AutoCAD Mechanical toolset commands creates mechanical layers on the fly and there is usually no need to create layers manually. However, if required you can manually create mechanical layers with the AMLAYER command. The AMLAYER command displays the Mechanical Layer Manager, which enables you to create a mechanical layer from an existing layer definition or create a completely new mechanical layer (and definition).
As with the Layer Manager (AutoCAD LAYER command), the Mechanical Layer Manager lets you set the properties of layers. You can also set the properties of layer definitions, which is not possible with the LAYER command.
If you use the LAYER command to change the properties of a mechanical layer, the properties of the layer will no longer match its definition. If required, you can reset all mechanical layers to match the properties of their definition with the AMLAYRESET command.