SCARA Designs

A project log for A 2.5D Slew Ring

I need a slew ring for my SCARA. I don' have a 3D printer so it has to be either laser cut (2D) or 3 axis CNC milled (2.5D).

agp.cooperagp.cooper 7 days ago0 Comments

SCARA Designs

Here are a couple of SCARA concepts:


And something that looks almost there:

There looks like three sheets for this design, one 3mm and one 12mm, and a 1mm gasket.

Beam Stiffness

The stiffness of the arms can be increased by using a stiffer material or increasing the thickness (or both). Alternately I can add stiffening elements (flanges)  to the arms.

I have decided to add flanges to the arms to increase the arm stiffness. Think of "U-channel", for what I am planning.

Another Day of Design Work

After another day of design:

All cut from 12 mm thick (MDF, plywood or Lexan). Plus a limited number of design pieces (three plus the base board and two arms). The bolt length are based on what I have available.

I have made a layout (except for the base board):

These layouts (two)  are for my CNC machine. The extra holes around the stepper motor mounts, allow for -0.5mm, 0mm, 0.5mm and 1.0mm relative adjustments of the stepper motor position. This allows adjustment of the belt tension.

I have also looked at the 2 to 1 SCARA working area:

The bottom of the red box is does not clear the second stepper motor and need to be lifted at least 10 mm. The effective working area is 330 mm wide by 165 mm high, and both arms are 165 mm long.

Another Day of Design Work

The design is progressing. Other than two 3 mm shims (for clearance), the design is all 12 mm thickness. I have laid it out for cutting on my CNC machine. Unfortunately I don't a bit small enough and long enough to cut the pulley. I have ordered a 17mm long 2mm (2 flute) bit from within Australia. And the base board is too big for my CNC machine. I will have to hand cut and drill that.

Hers is the plan and section views:

Note the stepper motor has four rotated locations providing -0.5mm, +0.0mm, +0.5mm and +1.0mm offsets for timing belt adjustment.

I have looked around and I can get the 6808 bearing in a 6mm width (i.e. 6708). This means I can laser cut a design for the slew ring (no need for 2.5D machining). This will be looked at for the next prototype.

I have also sourced some 80mm long M3 bolts so I can add more layers.

Hers is the layout:

And here is the base board:

It is a 45 degrees to keep the base board as small as possible.

The next problem to solve is the location of the homing switches.