(203) 654-6230 The Improvement of Bicycle Design and Building Methods info@cycledesignusa.com

Introduction to Inspection Process

Although quality of production in the past decades has been generally better applied and regulated, production quality anomalies still occur. As a responsible fabricator/builder, one must be able to perform inspection of materials and parts in an objective and precise manner to ensure the assembled product quality. All complex structural assembles are subject to their weakest link. Skin tags and crystalline spiders, skin tag irregularity or crystalline matrix upsets and non homogenized sections, in as-delivered material, are invisible in visual observation but may be present. The process to rule out this presence must be understood to ensure 100% zero defect in each individual part.

Fortunately, since the bicycle is the red-headed step child of the aviation and aerospace industry, all necessary technical inspection procedures, techniques, tools and processes are readily available and updates to these processes are mandated to be ongoing.

Generally, advanced inspection procedure such as electron magnification in the construction of a bicycle is overkill but that overkill will be explained later and under certain circumstances might be applicable.

More common procedures such as the use of torsiometers (torsion section meter) reactive dye check to detect spiders, crystal groups or full emerging cracks.

Measuring internal external (equal profile section) straightness checking

Specific gravity testing (for use in multiple builds in conjunction with /torsiometer tests to match tubing specifications when two or more bicycles are to be made as close to identical as possible.

Production runs vary from when the run begins and ends. Factory production criteria allow for these variances. A go/ no-go criteria exists in all mill runs. Only items that grossly exceed the minimum criteria are scrapped. Thus a supplier catalogs parts and tubes in a much more general manner than is apparent. To put that in a simple phrase, out of any given number of tubes, none will be totally identical . Depending on the designed use, minor differences present no cause or effect to be considered in most cases, however, in tubing since each tube is in itself a single structure, at any point along that point (the skin) the tube performance can and will be different with each grain pattern.

Grain pattern: there are as many grain patterns in a mill run as the sands of time. As technology advances, much study is always invested in metal strengthening. Currently NANO level metallurgy is being studied on all fronts. New processes to homogenize are emerging. More advance technologies to treat crystalline structures using methods involving cryogenics, thermo conditioning, chemical-thermo conditioning and thermochemical crystal laminate bonding. (Ceramic like bonding of crystalline matrix)

In addition to inspection of products obtained through credible distribution, I must note that beginning with all mills, a process of culling removes non-conforming products from shipments. Unfortunately, this is not a completely foolproof or dependable process. Articles culled are often pirated directly from the plant or from disposal areas relegated to surplus distribution or even offered as new products from distributors that specialize in buying them and redistributing them.

Learning inspection skills in addition to good business procedure and buying from reputable suppliers will provide the ultimate failsafe in knowing that the tube that you have just used in a construction is going to meet the needs of your design.


Types of Skin tags: nearly all tubes contain skin tags of some sort
  1. Inclusion; general debris (can be small fragment of base material present from first drawing to final reeling)
  2. lubricating element
  3. First draw matrix non-homogenized portion
  4. In addition, occurs with damaged or bent mandrels allowing for improperly compressed material buildup (second most common)

Types of Spiders:

  1. Spidering automatically occurs in no-homogenized crystalline structure along crystalline grain alignments
  2. Spidering occurs in focused over compression often caused by improper intermediate annealment during working the tube section
  3. Post draw construction spiders can occur when installing a water bottle box. ( High angle, high-speed drill bits can initiate spider, use of any type of pre drill alignment device such as a center punch in non annealed tubing will cause spider in the crystalline matrix.
  4. Machine mitering; high angle cutter, excessive feed speed, allowing cutter to chatter all automatically initiate spidering.

Types of crystalline matrix upset:

  1. These occur in all tubing and sheet metal structures. the most simple explanation is lack of homogenized raw materials.
  2. Minor upsets will precipitate (increase) under certain heating cycles
  3. As mill delivered, tubing can change or upset at matrix level by improper heat cycles

Interesting history

In days gone by, common place technique used by Master Builders in Europe, when building for the cycling giants was to generate numerous frames based on the design criteria from which the cycling star would take out riding to select the ones he wished to race on.

Some times this production acceptance ratio could be as high as 10:1 or at least this is what I have been told over the years by the builders.

A Glossary of Tubing Definitions


– The heating and cooling of steel to remove stresses, alter physical, mechanical and metallurgical properties, increase corrosion resistance, or to thermally treat steel prior to age hardening.

Cryogenic Treatment

– Use of extreme cold to enhance strength.

Heat treating

– Use of heat to provide increased strength.


– Chemical Treatment-Use of chemical compounds and controlled heat to increase strength.


– Tubular products not subject to thermal treatment after welding.


– Same as above.

Bright annealing

– Annealing in a controlled atmosphere to prevent formation of dark, adherent oxides.

Cold drawing

– Drawing tubular products through a hardened die while at room temperature. Cold drawing is usually done with a supporting inside mandrel (drawn over mandrel). The purpose of cold drawing is to reduce the O.D. or wall, or both, to produce smooth surface finishes, obtain closer tolerances and to promote weld area recrystallization during subsequent annealing.


– As applied to tubular products, the center of the diameter is consistent with the center of the outside diameter.


O.D. – Outside diameter, specified in inches and/or decimals of an inch or specified in fractions of an inch or metric measure. I.D.- Inside diameter, specified in the same terms as O.D. Wall thickness- Preferably specified in decimals of an inch or metric measure. Nominal- The O.D., I.D. or wall dimension exclusive of tolerances. Maximum and minimum- The dimensions resulting after applying the proper tolerance to the nominal dimensions. Mean-Intermediate between maximum and minimum dimensions. Average- Dimensions obtained by averaging a number of measurements usually applied to wall thickness and less frequently applied to the O.D. or I.D.

Minimum wall

– A length of tubing or pipe in which the wall thickness is not permitted to be below that in the specifications.

Full finished

– Refers to tubular products in which the weld has been processed to produce uniform strength and dimensions, and is subsequently annealed to obtain proper corrosion resistance.

Mandrel (or bar) drawing

– A cold finishing operation in which a tube is placed on a mandrel of the final desired I.D. size of the finished tube, then drawn through a die. It is removed by reeling, or run through a straightener to cause it to spring away from the mandrel. It is usually given a sink draw to make the final size tube. Small ID/OD decrease or increase may only involve mandrel and reel.(8-9%)

Complex Shaping – Post Drawing

– Shape re-drawing or re-reeling to create ID/OD shapes.


– Forming Ovalizing in supported and unsupported manner. Using block forms or linear reels.

Manipulation tests

– Deformation of full sections or sector specimens to evaluate quality. Various tests are crush, flare, bend, flange, flatten, reverse flatten, reverse bend and expanding. To produce face or root bend specimens, sector samples and guided fixtures are used.

Mechanical properties

– Properties that reveal elastic or inelastic behavior where force is applied. Examples are elastic and proportional limits, modules of elasticity, yield strength, ultimate strength, elongation, hardness, impact strength, creep strength, and stress rupture strength.


– The difference between the maximum and minimum diameter of a tubular section.


– A tubular product made to dimensions specified by American Standards Association.


– Chemical or electrochemical removal of surface oxides.

Plug drawing

– A cold finishing operation in which a tube is drawn through a die over a plug, to produce a precise O.D. and wall tube.

Pressure test

– Subjecting tubular products to a specified hydraulic or pneumatic internal pressure to detect defects and weakness in the tubing wall.

Sinking (or sink drawing)

– A cold finishing operation to obtain exactly the desired diameter and/or to improve mechanical properties. This operation usually is performed by pulling a tube through a die without using an interior tool (mandrel).

Straightness tolerance (or camber)

– Maximum deviation, or bow, within a specified length. Usual method to determine straightness deviation is to use a straight edge and dial indicator or a flat plate and feeler gauges.
Each length should be straight within .020 inches per foot of length. In excess it is considered to be cambered.