Cannula: Another term used for tubes, especially in medical industries

Centerless Grinding: A method of grinding round bars in a free state

Concentricity: In a round tube, the relationship between the inside and outside diameters

Deep-hole drilling: Synonymous with “gundrilling”

Gundrilling: The process by which holes are drilled into and/or through long bars of ferrous materials, e.g., barrels for firearms

Seamless Tubing: Lengths of tubing that have not been rolled and welded

Trepanning: A machine drilling process that leaves a solid core

Tube Conditioning: A method of machining to achieve more precise concentricity

Tube Hollow: A hollow made to a specific size and tolerances for use as a starting tube, which is then reduced in size and extended in length by various techniques, while being drawn over a mandrel and through a die

Wall thickness variation: In a round tube, the measured thickness of the wall and how it varies from one point to the next along its full length

Documents & Examples


Eccentricity is the measure of offset of the center of the circle formed by the OD, (outside diameter) and the center of the circle formed by the ID, (inside diameter).  Eccentricity can be determined by measuring the wall thickness for maximum and minimum values at any cross section, (typically 180⁰ apart for bars that are round and not lobed).


Eccentricity= W1-W2                                      Ex.          0.120” – 0.110”          =.005”
                            2                                                                         2


% of Eccentricity= W1-W2 x 100                                 (0.120” – 0.110”) x 100          =4.35%
                                     W1 + W2                                               0.120 + 0.110”



TIR, (Total Indicated Run Out): Is related to eccentricity.                              

TIR=2 x eccentricity

Example: (from above) TIR=2 x .005” or .010”

Surface Finish: The measure of the surface roughness of the ID or OD of the machined tube.  While typically working to the RMS roughness parameter, Confluent Maine works with the Ra and Rz parameters.

Drill Ratio: The ratio between the depth of hole to the drill diameter.  For deep hole drilling this usually starts around 10:1.  Depending on material to be drilled and the hole size, this ratio can exceed 400:1.

Typical range of hole sizes provided by Confluent Maine:

.055” / 1.39mm                   thru                     3.000” / 76.2mm

Dimensional Variations: Confluent Maine vs. General Industry

Permissible variations in a machined hollow from Confluent Maine are all based on customer specification and requirement:

  • “TIR”, (Total Indicated Run out) measurement. 
  • Hole size and tolerance
  • OD size and tolerance
  • Straightness

Typical concentricity target range met by Confluent Maine:

  • .010” TIR, (routine) to:
  • .004” TIR, (best effort for .003” or less)

Typical dimensional tolerance ranges met by Confluent Maine:

  • OD +/- .001”
  • ID +/- .001”

Typical surface roughness ranges met by Confluent Maine:

  • As drilled, (usually between 63Rms and 100Rms) to:
  • 16Rms and finer, (as fine as 10Rms)

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