A printed rack beats a store-bought one when it fits the exact gap on your rockwork or glass and holds your exact plugs. This walkthrough uses the ReefCAD frag rack generator, which is free to design with in your browser.
1. Measure the spot
- Measure the width and depth you have, in millimeters, and leave a little room to get your hand in.
- Racks go from 40–400 mm wide and 30–250 mm deep. Need more than your bed can print? Make two racks.
- Note how it will hang: on the glass with magnets, over the rim, on legs, or resting on rails.
ReefCAD knows these print beds and warns you before you export a rack that won’t fit:
| Printer | Bed (X × Y) |
|---|---|
| Bambu Lab A1 mini | 180 × 180 mm |
| Bambu Lab A1 | 256 × 256 mm |
| Bambu Lab P1S | 256 × 256 mm |
| Bambu Lab X1 Carbon | 256 × 256 mm |
| Prusa MK4 | 250 × 210 mm |
Different printer? Enter your own bed size and nozzle in the app.
2. Calibrate your holes
Pick your plug type (standard plugs start at 10.5 mm), then print the free Fit-Test Coupon in the filament you’ll use for the rack. Push a plug into each hole, tap the one that fit, and every rack after that uses your fit. The plug size guide explains why this matters.
3. Design the rack
- Size. Drag the knobs on the 3D preview or type the width and depth. Holes re-flow as you drag: always whole, always evenly spaced.
- Layout. Grid, staggered, honeycomb or one row. Staggered often fits more plugs in the same space; honeycomb lets you set a frag in any cell.
- Count. Leave it on max fit, ask for exact rows × columns, or set a fixed spacing. With standard plugs and the default 14 mm gap, a 200 × 100 mm grid holds 24 plugs.
- Gap. The gap is edge to edge between holes. Plug heads are wider than their stems, so leave room for them.
- Extras. Flow slots between holes keep water moving, the countersink eases plugs in, and a debossed label tells your racks apart.
4. Choose how it mounts
- Magnets: a back plate with glue-in pockets sized to your magnets, for racks on the glass.
- Rim hanger: hooks over the top of the tank.
- End rails: two solid rails along the short ends lift the rack off the sand or rock. Or pick no mount and set it straight down.
- Legs: printed on, screw-in (threads that print without supports), or sockets for ½″, ¾″ or 1″ PVC pipe. ReefCAD tells you how long to cut the pipe.
5. Export and slice
- Export a watertight STL or 3MF. It’s already laid out flat for your bed, so you can slice it as is.
- Slice in PETG for most tanks, or ASA under strong lights. See the filament guide.
- No supports. Racks print flat; racks with legs print upside down so the legs grow straight up.
- Use three or four walls so the shell is solid, and keep the slicer settings you printed the coupon with.
Plugs tight only at the bottom of the hole? That’s elephant’s foot from the first layers. Turn on your slicer’s elephant-foot compensation, or print the coupon and the rack with the same first-layer settings.
6. Finish and install
- Clear any strings inside the holes so plugs slide in cleanly.
- Rinse the rack in fresh RODI water before it goes in the tank.
- Mount it, then load it with plugs. They should push in by hand and stay put when you lift the rack.
Design your frag rack: designing is free, and your share link keeps the exact rack for next time.
