The Frame That Wobbled (Aluminum, Too Thin)
We built a machine frame (a machine’s structure, article 161). We used aluminum extrusion (article 161). On the floor, the frame wobbled (the machine shook). The problem: the aluminum extrusion was too thin (the wall was 2 mm). The machine (a vibrating press, article 63) shook the thin extrusion. We either upsized the extrusion (a bigger profile, thicker wall) or added gussets (triangular braces). We upsized (a 90×90 profile, instead of 45×45). The frame was stiff. It didn’t wobble. The mistake was picking a thin extrusion (for a vibrating machine). The aluminum was fine — the profile was too small.
Aluminum vs steel for machine frames — pick the material. This article covers the comparison.
Aluminum Extrusion (Article 161)
Aluminum extrusion (article 161, a T-slot profile) is modular. You build the frame from the extrusion (cut to length, bolted). It’s light (aluminum). It’s fast (no welding). It’s adjustable (you add/remove profiles). But it’s less stiff (aluminum is softer than steel). For a light machine (a vision system, a conveyor), it’s fine. For a heavy/vibrating machine (a press, article 63), it wobbles (unless a big profile).
Steel (Welded)
Steel (a welded tube, or plate) is stiff. A welded steel frame (article 145) is strong (and rigid). It’s heavy. It’s welded (not adjustable). It needs machining (after welding, article 145, stress relief). For a heavy/vibrating machine (a press, a mill), steel is the choice. For a light/adjustable machine, aluminum.
| Material | Stiffness | Weight | Use |
|---|---|---|---|
| Aluminum extrusion (article 161) | Less (soft) | Light | Light/adjustable (conveyor, vision) |
| Steel (welded, article 145) | High (stiff) | Heavy | Heavy/vibrating (press, mill) |
Step 1: The Load (Vibration?)
Is the machine light (a conveyor, article 121, a vision system)? Use aluminum (modular). Is the machine heavy/vibrating (a press, article 63, a mill)? Use steel (welded, stiff). The wobble (the frame that wobbled) was aluminum on a vibrating press. Steel (or a big aluminum profile) fixes it.
The material rule: Light/adjustable → aluminum (extrusion). Heavy/vibrating → steel (welded). The frame that wobbled was a thin aluminum extrusion on a press. Use steel (or a big profile). Don’t use thin aluminum on a vibrating load.
Step 2: The Stiffness (Deflection)
For a given load, the steel frame deflects less (it’s stiffer). The aluminum (modulus is 1/3 of steel) deflects more (for the same section). For a precision machine (a vision system, a coordinate measure), the frame must be stiff (no deflection). Use steel (or a big aluminum profile).
Step 3: The Cost
Aluminum extrusion is expensive (per kg), but fast (no welding, no machining). Steel is cheaper (per kg), but needs welding (and machining, article 145). For a one-off machine, aluminum (fast). For a production machine (many), steel (cheaper per unit, with the welding setup).
Step 4: The Adjustability
Aluminum is adjustable (you add/remove profiles, change the layout). Steel is welded (fixed). For a machine that changes (the layout evolves), aluminum. For a fixed machine (the layout is set), steel.
A Frame Material Checklist
- Is the machine light? (Conveyor? Vision?)
- Is it vibrating? (Press? Article 63?)
- Is it precision? (Deflection?)
- Is it adjustable? (Layout changes?)
- Is it one-off? (Aluminum fast?)
- Is it production? (Steel cheaper?)
- Does it wobble? (Test?)
- Is the profile big enough? (Article 161?)
- Is the welding done? (Article 145?)
- Is the stiffness enough? (Deflection?)
The Bottom Line
Aluminum vs steel for machine frames matches the material to the load. The frame that wobbled was thin aluminum on a press. Use steel (for heavy/vibrating). Use aluminum (for light/adjustable). The frame that was stiff wasn’t the cheapest material — it was the right one.
