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    December 31, 2021

    On-Machine Inspection: The Key to Precision Machining


    When it comes to precision machining, the smallest decisions could result in wasted time and money. Luckily, there are certain tips to help you avoid these pitfalls. One of the big tips is to implement on-machine inspection.

    Our machining experts put together this piece all about on-machine inspection. We’ll tell you how it works, why it’s great, and how it can help your operation.

    How Inspection Is Typically Done 

    We probably don’t have to tell you how inspection is typically done with precision machining. You finish machining the piece then take it to a separate area and use a jig or a series of measurement gauges.

    The inspector will measure a dimension then match it to the original drawing. If it’s within the specified tolerance, then that measurement is good to go. If every measurement matches the drawing, the piece is approved to get sent to the customer.

    If even one dimension is out of spec, then the part has to be scrapped and re-made since it’s too late to make touches with the CNC. 

    Defining On-Machine Inspection

    With on-machine inspection, you perform the full inspection while the piece is still on the machine in the vice.

    After making all the cuts, your CNC can be outfitted with a probe that measures dimensions. Since you didn’t move the part at all, it’s still in a position where changes can be made if dimensions are out of spec.

    The machinist will perform the full inspection before taking the part away from the CNC machine.

    How Does On-Machine Inspection Help with Precision Machining?

    The difference between traditional inspection and on-machine inspection seems so trivial. How does this new inspection technique help with precision machining at all? There are a few major ways that we’d like to discuss.

    Reduces a Massive Bottleneck 2 Precision Measuring Machine

    Most shops opt for a tabletop Coordinate Measuring Machine (CMM). These can get pretty pricy, so shops usually only have one CMM that’s shared for all parts.

    Every part needs to go through this single machine before they can be sent out to a customer.

    The result is a massive bottleneck. Inspectors can’t rush the process. As more parts are completed on the machines at the shop, the queue to go through the CMM grows even more.

    This means longer lead times for your customers.

    By performing on-machine inspection instead, there is no delay or wait for machine availability after a part is machined.

    Better Overall Efficiency

    Once the part is oriented in the vice and machined, it’s already in the perfect position to have its dimensions checked. 

    Plus, the probe can automatically perform a process that would otherwise be done manually in a CMM. You could be saving upwards of 10 minutes for each part that gets manufactured in your facility.

    Higher Levels of Accuracy 

    On-machine inspection is another example of how automation can improve accuracy. Human error is eliminated altogether. In addition, there’s no way that a gauge can be misused or misread. 

    With on-machine inspection, the total accuracy of measuring becomes better. This is great news for shops that manufacture a lot of parts for different customers.

    You won’t run into an issue where the customer receives a part out of spec due to a failed inspection check.

    Find Errors Earlier Calipers Rapid Axis Machine Quality

    One of the biggest benefits of on-machine inspection is that the part is in the right place if a discrepancy is found.

    What happens if you’re inspecting the dimensions on a piece and notice that one feature is too wide? If the part is still in its original position in the vice of your CNC mill, you can quickly set up the cut and make another pass. 

    Just like that, you corrected the error with no time wasted.

    If you are using traditional inspection methods instead, you’re already starting at a disadvantage. You have to take the part back to the mill, re-orient and position the piece, re-zero it, set up the machine, then make the cut.

    Even then, the slightest misorientation could ruin your attempt at fixing the discrepancy.

    You’re going to spend a lot of time trying to correct an error that could have been fixed in less than a minute with on-machine inspection.

    It also allows you to find errors way earlier. For some parts, multiple machines might be needed to fabricate a single piece. When you catch the error early, you can avoid performing these extra steps until the dimensions are confirmed.


    As you can see, on-machine inspection is a huge key to precision machining. It can save you time and money while improving your overall efficiency and accuracy. If you want more machining tips or you need parts fabricated, reach out to our experts at Rapid Axis

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