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Are there reliable vernier calipers with plastic blades?

Discussion in 'Other Quality and Business Related Topics' started by TravisTheInspector, Mar 22, 2019.

  1. TravisTheInspector

    TravisTheInspector New Member

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    In our inspection department, we get a lot of parts that are anodized, and our metallic vernier calipers tend to scratch and mark up the anodization. Does anyone know of a type of reputable caliper we can use to measure inner/outer diameter, as well as depth, made of some material other than metal?
     
  2. Andy Nichols

    Andy Nichols Moderator Staff Member

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    What precision are you trying to achieve, Travis? Can I also ask why you are inspecting finished product for dimensional accuracy? Can you check before anodizing?
     
  3. TravisTheInspector

    TravisTheInspector New Member

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    I apologize for not giving more detail. We do incoming inspection from our suppliers. Any parts that come into the building that go into our products undergo some form of inspection, from screws and washers and nuts, to plastic, stainless steel and bronze housings, to cables and cable assemblies. Our suppliers will machine a tube for example, and then send it for anodization, then it gets sent to us and we will inspect it to ensure that the purchased parts meet our specifications. We build transducers and 90% of our products end up in the ocean. This means that any voids in the anodization are no good. We have always used metal Mitutoyo calipers, but we have been trying to find an alternative to avoid damaging any anodized parts. As far as precision, many of our parts have tolerances ranging from +/-.005 to +/-.001, so whatever instrument we use has to be quite accurate. We generally require all of our hand tools to be calibrated yearly and to come with calibration certificates whenever possible.
     
  4. TravisTheInspector

    TravisTheInspector New Member

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    This is one example of an anodized part that we inspect. The o-ring groves are the most critical part of this piece and measuring them also can easily result in some damage if we are not very careful. But, when we have to inspect 100-200 at a time, its inevitable that we will cause some type of damage to them while measuring.
     

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  5. Andy Nichols

    Andy Nichols Moderator Staff Member

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    OK, so having been in this situation (almost identical) I'd offer the following options:

    Stop inspecting proprietary parts - you can't be certain of finding anything of importance, other than simply identifying them and counting them.

    Get "before finishing" data from your suppliers and have them send that in - stop touching parts which are finished.

    Reduce inspection on parts to your drawings, and identify key important characteristics to verify (only) or things the suppliers typically get wrong (past performance).

    Use a cmm to check anodized parts if you really must.
     
  6. Andy Nichols

    Andy Nichols Moderator Staff Member

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    Wow! Parallel universe! Do you have anything on your drawings about key features which are really most important to the fit/function?
     
  7. TravisTheInspector

    TravisTheInspector New Member

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    Haha, spoken like a true inspector. Unfortunately, I am just an underling, and those things are not left up to me to decide. We inspect these parts because, honestly, we get cheap parts from not so great suppliers, and even though we send them our prints to build to, we consistently find issues with the parts we receive not being built to our specifications. To keep our cost to our customers low, we tend to get our parts made for cheap by our suppliers and, you get what you pay for. We've had so many issues with our anodized parts that we've been instructed by our management to inspect 100% all of our anodized parts coming in. As far as the before finishing data, we've had many cases where the suppliers inspection results do not match the results that we get after we perform our incoming inspection. We do use sample sizes and AQLs, and generally inspect to "Critical Dimensions" on our prints, unless its a first article. But anodized gets 100%

    So long story short, we have to inspect our anodized parts, and because of that, we are really trying to find a measuring tool that wont damage the anodization. we do have a couple CMMs but with all of the angles and small spaces, we cant always use them. Thus, the search for some type of non-metallic vernier.
     
  8. hogheavenfarm

    hogheavenfarm Well-Known Member

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    I have seen plastic calipers that were fairly accurate, I remember using them in school, but I have not seen them in years, they do exist though. As a backup however, what about making checking jigs from non metallic parts? O ring grooves might be a candidate for a go-nogo plastic gage, we print ours on a small desktop 3d printer. It may mean more checking jigs than just a caliper, but it is an option, especially if there are many parts to check. Of course you end up with attribute data rather than variable data, so sometimes that can be a concern.
     
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  9. Andy Nichols

    Andy Nichols Moderator Staff Member

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    Harbor Freight? I think their stuff is pretty reasonable. If you checked them against a couple of jo-blocks set to the drg dimensions, you won't have to calibrate them and you can also detect any wear before it causes a problem.

    BTW - "cheap" doesn't equal poor or sub standard quality. But if you don't pay enough and you are adding cost, the buyers/Purchasing manager needs to own that increased cost of your inspection, otherwise his boss is going to think he's better than he really is.
     
  10. hogheavenfarm

    hogheavenfarm Well-Known Member

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    Here is one similar to what I remember - DigiMax, farnell.com
    Disclosure - I am not associated with Farnell, or any other sales entity
     

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  11. Andy Nichols

    Andy Nichols Moderator Staff Member

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