Step 2 - The Cheapo Connection
Check here for our cross dowel nuts
that are used in this tutorial. These are a great way to create joints in wood. If you are looking for some great CNC machine kits, look here
Making corners, connecting two pieces of MDF can be a challenge. I am going to run through a technique, and a vital element in the CNC machine of this tutorial. This step is not as glorious as building an actual working component of one of the CNC axes; however, this type of connection is used on almost every part of the machine. The idea is very simple: with two large holes to receive nuts, and two transversal holes to receive screws (long enough to reach the nuts), a tight and strong connection can be achieved. Not only is this connection strong, it also helps to create the tension desired to tighten an axis assembly around the rods/angles for snug no-play sliding. Other types of connections that I have tried are weak and prone to splitting. I have had no splitting or failures with this method.
You will need a 3/4" drill bit to cut the larger holes. I also like to use three of the normal drill bits, a 3/32" to create a pilot hole, a 5/32" to drive through the wood accurately, and finish off with a 1/4" to match the screw/bolt size. I'm sure with a drill press, this is not needed.
First, gather the two pieces that need to be connected. Mark the overlapping piece (the piece to the right in the above image) with a line that represents half the thickness of the wood to which it will connect. Make two marks on that line one inch or so from the outside edge of the overlapping piece. Drill pilot holes through those marks.
The next part of the process is particular important. Use clamps to hold the piece together. I used my hands, but it is a pain to hold perfectly. You can see where the overlap is not perfect in the image. It's about 1/32" out of alignment, but it's for demonstration purposes only. You can actually drill the holes a little larger to have the ability to re-align, so don't fret if you don't get it right.
On the second piece you will drill two 3/4" holes in alignment to the previously drilled holes so they intersect. This will make it possible for the screw to intersect with the nut for extreme tightening (not to the point of splitting the MDF, of course. Note: there has been comment on the fastening parts, to prevent splitting, flatten out one side of the large hole and add a washer. Also add a lock washer to prevent loosening.)! That's pretty much it. The video will show the complete process. With some practice, you should be able to do these in about 7 minutes.
Benefits of Using Cross Dowels
I created a video to show the use of cross dowels as an alternative to the usual connections. A cross dowel is a piece of hardware to mechanically join two materials usually at right angles. This video will most likely be sent over to step 2 and exhibited as an alternative. The cross dowels are clean, won't turn through vibration by virtue of it's shape, and spans more wood area so the possibility of splitting or crushing the wood is minimized. Check it out and tell me what you think. In my stuff for sale (coming soon), it will provide the buyer a glimpse of how to use the hardware.