Having used my MX518 for the better part of a decade, when I wanted to convert my setup to wireless, I didn't want to give up on it that easily. Plus, none of the mice I tried were as comfy. So, two months and ~$300 worth of prototype development later, the G518 has been completed! I aimed to keep it the same weight as the MX518, same form factor, and with all components mounted to the bottom so that the top could be easily removed. It's 103g, but that will vary based on how much plastic you remove and how dense your 3D prints are. I generally aimed for 30% infill, but most of the parts don't have thick enough features for that to matter.

Be warned: this is not for the faint of heart, and requires 3D printing, soldering, spending more money than you expect, epoxy work, trial and error, and too many McMaster orders to count. Enter at your own risk.

Supplies

(1) Logitech G703 Lightspeed Wireless Mouse

(1) Logitech MX518 Mouse, only needs functioning side buttons (Legendary preferred, due to PCB thickness)

(20) M1.4 x 0.3mm heat set inserts, 3mm long (McMaster sells them by 100 packs)

(20) M1.4 x 0.3mm Stainless Steel screws, 3mm long (also from McMaster)

(1) Magnetic Micro-USB charger (I used this one from amazon) (view disclaimer later on regarding battery reporting)

Mouse feet of your choosing

3D Printer

PETG filament (PLA probably works, but I wanted more durability, plus my only black filament was PETG)

TPU filament for the charger plug if you don't want to tape it shut (Also could probably be PLA)

0.2mm and 0.4mm nozzles (0.2mm only needed if you're picky about the logo print)

Soldering Iron

Desoldering pump/wick

Dremel w/ milling bits

Power drill

#00 Philips head screwdriver

Thin (3/32" or so) Flathead screwdriver

Tweezers

Utility knives, probably

Epoxy

Saran wrap

Sandpaper (180 to superfine epoxy polishing grit)

Step 1: Dismantle the Mice: G703

First, you're going to need to remove the PCB and battery internals from the G703. This video is what I followed to locate all the screws, you just have to completely remove the PCBs and other internals from the mouse. The PCBs should be the base w/ wheel, and the top-shell wiring harness. As the video says, be careful not to damage the ribbon cable. Keep the screws in a bag or something, we'll need a couple. The rest of that mouse can be used as a paperweight.

Step 2: Dismantle the Mice: MX518

From the MX518, we need the top shell (including the shiny click button part, and the plastic surrounding the mouse wheel, as well as the top and side buttons). The PCB for the side buttons is also needed, but we can set it aside for later. Same process as the G703, get all the PCB components separated from the shell, just unscrew everything. Keep these screws somewhere separate from the G703 screws, as I didn't use these. Make sure not to damage the side or top buttons. Leave as much of the stock plastic in place (i.e. the side button lever, the top shell stuff).

Step 3: Print the Base

YOU, lucky reader, get to skip the ~12 prototype bases I made, and the weeks of CAD modeling, and just print the base. It's attached as a file for this, titled "G518 Baseplate". I'll attach the picture of all my prototypes so you can feel like you made the journey with me.

G518 Baseplate.stl
Download View in 3D

Step 4: Print the Accessories

We'll also need:

Front Plug
G Logo (if you want emblem lighting)
MMB Plate

Print these out, preferably printing the front plug in TPU for a little flexibility. All others can be in whatever plastic you like the color of. The front plug and the logo should be printed with a 0.2mm nozzle if you have it.

Step 5: Battery Cover Modification

Dremel time! Have to cut the battery cover to make it fit, plus y'know, weight savings on excess plastic or something. Also, drill a tiny hole in the right foot of the battery cover, overlapping the hole on the right side of the baseplate. That's gonna be our second attachment point. More details in the photo alt-text boxes.

Step 6: PCB Modification

This feels SUPER wrong to do, but i can certify that it all still works. Basically, using 220 grit sandpaper, file away at the edge of the PCB in the marked spots so that it fits into the printed baseplate. As long as you don't touch any traces, you're fine, and not much was needed. Additionally, use a cutoff wheel on your Dremel to remove the front-most support of the rotary encoder for the mouse wheel, as it's gonna be in the way later.

Step 7: Heat Set Inserts

Now that your base is done printing, we can make it ready for installation. This website had a good guide for using them, but basically you just press them into the holes printed in the model, using a soldering iron. The heat lets the insert melt its way in, and then solidify, locking it into the plastic.

Step 8: Battery Cover Mod Pt 2

I apologize for the lack of direction here, as it really was eyeballed and trial/error. All you're trying to do is mount the printed battery plate onto the G703 battery cover, to match the CAD screenshot above.

Drill a couple holes in the battery cover for mounting the Battery Plate. The 3 holes in a line are clearance holes for the switch pins. Feel free to comment questions if I've missed something.

Step 9: PCB Hybridization

We need the side button PCB from the MX518, as opposed to the one attached to the G703, as the switch contacts are in a different place on each. The easiest way to do this is as follows:

Desolder the MX518 side switch wire from the MX518 plate, leaving the wire connected on the switch end
Desolder the G703 side switch wire from the G703 plate, in the same manner as above (i.e. remove the wire from the main PCB harness)
- Careful, if you damage the G703 plate you'll have to buy another one like me
Solder the MX518 Side Button Plate wire to the G703 Plate, where you removed the plate

The square contact on the PCB plate is the ground, which should correspond with the red-stripe side of the MX518 wire.

Step 10: Test the Mouse

Before getting into the finishing part, let's make sure all components work. Turn the mouse on, connect it to your computer, and test each button a few times by pressing on the white contact bar for the mechanical switches. Don't forget to test the mousewheel click.

Step 11: Mounting the Components

Place all the components into the G518 baseplate, securing them with the McMaster screws into the inserts. Also, if you're using the magnetic connector, insert the microUSB side before mounting the bottom PCB, it's a lot easier.

Notes:

DON'T FORGET THE POWER SWITCH BELOW THE MAIN PCB
- really hard to install this afterwards
I thought screwing those little metal contacts into the base would help the below battery issue, but it doesn't seem to have happened, so that's optional
Route the side button wire OVER the top, not under the printed support as the pictures show. I did that on my second attempt and it works better. Good image on the previous step.
Some filing/clipping of the PCBs and switch contacts is needed for the RMB/LMB PCBs, just avoid contacts and you should be fine. Apologies for not having great pictures of those.

DISCLAIMER: I've been having weird bugs with the magnetic cable, where it makes the G HUB software think my battery is at zero. Only way I can fix it is to turn the mouse off and plug it in for ~15 minutes with a normal cable. Use at your own risk.

EDIT: If you turn the mouse off before connecting the magnetic charger cable, it avoids this battery reporting issue, I'm just now finding.

Step 12: Top Shell Modification

This is where you have to do some trial and error to make the switches fit. Grab your Dremel and your favorite milling bit (I used this and this for most of it) and try to match to the pictures. It WILL require test fitting and figuring out where the interferences are, but the less you can remove, the better it'll be for rigidity. Filament/wire cutters also help for some of the injection molding pins that are superfluous to the structure. If you mess up, you can buy the whole shell for like 15 bucks on eBay, which I had to do a couple times.

The hole in the back is where the logo will go, so if you don't want to work with epoxy, and don't care about backlighting, leave that intact.

Additionally, trim the plastic for the top buttons so that only the DPI reset button remains, then glue the plastic in place as shown.

Step 13: Epoxy Logo

The goal here is to make a logo as nice as we can, without owning expensive lab equipment. Process goes as follows:

Sand the printed G Logo until it is BUTTERY smooth (i used up to 2000 grit)
- any layer lines remaining will be visible in the final product
Clean it with isopropyl alcohol
Print a 50mm ring, or find something similar (the white ring in above pics)
Put Saran wrap over the top, and tape in place to make it as taut as possible
Mix your epoxy, ensuring zero bubbles (leaving the epoxy in ~40 C water for a few minutes can help)
Place a small drop on the Saran wrap
Gently lay the logo on it, rounded side down
- REALLY careful of bubbles. It's better to adjust now than regret in 10 hours when you pick it up and see a huge bubble
Put some sort of gentle weight on the logo. I used a manual drill press, just enough to get the Saran wrap to form to the curve of the logo.
Leave it there til the epoxy cures
Remove and polish until satisfied
Spray the backside of the logo with window frosting spray to give the diffuse lighting

A lot of this is up to you, depending on how you want to have the final product look

When done, you can superglue it in place on the mouse. If the curvature doesn't match, heat it with a hair dryer to bend it.

Step 14: Mousewheel Plastic Modification

As you probably have realized, the MX518 wheel is notably smaller than the G703 wheel. That plastic is vital, so we have to modify it to fit the new wheel. Good thing the G703 doesn't have the +/- switches of the MX518, so we can use their space for expansion. Grab your Dremel and your steadiest hands and go to town.

Step 15: Click Shell Modification

The RMB switch is mounted just a tad bit high, so you've got to shave off the contact point on the click shell. Remove the Teflon (?) square and either Dremel or utility knife the plastic pedestal to just below where the bottom of the Teflon was. Can take trial and error, but remember it's easier to cut more off than less.

Step 16: Final Assembly

Assemble in order:

Click shell onto mouse shell
Mousewheel plastic onto mouse shell
Assembled top onto bottom
Insert Front Plug
Add mouse feet, with cutouts for the screws if you ever plan on taking it apart

Make sure to screw the click shell onto the top shell, as I forgot that a few times. You're done! Go click things to celebrate.

Introduction: Logitech MX518 Wireless Mod