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Putting Together Parts Lists

by George Martin

Start ı Phase 1ıIn the Beginning ı Phase 2ıCreating a Database ı Manipulating the Files ı Phase 3ıAn Entry-Level MRP Program ı Added Benefits ı Sources and PDF

PHASE 3ıAN ENTRY-LEVEL MRP PROGRAM

The MRP program is usually driven from the parts list. These programs typically have all that Iıve talked about and more. Two of the key features that an MRP program includes are indented bill of materials and master items.

An indented bill of materials is a parts list that groups parts into assemblies or build steps. These groups are to hardware construction what subroutines are to software construction. I once worked with a group of people on a printed circuit test set that had over 2000 line items in total but only about 1200 unique items. The indented bill of materials software saved our hide. We entered each assembly and could produce a total for how many 1K resistors or ı to 20 ı pan head screws we needed. We could also see if parts from different assemblies were or could be made with one common part. The power of the indented bill of materials is obvious. It helps you divide and conquer.

Master items is also an indispensable feature. Letıs step back and discuss what youıre purchasing. Classical thinking identifies purchased parts as either specification or source-controlled. Source-controlled parts are items such as a microprocessor. If youıre using an Intel 80C196KC, you are going to use whatever Intel ships you. You could, of course, reject parts that donıt function properly, but the bottom line is that you are controlling the source of the part.

Specification-controlled items are typically specified by a drawing you have created. Only parts that conform to that drawing will be accepted. Printed circuit boards or custom sheet metal front panels are standard spec-controlled items.

There are other classifications such as artwork or processes for parts, but they are refinements of the basics of source- and spec-controlled.

The benefit of master items is that, when you create the part number, you also add all (and I repeat, all) the supporting information. Information such as whether itıs source- or spec-controlled, where to purchase, pricing, and price breaks can all be contained in the database for your master items. Also, different projects with the same requirements should all use the same master items program. Using master items also gives you the benefit that, after the item is entered into the database, the documentation process is complete. This becomes a project milestone that you can use to identify the parts lists as complete.

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