Rounded surfaces

Discussion in 'Tips, Tutorials & Tools' started by Arjun, Dec 2, 2006.

  1. Arjun

    Arjun Member

    Some models require rounded surfaces. I've tried making prisms with flat surfaces, then rubbing into them with something round to make the surfaces rounded. Is there a better way to do it? How can I do it for spherical surfaces? I'm talking of something like a ball or a tyre.

    Then there's the task of making a model that's prismatic on one side and cylindrical on the other. How can I do this? Something like a pencil or an engine of a fighter aircraft.
  2. marian

    marian New Member

    In a strict sense paper can only be curved in one direction. So you design a
    model by decomposing it into parts where each is only curved that way.

    An aircraft fuselage may be made up from several sections round around the
    hull and straight along the axis. So when viewed from the front you get round
    cross-sections, viewed from the side you get a prism.

    To a very limited extent paper can in fact be bent to make compound curves.
    You can use moisture to soften it, and such tricks. But this generally is used
    on small scales only.

    To make a ball you either cut it up into segments like an orange for a round
    side-view and jagged top-view or into a series of cones making it look round
    when viewed from the top and prismatic when viewed from the side.

    Tyres are often built up solid from thick card and sanded into shape but can
    also be decomposed to only curve in one direction.

    You find the intersection of the cylindrical and the prismatic part and unroll
    accordingly. Although perfectly possible that is rather hard to do by hand,
    older books about working with sheet-metal have instructions for common
    cases. These days it is much easier to do it with CAD-Software.

    In the screenshot I used a program called Rhino. I made a hexagon, extruded
    that for the shaft of the pencil. Then I added a cone for the tip. I trimmed
    both surfaces to their intersection. The resulting 3D-surface is at the bottom.

    I then unrolled both the shaft and the tip. The parts are at the top. Export
    into a 2D program like Inkscape. Color, texturize, add connecting strips and
    you have a card model kit of a pencil.

    Attached Files:

  3. A perfect compound curve in paper is pretty much impossible with one exception. That is make a master from another material, produce a mold from the master and cast the part in paper. For an good discription of this ask Gil. He's the resident materials guru. The traditional sphere composed of lunes or conic sections can actually be combined into a "sphere" made up of facets ala the test build on this project


    Like the Lune or Cone method it is not perfect
  4. popala

    popala Member

    Have you guys seen this cowling from a construction report on This is just one example of compound curves in paper. I deeply believe that NOTHING is impossible in paper :) All one needs is a lot of determination to experiment with new ways of doing things.

    Btw: the author said that individual pieces of this cowling were not touched up on edges.

    [​IMG] [​IMG] [​IMG]
  5. Amazyah

    Amazyah Senior Member

    That cowling looks awesome!

    I cannot think of anything else to say about it except that I would love to see the process that produced it!

  6. ekuth

    ekuth Active Member

    Moulding with wet paper? No, that would destroy the ink print...


    Ahh, okay I see. Looked at the link and a few posts up from these pics, they give better pics of the inside. Standard technique, just done in very exactly placed thin strips that are butt-edged together. Very nice work.
  7. cmdrted

    cmdrted Active Member

    WOOOWWWW!!!! In one short series that example set me back to the stoneage! Amazing!
  8. popala

    popala Member

    In the original thread, in the pictures above the ones I posted, the author shows the first version of the cowling. The lines on the kit's original parts were out of alignment and the publisher issued a correction in the Kartonowy Arsenal 04/2005 (Bf-109F). The cowling in pictures above is a second attempt, made using the corrected parts. It was made using "round tip + eraser" method, described in Lukasz (Swinger) Ju-88 construction report (give it time to load and scroll), in the post highlighted in the link. Second picture down, top/left corner has a thumbnail demonstrating this method and tools.
  9. Arjun

    Arjun Member

    I can't understand a word of what's on those pages, since I don't know Polish. Someone suggesting wetting the rounded surface a little and then tapping it, but the finish won't be too smooth and even. How do you get a better finish?
  10. rjm

    rjm Member

    Hi Guys 'n Gals,
    I'm wondering if someone could develop a small version of
    what the Guys in Orange County Choppers or Boyd Coddington's
    Hot Rod Show call an "English Wheel" used to put compound
    curves in metal body parts.
    I know they are probably rearrainging molecules under pressure,
    but we have been talking about paper having "grain" so maybe
    it could work. ?
  11. Arjun

    Arjun Member

    Are there any Maya users here? I've got MayaPLE8, so I'd like to know how I can create these surfaces, and then develop them, which will help in making plans.
  12. cdavenport

    cdavenport Member

    Funny you should ask about an English wheel. I went to my friend's machine shop and made a version. I'll test it out to see if it works as I think it should. My digital camera is out.

    I'll post some plans if this thing works.
  13. cdavenport

    cdavenport Member

    I just tested my "English Wheel" out and it works reasonably well. The limitation is the structure of the card. Unlike metal which is a crystalline solid whose atoms can be rearranged, paper is made from essentially plant cellular tissue which overlaps in strands held together in a matrix of chemical bonding agents.

    In short, whereas soft metals are extrememly malleable, our paper card is only slightly so. The real problem is at the edges where the card has a tendency to crimp on itself. In metal, you can force the atoms to rearrange themselves to eliminate crimps and bumps. You cannot with card.

    At least that is where I am at now. I am going to try a couple of binders and liquids to see if I can soften the card without adversely affecting its surface finish.

    Guidance from anyone out there with some chemical knowledge pertinent to this investigation would be greatly appreciated. I am a mechanical guy.

    The good news is that you can make your own set of "wheels" out of wooden dowels and balls from the hardware or craft store.
  14. Gil

    Gil Active Member

    The Art and Zen of Forming Paper...,


    First, forming paper in such a manner is a combinatorial art and requires patience to master.

    Some things that you need to know.

    1.) The paper must be treated with instrument lacquer which is another name for nitrate dope. The dope will not degrade print quality nor will it yellow with age. The dope should be thinned with acetone and applied liberally to the parts to be assembled. The doped surface also allows any excess glue to be easily removed. Acrylic spray sealer will work but not as well.
    2.) Thinned PVA (Poly Vinyl Acetate or plain white glue) should be used for all glue joints. It's important that it be thinned as the extra moisture is required for the process to work.
    3.) A backing surface must be prepared before any burnishing work. The backing acts as an "anvil" against which the wrinkles are worked out through the burnishing process. It must at the very least conform to the area of the surface which is being burnished "down". This can be accomplished from the back or the front surfaces. The use of a vinyl eraser has become popular since its "invention" sometime ago. A nice addition to any builder is a block printing pad called soft cut. It's available in several different sizes and is basically one big vinyl eraser. Having several on hand will come in very handy especially when thin walled, small diameter paper tubing is desired.
    4.) A layer of plastic wrap to cover the surface being worked is recommended to prevent abrading the paper surface.
    5.) An assortment of burnishing tools. These can range from hand carved "spoons" from hardwood to actual kitchen spoons. Japanese boxwood forming tools can be found in most all art stores. I have an assortment of dapping punches which consist of varying sized polished spheres on the end of rods and are the preferred tool for burnishing cowls.

    The Art

    Assemble the cowl. The assumption is that the cowl design is segmented enough to closely approximate the desired curve before burnishing commences. Gently begin burnishing each segment against the burnishing pad with the burnishing ball. Work each segment gently around its circumference till it becomes better blended with the other segments. A small ball will slightly stretch the middle of the segment a lager ball will not stretch the segment as much but instead works to blend the segments with the other segments. This is where you must judge which tool size to use. Note also that the assembly is not allowed to dry but is worked damp with the thinned PVA glue. Working the ringed segments in this way will, in short time, blend the segment rings into a smooth continuous curve. Working the surface has the additional benefit of closing up the joints or "mushing" them together. Note also that the plastic wrap wasn't required for the cowl burnishing as the vinyl surface is soft enough not to cause any abrasion problems. Make sure that it is kept clean and dry while working. Plastic wrap is used in cases where the burnishing work is done directly on the printed surface. It helps preserve the surface from being abraded by the burnishing process.

    Don't expect to become an expert the first time out. Make scanned copies of the piece and practice till you become proficient. It doesn't take long to master but does require some persistence to master.

    This technique can be used to form all sorts of curved surfaces with a high degree of success but always perform practice runs on sacrificial scanned copies.

    Good Luck!


  15. cdavenport

    cdavenport Member

    Excellent dissertation, Gil and one easily followed. Based on what you have written, I just machined a series of burnishing balls and conical shapes. Each has a shaft that slides into a couple of ball bearings which are, in turn, mounted inside a knurled brass handle. This allows each burnishing shape to rotate freely. I am looking forward to trying them out using your technique.

    Merry Christmas

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