Couch Cupholder
Two printed parts and no fasteners. A saddle drops over the arm of the couch and grips it, a pocket in the top takes a drink, and a separate insert drops into that pocket to narrow it down to a cup. Nothing is glued and nothing is screwed — you lift it off when you want the arm back.
The catch is that a saddle is sized to one arm, and that arm is mine. Measure yours before you commit a quarter of a spool to it, because there is no strap and no adjustment: it either sits on your couch or it doesn’t.
Will it fit your couch?
The arch on the underside is 85 mm deep and it pinches: 193 mm across at its widest, closing to about 187 mm at the mouth. That pinch is what stops the holder lifting off a padded arm.
| Your arm | What happens |
|---|---|
| Under ~180 mm (7 in) | Slips on, but rocks. Rubber bumpers inside the skirts take up the slack |
| 180–190 mm (7–7½ in) | What it is drawn for |
| Over ~190 mm (7½ in) | Won’t go on. Upholstery compresses a few mm, a hardwood arm doesn’t |
It also needs 85 mm of clear side on the arm below the top surface, and it takes up 93 mm of the arm’s length. Measure the arm at its widest point, which on most sofas is a little below the top, not at the top.
Parts
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Everything here is filament and tooling. There is no hardware in this build.
- Carbon-fibre PLA, 1.75 mm — the black matte finish is the whole point; it reads as furniture rather than as a 3D print, and it hides layer lines on a part that lives at eye level in the living room
- 0.4 mm hardened steel nozzle — not optional with CF filament. Chopped carbon fibre eats a brass nozzle in a couple of spools. This is a 20-pack, so it’s cheaper than one branded nozzle
- PLA+, black — the alternative if you don’t want to change nozzles, and honestly the tougher plastic of the two. See the caution below
- Digital caliper — for the arm measurement above, and for checking the insert against the pocket
- Self-adhesive rubber bumpers — a few dots inside the skirts stop a narrow arm rattling and keep the plastic off the fabric. A 200-pack; you need four
- Deburring tool — the pocket is printed against supports and the insert is a 1 mm fit. One pass round the pocket lip is usually the difference
- Assorted wet/dry sandpaper — 240 and up, for the insert if it binds
The body’s footprint on the plate is 206 × 141 mm, so it wants a 220 mm bed or bigger — a Bambu Lab A1 swallows it, an Ender-class 220 × 220 bed takes it with 13 mm to spare on the long axis. Square the part up on the plate; don’t eyeball it.
Carbon-fibre PLA is stiff and it is brittle. The skirts have to spread to go over the arm, and CF-PLA would rather crack than flex. If your arm measures at the top of the range, print it in PLA+ instead — you give up some of the matte look and you get a part that survives being forced on. Either way, both are PLA: it lives permanently sprung open around the arm, and PLA creeps under a sustained load. Expect the grip to soften over a year or two.
Print settings
The body is 276 cm³ of model and the insert 119 cm³. At 20% infill with four walls that comes out around 250 g and 90 g — your slicer will give you the real number. A 1 kg spool prints the holder and three inserts with room for supports.
| Setting | Body | Insert |
|---|---|---|
| Layer height | 0.2 mm | 0.2 mm |
| Walls | 4 | 4 |
| Infill | 20% | 20% |
| Supports | Yes | None |
| Material | CF-PLA or PLA+ | Same |
| Orientation | Standing on one of the two flat faces | Flat on its closed end |
The body prints standing on one flat face, not the way it lands when you open the STL. In that orientation the whole arch profile becomes a straight extrusion — every layer is a copy of the one below, the bed contact is a broad flat face instead of two skinny skirt edges, and the layer lines run along the arch rather than across it. That last part is the one that matters. The load on this thing is the arm pushing the skirts apart, which is bending at the corner where each skirt meets the deck. Printed the other way up, that corner is a glue joint between two layers and it will split.
Supports are only needed around the cup ring — under its lower half, and inside the pocket where the wall arcs over. Everything below the deck needs none.
The insert prints closed-end-down with its whole 101 × 91 mm base on the plate. No supports, no brim, nothing to clean up except the first layer.
Assembly
-
Break the supports out of the pocket. They come out in one or two pieces. Get everything out — the pocket wall is what the insert registers against.
-
Dress the pocket lip with the deburring tool, one pass. Elephant’s foot on the first layer of the pocket floor is the other place to check.
-
Drop the insert in. It should slide down under its own weight and stop 2 mm below the rim. If it binds, the fit is 1 mm per side — take material off the insert with 240 grit, not off the pocket, because the pocket is the part you can’t replace in an hour.
-
Stick four rubber bumpers inside the skirts, two per side, roughly a third and two thirds of the way down. They add grip and they keep bare plastic off the upholstery.
-
Fit it to the arm. Start it square, push it straight down, and let the skirts spread evenly. Rocking it on corner-first is how you crack a skirt.
The pocket and the insert
The pocket in the top is an obround — a 93 mm circle pulled 10 mm apart along the arm — so 103 × 93 mm and 50 mm deep, with a 4 mm wall and a 6 mm floor. On its own it is a bowl: big mugs, a phone and a remote, a handful of popcorn.
The insert makes it a cupholder. It is the same obround 1 mm smaller all round, 48 mm tall, with a 78 mm round bore and a 3 mm floor — a 78 mm well, 45 mm deep. That is a mug-and-tumbler size, not a can size. A drinks can is around 66 mm and will rattle in it.
Changing the size is one dimension. The insert’s outer profile has to stay as it
is or it stops fitting the pocket, so the only thing you touch is the bore: it is
a single cylindrical face in bruh_couch_arm_cupholder_insert.step, and you can
push-pull it in Fusion without unpicking anything else. Keep 4 mm of wall — that
puts the practical ceiling around 83 mm — and raise the floor if you want a
shallower well for a short glass. Print one per drink you actually own; they are
90 g each.
There is a strip in the middle of each flat face where the pocket wall tapers away to nothing. That is not a slicing fault. The pocket is 93 mm across and the body is 93 mm deep, so the wall runs out exactly at the centre of both faces. It prints as a ragged 10 mm edge and it lets a spill drain instead of pooling in the pocket.
Troubleshooting
The insert won’t go in. Support debris in the pocket first, elephant’s foot second. Check the insert’s first layer with the calipers against the layer above it — a squashed first layer is a fat first layer, and 1 mm of clearance doesn’t leave much.
The insert rattles. It is a slip fit on purpose; you have to be able to lift it out with a wet hand. Two rubber bumper dots on the insert’s outside wall take the play out without gluing anything.
It rocks on the arm. The arm is under the range. Bumpers inside the skirts are the fix, and more of them than you think — build up the thin side until it sits flat.
A skirt cracked going on. Your arm is over the range and the plastic told you so. Measure again at the widest point. If it really is 190 mm or more, this model isn’t the one — the arch is not a parameter you can nudge without redrawing the profile.
Files & downloads
Printable parts
CAD source
The design itself, if you want to change it rather than print it. A STEP file is exact geometry and opens in almost anything; a Fusion 360 archive keeps the modelling history, so you can go back and edit the sketch that made the part.
- bruh_couch_arm_cupholder.step STEP — opens in Fusion 360, FreeCAD, Onshape, SolidWorks
- bruh_couch_arm_cupholder_insert.step STEP — opens in Fusion 360, FreeCAD, Onshape, SolidWorks