James
A part can appear good and not pass an inspection. There is a hole out of center or an edge is not within spec. Only measurements can reveal this.
There is always some form of inspection involved with manufacturing. It would be foolish to go without inspection, but inspection can also slow down production.
So when should a digital comparator be used over a traditional manual inspection method? That all depends on your application, amount of parts to inspect and what you do with the data.
What you’ll learn:
- Where Manual Inspection Still Makes Sense
- What Changes With Digital Inspection
- The Inspection Costs Worth Counting
- How to Compare the Two Methods Fairly
- Building a Business Case for the Upgrade
- Wrapping It Up
Where Manual Inspection Still Makes Sense
Many shops are used to using traditional profile projectors. Light passes through or reflects off a part to produce an image on the viewing screen of the comparator. Using the magnified image, the inspector can check a part against the print.
Some common applications for these instruments are inspecting angles, radii, threads and other small machined part profiles. Comparators also allow for non contact inspection of parts which is beneficial for fragile parts.
It can be easy to place a part under a manual inspection method, focus the image and view features. You can quickly inspect a profile and identify edges that may need to be examined further.
If your application only calls for profile inspection of prototypes or lower volumes of simple 2D part profiles a comparator may be sufficient. As long as the method yields good results, there is no need to replace equipment just because it is older.
As the volume of parts increases, issues begin to arise. Placing parts, obtaining measurements and logging data can be tedious. If multiple measurements need to be taken on each part this becomes even more laborious. Measuring an edge or lining up an image can vary from person to person.
This is where having a more consistent digital method can be beneficial.
What Changes With Digital Inspection
When using a digital comparator you can use cameras and software to take your measurements instead of using only a screen. Depending on the model and software, you can compare images to CAD files, run a pre-programmed inspection and have the results logged.
Once you understand how optical comparators work you can start to understand the difference. Using a traditional comparator can help the inspector check and measure a profile. Having a digital machine that can assist in performing the same check on many parts can be very useful.
For example, you are inspecting a part with multiple cut edges that you want to make sure are true to print. Using a traditional method, you may have to align and log each measurement individually. You can program a routine to take these measurements, reducing the number of actions your operator has to perform.
Of course, there are some caveats. Proper lighting, part fixturing, lens selection and software functions all play a role when choosing a digital inspection machine. You will need to ensure your pre-programmed routine meets your inspection needs.
You may not be able to measure 3 dimensional features using some models of cameras as well. There are other features you can gain but be sure you understand what you’re looking for.
One key thing to note about digital inspection is that your computer will not always yield a good measurement. But if a good routine is established it can help reduce repeated manual measurement steps and allow data to be retrieved more easily.
The Inspection Costs Worth Counting
Equipment can be a costly purchase. When inspection slows your production line or does not provide consistent measurements, there are more costs involved that may not be obvious.
A study conducted by ASQE on Insights on Excellence showed that in 2025, 89% of respondents reported at least a moderate financial impact from poor quality in 2025. This is a broad category of costs associated with quality, not specific to comparators. But there are areas to look at when deciding to upgrade your inspection method.
Time that is being wasted while trying to obtain measurements:
- Inspection Labor – It can take time to position a part, align and measure a feature.
- Time waiting on a job to get inspected
- Labor to catch an error at a later operation
- Record management – Time it takes to obtain or determine data for a part or lot
There can be errors made with a manual method of inspection that are not related to the equipment. Having improper fixtures, print or software will also cause issues.
Be sure to identify which costs your upgrade will help improve.
It is beneficial to reduce your inspection time if you are performing that same inspection on many parts. If you only inspect a few parts here and there you may want to skip the upgrade.
How to Compare the Two Methods Fairly
There are many benefits a vendor will show you when presenting a digital comparator. These demos will not give you a full picture on what to expect when using the machine in your facility.
If you want to accurately compare the two methods use similar parts, prints, tolerance and criteria for accepting or rejecting parts. It’s important to test parts that will normally be inspected in addition to problematic parts.
Time it takes to:
- Complete a full inspection on a part. Not only time spent taking the measurement, but also placing, logging, aligning and reporting data if applicable.
- Measure similar parts. Have different inspectors measure the same parts and check for variances in data.
- Obtain measurements of smaller features. Some parts may be difficult to get a clear image on, make sure your machine can measure these features if required by the print.
- Retrieve your inspection results. Be able to pull results and find the part/lot information easily.
Performing a gage R&R (Repeatability & Reproducibility) can also help assess repeatability and variation between operators and how your users vary from each other.
Keep in mind the amount of time it will take to program your inspection routines as well. Automated inspections can be beneficial if the process does not take too long to create.
Building a Business Case for the Upgrade
After you have performed your test, calculate your savings based on time spent inspecting parts. Once you have determined your frequency of inspection, Multiply measured time saved per inspection by the expected number of inspections, convert that total to hours, then apply the relevant hourly labor cost. Also take into consideration the cost of your software, labor, training, fixtures, maintenance etc. If you save time, that is just additional hours you can spend on other tasks. You should also consider the amount of parts you may scrap or have to re-work if the upgrade helps.
Depending on what type of parts you manufacture and how often your print changes, you may not benefit from using a stored routine on a digital machine.
Another factor to keep in mind is employee training. Make sure your inspectors are trained on the new method and know where to obtain their data. They will also need to know how to pull results, in case there is an issue with a lot of parts.
There is no single answer for every shop when it comes to upgrading to digital inspection. You can use both methods to your benefit when inspecting parts. Start with one product line that has trouble meeting a demand, then work from there.
Wrapping It Up
Inspecting your parts is important, but can eat up valuable time on your production line. If you spend time comparing the two methods and understand what each offers, you can find a solution that fits your needs.
