14. Machine Design Assignment

Machine Design Assignment

This assignment was a hands-on approach to making a MTM machine

In this case, the instructors chose to make a MTM Snap mini- Milling machine. We worked in the assembly of the mehanical and structural parts, but not the Electronics/control. The MTM Snap is a 3-axis smal milling machine, before talking about the assembly, I'll mention a few details about the machine.

Construction Material: 12mm HDPE
Measurements: 18'' x 36'' (45 x 90 cm)
Motors: 3 NEMA 17 Stepper Motor and 1 DC Motor.

The three axes of movement are given by the stepper motors in the axis, and the DC motor provides the motion for the endmill spindle. The design of the machine is conceived to be press-fit, and the press-fit snap unions (so the fitting does not depend on the material thickness) are the reason for the machine's particular name. As it can be seen in the images below, the asembly of the framing parts is straightforward and only requires a few hits from a rubber mallet.

MTM frame assembly

The first piece to start the asembly is the side frame. The holes designed for the snap press-fit can be seen in this image.

Snap Machine cover

The Z- axis movement, which will determin the height of the mill is governed by the montage below, as it can be seen, the stepper motor uses a threaded rod to move the assembly on the Z-axis, in this image the assembly for the X- axis can be sen on the side, the spacers for the reference shafts and the center piece for the threaded rod, still not fully assembled..

Left Assembly

The Y-axis array is moved through a similar mechanism as the Z and X-axis, only in this case, the container is the moving table for the stock material to be milled, so the moving array is essentially moving a box in the axis.

driver box

Below a detail of the endmill assembly can be ssen, the shafts and the coupling for the threaded rod.

Right assembly

This is a detail view of the Z-axis array.

Stepper assembly

As the assembly progressed, more and more details of the integration can be seen, the image below, the Y-axis array integrated to the framing, the moving table can be seen too.

z-axis mechanism view

To make a machine of this kind, the usage of elements such as bearings, nuts, bolts, washers and couplings is mandatory, here can be seen a helical coupling attached to the stepper motor.

stepper bearing

After some hours of work, the final design could be seen:

machine done

From another angle, the machine assembled:

machine full

Conclusions?

It is necessary to know about the mechanical elements before assembling the machine.

Even though the work was very thorough, more is needed in order to really understand the details

Third, making a machine requires careful planning and testing, well established tolerance margins are needed.