Mark 4 build - step 4: Arm construction

Step 4 is to assemble the carbon fiber arms, six of which will connect the hotend effector to the rail effector.

Vitamins:

• 1  * 325mm Carbon Fiber Square Tube, 8mm OD, 6mm ID
• 4  * M5 nuts
• 2  * IGUS KARM-05 rod ends

RepRapped Parts :

• Rod End (rod_end.stl)

Tools :

• Saw, if your rods aren't cut to length.
• Knife for part cleaning - exacto or similar
• Long tweezers - getting those nuts in is a pain.
• Super Glue - thin cyanoacrylate adhesive 

Assembly:

1. Cut your rods to length.  The best way to do this is a chop saw, table saw or similar with a repeatable stop - making all the rods the same length is pretty critical.
1. Use a fine-tooth blade.  They're expensive, but worth it.  Mine was 80 tooth, on a 10 inch radial arm saw.
2.  WEAR PROTECTION!  Eyes, lungs, ears and hands.
1. Carbon fiber fibers flit about, and will take up residence in your lungs or eyeballs.
2. Do I need to tell you why that's bad?
3. Vacuum up all the bits BEFORE you take off your protections.
4. Alternately, you can hand-cut with a hack saw; the rod ends are adjustable enough that you should be able to shore up the lengths.
2. Clean the parts.  Where the rods insert should be OK, but the nut insertion hole is finicky.
3. Assemble the rod ends.

1. Take a KARM and thread a nut all the way down.
2. Take a rod end and slip a nut into the long slot.  The slot is wider at the base.
3. Screw the KARM into the nut in the rod end - tighten it down lightly.
4. Do this twice - each rod has two ends :-)
4. Place the rod end assemblies onto the ends of the rods.
5. Tap the rod ends into place.  The square rod hole becomes hexagonal halfway up - you want the square rods to be touching this hexagonal transition.
6. When the rod is all the way in, place a few drops of cyanoacrylate in to hold them in place.
7. Repeat for the other 6 rods.
8. Align the rods - I did this by inserting threaded rod through each rod end eyelet.  Adjust the rod ends 1/2 turn at a time, then tighten them down.

1. Accurately measuring this length is crucial!
2. Making sure it's the same length for each rod is also crucial!
3. Write down your length, the firmware will need to know about it later.
4. 400mm even is the design length with the given parts.
5.