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perfect circle on cylinder

Discussion in 'Tips & Tricks' started by scott pagan, Aug 21, 2019.

  1. scott pagan

    scott pagan Member

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    i have a project that will require a perfect circle when viewed on a tanker truck. i did a test install and the cut perfect circle looks oval when applied. i'm sure there is a math formula or trick to distort the cut circle so it will look like a true circle when applied.

    here is an example of what i am trying to do. customer is adamant about true "perfect" circle when viewed.
     

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  2. bannertime

    bannertime "You guys do banners, right?"

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  3. James Burke

    James Burke Being a grandpa is more fun than working

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    We deal with this a lot when we etch round logos on mugs.

    You need to stretch the vertical distance and make the decal an oval. The width of your decal must remain the same, but the new height of your decal will the length of the arc when the diameter of the decal is projected against the side of the tank.

    NOTE: Do your entire layout, including text and graphics and then stretch it to make an oval. Everything will distort to correct proportions when it gets wrapped around the tank....seem's crazy, but it works.

    I do all my calculations in AutoCAD. If you need, I can do a quick layout for your dimensions. PM me.

    If you want to take a stab at it yourself, here's an online arc length calculator. Circle radius (r) is the radius of your tank. For chord distance (S), input the diameter of your decal. Your new decal height will be arc length (l).

    Hope this helps.

    https://rechneronline.de/pi/circular-segment.php


    JB
    Arc.JPG
     
    Last edited: Aug 21, 2019
  4. woolly

    woolly Active Member

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    agree with above but i think to add to the problem the pic shows a oval in section tank best of luck
     
  5. scott pagan

    scott pagan Member

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    thank for all the great tips. another variable i forgot to mention. the tank is oval shaped (see photo).

    JB i may send some measurements when i get them back.

    thank you all !
     

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  6. James Burke

    James Burke Being a grandpa is more fun than working

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    Hard to tell, but the cross section of your tank does look like an oval. If that is the case, you're going to have to establish some sort of radius and then tweak things until you get the desired results.

    I would pen plot a small scale version on paper, hold it up against the tank and then adjust accordingly.

    JB
     
  7. James Burke

    James Burke Being a grandpa is more fun than working

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    This is where AutoCAD shines....give me the true-shape cross section of your tank in a (.dxf file, if possible) and the dimension of your decal and we can go from there.

    Some tank manufacturers may have .dxf specs online.

    If you think the tank is truly elliptical (which I'm guessing is the case), give me the overall height and width and we can give that a try first.

    JB
     
    Last edited: Aug 21, 2019
  8. bannertime

    bannertime "You guys do banners, right?"

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    Once you get that, there is a way to flatten that out right? Kind of like they do for packaging?
     
  9. Modern Ink Signs

    Modern Ink Signs Member

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    I’d really like to know in the end how much time and resources you end up putting into this project vs. the cost

    I picture several hours and various amounts of proofs/test prints


    What happens when you change the viewing angle? Hmmmmmmmm.....
     
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  10. James Burke

    James Burke Being a grandpa is more fun than working

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    No...that is this software: https://www.esko.com/en/products/studio-18/modules

    For the OP's project, we're basically looking for the length of an arc....either on a circle, or on an ellipse. That length will become the new height of the OP's circle decal.

    What you're describing is a bit different and requires more sophisticated software (3D/Solid modeling). Anything that can create a flat development from a solid model.

    Think of all the shrink wrapped labels on bottles now days.

    Isn't it amazing how everything is in perfect perspective when a full wrap-around label conforms like skin to some funky shaped bottle? That takes some pretty awesome computing power.


    Tale a look at how they do it here: http://www.claytowne.com/beats-digg...ve-label-shrink-sleeve-packaging-design-tips/

    JB
     
    Last edited: Aug 21, 2019
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  11. James Burke

    James Burke Being a grandpa is more fun than working

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    Just the same as if viewing any circular object at an angle...a wheel, a manhole cover...etc...it loses true shape and size and becomes an ellipse. I believe the main goal here is to get is as close to circular as humanly possible.


    JB
     
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  12. James Burke

    James Burke Being a grandpa is more fun than working

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    Just did a test run on AutoCAD and the process works well for determining a segment length of an ellipse. It took a bit of creativity to get usable numbers because ellipses do not contain any specific data other than minor/major radii and the lengths and coordinates of vertices.


    JB
     
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  13. equippaint

    equippaint Very Active Member

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    Would this work:
    Measure top to bottom height flat.
    Measure curve total length.
    Stretch the circle height the difference between the 2 measurements

    Edit: i think this is what jb already said
     
    Last edited: Aug 21, 2019
  14. James Burke

    James Burke Being a grandpa is more fun than working

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    Heck yes...scrap the math, assuming that you could accurately space masking tape on the tank that represents the top and the bottom of the decal.

    Looking squarely at the side of the tank, they'd be spaced at whatever diameter the decal measures. Then wrap a string around the tank between the two pieces of tape and use that measurement to stretch the decal.

    Definitely need to use something non-stretchy like the heaviest Spiderwire braided fishing line or fly line.


    JB
     
    Last edited: Aug 21, 2019
  15. equippaint

    equippaint Very Active Member

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    2x4 top and bottom to get flat measurement away from the curve. Roll a tape measure around it for the curve length. Its close enough for govt cheese as long as what I was thinking is correct.
     
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  16. Andy_warp

    Andy_warp Member

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    We have to think around geometry all the time around here. Things like locating logos...as shown on the left.
    The funnel (at right) is a weird one. We have to pre distort any type of long text or logos. If we don't, objects will appear to bow up due to the compound angles.

    Doubly curved stuff is where it gets trickier! Domes and spheres are a pain!

    The best thing I could have done as a printer was to learn cad and 3d modeling! It really cuts down on printing surprises!

    OP dilemma is a tough one. As stated before, it will only solve a single point perspective.

    Best of luck!
     

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  17. James Burke

    James Burke Being a grandpa is more fun than working

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    Yep...on smaller diameters the differences will tend be less and might be better served by crunching numbers or using CAD. It all depends on the project.


    JB
     
  18. James Burke

    James Burke Being a grandpa is more fun than working

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    Definitely. Looks like you're doing some pretty cool stuff.


    JB
     
  19. shoresigns

    shoresigns Very Active Member

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    What none of you are taking into account is perspective. If you stretch a circle into an ellipse that matches the chord:arc ratio when the height of the circle is supposed to be as large or larger than the tank, you might get a shape that appears to have 1:1 proportions like a circle, except it's going to look more like a superellipse, or more specifically a squircle.

    There might be a way to compensate for that using a 3D modeling tool like CAD. Not my area of expertise.
     
  20. Andy_warp

    Andy_warp Member

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    It's fun...but challenging!
    The dye sub process heats the fabric up to 400 degrees!
    We deal with tension, and stretch factors for fitment.

    Have had material go shrinky dinks...we did a 120' sign on specialty material...the heat shrank it to 116' ish!
    It was quicker and more cost effective to cut down the frame!

    It can get hairy!

    Rhino is great for surface geometry!
     
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