i have created and laminated my endcaps for my sonosub build...i was getting ready to mark the mounting holes and noticed that the holes are partially blocked by an inner lining...i think it is plastic...as it seems a little flexible...
should i just sand out all the plastic around the mounting hole area (so the bolt will be flat against the metal)...or do i not even need to be concerned with it...
what size bolt should i be using for mounting...i was thinking 10-32...but also have heard to use 1/4...does it matter...or should i just go with whatever fits and will hold the sub to the endcap....
also...should i be worried about drilling a 5/16" inch hole for the 1/4-20 t-nut when there is not much wood between the subwoofer cutout and the 5/16" inch hole...thanks...
Many recommend wood screws. You can likely re-use the holes if you need to remove the driver, but you could also turn the speaker and drill new holes without having it look weird. For instance, align the screws on the vertical centerline instead of the horizontal for the re-drill. However, I understand your desire to avoid wood screws. I have used 10-32 Hurricane nuts and black oxide socket head cap screws on all of my builds so far.
hurricane nuts: http://www.parts-express.com/pe/showdetl.cfm?partnumber=081-1082
screws (these are 1", but many other lengths are available, and the ones I got are black despite the "gray" color listed): http://www.amazon.com/dp/B000FN3VTY
Wood screws are fine too until you remove the driver more than about 10 times. At that point you will have to go to T-nuts.
I would not use threaded inserts on MDF. It runs the risk of causing the layers to split apart and the area where the insert goes in to swell making it impossible to get an air tight seal. They really only work in soft woods.
T-nuts or hurricane nuts work fine even with the hole really close to the edge. They have the "T" part to hold them in place like a clamp. Don't over think it. No worries.
I used the metal inserts for 2 DIY subs now. I used a piece of scrap to find the perfect pilot hole for them by using several different sized bits and installing the insert to a nice torque without stripping out the MDF. I believe it was something like 9 or 11/32. I used a slightly larger one for the flange, but for me, it isn't really required since I use duratex finish which is quite thick. I used gorilla glue on the threads when installing the inserts to fill any voids and keep them from turning when mounting the driver with screws. I have had no issues at all with this method. I would say hurricane nuts are another option but I would avoid T-nuts. They have a barb on the flange, meant to be hammered into the backside of the baffle. This doesn't work so well with MDF but if you used a softer wood, I wouldn't see an issue.
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On the other hand, the barbed nuts that PE sells I've never had any problem with. I've been able to put screws in them with a power drill/driver without starting them by hand first and haven't had any issues with cross threading or the like.