Catalog items such as bearings, cylinders, electromotors, and gearboxes often get imported with incorrect mass values. Although the mass may be overridden as we import the model, it can still be incorrect. Here is a comparison between imported and actual mass for an SKF bearing:
Using an item with the wrong mass in your assembly can lead to incorrect assembly mass, which in turn affects all upper-level assemblies. To compound the issue, the mass is typically displayed in the title block, which means that any associated drawings will also be incorrect.
For instance, I once overlooked verifying the weight of a lifting table model. The error wasn't just 1 kg or 10 kg - it was off by 600 kg! This meant that the lifting table weighed not 600 kg but 1200 kg. Unfortunately, this went unnoticed for some time. By the time we found the mistake, the lifting table model had already been used in approximately 20 other assemblies, all of which had already been released. As a result, we had to revise 20 models, 20 drawings, and a few Excel BOMs to correct the mistake.
As demonstrated, mass is a critical property that affects assemblies, drawings, and other documentation. When designing on a computer, we may have poor judgment of how large or heavy an item is, which can lead to such errors.
So, why is mass so important that we had to dedicate an entire blog post to it? Here are a few reasons why incorrect mass values can cause problems:
- flawed design in case of mass optimization
- inaccurate transport cost estimates
- unreliable CAE results
- incorrect transport and handling instructions
To minimize the likelihood of such errors, here's one idea:
When downloading a neutral file (step, iges,…) from the web, check the item's mass and include it in the filename as you save it. For example: “SKF bearing 6013-2RS1 0.45kg.step“
The mass will automatically transfer to the Solidworks file’s filename, eliminating the need for further website searches. For example: "SKF bearing 6013-2RS1 0.45kg.sldprt".
If you can't find the mass (which can happen), you can add a note to the filename such as "MASS MISSING" to indicate the need for verification before proceeding with the drawing release.
Once you are certain which catalog items you will use in your project, you can take the time to override the mass in Solidworks for those specific items. This way, you won't waste time overriding the values of unnecessary items.
This approach also gives you the possibility to compare the mass in the filename with the mass in the model as one of the final steps before you release the drawings. This can be done with or without PDM.