superior to a sheet metal screw.
The driver mount would not take kindly to finishing washers which depend on backing at the centre. I've had them warp and bend when not well supported.
As mentioned, there is not enough meat between the mounting hole and driver cutout to use a threaded insert, at least not in the PB these cabinets are made of...
As mentioned, there is not enough meat between the mounting hole and driver cutout to use a threaded insert, at least not in the PB these cabinets are made of...