Everything starts with hardware. So if we want to build a functional 3D printer we first have to build good hardware. Then we make all of the other things based on the hardware itself. The mechanical part of my 3DP printer consists of two units. First one being the gantry, and the second one being two "pistons" which have powder inside.

GANTRY

This part isn't really anything special. It is basically Y axis mounted on an X axis. Simmilar gantries are common on CNC routers and a lot of FDM printers (makerbot and ultimaker). Even though these are realy simple systems there are few factors that should be taken seriously. First one being that X axis should have drive pulleys or screws on both sides. This prevents wiggle, which gets even more noticeable when the X axis guides are further apart. This is one thing I have to make/improve on my device. Other factors are mostly the load that the gantry is going to be moving.

In most cases people use steppers and pulleys to move the gantry. For X axis I have used DC servo motor driven by L298 and arduino which is connected to a 500PPR quadrature encoder on the motor. Arduino is running misan's DC servo firmware. With good PID tunning i have managed to move the motor with 2000 steps per revolution. In combination with pulley I got a very fast speeds with approximaetly 0,01mm resolution. Y axis is a little bit more problematic as it uses stepper motor and a M6 screw, thus being very slow. Motor is also being underpowered which makes it even slower. This is why I am exchanging stepper and the screw rod with system simmilar to one used on the X axis.

"PISTONS"

Two pistons have been made out of plexiglass. They are basically a rectangular box with divider in the middle and a double bottom. The two bottom plates hold the gears in position. There are three gears used in one cylinder. Two of them act as nuts for M6 threaded rods and one is mounted on the stepper. This one also turns the other two gears. I used the cylinder itself as a guide. This way I screwed two 5mm plates of plexiglas that fit in the cylinder. One of them is attached to two threaded rods with hole and slot that prevent the rod from rotation. Between the plates i used felt that acts like a seal and a spring that holds the piston in place.

I used two NEMA 17 stepper motors. This unit does not need to be fast but it needs quite a lot of torque. This is why the steppers were ideal solution. If I were to build a bigger piston I would have to use bigger motors.