Bills of Material

Define assembly structures and component relationships

Overview

Bills of Material (BOMs) define the components, quantities, and relationships needed to manufacture or assemble a part. The BOM view in Backbone MRP provides a clear breakdown of assembly structures, rolled-up costs, and component management tools to keep your manufacturing data accurate.

Assembly Definition

Define parent-child relationships between assemblies and their component parts.

Cost Rollup

Automatically calculate total assembly costs from component costs and quantities.

Multi-Level BOMs

Support for sub-assemblies within assemblies, creating hierarchical structures.

Component Management

Add, remove, and configure component parts with quantities and units of measure.

BOM View

The BOM view is accessed from the Part Editor by selecting the BOM tab. It displays the full component breakdown for the selected assembly part.

Accessing the BOM

  1. Open the Part Editor for the assembly part
  2. Click the "BOM" tab
  3. The BOM view displays with the assembly units dropdown and cost summary at the top

Assembly Units

At the top of the BOM view, a dropdown allows you to select the unit of measure for the assembly (e.g., Each, Set). All component quantities are defined per one assembly unit.

Cost Summary

The BOM view displays read-only summary totals at the top of the component list:

Field Description
BOM $ Total rolled-up cost of the bill of material
Mat. $ Total material cost from all components
Non-mat $ Total non-material cost (e.g., tooling, consumables)
Labor $ Total labor cost allocated to the assembly
Overhead $ Total overhead cost allocated to the assembly
Note: The cost summary fields are read-only and are automatically calculated from the component costs and quantities in the BOM.

BOM Items Table

The BOM items table lists all component parts that make up the assembly. Each row represents a single component with its quantity and cost information.

Table Columns

Column Description
# Line index number for the BOM item
Part # The part number of the component
Name The name of the component part
Description Description of the component part
Type Part type (Raw Material, Manufactured, Assembly, etc.)
Unit $ Unit price amount for the component
$ U/M Unit of measure for the unit price (price per quantity units)
Qty Quantity of this component required per one assembly unit
Qty U/M Unit of measure for the quantity

Actions

  • Add BOM Item: Click the "Add BOM Item" button in the title bar to add a new component to the assembly
  • Context Menu - Open Part(s): Right-click on a BOM item and select "Open Part(s)" to navigate directly to the component's Part Editor

Adding BOM Components

To add a component to an assembly's bill of material, follow these steps:

  1. Open the Part Editor for the parent assembly part
  2. Navigate to the "BOM" tab
  3. Click the "Add BOM Item" button in the title bar
  4. Select the component part from the part selector
  5. Enter the quantity required per one parent assembly unit
  6. Set the appropriate unit of measure for the quantity
  7. Save the BOM

Multi-Level BOMs

Components added to a BOM can themselves be assemblies with their own sub-BOMs. This creates a multi-level BOM hierarchy where a top-level assembly contains sub-assemblies, which in turn contain their own components. Backbone MRP supports these nested structures and will roll up costs through all levels of the hierarchy.

Tip: When a component part is itself an assembly, its BOM costs are included in the parent assembly's cost rollup automatically.

Cost Rollup

The BOM cost rollup calculates the total cost of an assembly based on the costs and quantities of its components. Costs are broken down into the following categories:

  • BOM $: The total rolled-up cost of all components in the bill of material
  • Material Cost (Mat. $): The sum of material costs from all component parts, weighted by their quantities
  • Non-Material Cost (Non-mat $): Non-material costs such as tooling, consumables, or other indirect costs
  • Labor Cost (Labor $): Labor costs associated with assembling or manufacturing the components
  • Overhead Cost (Overhead $): Overhead costs allocated across the assembly

Each cost category is calculated from the individual component costs multiplied by their respective quantities. For multi-level BOMs, costs roll up from the lowest-level components through sub-assemblies to the top-level parent.

Important: If component costs change, the parent assembly's rolled-up costs will reflect those changes. Review cost rollups regularly to ensure your assembly costs remain accurate.

Assembly Units

The assembly unit of measure defines how the finished assembly is counted and tracked. This setting appears as a dropdown at the top of the BOM view.

  • Select the unit of measure that best represents the assembly output (e.g., Each, Set, Kit, Box)
  • All component quantities in the BOM are defined relative to one assembly unit
  • Changing the assembly unit may require updating component quantities to maintain correct ratios
Example: If the assembly unit is "Each" and a component has a quantity of 4, then four of that component are needed to produce one finished assembly.

Order BOMs

In addition to the standard BOM view on the Part Editor, Backbone MRP provides a separate Order BOM view. The Order BOM shows the bill of material in the context of a specific sales order, allowing order-specific component tracking.

  • Order Context: View the BOM as it applies to a particular sales order
  • Component Tracking: Track which components are allocated or consumed for a specific order
  • Order-Specific Quantities: See component quantities scaled to the order quantity
Tip: Use Order BOMs to track material requirements and costs for individual customer orders, especially when order quantities vary.

Best Practices

Keep BOMs Current

  • Regular Updates: Update BOMs whenever component parts change or new components are introduced
  • Review Periodically: Schedule regular reviews of BOMs to ensure accuracy
  • Document Changes: Keep a record of why BOM changes were made for audit purposes

Verify Component Quantities

  • Accurate Quantities: Double-check that component quantities per assembly unit are correct
  • Unit Consistency: Ensure the quantity unit of measure matches how the component is stocked and consumed
  • Cross-Reference: Compare BOM quantities against engineering drawings or work instructions

Review Cost Rollups Regularly

  • Monitor Changes: Watch for unexpected cost changes that may indicate data entry errors
  • Validate Totals: Periodically verify that rolled-up costs align with actual production costs
  • Component Cost Updates: When vendor prices change, review the impact on assembly costs

Use Consistent Units

  • Standardize Units: Use consistent units of measure across related parts and assemblies
  • Assembly Units: Choose assembly units that align with how you sell and produce the finished product
  • Conversion Awareness: Be mindful of unit conversions when components use different units than the assembly