To make a modification to a component, the most logical way is to add some features directly in it and make a drawing to describe the modifications. A note can be displayed to identify the source component. But in the Bill Of Materials, the unaltered component never appears which leads to a high risk of forgetting to acquire it in the first place.
This is especially true when the designer is not taking care of the procurement. If the person in charge does not open the drawing he or she won’t have any idea that an antecedent needs to be ordered. If you decide anyway to directly modify the component where do you put the drawing? In the project or in the component database? Or maybe you just want to use the Description Property to detail the modification so it appears in the BOM… that might be difficult and hard to describe in few characters. And what if someday you need to use the unaltered component in your project? You will have to either duplicate it (which is a bad idea if you want to keep your component database clean) or make an unaltered configuration in the modified component (which might be too complicated and confusing).
The trick is to create a modification assembly and drop the unaltered component in it. You can then use material removal functions at the assembly level but you cannot use material addition functions. Which make sense actually because in the real world you can always remove material from something but never add to it… If you want to add something then just do what you do all the time: make an assembly of components and attach them together with hardware, glue, or whatever binding technique you want.
The parent assembly then becomes an internal component because the alteration is designed in house. This is true even if the unaltered component is external. See the article about the Definition of the Word Component.
In the modification drawing, the properties of the unaltered component can’t be directly displayed in your titleblock or in your notes linked to some properties.
The trick is to replace in the text expression of the property, the name of the assembly by the name of the unaltered component.
Instead of having “SW-Material@0000000017.SLDASM” replace it by “SW-Material@0000000016.SLDPRT” to have the property to read the part’s material instead of the assembly’s material.
External components modification
If you want to modify a component that has not been designed in house, you have two options:
- The vendor can modify it for you and give you a specific part number. In this case you have nothing else to do than storing this component in your component database in following the good CAD Importation practice.
- You have to modify it yourself. In this case you have to get the component first to be able to modify it with a drawing or any referenced document like a specification for example.
Let’s take a look at the following example. We have a leveling foot and we want to add counterbore holes to be able to secure it. If it is not already there, we create the unaltered component and save it in our component database.
Select “Make Assembly from Assembly” (or “Make Assembly from Part” if you are modifying a part):
At the assembly level, use the material removal features you want to modify the unaltered part. Make sure that the features appear below the mates icon to be certain your are not modifying the source component.
You can now make a modification drawing. In a higher level BOM you will see the following:
This way you have the unaltered component and the alteration drawing listed.
Most of the time you let the machine shop source the material and decide what is the best size to make a part given the machining allowance. But a material is also somehow an external component that you modify to make a part. This mean that you can also apply this method to define the original piece of raw material from which the part is made. This is particularly useful if you are making several parts from the same piece of raw material (see the article about the Fractions of Components) or if it is an expansive exotic material that you prefer sourcing yourself (see the article about the Scope of Supply).
If we look at the pulley used as example earlier, we actually obtained it from a peek bar stock and inserted multiple “Assembly Features”:
If you want the machine shop to source it, just “Exclude from bill of materials” the piece of material and it won’t show up in your BOM.
Internal components modification
If you want to modify a component that has been designed in house, you have tree options:
- You don’t want to keep the unaltered version. In this case, you just follow your company’s workflow and increment the revision of the drawing.
- You want to obtain the altered component directly without a preceding stage. In this case, make a copy of the existing component, apply your modification directly to it and create a drawing with the first revision of your workflow (rev. A, rev. 0, etc…).
- You want to obtain the altered component from the unaltered component. In this case, you need to have a finished unaltered component before being able to move to the next stage which is the modification.
The last case that interest us here has to be considered like a one time thing. It is a waste of time and resources to get something made and then modified. If it happens often then it is more reliable to be in the second case to manufacture directly to the final design. The last case applies for example when you want to make a new revision of a component but you still have some components of the previous revision in stock. You want to modify them to be able to merge them with the stock at the latest revision.
Let’s say we have this plate in revision A. During the assembly we realize that the center hole is too small so we make a revision B. The revision A has already been manufactured.
We want to modify the parts already made in order to have them compliant with the drawing in revision B. Insert that part into an assembly and extrude a larger hole:
The drawing of this assembly will be in revision A but it will permit to push these parts in the revision B of the main drawing.
With this method of using assemblies to modify a component, we have introduced the idea of a chronological order. The modification cannot be done without having the precedent component. Take a look at the article about the Operations to see what can be achieved with this method.