brombo wrote:
For open baffles glue is enough since the forces on the joints are not great. If you are using mdf for a closed box system in addition to glue I would use confirmat screws.
https://www.amazon.com/HighPoint-Confir ... B0031TGSB2They are especially made for mdf.
I have given up on screws and use biscuits because the plate joiner cuts slots in the wood that accept the biscuits so there is no spreading force on the MDF. There are also no holes to fill and sand. I recently found another problem with screws. For years I have used MDF screws to hold drivers in the enclosures with no problems. With the eggs, using the same screws and pilot drill, after about two months I started to see small lines appearing in the finish of the eggs near the screws. I removed the drivers and noticed that the screws were causing the MDF to separate slightly. The same setup in the bass cabinets where the screws were inserted perpendicular to the surface has caused no problems. This is the first time I have fastened the driver into what is the end of the MDF since the egg is made of stacked cutouts from sheet stock. Apparently screwing into the end of the sheet is a problem.
I immediately removed all the screws to prevent the problem from spreading. I then purchased some EZLok threaded inserts so that I could use metal screws to install the drivers. I did not want any sideways force on the ends of the layers so I did a test on a scrap piece of MDF with incrementing size holes from a series of numbered drills. I found for these fasteners a "K" bit that is 0.281 left just enough wall material to allow the threads of the inserts to pull them into the holes with barely any wall contact.
To insure holding power. I coated the inside of the test hole and the outside of the insert with JB weld epoxy and screwed the insert into the test hole. The bottom of the insert had a small circle of masking tape over it to prevent the epoxy from entering the threads. After two days, I began a test to see at what point the bond to the insert would fail. I put a large washer around the insert to allow it to pull out of the hole and used a machine screw and washer to apply tension to the insert. I tightened it as far as I ever dared with a screw and it held. The next day I continued to tighten the screw with a ridiculous amount of force until the washer deformed. At that point the insert pulled very slightly out of the hole. Since that amount of force was totally over the top and far more than the screw was designed for I considered it a success and installed all the inserts in the new pilot holes. I'm including photos of the process. Time will tell how it works. but I would suggest caution when using screws into the edges of MDF sheets.