Monday, February 7, 2011

What is a Mylar drawing?

Mylar is a trade name for bopet (biaxially-oriented polyethylene terephthalate) polyester film. Also known as Melinex or Hostaphan, this transparent, durable material is used in food storage, insulation and sailing, but it is perhaps best known for its applications in the graphic arts, most notably for CAD drawings. A few customary drawing techniques enhance its positive attributes.

Architects and engineers use Mylar in designing their work. The schematics are drawn up, usually by a computer program such as AutoCAD, and then printed. Schematics on Mylar reflect the depth and dimension of the finished project more easily than blueprints. Once the Mylar is drawn up, these illustrations become part of the legally binding agreement between contractors, the employer and the design firm. 

Many companies today are in the process of taking their un-dimensioned drawings on stable-based material (Mylars) and preserving them by fully integrating the legacy Mylars into the automated work environment through digitization and subsequent storage capacities.

One frequent problem often encountered in this transfer of data is projects may require a very precise tolerance of +/-.005" accuracy over any five- or ten-inch area for the digital scanned files. The drawings are on Mylar, which is a plastic sheeting material that may be affected over the years by changes in temperature. This means that the older drawings may have stretched or otherwise changed in size, affecting the accuracy of the drawing itself. The accuracy of the final digital file is of paramount importance. These digital files are stored in an electronic repository as a permanent archive for all of our drawings. If we need to refer to these digital drawings, or print out a new paper drawing, it is essential that the measurements be as accurate as, if not better than the original Mylar drawing when it was new.

  More information on un-dimensioned Mylars:

  • An un-dimensioned drawing presents the engineering definition graphically without the use of numerical dimensions.
  • Sizes and relationships of un-dimensioned features are determined by scaling the original drawing or by scaling a stable reproduction made from it.
  • Un-dimensioned drawing forms are identified by the letters PCM or "Photo Contact Master."
  • Effectivity notes indicate part replacement, upgrades and modifications for various models.
Un-dimensioned drawings are typically used to define parts with all or a majority of tolerances plus or minus .030" or greater. This includes sheet metal parts, extrusions, cable assemblies, and wiring harnesses.

What are the components of a Mylar drawing?

  • Title block
  • Bill of materials
What information can be found in a bill of material?

  • Part number
  • Description
  • Zone
  • Quantity
  • Material Specifications
  • Extrusion callouts
  • Thickness and size
  • Flag notes
  • Revision level
What are common abbreviations found on Mylar drawings?

  • ECN: Engineering Change Notice
  • ECO: Engineering Change Order
  • PCR: Project Change Request
  • PCM: Photo Contact Master
  • A.N.D: Army Navy Drawing
  • BDN: bend down
  • BUP: bend up
  • BR: bend radius
  • R: radius
  • TYP: typical
  • JOG: joggle
  • SHN: shown
  • OPP: opposite
  • FLG: flange
  • EOP: edge of part

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