Aluminium Stand Designer
A two-tier 4040 stand for a 1200×500×800 tank has a clear beam span of 1120mm; with 400kg on the top tier it deflects about 4.9mm, well past L/500 (2.2mm). Add one middle post per side, cutting the span to 540mm, and the same profile deflects about 0.3mm. Conversely, a stand with only a top frame — posts unrestrained at the foot — will rack sideways no matter how heavy the profile is.
What a T-slot aluminium stand carries is set by the clear span of its beams, not by how chunky the profile is: cutting the clear span of a 4040 beam from 1120mm to 540mm cuts deflection to about one eighteenth.
B-01 · 3D structure view
47.24×19.69×31.5 inA-01 · Structure
4040Layout
Tank on top, sump and equipment inside
Stand dimensions
Usually the tank footprint; a stand slightly narrower than the tank is more stable and easier to clad
Height of the bottom face of the lowest rail above the floor: 0 = on the floor. Lifting it keeps the rail off the ground for cleaning and moisture, and leaves room for the levelling feet to adjust. Only the rails move — the posts still run full length to the floor (same length) and the overall height H is unchanged.
Profile and structure
4040 40×40 (slot 8): 4.4 lb/m, Ix 10.88 cm⁴, M8 bolts recommended in the slot
Middle posts per side
Clear span per beam segment 21.26 in, 6 posts in total
Beam levels
2 beam levels including top and bottom
Horizontal bracing (internal)
Cross braces run along the width and depth braces front to back — pick one, since using both at once would cross. Each brace runs the full clear span unbroken: cross braces sit between the left and right short beams, depth braces between the front and back long beams, which is exactly the inner zone that the middle posts (on the front and back edges only) never occupy. So one brace is one whole piece, with a single cut length, and the tank base or shelf rests straight on it. Connectors are only placed on ends that land on a post side face (the brace running exactly on a middle post axis); ends butting a beam have no post behind them and get none.
Post base
Vertical connectors (beam ↔ post)
Just two standard parts. The **die-cast corner bracket** (an aluminium die casting with a triangular reinforcing rib, bolted into the profile slot with T-slot nuts and hex bolts) takes shear best. The **corner slot connector** (a T-head section part slid into the slot cavity of both profiles) is locked with set screws and shows nothing from outside. **'Both' splits by direction**: the horizontal joints (beam to beam, one per corner per level) get die-cast brackets that lock the rectangle, while the vertical joints (beam to post) get hidden slot connectors — so the only visible hardware is a handful of brackets at the corners, with no load-bearing joint left out. Pick slot only and the viewer switches on X-ray automatically. No anchor connectors anywhere.
Load per level
Top level: the whole tank weight (glass + water + substrate + hardscape)
The long-term weight on this level; use the real figure for equipment only
C-01 · Results & checks
6- Posts
- 6
- Beam clear span
- 21.26 in
- Total profile length
- 38.1 ft
- Profile weight
- 51.4 lb
- Full bars needed
- 2
- Stand weight (with hardware)
- 54 lb
- Total laden weight
- 1068.1 lb
- Average floor load
- 165 lb/ft²
Structural checks
| Check | Result |
|---|---|
| Beam deflectionCalculated 0.01 in · Allowable 0.03 in · Safety factor 1,650Top level Short beam: span 16.54 in, line load 321.3 lb/ft, simply supported with a uniform load δ = 5qL⁴ ÷ (384EI) | Pass |
| Beam bending stressCalculated 19.0 MPa · Allowable 85 MPa · Safety factor 6.7Top level Short beam: maximum mid-span moment 915 lb·in, σ = M ÷ W | Pass |
| Post stabilityCalculated 1.15 kN · Allowable 47.37 kN · Safety factor 123Post: effective length 28.35 in (largest clear opening between beams), pinned ends, Euler load Pcr = π²EI ÷ (KL)² | Pass |
Beams are treated as simply supported and posts as pinned; no credit is taken for the rotational stiffness of the brackets, and overall sway and tipping are not checked.
C-02 · Cut list & hardware
38.1 ftProfile cut list
| MemberCut length | QtyTotal length | Weight |
|---|---|---|
| Top level Long beam47.24 in | 294.49 in | 10.6 lb |
| Bottom level Long beam21.26 in | 485.04 in | 9.5 lb |
| Short beam16.54 in | 466.14 in | 7.5 lb |
| Depth brace16.54 in | 233.07 in | 3.7 lb |
| Post29.92 in | 6179.53 in | 20.1 lb |
Lengths are clear spans and exclude end-machining allowance; add about 5 mm per piece and let the supplier cut to size.
Packed into full bars
- Bar 1Offcut 0.08 in
- Bar 2Offcut 12.2 in
Utilisation 97% · Packed into 236.22 in bars with a 0.12 in kerf: identical lengths are merged and long pieces are placed first.
Hardware list
| ItemNote | Qty |
|---|---|
| Die-cast corner bracketOne per beam-to-post joint, on the outside of the corner, with T-slot nuts and hex bolts | 8 pc |
| Corner slot connectorSlides into the slot cavity of both profiles so nothing shows from outside; locked with set screws, strongest when paired with the die-cast bracket | 28 pc |
| T-slot nut + hex boltTwo per die-cast bracket (one per bracket leg); check your bracket hole pattern | 16 set |
| Set screwTwo per corner slot connector, driven in from the outside face | 56 pc |
| End capPost tops, plus any floor end without a levelling foot | 6 pc |
| Adjustable levelling foot (stud + base)One per post; levels the frame and loads every post evenly | 6 pc |
- Section inertias and masses come from the supplier datasheet (APAS, 6063-T5), not from a geometric approximation of the section
- Deflection uses a simply supported beam with a uniform load, δ = 5qL⁴ ÷ (384EI), with E = 68,600 N/mm² for 6063-T5
- The criterion is δ ≤ L/500: a tank base that sags unevenly puts extra stress into the glass, and eventually cracks it
- Bending stress σ = M ÷ W with M = qL² ÷ 8; the allowable is 85 MPa (127 MPa yield with a 1.5 factor)
- Post stability uses the Euler load Pcr = π²EI ÷ (KL)² with a required factor of 3, and takes the largest clear opening between beams as the effective length (with a floor gap, the free length from the floor to the lowest rail also counts)
- Both the long and the short beams are checked as if two of them carried the whole tier load (in reality it splits by stiffness), which is conservative; hardware is estimated at 5% of the profile mass and excludes shelves and cladding
The calculator above follows the unit system selected at the top of this page; the explanatory text below stays metric (mm / L / kg / ℃).
Need a full design?
- Want to turn the dimensions into a 3D model and a complete bill of materials
- Enter length, width and height in the aquarium designer and it generates the 3D model, dimensions, glass cut list, silicone usage and equipment selection, all exportable as CSV and PNG.
How to use it
- Step 1Measure the tank footprint and total weightThe stand is usually the tank footprint; take the total weight from the volume calculator (glass + water + substrate + hardscape).
- Step 2Pick the profile and post countChoose by clear span: 3030 up to about 600mm, 4040 up to about 1000mm; beyond that either add a middle post or move to 4080 / 6060.
- Step 3Set the number of beam levelsAt least a top and a bottom frame: the top carries the load, the bottom locks the post feet. Fill in a load for the sump tier if the sump rests on one.
- Step 4Read the three checksDeflection (δ ≤ L/500), bending stress (σ ≤ 85 MPa) and post stability (factor ≥ 3). If any of them fails, add a post or step up a profile size first.
- Step 5Take the cut list and hardwareThe cut list merges identical lengths and packs them into full 6m bars so you know how many to order; brackets, T-nuts and bolts, end caps and feet are counted from the joints.
Frequently asked questions
- Should an aquarium stand use 4040 or 3030 aluminium profile?
- Choose by clear span, not by tank size. Up to about 600mm, 3030 is fine; around 1000mm use 4040; beyond 1000mm either add one middle post per side to halve the span, or move to 4080 (strong-axis Ix 81.73 cm⁴, about 7.5× that of 4040).
- Does a 120cm tank stand need a middle post?
- Yes. At 1200mm outer width with 4040 profile, the clear beam span is 1120mm and a 400kg top load deflects it about 4.9mm, past the 2.2mm allowed by L/500. One middle post per side brings the span down to 540mm and the deflection to about 0.3mm, so 4040 is then plenty.
- How much weight can an aluminium profile stand actually take?
- The limit is almost always beam deflection, not post buckling. An 800mm 4040 post has an Euler critical load of about 115kN (roughly 11.7 tonnes), so even with a factor of 3 it carries about 3.9 tonnes; a 400kg stand puts only about 1kN on each post. Watch deflection and floor loading, not post size.
- Will an aluminium stand rack sideways?
- It can, if there is only one beam level or the stand is too shallow. With the post feet unrestrained the frame can lose stability sideways. Build at least a top and a bottom frame, and keep the depth at least 45% of the stand height. Above about 900mm tall, or wherever it can be knocked, add a back panel or bracing and put it against a wall.
- How many 6m lengths of profile should I order?
- Let the packing decide. A two-tier 4040 stand for a 1200×500×800 tank with one middle post per side uses about 11.6m: six 760mm posts, two full-length 1200mm top beams, four 540mm beams on the lower tier, four 420mm short beams and two 420mm depth braces, which packs into two 6m bars with a 3mm kerf — about 97% utilisation.
- Why are the posts shorter than the stand?
- The two top long beams run the full width and rest directly on the post ends, so each post is cut to stand height minus one beam height. The top face is then made of beams only — no post end grain showing, and no steps from end-face tolerances — and the long beam becomes a continuous beam over several posts instead of a simply supported span between two, so it stays flatter the more middle posts you add.
- Will the stand wobble sideways?
- A rectangular frame is weakest against rotation at its corners — the classic parallelogram racking. By default the tool adds a flat corner bracket at all four corners of every level: both legs lie in the horizontal plane and tie the long and short beams into a rigid rectangle. Vertical brackets handle beam-to-post; flat brackets handle beam-to-beam. If you expect serious sideways load (a coastal site, people leaning on it), diagonal bracing is the real answer — that remains a known limit of this version.
- Will the connectors show?
- The whole stand uses just two standard parts: the die-cast corner bracket (an aluminium die casting with a triangular reinforcing rib, bolted into the profile slot with T-slot nuts and hex bolts) and the corner slot connector (a T-head section part slid into the slot cavity of both profiles, locked with set screws and invisible from outside). The default scheme splits by direction: the horizontal joints (beam to beam, one per corner per level) get die-cast brackets that lock the rectangle, while the vertical joints (beam to post) get hidden slot connectors — so the only visible hardware is a handful of brackets at the corners, with no load-bearing joint left out. Pick slot only for an all-hidden frame (the viewer opens X-ray automatically) or die-cast for an all-visible one. No anchor connectors anywhere.
- Levelling feet or casters?
- For a heavy tank always use levelling feet: they let you bring all four posts into even contact, whereas an uneven floor leaves one post hanging while the others are overloaded. Casters only suit small tanks that really move, and they cut both capacity and stiffness.
- Where do the profile section values come from?
- The moments of inertia and masses come from the supplier datasheet (APAS aluminium extrusion, 6063-T5) rather than a geometric approximation of the section: the slots, centre bore and internal ribs make the section impossible to calculate by hand, so measured catalogue values are more reliable. A custom-section option lets you enter Ix and mass from any other supplier.