Saturday, October 19, 2013

Uhler-Birch Cripple Hip Rafter Method

I laid out cripple hip rafters the other day using three different layout techniques. After laying out the cripple hip rafters it was obvious that the Uhler-Birch Cripple Hip Rafter Method was the fastest and easiest method for laying out and cutting the cripple hip rafters.

I call it the Uhler-Birch Cripple Hip Rafter Method, because in the Hip Roof Framing article in the JLC magazine  by Tim Uhler, he said he likes to mark both hip rafter plumb lines on the same side of the hip rafter material so he doesn't have to flip the hip rafter material over to make the second plumb line cut at the hip rafter head cut. Richard Birch's One Length  could have been used with all three different layout techniques, but it seemed to be the easiest method to apply to this layout.

I wish I had taken more pictures of the process, but the drawings should show how simple the process is.










  1. Mark 2 Hip Rafter Plumb Lines the length of the Cripple Hip Rafter.


2: Use a scrap block the width of the hip rafter material and mark the second Hip Rafter Plumb Line


the width of the Hip Rafter Material.





3: Cut the OutSide Hip Rafter Plumb Line Bevels @ 45°


4: Cut the InSide Hip Rafter Plumb Line Bevels @ 45°





The main concept of the Uhler-Birch Cripple Hip Rafter Method is to use one length-dimension to mark off the length of the cripple hip rafter and use the width of the hip rafter material to layout the bevel lines of the cripple hip rafter.

Here's an example using 70 x 120 cm for the cripple hip rafter material.







9 comments:

  1. This comment has been removed by the author.

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  2. Sim,

    The Cripple Hip, or Broken Hip, (Rafter) is the bare essence of H/V rafter cutting. If the Effective Run of a Hip was equal to the Effective Run of a Cripple Hip, the only differences in the two rafters would be a Birds-mouth and possibly a tail. The geometry of the Cripple Hip would be a match for the Regular Hip, both in length and Cheek for Cheek . The Regular Hip back bevels offsets for standard 1-1/2" thick materials can be marked with the Tongue of the Framing Square.

    Also depending on which saw is being used, you may be able to forgo the extra lines because the saw has a scale that can be used to guide the cut at the required thickness offsets. I have never seen a worm-drive saw with such a scale but many sidewinders come with scales or it is easy enough to mark the extra offset mark on the foot plate yourself. Very easy with Regular Pitch H/V Rafters.

    If you are familiar with your saw and have the confidence that comes with experience from using it, then knocking out these diamond cheek cuts becomes as routine as making any other rafter cut, and rarely any extra lines would be needed. But for an JLC articles sake, and for the readers benefit, the extra lines are needed.

    The way this concept also applies to Irregulars is the real secret that breaks the code for complex multi-pitch roof cuts.

    RB

    ReplyDelete
    Replies
    1. Yes, using a framing square or the saw as a guides works for 2x lumber in the USA, but not in the UK, Ireland, Australia, New Zealand, France, Germany, Russia, South Korea, Belgium, Brazil, Spain and all the countries that don't use the Imperial/English Inch base 12 for their lumber.

      The main concept of the Uhler-Birch Cripple Hip Rafter Method is to use one length-dimension to mark off the length of the cripple hip rafter and use the width of the hip rafter material to layout the bevel lines of the cripple hip rafter. This makes the method universal. Whether you're using inches or centimeters. It also works with 4x or 300cm material as well.

      Delete
  3. This method has been around for years and is called the hopper cut , layout parallel lines the stock thickness apart and connect across the top and PRESTO the layout line for the cut

    ReplyDelete
    Replies
    1. Where did the term "hopper cut" originate? And what type of saw were the "hopper cut" sawyers using? (Worm-drive or Sidewinder)

      They way the "hopper cut" is described, with two parallel lines spread by the materials thickness, w/ 45* bevels, at each end of a board, it must refer to regular pitch H/V rafter cuts only?

      The reason I ask is because I was taught to make these cuts in the early '70s with the PC-315 saw and w/o the extra lines. The same guide on the 315s was good at any angle, zero to 45*, no variable site line as is common on the newer saws.

      Delete
  4. Hopper Cut
    French -- Trémie coupé
    German -- Trichter geschnitten

    ReplyDelete
  5. Radford's cyclopedia of construction: carpentry, building and architecture, based on the practical experience of a large staff of experts in actual construction work, Volume 8
    William A. Radford Alfred Sidney Johnson - January 1, 1909
    The Radford architectural Co. - Publisher

    Hopper Cuts are similar to the cuts required for fitting boards in or over a valley or hip roof; consequently the figures on the square that give the cuts for the roof boards must give the cut for a hopper of the same pitch.

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  6. If I am understanding what Billy said and what is in Radford's, the 'Hopper" is the process of developing the required compound miters found on H/V roofs, including the Hips, Valleys, and Jacks. Billy's example is for regular pitches, and squares are also limited to Regular Pitches as found on both the "Side Cut ..." scales, (per Radford's).

    "Irregular Hopper"
    The development of the bevel angles is proportionate for irregulars. Mjr/Mnr * stock thickness, and Mnr/Mrj * stock thickness. (Plan-view ratios)

    It is the "Equal Height" relationship of the long and short points found on H/V rafters, to the "One Length" found at both "Sides" (shoulders) as well as the (top) "Center" that seems to be absent in most of the books. (at least most of the American Books, except the "Swanson's") Sort of a "void" in the process of H/V rafter cutting as it seems they didn't connect the dots, or maybe just not enough emphasis on the significance of the "Hopper" geometry that is found at both ends of the H/V rafters.

    The missing link that my "One Length Method ©" completes.

    ReplyDelete
  7. Way off the subject, butt relevant to roof framing geometry is the book Will Holladay used as a reference and recommends in his book, Simplified Roof Framing by Wilson & Werner. The book was written by two teachers in the trade schools in Los Angeles in 1927 who wrote:

    While a knowledge of mechanical drawing and geometry is an invaluable aid in the study of roof framing, and these subjects form the foundation upon which much written material is based, yet the subject can be studied and mastered without this background.

    If I blame anyone for the poor understanding of roof framing it has to be these two teachers, and it's no wonder that the carpenters in California SUCK at roof framing geometry that is the basis of roof framing. It can not be mastered without a full understanding of the basic geometry of roof framing and it shows in Will Holladays book.

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