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Thread: Metrology for the cabinetmaker

  1. #61

    Metrology for the Cabinetmaker - Page 4

    Johansson Blocks or ‘Jo’ blocks are a gauge block system for producing accurate lengths. These are lapped to size and calibrated by Mitutoyo, the deviation from standard is provided in a sheet and measured in millionths of an inch, they’re effectively perfect to my ability to measure.
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    1,2,3 and 4,5,6 blocks are similar to Jo blocks but they’re not quite as accurate in most cases. These blocks are ground square and to size. These are a fairly inexpensive set of blocks that I use for setup on the milling machine (mainly). They’re also handy for other forms of setup and reference. The block is being used as a stop in this situation.
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    Standardization

    With our inspection tools in place we can begin the process of checking them to ensure that they are reading accurately. ASME outlines exactly how to calibrate inspection equipment, however for the purpose of this post I will detail my own more basic process. The goal of this exercise is to ensure that all of the tools are reading within a reasonable degree of one another. That degree varies depending on the tool class and its manufacturer spec along with the requirements of the workshop.

    Initial testing will be conducted with the use of gauge blocks. I make assumption that the gauge blocks are accurate and one can reinforce the quality of that assumption by measuring multiple blocks with each instrument. These blocks are certified and come from a manufacture held to international quality standards for accuracy, they’re graded for accuracy and provided with a certification.

    These blocks are made to be accurate to size at 20 degrees Celsius (68 degrees Fahrenheit), so the first thing to be aware of is the temperature being measured it. Steel expands at a coefficient of 0.00000645 per inch degree F, so a 4″ block could increase in size by .0005″ if it were measured at 90 degrees rather than 68 degrees. Doesn’t sound like much, but that always depends on what your after and it should be calculated for when measuring outside of 68 degrees.

    In order to eliminate possible variables I decided to check a few things before getting started with comparison testing. My first step was to apply compound to my granite plate and check my indicator bases for contact. My indicator bases are flat so I won’t need to worry about them rocking and causing a false read during any of the tests. I’ve verified all squares against each other and against the angle plate, they all agree with one another, save for the combination squares which deviate by a couple thousandths except the mini Starrett.

    Using the standards I begin by checking my calipers. It’s important to have the feel for measuring down pat, but having a number of years on micrometers and calipers I have a consistent feel. The calipers much be clean where they will touch measuring devices and the standards must also be clean. I oil things between uses and so I wipe the oil off before starting. This should be done with multiple standards to see if the error remains constant or if it increases.

    The main jaws I measure in three places using the thin side of the measuring block to ensure that the jaws are parallel to one another. These are spot on, so far, measuring exactly as they should.
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    Next I measure the standard using the back of the main jaw, this provides a deviation of .0015″. More than I prefer, but it’s within a reasonable standard, especially for a part of the tool I don’t much use.
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    Next I measure the prob, while the measurement doesn’t show in this photo, it is 2.000″
    xv7rqMNoSbuyQV0zsrqZ3Q-2150841826-1564283444310.jpg
    Last edited by Lee Schierer; 08-06-2019 at 4:53 PM.
    Lee Schierer
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  2. #62

    Metrology for the Cabinetmaker - Page 5

    Next I check the depth micrometer and the outside micrometer to ensure that they’re reading accurately. The first step I take is to ensure an accurate zero position. This is one in which the dial stops at exactly 0.00000″ when the spindle closes against the anvil on the micrometer and when the spindle is flush against the surface plate on the depth micrometer. The digital aspect of the gauge can be easy reset to zero if it reads otherwise. I use the micrometer’s ratchet’s to ensure that the positions are closed down to accurately.

    After which I want to establish that the micrometer is reading distances accurately, so I use two blocks, one in the middle of the range and one at the extreme of the range to ensure that these measurements are accurate.

    It’s important that the tools be in good order as well, in this case the depth mic shows staining on the side of the spindle, this is due to how it was stored before I received it. The spindle is in the process of being replaced and the new spindle will be calibrated again once it arrives. Its important that precision instruments be kept in good condition, their tolerances can be deteriorated by rust.
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    Last edited by Lee Schierer; 08-06-2019 at 4:52 PM.
    Lee Schierer
    USNA- '71
    Captain USN(Ret)

    My advice, comments and suggestions are free, but it costs money to run the site. If you found something of value here please give a little something back by becoming a contributor! Please Contribute

  3. #63

    Metrology for the Cabinetmaker - Page 6

    The same procedure is applied to the height gauge, first setting it to zero using the surface plate.
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    The digital indicator is affixed to a comparator stand. The probe is mounted so that it contacts the top of the anvil, then the indicator is set to zero. The probe is lifted, checking blocks are slid into place and the probe placed on the blocks. This measures the amount of travel. A comparator stand maintains a square position for the indicator so the travel is accurate.
    4dIrQAdSmu3B2VgeNB2HQ-3790231237-1564576565684.jpg VVmPqlrQGKXI4z8agJwWw-2049820915-1564576583373.jpg

    In the next post of this series I will begin detailing my process for standardizing machine fence read outs and specifying a few cases where transferring measurements is an improvement in accuracy and expedience. Thank you for reading this post and I look forward to your comments.
    Last edited by Lee Schierer; 08-06-2019 at 4:52 PM.
    Lee Schierer
    USNA- '71
    Captain USN(Ret)

    My advice, comments and suggestions are free, but it costs money to run the site. If you found something of value here please give a little something back by becoming a contributor! Please Contribute

  4. #64
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    Thank you, Lee!
    Bumbling forward into the unknown.

  5. #65
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    I don’t understand the criticism of this thread. Some are happy to mark with chalk and cut with an axe, which is fine in some situations. Seeking to better understand ALL of the factors that influence the final outcome does not diminish craftsmanship, nor does it dishonor the wood. Using machinist tools to set up our tools seems very sensible. Indeed, it seems to be the best way to make sure the only variable is the wood.

    A deeper understanding of the process is simply additional knowledge; additional knowledge/understanding is inherently a good thing.

    Less knowledge and less understanding of any subject would seem to present more danger. One need not always use the entirety of the font of knowledge they are able to acquire, but that reservoir of information/understanding can only add to the overall appreciation of the risks/dynamics, and thereby help avoid problems or solve them when they appear.

    I didn’t perceive that Brian was advocating that one must do anything “his” way. He was prompting a thoughtful discussion.

    Even those that just read comic books (or “graphic novels”?) wouldn’t suffer by being exposed to prevailing thoughts on literary analysis as to the structure of a novel, or why Melville’s Moby Dick is considered important, nor what Cervantes was addressing in Man of La Mancha/ Don Quixote, or why that English fellow who wrote all those plays is still quoted (and, often as not, misquoted . . . . “The lady doth protest too much, me thinks” rather than vice versa) frequently today. Breath of knowledge can only be of benefit. Being familiar with William Shakespeare does not mean that we must speak like him.

    No wonder this forum is dying a slow death.

    Brian, i believe - despite my pessimism - many here still have open minds and are appreciative of the information and content you provide.

  6. #66
    Quote Originally Posted by Brian Holcombe View Post
    Thank you, Lee!
    No problem, if you do future posts, remember that photos are limited to 8 per post so immediately make multiple replies to your own post so that you will have consecutive space to cover your entire post with many photos.
    Lee Schierer
    USNA- '71
    Captain USN(Ret)

    My advice, comments and suggestions are free, but it costs money to run the site. If you found something of value here please give a little something back by becoming a contributor! Please Contribute

  7. #67
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    Some of the discussions remind me of this particular piece of sage observation, rendered in a timeless artistic fashion.
    dilbert _ the right approach.png

  8. #68
    This is the appropriate venue for the OP's topic. Set up and measurement applies to all 'types' of woodworking. Given that his article is a reflection on his desire for efficiency for production, repeatable work, one might argue that it's MORE appropriate here than in Neander. The OP usually posts there, so I am sure his decision to post here was not cavalier.

    I think we don't give the 'beginner' enough credit. They can appreciate a variety of threads for what they are.

  9. #69
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    Thanks, Patrick. I’ve gotten a lot of positive respondents here and via email. I am glad that many people find it useful or thought provoking.
    Bumbling forward into the unknown.

  10. #70
    When is part 2 coming?

  11. #71
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    One's "art" is whatever one wants it to be. Some artists throw paint on a canvas with a brush (Pollock) and others will be technical masters (Degas).

    I love Brian's work. If I had the means, I'd hire him to build me something : )

    To each his/her own.

  12. #72
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    Thanks, Andrew!

    Dan, maybe never. Probably in a few weeks.
    Bumbling forward into the unknown.

  13. #73
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    I have not been around much “working” like freakin crazy again.

    But it seems to me you might and I say might be keeping the nightly skilled talented portion of this website kicking at the moment.

    I agree all perfective are of value and interest. Depending on where one starts and ends and is in the process clearly ones interest will be peaked by beginner topics, intermediate or advanced.

    What I think is important here is that if you don’t know the question to ask you can’t seek the answer. And this website from my infancy in cabinet making offered me many perspective of many people at various stages of the learning or execution curve. I found that extremely valuable.

    I personally even when in the infancy stages find the advanced topics and or subject matter most useful as if you read between the lines there is so much to learn.

    It takes so much of ones time to share even on a forum based platform. Without those willing to take that time and the desire to share we are all left where we were 20-30 years ago to learn. A library, paying for instruction of some sort or if you like me teaching yourself.

    Anyway, thanks Brian and hope life is well.

  14. #74
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    Glad this thread is back! I’ve enjoyed it and absolutely think it belongs here. Some recent machine restorations have peaked my interest in metalworking.


    My business is millwork and joinery and the thread has me thinking about how my measuring process has evolved over 40 years. No doubt it’s possible to do first class work with minimal measuring methods. In my early days precision measuring was done by pulling a inch on the tape. Advanced and more precise measuring can make machine repeatability- setup quicker and more accurate. The days of producing large quantities of woodwork are gone, now it’s more about small batch sizes and one off work in the custom sector. And also for the home shop that wants to work more efficiently.


    No machinist skills here but I have some thoughts on how woodworking machines can be adjusted and maintained for accuracy with a few tools. For machine setup it think the essentials are a couple good squares, ( the Lamb square is my favorite) a good straight edge, feeler gauges, digital height gauge, dial indicator, digital calipers and a protractor. The protractor and cheap dial indicator are marginal and on the list to upgrade. The long measuring stick in the photo is for site measuring and should not be in the picture for machine setup.

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    For checking wood parts for accuracy the digital calipers, small Starrett square, tape, folding rule and 10 mm square bar are my go to. Last picture shows how the square bar is used.
    I work in millimeters and find 0.1 or 0.2mm is close enough for most joinery. That’s about .004-.007 inch.


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  15. #75
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    You can quibble about the proper forum for this topic but Patrick is right to point out the value of sharing information, especially when it comes from a craftsman with technical expertise who can write clearly. I can't link to it, but there is currently an intriguing thread about handrailing and stairbuilding on the architectural woodworking forum at woodweb with reference to what might be the market value of a book on the field by a working professional who can't take the time from making a living to document how he does it. How much would you pay for a new classic on stairbuilding, or whatever branch of woodworking you are devoted to- and how much are you willing to pay to keep this site going?

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