Scraping perpendicular surfaces questions
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    Question Scraping perpendicular surfaces questions

    Hi, I'm building a little fixed gantry cnc mill and I struggled a little bit with scraping surfaces for rails installation. I understand how to scrape them flat but I can't find a way to scrape them perpendicular.

    Here's a picture of what I want to achieve.

    img_20200606_213139-2.jpg

    My tools are scraper, granite plate, dial indicator and try square.I don't have access to big machines like mill or lathe.

    The problem is that it's not continuous surfaces but just stripes and my square is smaller than gap between them, so I can't figure out how to check them for squareness. Is it even possible in this case? If possible what would be the easiest way to do so in terms of required tools?

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    Another option to consider is a replicated joint.

    Scrape your rail mounting surfaces flat (single plane).
    For the column mounts you either have a series of set screws or a firm but compressible material (copper wire is one option) around the mounting perimeter. You use the mounting bolts and the set screws in opposition and precisely align the column / axes.
    When all aligned you inject epoxy (making a 'replicated joint').
    Specialist epoxies for just this purpose exist.
    If you want to take it apart in future, wax one side of the joint well. Pin the joint for alignment.

    I haven't given all the details. There are guides and videos on how to do this.

    Advantage is that you don't have to scrape the parts for perpendicularity. You are handling alignment at the same time so takes care of a few issues.

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    He still needs a acurate enough 90°reference

    Peter

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    You may be able to get the accuracy you need by using a right angle artifact (RAA, steel or granite) to go from the vertical to the horizontal plane. This could work for you: China High Precision Granite Right Angle Ruler - China Granite Right Angle Ruler, Granite Square L Shaped Tri Ruler but you might find better choices with additional searching.

    Even if the RAA isn't tall enough on its own, you can scrape some spacing parallels to raise it up high enough to engage the upper rail mounting strips.

    Your "try square" is almost certainly not accurate enough to make a precision right angle. The RAA I linked is doubtless low grade, but still should be closer than what you have now. If you buy two you can check your current square and other features by doing A:B:C: comparisons (angle 1 to angle 2, angle 2 to angle 3, angle 3 to angle 1 - if they all mate correctly, each one is accurate).
    Last edited by Milland; 06-15-2020 at 05:59 AM. Reason: scrape, not scrap...

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    The OP may want to add a sensitive level to his list of tools. One with a 90deg face would be even better.

    L7

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    A rounded nose surface gauge can be fabled-up to transfer the check of a good square block as reference to check your part.
    Just a block with two parallel sides and a little out of square can be the master, you just have to figure in the out of a square condition of the master. Perhaps the master is .005 mm off so you add/subtract that...yes likely need a true surface to do your gauging on.

    A surface gauge that has a V notch at one end can be used with putting a ball or good round thing in the v like the OD of a bearing.

    Vintage Starrett Surface Gage #257-A, Original Box | eBay

    This so from one point to another you can make a right angle. yes, likely still need a precision straight edge to go from one point/place to another.
    Last edited by michiganbuck; 06-15-2020 at 10:16 AM.

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    If you're spindle carrier and it's rails were finished you could (tram) the upright to the finished bottom rails with your indicator

    No new tools needed

    Bravo and good luck on this very ambitious project

    Ps have you read Moore or Connlley?
    If not you NEED to

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    Thanks for replies
    Quote Originally Posted by Milland View Post
    Your "try square" is almost certainly not accurate enough to make a precision right angle.
    I think I named it wrong. I have a din 875 square, exactly like this one:
    abea59314d1aaae133ffbc94b389.jpg
    Of course some granite or cast iron square with higher precision class will be better, but it quite expensive.

    Quote Originally Posted by lucky7 View Post
    The OP may want to add a sensitive level to his list of tools. One with a 90deg face would be even better.

    L7
    Like this one?
    ae5899cb7a43bafc620d096f1366318bc1b97ba1_____099530.jpg
    Maybe I can buy one, but I don't know how to use it in my case.

    Quote Originally Posted by michiganbuck View Post
    A rounded nose surface gauge can be fabled-up to transfer the check of a good square block as reference to check your part.
    Just a block with two parallel sides and a little out of square can be the master, you just have to figure in the out of a square condition of the master. Perhaps the master is .005 mm off so you add/subtract that...yes likely need a true surface to do your gauging on.
    It is a good way to go, but I still need a bigger square and straight edge. So far it seems like the only solution so maybe I need to make them myself.

    Quote Originally Posted by Hbjj View Post
    If you're spindle carrier and it's rails were finished...

    Ps have you read Moore or Connlley?
    If not you NEED to
    They are not finished.
    Thanks, I didn't read but definitely will.

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    I'm going to address the issue of the horizontal bearing surfaces only covering a small fraction of the "frontage" of the vertical bearing surfaces. If the original bearing surfaces protrude above the cast peanut butter, place a precision parallel across them. You can then rest the square or RAA on the parallel and access the width of the vertical face. Better would be a matched pair of precision parallels. (Parallels for vise work are not what I am talking about. You want nice fat ones.)

    If the horizontal bearing surfaces do not protrude above the cast peanut butter, you will need a set of matched spacers, with surfaces either ground or scraped parallel and equal distances apart. Put those on the bearing surfaces, and rest your precision parallels on the spacers. I would probably surface grind spacers as a set, and call that good after a quick sanity check with a micrometer at three places around the perimeter of each spacer.

    If you happen to have a surface plate that is parallel on the top/bottom, not just flat on the top surface, you can obviously use that instead of one or a matched pair of precision parallels.

    In a pinch, you can make your own parallels, especially if you don't care about hardening them. If you buy used ones, you need to evaluate them and probably correct them (knock off burrs if nothing else).

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    Quote Originally Posted by vnuEndru View Post
    Thanks for replies



    abea59314d1aaae133ffbc94b389.jpg



    Like this one?
    ae5899cb7a43bafc620d096f1366318bc1b97ba1_____099530.jpg
    Or like this

    img_6528-1-.jpg
    img_6529-1-.jpg
    img_6530-4-.jpg
    img_6525-2-.jpg




    Denis

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    It would be very helpful to know the length and width of each way, the distance between them, and the height of each of the ways above the base. It would also be helpful to know the length and width of the surface plate, and the lengths of the square base and arm.

    Were you able to use the surface plate to spot and scrape the two pairs of ways at the same time? Are the two pairs of ways in the same plane?


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