“About 5 years ago, I made a plotter for making drawings in quite big size. It was a 2 and half axis CNC machine, because the pen had only up or down position. It turned out soon, that it is one of the painful disadvantages of the machine. The other was that I moved the whole table with the paper in the X direction, so it required large room during operation.
I decided to rebuild the whole thing to have real Z axis, fix table and ability to move others than a pen. After a long planning and printing time of components I made a second version. It was already a real 3 axis machine. Its disadvantage was that the mechanical construction was not able to hold properly a spindle motor, so it bent down in the middle. Furthermore the flying particles contaminated the threaded rod of the X axis. Furthermore the mechanical and the electrical parts limited the size of longer materials. Furthermore I ran out of other ideas in my mind so I designed and build this machine I show now.
I used 15mm beech plywood for the main elements. For fix wood joints I glued them together, sometimes I made the joint more stable with screws too.
For metal/plastic connections I used wood screws for smaller parts. The bigger parts are fixed with metric screws and wood insert nuts.
The drilling of holes for screws must be very accurate otherwise they will not fit the bearings and they will not run smoothly.
For fixing material on the table, I put M6 T-nuts in a matrix. On the other side I use wing screws and if they are too long, then wing nuts too. A too deeply driven screw would make crash under the table
All the 3 axis slides with SBR12UU bearing blocks on SBR12 linear rails. This type of linear rails help to keep the rails rigid and straight, furthermore it is easy to fix them to plywood elements. The X axis is 700mm, so I doubled the plywood behind to enforce it.
8mm threaded rods and nuts move the axises. The threaded rods are fixed with KP08 (Z,Y) and KFL08 bearings (X).
I used nema23 steppers, 4.2A version for the X and Y axises, and 2 pcs 3A for the Z. The connection between the motors and the threaded rods are made with 20T GT2 pulleys and 9mm belts.
Under the KFL08 I made plastic elements to solve the belt tensioning, otherwise the motors also can be slided slightly for the same purpose.”