UODATED 12/11/16 - Linked to a new 15mm blower. The original one, for whatever reason, wouldn't run at speeds below 100%. This new one has a much wider speed range. I've updated the STL files to match the new blower, which was slightly narrower than the original 15mm blower.

UPDATED 12/3/16 - Design complete! 15mm blower duct confirmed to fit and function as designed! Thanks BMEmike for building it!

If your printer needs a slight tweak in the design, please contact me.

UPDATED 11/30/16 - Fixed 15mm blower holder, downtube, and right and left duct to fit the 15mm blower. Thanks BMEmike!

UPDATED 11/28/16 - Added site link to smaller quantity heat inserts. Thanks BMEMike

UPDATED 11/20/16 - The ductright20mm and ductright15mm have both been updated to -2, I moved the nozzle away from the hot end by 3mm. It was just a bit too close for me. The down level nozzle will still work as it is in the exact same position as the stock nozzle. Please use the -2 from now on.

Added assembly images.

UPDATED 11/19/16 - Added (hopefully) helpful images showing the assembly process step-by-step.

Please read the entire description where I cover the details of this thing.

The Lulzbot Mini is a great printer. However, one of the areas where it can be improved is in the area of part cooling. The printer uses an axial fan, which are not very good and building air pressure behind a nozzle. The other issue is the cooling is only on one side of the part, which can lead to uneven looking prints depending on what side of the part is directly facing the fan.

This modification adds a second duct and a blower. This allows for much more efficient cooling. Both sides of the print are cooled at once and the airflow is much higher.

The modification uses the same holes and screws that are already attaching your stock cooling duct. However, you will need a few parts:

M2 heat inserts for reattaching the limits switch:
https://www.mcmaster.com/#94180a307/=14zapiq

If bulk inserts aren't your thing, you can order them in smaller quantities here:
https://itworks3d.com/product/metric-brass-heat-set-insert-plastics/

50x50x15mm blower:
http://www.digikey.com/product-search/en?keywords=BFB0524HH

Note: This particular blower operates on the mini between M106 S40 and M106 S255. Tranlation: in your slicer, zero blower speed is 16% or less and full blower speed is 100%.

Note: I used a 50x50x20mm blower I had laying around my shop. Unfortunately is has been discontinued so I modified the thing to accept the 15mm blower. Since I have not tested the new blower, there's a chance we may need to modify the blower holder slightly. If you give this a try, please let me know if the blower doesn't fit. Do not assemble anything until you check to blower fit into the blower holder. It doesn't have to be a tight fit, but it shouldn't allow the blower to rattle around. Please contact me if modifications are needed. Thanks! Alternatively, you can design your own blower holder and attach it to the rest of the duct.

Please download the STL files for the blower size you use. When complete you should have the following files:

mount.stl (common)
cover.stl (common)
blowerholder15.stl
downtube15.stl
ductleft15.stl
ductright15.stl

or select the 20mm equivalent parts.

Do not mix 15mm and 20mm parts. Pick one set or the other.

Double note: On the part labeled "mount.stl" and "blowerholderxxmm.stl" there are two holes on the front about 2.7mm in diameter. Ream these out to 2.85mm diameter and use your filament in the holes to assure your blower holder is aligned with your mount when you start gluing (or acetone welding in my case).

NOTE ABOUT SUPPORT MATERIAL: All parts can be printed without supports EXCEPT "Downtubexxmm.stl". It requires minimal supports. Please see the image showing how to orient the parts on the bed to eliminate support material.

You can run the blower off the same wires that power the stock fan. You can either cut the wires and solder on the new blower or add your own reusable connector on the wires. Just make sure your blower is 24V.

WARNING! I've tested this design and, while the clearances are tight due to space constraints, my version worked perfectly. Please please please make sure the first time you try it you are ready to power the printer down just in case there is variation printer to printer.

Results: I've attached an overhang using the same Gcode model. One with the stock duct, one with the new duct and 20mm blower (only running at 50% speed, 12V right now). The improvement is quite good. I'll hopefully have it hooked to 24V in a few days.

LulzBot

Mini

No

Yes

.18

20%

I did 2mm thick walls to ensure the heat inserts had enough material to melt into. Shouldn't matter much, though.

Ream out 2x M2 holes with a .120" (or metric equivalent) drill for limit switch on back of mount.stl just enough so M2 inserts can be heat staked into place. They are NOT press fits so don't ream the hole out too much.

Heat stake M2 inserts into place.

Ream out holes on front of mount.stl using .111" or 2.85mm drill bit to fit locating filament "pins".

Ream out holes on blowerholderxxmm.stl using .111" or 2.85mm drill bit to fit locating filament "pins"

Add short filament pin into mount.stl holes, add glue (or acetone weld for ABS) to surface between pins. Press on blowerholderxxmm.stl using filament pins to ensure proper location

Glue or Acetone weld downtubexxmm.stl to the bottom of the blower holder. Be careful to make sure the part is attached squarely underneath the blower holder. You can use a flat surface to ensure the two parts are flush while drying.

WARNING: BE SURE TO CHECK ORIENTATION OF DUCT FILLET TO ENSURE PART IS ORIENTED IN THE CORRECT ORIENTATION. THEY WILL LINE UP WITH HOLES IN DUCT. (See Picture)

Caution: Misalignment of this part will misaligned the cooling nozzles and possibly bring the cooling nozzle too close to the print head. Just take care to make sure everything is flush.

Attach ductleft.stl to left side of downtube.stl using a flat surface to ensure the duct is aligned properly (flush) to downtube.stl.

Repeat this step for ductright-2.stl

TIP: Use a flat surface to align end of duct to downtube.stl and once semi dry, rotate to align bottom of duct to bottom of downtube.stl. (See images)

Note: Your left and right duct should be pretty much parallel to the arms on mount.stl if you did this correctly.

Optional But Recommended: Make sure to go around your joints with extra glue/acetone to ensure there are no holes. Holes reduce airflow efficiency!

Apply acetone glue/super glue to surface as shown in the following image.

Be sure to keep track of your "B" and "O" inserts as they are free pieces you'll need to insert using tweezers.

Apply cover and small inner-letter pieces to front of assembly.

Congratulations! Your duct is now completely assembled!

Remove the old fan and duct using step 4 in the official OHAI manual going in reverse order. (Do not throw away screws. You will need them)

https://ohai.lulzbot.com/project/86797b55-7d08-4c6d-be77-3c116a320547/mini/

Slide the mount onto the print head. Note the left side of mount.stl slides into the slot formed to left side of the aluminum piece that is sandwiched between the two black 3d printed pieces. The right side of mount.stl slides over the holes where the old duct used to screw into.

Use the two tapered screws you just removed from the old duct to attach your new duct assembly.

Use the two M2 SHCS you just removed to reattach the limit switch to the back of mount.stl.

Insert blower motor into top of blower motor holder. It should be somewhat of a press fit.

Cut the wires from the old cooling fan and solder them to the new blower wires making sure you get the + and - wires in the right order or else the blower will run in reverse (Can you suck heat away anyway? :) )

REMEMBER: Add insulation to isolate newly soldered wires to prevent shorts.

Run a test print WITH YOUR FINGER ON THE POWER SWITCH and carefully watch clearances while the nozzle is wiping and during bed leveling.

The clearance of the left duct will be VERY close to the green acme screw holder during bed leveling but it should not bind. There is small variation printer to printer so PLEASE PLEASE PLEASE just double check to make sure parts don't crash. They shouldn't.

Congratulations! You have improved cooling on your lulzbot Mini!

Siemens NX CAD software

You may never need this much airflow; but it's nice to know cooling will never be an issue again! Plus you are getting even cooling on both sides of the part.