3D CNC Designs

Our goal throughout designing this machine is to maximize cutting area to CNC size ratio in order to get the "best value" out of our machine. We obtained aluminium extrusions as a donation and decided use these for the framework. It would have been nice to use a wide aluminium plate (like this) for the legs of the gantry to provide better resistance against a moment around the y axis (y axis the direction is parallel to the rails mounted on the gantry in the pictures below). However, blowing hundreds of dollars on two aluminium plates (2ft x 2ft x 1/2 inch aluminium plate = approx $120) for the legs of the gantry did not seem practical since we have aluminium extrusions readily available. 

Slim Mils Gantry Design 0.1:

This was our original gantry design but the development for this design was discontinued after noticing some difficulties that would come during manufacturing and assembly of the ballscrew. It is visible in the picture below, but there is a bearing block that is inside a hole (in the aluminium extrusion) behind the motor mount plate on the right hand side. This would require a mill to make a square hole for the bearing block and also weaken the aluminium extrusion. Also, if future upgrades took place, the aluminium extrusion with a hole in it would be harder to reuse in other applications. 

However, this design does optimize the length of the linear rails and ballscrew and maximize y direction travel. Some concepts were taken from this design and used in the following designs.

Slim milS CNC 1.0:

This was version 1.0 of the our CNC machine. The gantry design has changed so that the crossbeams are removable which allows for heigh adjustment. Also, none of the aluminium extrusions have any slots milled into them, only small holes along the front face to mount the linear rails. Minimal alterations to the extrusions equals to a higher re-usability factor. The crossbeams also have big gusset plates joining it to the gantry legs. The previous gantry allowed for a 15 Series 4334 4-hole inside corner gusset while this newer version allowed for a 15 Series 4338 8-hole inside corner gusset. 

Although this design improved upon some of the old gantry design weaknesses there was still room for improvement. The major flaw found in this design can be seen in the bottom center pictures. The router(9.3lbs approx) is about 22cm from the center of the gantry leg which will create a large moment around the y-axis and cause a slight bending of the gantry leg. If this design was implemented and began to cut material, cutting forces in certain directions would add to this moment force and increase error to the machining operation.

Also the base show in the top center picture has a slight weak point, the beam which the motor is connected to. All the axial force in the x-axis direction is eventually channelled to this beam. The aluminium plates, having a relatively small thickness in comparison to the extrusions, would be the component that deforms the most.

After recognizing these weak points, a 2.0 design was set into motion. 

Slim milS CNC 2.0

The major changes from version 1.0 to 2.0 is that the gantry obtained another set of legs for more support at the base. Also there is a aluminium beam that runs across the top of the two aluminium extrusions in the base (middle right picture). 

Now the machining begins...