Profile diameter or circumscribed circle: how to read a tube laser working range ART-171

What a circumscribed circle is

A circumscribed circle is the smallest imaginary circle enclosing the whole profile cross-section. For round tube it equals outside diameter. For a square it passes through outside corners, so it is larger than the side: for side a, it is a × √2.

For a rectangle with outside sides a and b, the simplified value is its diagonal: √(a² + b²). Complex, open, channel, angle, and non-standard sections can require consideration of extreme points, projections, orientation, and rotation.

These formulas are a preliminary envelope check; they do not prove safe clamping and processing. The usable range can be reduced by the chuck, steady rests, head, collision zone, or loading system.

Why a 100 mm square is not always a 100 mm machine profile

A square tube with a 100 mm side has a diagonal of about 141.4 mm. If the stated maximum circumscribed circle is 100 mm, it does not geometrically fit. A maximum square side of 100 mm is a different specification and must be read exactly that way.

Also establish whether a number applies only without rotation, to one chuck, or to a particular length. A section can enter the clamping area but exceed the permitted head path; geometric compatibility then is not technological compatibility.

Dimensions to collect from production

For every section record:

• type: round, square, rectangular, oval, or special;
• outside dimensions and supplier tolerance;
• wall thickness, actual blank length, mass per metre, and total mass;
• material, surface condition, seam, holes, or projections;
• required accuracy and hole orientation;
• its monthly or annual share of the production mix.

Finished-part drawings matter too. Two sections with the same circumscribed circle can differ because of end-near holes, slots, mitres, threads, or beam-access requirements.

How to read a tube-laser technical table

| Proposal statement | Possible meaning | Required clarification | |---|---|---| | Maximum round-tube diameter | Outside diameter limit | For which blank length and mass? | | Maximum circumscribed circle | Envelope around a profile | Which section forms and conditions? | | Maximum square section | Outside square side | Are diagonal, chuck, and head path included? | | Chuck size range | Mechanical clamping zone | Does it equal the cutting zone? | | Maximum wall thickness | Limit for a material/mode | Which source, gas, head, and edge requirement? | | Maximum length | Feed or machining envelope | Are supports needed; can remnant be processed? | | Maximum mass | Chuck, roller, or feed limit | How is mass distributed; are thin profiles limited? |

One figure never replaces a technical questionnaire. A reliable proposal addresses every constraint that affects the real cycle.

Round profiles

For round tube, compare outside diameter with the permitted range, but also check ovality, wall thickness, seam, length, and mass. Thin walls can deform under unsuitable clamping; long blanks require support and rotation assessment.

Do not confuse outside and inside diameter. The machine and head path depend on outside envelope and surface access. Wall thickness affects cutting technology; it does not turn 120 mm tube into a “100 mm profile.”

Square and rectangular tubes

For a square, both side and diagonal matter; for a rectangle, both sides and diagonal matter. If rotation is necessary, the angular position may define the largest dimension. An 80×120 mm rectangle has an approximate 144 mm circumscribed circle: an initial filter, not a guarantee.

For holes on several faces, verify stable rotation and holding without skew. Request an example on the actual drawing, not just the published range.

Open and special sections

Channel, angle, tee, oval, and bent sections cannot be assessed by “diameter” alone. Extreme points, flange thickness, open geometry, support, orientation, and deformation risk matter. The chuck and rollers can need special tooling or support.

Request confirmation for your geometry: standard configuration, option, special chuck, or individual process trial. “Works with profiles” is not a guarantee for every shape without a drawing.

Diameter is not the only limit

Even when the section passes the circumscribed-circle check, verify the chuck grips the necessary zone; the head avoids the section and chuck; travel covers the part; feed tolerates mass and inertia; supports are available; end zones can be cut; and positioning meets accuracy requirements. Material or thickness can alter the range.

For series work, assess the entire range, not only the maximum. If 95% of production is 40–80 mm tube and one section is 140 mm, review its frequency and cost before basing the whole purchase on it.

How to verify compatibility before purchase

Send a table of actual sections plus two or three drawings. Ask separately for maximum outside envelope, the rule for square/rectangular sections, usable chuck range, mass and length limits, required options, end-near-hole capability, and results on your material.

“Up to 160 mm” is inadequate for an investment decision until it defines the number and conditions. For a major purchase, include a real-blank acceptance test or agree the test parts in advance.

Examples of preliminary geometric checks

A 100 mm round tube has a 100 mm circumscribed circle. A 100 mm square has about 141.4 mm; an 80×120 mm rectangle about 144.2 mm. A machine confirmed for a 100 mm circumscribed circle can suit the round tube, but not the square 100×100 or rectangle 80×120.

This is only a preliminary filter. Then check the actual chuck, rotation, head approach, and blank length. If the manufacturer defines a maximum square side instead, use that definition; do not replace it yourself.

For special sections, prepare a cross-section drawing with extreme dimensions, projections, radii, flanges, and weld-seam position. A photograph can clarify form but never replaces a drawing. State whether all faces require machining or fixed orientation is acceptable. A profile can fit an envelope but require different support or have a forbidden head-approach zone.

Build a “profile — operation — constraint” matrix: envelope pass, clamping, face access, stiffness, support, and difficult end zone. Check the worst serial case, including tolerance, ovality, and transport distortion. Nominal compliance does not ensure every blank passes safely.

Consider the tube start and remnant too. First and last zones can be restricted by clamping, support, or end approach. Make end-near holes an explicit test requirement.

The result should be specific: “profile A—standard configuration; profile B—option required; profile C—test required or not recommended.” This gives purchasing, process engineering, and supplier one shared decision boundary.

How to write the supplier's technical request

Start with type, outside dimensions, wall thickness, length, mass, material, and frequency; attach typical part drawings and separate accuracy requirements. Ask for an item-by-item answer. The supplier must state whether “160 mm” is outside diameter, circumscribed circle, square side, chuck, or cutting zone, and what is standard versus optional.

If the borderline section matters commercially, include a real-blank trial. Assess clamping, head access, feed stability, hole quality, end remnants, and cycle time, not just whether material can be held.

Why the machine limit is not your production-mix limit

A correctly read limit is not automatically an operating norm. A borderline section can be permitted only with one configuration, length, support, and orientation. Consider actual-size variation, ovality, distortion, tolerances, and storage.

Do not transfer limits between models of the same manufacturer. Chucks, working-zone length, head size, support, options, and software vary. Equal advertised “maximum diameter” does not mean equal permissible sections or fixing method.

Separate three conclusions: geometrically fits, can be clamped, and can be processed reliably with the required technology. Dimensions establish the first, chuck and tooling the second, while the third also needs head access, support, material, thickness, quality, and a test part.

When a borderline item is rare, another process or route can be more rational than designing the whole purchase around it. When it is a key serial product, testing and special tooling belong in the initial specification.

Common mistakes

Typical errors are comparing a square side with round diameter, not calculating a rectangular diagonal, ignoring mass and length, treating a chuck value as maximum diameter, checking empty geometry without part drawings, not identifying options, and accepting “works with all profiles” as a guarantee.

Selection checklist

• [ ] The principal-section list is complete.
• [ ] Outside dimensions, thickness, length, and mass are recorded.
• [ ] Diagonal/circumscribed circle is calculated for square and rectangular tube.
• [ ] Chuck, clamping area, and collisions are checked.
• [ ] Support for long/heavy blanks is clarified.
• [ ] Real drawings are sent to the supplier.
• [ ] Included options are recorded.
• [ ] A real-profile test or acceptance conditions are agreed.

Limits of this answer

These formulas support preliminary understanding only. They do not replace drawings, kinematic checking, clamping analysis, or manufacturer confirmation for a specific model. Final compatibility depends on chuck, head, supports, length, mass, material, thickness, and tooling. Do not run an unfamiliar profile only because its diagonal is below an advertised figure.

Conclusion

Read the working range in the language of geometry and real production. Round tube is governed by outside diameter; square and rectangular tube by side, diagonal, and circumscribed circle; special profiles by complete cross-section, clamping, and head trajectory. Drawings, length, mass, thickness, and mix allow a supplier to confirm actual suitability rather than an abstract “diameter.”

Next step