roboc2-dual-spool-upgrade

Step-by-step instructions for upgrading the Robo C2 for dual filament spools.

Overview

The Robo C2 printer is awesome in many ways. Its included spool holder, however, has a number of flaws in its design:

The mounting hole for the spool holder is slightly too large for the included holders, resulting in the holder spinning inside the rectangular hole and sometimes falling out mid-print
The included holder for 1KG spools really isn't up to the challenge of all that weight
The holders, as supplied, often catch against Robo's own filament spools given the existing design
The location of the existing spool holder is too high and too close to the bottom of the filament run-out switch assembly, exacerbating any cross-filament problems and especially with infused rolls

To work around these flaws, I've created a completely new design to accommodate two 1KG spools at once.

The new design includes ball bearings, moves the spool(s) lower, re-orients them so that they're more inline with the filament run-out switch assembly and has a safety feature which helps on Shaxon and other problematically-wound filament spools.

I've decided to create two versions of the holder to include a second smaller version to hold two half-KG of filament. The only real difference between the two in printed parts are the lengths of the sleeves and the Under-brackets. And obviously, they use slightly longer dowels. If you like making these, double the amount of ball bearings and bolts and you should be able to make both models easily with the same materials otherwise.

Follow-up project

Soon enough, I plan to create an enclosure for this dual-spool assembly to keep both spools dry since I intend to print PVA on the second extruder.

Parts required

I've included pictures below to make this easier.

Parts to order/buy

Four non-flanged ball bearings, 8mm ID x 22mm OD, around $1.99 per pair, for example
Two types of dowel
- 7/8" x 36", around $3.59 each at arts & crafts stores, for example
- 3/16" x 36", around $0.79 each at arts & crafts stores, for example
Several types of #6-32 shouldered aluminum bolts, around $1.69 for quantity 25 each for example, or something like this would be a better idea
- 7/16" (11.11mm) @ eight each
- 1/2" (12.72mm) @ four each
- 1/4" (6.35) @ two each
Four or eight soft furniture stick-ons for the bottom
A 7/64ths hex wrench for tightening all the bolts
A hammer
A pocketknife or similar
A wood or hack saw

Parts to print

Here's the part list, all in PLA. I used the standard Robo 3D Jet Black for all the parts.

Dual KG version:

RC_DualSpool-1of4(PrintTwice).gcode x 2 => two Center Axis Brackets, two Center Axis Covers and four End Caps
RC_DualSpool-2of4(PrintOnceKG).gcode x 1 => two Assembly parts and four Sleeves
RC_DualSpool-3of4(PrintTwiceKG).gcode x 2 => two halves of the Under-brackets and two Mid-shims
RC_DualSpool-4of4(PrintTwiceKG).gcode x 2 => two halves of the remaining Under-brackets

Dual Half-KG version:

RC_DualSpool-1of4(PrintTwice).gcode x 2 => two Center Axis Brackets, two Center Axis Covers and four End Caps
RC_DualSpool-2of4(PrintOnceHalfKG).gcode x 1 => two Assembly parts and four Sleeves
RC_DualSpool-3of4(PrintTwiceHalfKG).gcode x 2 => two halves of the Under-brackets and two Mid-shims

Note

Given that the Robo C2 has a fair degree of inaccuracy when printing Z-oriented holes, it's important for you to print these parts using the GCODE I've provided; otherwise, your bolts won't fit. (I've already factored in the hole-shrinkage in this dimension.)

Assembly x 2
End Cap x 4
Mid-shim x 2 (needs raft & support)
Sleeve x 4 {Note that there is a shorter pair for the half-KG version of this project so choose appropriately}
Center Axis Bracket x 2
Center Axis Cover x 2
Under-bracket (both halves, needs raft & support) x 2 {Note that there is a shorter pair for the half-KG version of this project so choose appropriately}

Installation

After printing all the parts, here are the assembly instructions.

Do a test-fit to determine if the End Caps fit into the ball bearings; that the 3/16" dowel fits inside the Sleeves, End Caps and Mid-shims; that the #6-32 bolts fit into the threaded holes and fit through the clean ones
Use the pocketknife to clean the upper half of the ball bearing slots in both Assembly parts
Insert one ball bearing each into the related slots in both Assembly parts, use a spare raft or other thin plastic part on top of this and use the hammer to gently force them into the back of each hole
Add one End Cap to each ball bearing
Insert the 3/16" dowel into one of the End Cap & ball bearing combinations
Onto this, thread in this order: one Sleeve, one Mid-shim, another Sleeve and another End Cap (with the opposite orientation as the last)
Pushing everything together, mark the point where the dowel clears the last part and cut the dowel
Repeat for the other ball bearing
Sandwich everything together with another Assembly part on the opposite side
Match up the correct pairs of Under-brackets, aligning the holes on the bottom, use two 7/16" bolts to attach them together
Flip everything upside-down and begin attaching the combined Under-brackets using the four 1/2" bolts... if necessary, carefully use the hammer to set the Assembly parts evenly into the rectangular grooves in the Under-bracket parts, tighten each bolt firmly
Verify that all four sleeves spin freely
Add four cushioned furniture bumpers/feet to the bottom to protect your table top
Use the 1/4" bolts to attach one each Center Axis Cover to the Center Axis Brackets (don't over-tighten)
Use two each 7/16" bolts to attach both Center Axis Brackets to their respective Assembly part, tightening them firmly
Close one Center Axis Cover, insert the 7/16" dowel through everything and mark a line 2mm inside (the depth of the other Center Axis Cover), saw through the dowel
Orient the dual-spool holder behind the printer and add two filament spools so that the filament spools clockwise as seen from the right side of the printer, slide the dowel through the middle and close both covers, slightly tightening their bolts by hand