Diagonal rod for Rostock

by Johann, published

Diagonal rod for Rostock by Johann Feb 21, 2012
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Diagonal rod for Rostock by Johann is licensed under the GNU - GPL license.

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Rostock is a delta robot 3D printer. It uses 6 of these diagonal rods. The first version was using carbon tube and ball joints, but now these rods use universal joints and are fully printable.

Newer versions of the OpenSCAD source files will be published here: https://github.com/jcrocholl/rostock


Make sure you can use the full size of your platform. The rod length is 262 mm total (250 mm center distance of the universal joint M3 screws) and will fit diagonally on a 8x8 inch or 20x20 cm build platform. You may need to turn off "Skirt" in Skeinforge because the outline would be too large.

These rods printed very well in PLA with the following settings on my Prusa Mendel:

.35 mm nozzle at 185C
.2 mm layer height
.5 mm extrusion width
heated bed with blue tape at 60C

Send M106 to turn fans on while printing, to make sure the previous layer is cooled solid before the next layer is printed.

Turn off the heated build platform and let it cool completely before removing the rod, to avoid bending it while it's still soft.

If your printer is properly calibrated you should not need to predrill the holes for the M3 screws. Just screw them in, they are supposed to be somewhat tight for zero backlash. If you do need to predrill, use a 3mm or smaller bit. 1/8 inch (3.175 mm) would make the holes too big.

If your print bed is too small, you can print rod ends from joint.scad instead, and connect them with carbon fiber tube from the kite store.

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The rod lenght keeps on showing as 193mm in Slicer is this correct? because scad shows up as 250mm.

Where are the universal joint?

 I calculate 232mm, im going to cut a rod of glass fibre and this is the number after compare in openscad and see some files of the rod. The key is 250mm between holes.

What length m3 bolts do you use for the universal joints? My back of the envelope calculation is that m3x12 will just do it with proper clearance, but I have to cut down a longer one to get that with my supply. I have m3x10 that just catch the joint, but I worry about breakage.

Did manage to find some m3x12 locally. The length was perfect for the universal joints. They are pan head philips though, but a small screw driver works.

Anyone mount the heat bed to the front but with the element Or trace side up to transfer more heat,

Should there be anything like cork below the beg ,

Are the support pieces necessary? I'm refering to the square in between the ends and the angled bits along the sides. They do not seem to touch or contribute to the rod's construction.

The squares in between the ends are for the universal joint. You can see this clearly in the carriage thing (http://www.thingiverse.com/thing:21004)http://www.thingiverse.com/thi....

Yeah but I agree that the angled bits along the side seems to do nothing.

Vertical carriage for Rostock
by Johann

The squares and the angled shoulder bits are only for wiping the nozzle, to improve print quality and reduce manual cleanup. If retraction is properly calibrated for your printer, you don't need these wipers at all. If you don't want the tiny increase in print time and wasted plastic, you can disable them in the OpenSCAD file.

I fixed the .scad to ensure the rotate() functions all had [x,y,z] and removed the wiping boxes. Printed well!

how long were the carbon rods for the jaw ends?

Not sure, but the center-to-center distance of the M3 screw holes should be 250 mm. It's okay to use a different length, just make sure that they are all the same. Then adjust the following line in the firmware if necessary:

define DELTA_DIAGONAL_ROD 250.0 // mm


A simple jig (piece of plywood and two nails) would probably help: put glue in the rod ends, stick them on the carbon tube, put the rod on the jig with each nail through one of the rod ends, then wait until the glue is set. This would also help to make sure that the rod ends are not twisted, if the nails are parallel.

DONT_KNOW ? 230mm ?

How do these compare to the carbon tubes you used before? Are they stiff enough?

These rods only need to push/pull and they seem plenty stiff for compression/tension. I cannot bend them by manually pushing on both ends. They bend more than carbon fiber if I push against the middle of the rod, but the Rostock design doesn't have any bending/torsion/shear forces on them.