20-bead Rekenrek (Abacus)

This Rekenrek is assembled using two 2mm rods and four 3mm bolts. 

I used stainless steel rods from Amazon
Rods need to be cut to approx. 236mm - 238mm long. The holes they go into are 8mm deep on each end, so there is some room to move. 2mm stainless steel is tough to cut with cheap cutters - you might need a hacksaw or a Dremel. You could also use 2mm aluminium rod.

The bolts can be between 8mm and about 20mm long. I used a mix of 8mm and 12mm. 3mm nuts are dropped into the end of each support. There is an optional plug that can be pressed or even glued in to hold the nut in during assembly - this isn't essential.

To print:

1 x left
1 x right
2 x support
20 x bead (10 red, 10 white)
4 x plug (optional)

The left and right leg parts will need supports in the holes, but supports aren't needed anywhere else.

To assemble:

Add the nuts to the ends of the supports
Screw two supports into the left leg using two 3mm bolts.
Standing on the left end, stand the whole thing upright.
Press the two 2mm rods into the holes (I suggest pressing in the rough cut end on this side, as it makes the final end a bit easier when aligning everything)
Slide on the red and white beads. The standard config is 5 red followed by 5 white on each rod.
Align the right leg with the supports and the rods and press it on.
Screw in the last two screws.

In hindsight, I might have gone with square nuts, as there is potential for the nuts to spin in the holes, so go easy on the tightening. A drop of glue on the plugs before pressing them in will hold the nut tight.