Revolving objective selector (turret) for Galileo Microscope

This accessory replaces the standard single objective nut with a three positions rotating turret. This way you can "zoom in" or "zoom out" selecting a different magnification objective.

Bill of Materials

• One set of printed parts, printed with the same settings as the rest of the microscope. You can replace the spring retainer with a simple washer, it is mostly just for show.
• 6x M3x10 and M3 nuts (M3x12 will also work)
• 3x M3x12 SHCS screws and M3 nuts, (M3x16 will work as well, probably even M3x20 but if you go too long you start eating focuser travel)
• 1x M3x30 SHCS nut and M3 lock nut.
• 1x 8x20 mm spring (8x25 might work in combination with a longer screw)

Assembling

Use one of your objectives to thread into the holes on the petals, then remove it, we will actually install the objectives later. The petals have RMS threads on them but it is unlikely that your printer can resolve them correctly, they will help guide the operation, but you will be actually threading the plastic with the metal of the objective. Do it nice and slow, and pay attention to go straight, and sand a bit the inner surface if needed. Take your time while the parts are disassembled, you do not want to struggle with this once the turret is on the microscope and you won't have ay leverage any more.

Assemble the rotor by joining the petals together with the M3x10 screws and nuts.

Slide the M3 lock nut in the slanted slot of the hub, note that it slides flat side down.

The next steps are more comfortable if you remove the spider with the optical group from the microscope and keep it pointing upwards with the help of the smartphone support, just be careful not to scratch your eyepiece.

Add the gear nut to the bottom of the focusing tube, give it a couple of turns until it is out of the way.
Slide the hub in the slots of the focusing tube, careful, this will determine the orientation of the turret, I mounted mine pointing towards the bottom right, but you may prefer it pointing bottom left or even front, this is especially relevant if you also did the fine focusing lever mod, otherwise you can always just rotate the whole spider when you put it back.

When the hub teeth are level with the bottom of the optical tube, turn the ring nut back towards it, the holes on the ring nut and hub should align when there is a clearance of about 1 mm between the two.

Pass a screw trough each hole of the hub, then add the nuts in the ring nut, drawing them in until they reach the bottom of their seats, the 1 mm clearance  remains, and neither component is tilted.  
At this point the assembly is rigid, because the hub can't slide down any more, but the ring nut can't turn either.

Lean the rotor on the flat bottom of the hub, one petal flush with it.  Add the spring in the slot between the petals, and the M3x30 screw and spring retainer or washer.
Press the screw to compress the spring, then turn it to engage the lock nut and continue until it peeks out of the hole on the other side of the hub.  The lock nut may have slided a bit in its seat, you can press and hold it up with a toothpick or something similar until the tip of the screw locks it in place.

Adjust the tension of the spring to your liking, it should be easy to turn, but also hold the rotor firmly enough in its three stable positions.

You can now add the objectives, and if you had removed and flipped the optical module, you can now reposition it on the microscope, checking that the objectives can rotate freely all around.

The space should be enough to fit most objectives, but the longer ones may interfere with the thicker threaded standoff and smartphone holder or anything attached to it, so either may need to be reoriented.