Threading MDF

[Me2]

Hello all,
I'm currently getting all the materials together to finally start my own CNC wood router. The drives are completed and the motors spin in tune to the Gcodes I've put into Mach2 created from some solid modeling.
I'm basing the design on Joe's arrangement and building out of MDF. With this arrangement the threads are cut direct into the MDF to attach the various assemblies. I tried tapping the threads in the same way but found even the slightest bit of over tension resulted in the threads pulling out rendering them useless. I'm not sure if anyone else has tried to overcome this problem but I experimented with various ways to strengthen the threads and found coating them in Super Glue made all the difference. The MDF fibers when cut act like a sponge. The Super Glue being water like is soaked up very easily and when dried gives the thread and extremely hard face. The Super Glue that has wicked into the fibers creates a hard plug around the threads making them hard to pull out. To give you some idea of how strong the thread becomes through this process, the bolt when tightened against a washer is able to pull the washer into the surface deforming the MDF. Just going by feel I would say the applied torque between the treated and untreated thread would be almost doubled.

Cam

[Steve85]

Cam,

Thanks for this tip; it comes at just the right time as I'm about to start cutting threads into the MDF parts of my own first-time mill build.

Steve

[MxRacer19]

Would T-nuts be a practical application here?

[Cruiser]

The simplest solution of course is to use thin cyanoacrylate glues, It will toughen up the wood for sure. But, it is not as durable as you might hope for. The best bet is to find some brass thread certs that have a wood thread on the outside and the machine thread on the inside of it. They come in a varied group of sizes too.

[louieatienza]

I think even better, but more expensive, would be to buy some, I believe they're called "barrel" nuts or assembly nuts. They're a small rod section with a hole and threads cut cross drilled. You would simply make a tight hole for these to fit in to. Much stronger than grommets IMO.

A crappy pic, but hopefully illustrates the concept (a motor mount for a straight-line routing jig I made for guitar work...)

[JoeSixPack74]

My 2 cents. Why not drill oversized holes then fill with lab metal or jb weld then drill and tap that instead of the mdf directly. We put together a cracked in half 2nd gear on a Honda CBR with JB weld.