Building a one-meter vegetation sampling frame
 
 
  The assembled frame encloses an area one meter square.  For transporting the frame and  threading it through vegetation, the frame comes apart into four sides, or bars.  The bars are identical, so the assembly instructions are for one bar.

 One meter may not seem like much in open space, but hiking with the bars through brush, hauling them around in a crowded rig, or putting them through airport checked baggage can be awkward.  Therefore, most of these plans are for "collapsible" versions -- you can fold up the bars to take less space.  We also give a non-folding version, and "ultralight" versions.

  The collapsible bars fold up to about one third the length.  They work on the same principle as the shockcorded poles of dome tents.
 

Representation of a specific brand name or company does not imply a recommendation by us.


Folding sturdy PVC frame:
 
  Materials for one bar are:  Three sections of PVC pipe, two straight couplings, one 90 degree elbow, a length of elastic shock cord, and marking material.  Here is the parts list for the four bars that make up a complete sampling frame.

  These illustrations show "Schedule 40" PVC pipe, which has a wall thickness of about 3 mm (1/8 inch). You can use a lighter weight pipe such a "SDR 13.5", which has a wall thickness of about 1.5 mm (1/16 inch). This will be sufficiently sturdy while saving some weight.
Item How many you need Comments Click an image for larger view
PVC 90 degree elbows, half inch (nominal) 4 All this PVC is "nominal" half inch.  They call it half inch even though the inside diameter of the fittings (and the outside diameter of the pipe) is actually about 21 mm (7/8 inch).
PVC straight couplings, half inch (nominal) 8  
PVC pipe, half inch (nominal), ten-foot sections 2 This kind of pipe usually comes in ten-foot lengths.  You will need two of those to cut the 12 thirteen-inch sections you need.
Drill and 5/16 inch bit to use If you are constructing a frame while on the road, many hardware stores will drill the holes for you.
Elastic shock cord, 1/4 inch (7 mm) diameter 12 feet  
Black electrical tape (or black paint) one roll For marking calibration bands on the bars.

 
Drill a hole in the back of each 90 degree elbow, as shown.
 
   Cut 12 PVC sections 33 cm (thirteen inches) long.  This size allows for the length added by the connectors, and the length that will slip into them.  The finished frame fits almost exactly one square meter.

  You can cut the PVC pipe any number of ways.  If you are on the road, hacksaw blades are cheap and effective.  You can wrap one end of the blade with tape to make it easier to grip.

  There is no need to "bevel" the ends of the pipe sections.  Beveling will spoil the stiffness of the finished frame.

Drill a hole in the side of three of the PVC sections (one for each bar).
  Drill the hole about 33 mm (1-1/4 inch) from one end.  This distance is not critical.  It must be at least as far as the length that will slip into an elbow, 22 mm (7/8 inch), but it can be as much as 5 - 8 cm (2 - 3 inches).

  If you are having the holes drilled at the time you buy the pipe, drill them in each end of the two ten-foot sections.  Then you can cut the four needed 33 cm (13-inch) sections off of those ends.

 
Push one end of the shockcord through the side hole.  Easiest, from outside in, then down the inside of the pipe section.
  • When you have the shockcord through the pipe section and can get enough to work with, thread components together as shown:
    • pipe section with side hole
    • one straight coupling
    • a pipe section with no side hole
    • a second straight coupling
    • another pipe section with no side hole
    • a 90 degree elbow
      Thread the shockcord out the hole in the back of the elbow.
     Tie a knot close to one end.  Pull that end snug to the hole.  Bring the PVC pieces together so the shockcord is just about the same length through them.  Then, pull the shockcord out about a foot so it is stretched.
    Tie a knot close to the second hole.

      You can test it at this time to see if the tension feels right.  You should be able to pull the PVC sections apart easily and fold up the bar.  But when straightened out, the shockcord should hold the pieces tight enough together they don't slip apart by accident.  There is no need to glue the PVC sections together.

      When you are satisfied with the tension, you can tighten up the knot and cut the shockcord off to about an inch (few cm).

      Marking the bars in 10 cm bands of alternating color will make it easier to visually estimate percents of the enclosed 1 square meter area.

      Electrical tape is a convenient way of marking the bands.  Less messy than paint, plus it holds the ends of the shockcord from fraying.

     If you use the wrapping pattern shown, all the cut ends of the shockcord will be covered.

      While wraping the tape, simply skip up and over any couplings you come to.
      Note that tape is free of junctures, so segments can come apart
      Make the other three bars the same way.  It will be easier to get the shockcord threaded through the bars if you do not cut it first.  When you are done, you will have a length of cord left over.  You can tie this into a ring and use it like a big rubber band to hold the folded up frame all together in one bundle.
      To assemble the frame at a survey site, you push the "empty" end of a bar into the open side of the elbow on another bar.  This usually holds together for the minor movements of adjusting the frame position on the ground, but comes apart easily to go around stems and brush.


    Variant:  Non-folding PVC frame:

      To avoid the complications of the folding junctions, we offer this straight version.  Some people prefer this design and use the bars as walking sticks.
     
    Item How many you need Comments
    PVC pipe, half inch (nominal), ten-foot sections 2  
    PVC 90 degree elbows, half inch (nominal) 4 All this PVC is "nominal" half inch.  They call it half inch even though the inside diameter of the fittings (and the outside diameter of the pipe) is actually about 21 mm (7/8 inch).
    PVC glue    
    Black electrical tape (or black paint) one roll For marking calibration bands.

      Cut four sections of pipe, each 39-3/8 inches (about one meter) long.  If you are being precise, make them 99.8 cm to allow for length added by the elbows, but this is usually negligible.  You will be able to get three pieces out of a ten-foot length of pipe, but you will need another ten-foot section for the fourth bar.
      Glue one elbow onto one end of each bar.  It is necessary to glue them or the frame falls apart too easily in use, and the elbows get lost.
      Wrap with black tape, or paint bands, to mark the tenths of meters.


    Variant:  Lightweight folding PVC frame:

      This is the same as the regular folding frame except you use (nominal) half inch CPVC pipe and fittings.  This type of pipe is usually cream yellow in color, and much thinner and lighter.  Even though both these kinds of pipe are called "half inch" the CPVC is about half the size of the "regular" PVC pip3.  You can use thinner shock cord, or even flat elastic (from a fabric store) in a pinch.
     
    Item How many you need Comments Click an image for larger view
    CPVC half inch (nominal), 90 degree elbows 4 All this CPVC is "nominal" half inch.  They call it half inch even though the inside diameter of the fittings (and the outside diameter of the pipe) is actually about 16 mm (5/8 inch).
    CPVC half inch (nominal), straight couplings 8  
    CPVC half inch (nominal) pipe, ten foot lengths 2 This kind of pipe usually comes in ten-foot lengths.  You will need two of those to cut the 12 33-cm (thirteen-inch) sections you need.
    Shock cord, 4 mm (3/16 inch) diameter, or flat elastic 18 mm (3/4 inch) wide. 12 feet  
    Drill and 3/16 inch bit to use If you are constructing a frame while on the road, many hardware stores will drill the holes for you.  
    Black electrical tape one roll For marking calibration bands on the bars.

     
     Construction is the same as the folding frame above except that holes are 3/16 inch, and must be at least 14 mm (1/2 inch) from the end of a bar section.

      This design is a welcome saving in weight on long hikes.  However, the frame is "floppier", and more fragile.  It is hard to avoid cracking the straight couplings.

     For general use, we recommend a frame made of half inch (nominal) "regular" PVC; or if the greater expense is no problem, the tent-pole version below. 

    Left:  Ultralight frame made from CPVC, about 670 g (1.5 pounds)
    Right:  Standard frame made from "regular" PVC,
       about 900 g (2 pounds) if using "SDR 13.5" pipe
       about 1.3 kg (2.9 pounds) if from "Schedule 40" pipe


    Variant:  Ultralight folding tent-pole frame:

      This design has proved as serviceable as the sturdy PVC, though at a higher cost in materials.  It is a great saving in size and weight: about 0.7 pounds or 11 ounces (300g).
     
      Materials for one bar are:  Three tent pole sections, two grommet tips, a length of elastic shock cord, and materials for marking and connection.  Here is the parts list for the four bars that make up a complete sampling frame.

      You can order starred (*) items from the address given below.

    Item How many you need Comments Click an image for larger view
    Standard 13-inch tent pole sections, with end insert* 8 The length is 13 inches, not including the insert.

    The diameter you need for all sections is "three four three", which means 0.343 inches.

    Standard 13-inch tent pole sections, without end insert* 4  
    Elastic shock cord, 1/8 inch (3 mm) diameter* 12 feet (about 4m).  This is sold by the foot. This is a standard diameter to fit the tent pole sections.
    Tent pole grommet tips* 8  
    Adhesive backed velcro, two contrasting colors 4 inches (10 cm) of each color.  This is typically sold by the half foot, so 6 inches is probabaly the minimum you can buy. You will only use the hook of one color and the pile of the other color, but the hook and pile are usually sold together.
    Nylon cable ties. 8 Get the smallest ones available.  If possible, match the velcro colors, 4 of each color.
    PVC "electrical tape", two different colors. one roll of each color For marking the calibration bands on the bars.  One color should match one of the velcro colors, the other should contrast with the bar color (see below).

     * Tent pole sections, and related items, are available from:

    Tentpole Technologies, LLC
    8212 NE 99th Circle
    Vancouver, WA 98662-1300
    Phone: 360-260-9527 or  800-266-9527
    Fax: 360-260-9937
    E-Mail: tentpoles@comcast.net
    Website:  http://www.polesforyou.com/


      If you explain what you need, Tentpole Technologies will now pre-assemble the one-meter "legs".  This is a great convenience.
     
      In this case, you can skip the assembly instructions below, down to the section on marking with colored tape.
     

     

      Tent pole sections made of fiberglass are becoming available.  These are lighter and cheaper.
     
      Assembly is slightly different than shown below, but the principle is the same.  The finsihed frame weighs only about 240g, compared to 300g for aluminum poles.
     

     

    Before you begin to assemble the tent pole sections, note the following:
     

      Some of the tent pole sections have an "insert", a narrow extension on the end, which slips into the adjoining section.

      Each bar is made up of two "insert" sections and one "plain" section.

      You should assemble the bar with the two "insert" sections in series, and then the "plain" section.  Then, the completed bar will fold up to minimum length.  Miminum length is preferred, to carry the equipment in the smallest possible space. 
     


    shortest folding pattern -- preferred

    schematic -- preferred

    longer -- avoid

    schematic -- avoid

     
      Thread the shock cord through the tent pole sections as shown.
      Tie the free end of the cord to a grommet tip. A double half-hitch knot is good. Pull the knot tight to make it as small as possible. It will be a close fit inside the tube.

      Push the grommet tip down into the tube.

      Pull the other end of the shock cord out about 4 inches (10 cm) beyond slack and mark it to cut.

     While working on this end, you can keep the cord from pulling down into the pole section tube by tying a slipknot and putting a small stick through the loop of the knot.
      .

      You can cut the cord with a soldering iron, which will melt the ends and prevent any fraying.  However, just cutting with scissors works acceptably well. 
      After tying on the other grommet tip and assembling the bar, note that the 1-meter length goes slightly beyond the ends of the pole sections.  This 1-meter point is where you want the poles to connect, though a little variation is not critical.

      You will use velcro to "connect" the bars, hook velcro on one bar end and pile velcro on the other.  The connection does not have to be rigid.  In fact it's useful to have the junction flexible, with the ability to easily disconnect and reconnect.

     Visual cues help you quickly see which points will stick to each other, so we will make the two ends different colors.

      We'll refer to the ends of the bars as the "red end" and the "black end", though of course they can be any contrasting colors.  Also, the hook and pile velcro can be switched from how we describe them here.

      Cut a strip of red pile velcro about an inch (few cm) long and wrap it around the grommet tip on what will be the red end of a bar.  Also, wrap the end of the bar, for 10cm, with tape of the same color.

      The adhesive back of the velcro makes it easy to apply.  However in the field it will tend to come loose with dirt and moisture.  So use a cable tie to hold it on securely.

      You can even hold the velcro on with a cable tie alone, if you can't get adhesive back velcro.

      Wrap the rest of the bar in alternating bands of the constrasting color tape.  These 10cm bands make it easy to visually estimate percents within the enclosed one square meter area.

     Use the brightest colors you can find, to make the frame visually evident in the field and avoid losing it in the brush.

      Assemble the black end the same as you did the red end, except use hook velcro.
      Assemble the other bars.

      The red end of one bar will stick to the black end of another bar.

      The bars will stay together strongly enough to pick up the frame as a piece.

      In practice, in the field, you will often assemble the frame in place by threading the bars between stems and branches.  The ends will stick when you bring them in contact.

      Folded up, the frame makes a small bundle weighing only 300g (aluminum poles) or 240g (fiberglass poles).

      You can use a left over piece of the shock cord to make a band to hold the bundle together.  If you buy the poles pre-assembled, a rubber band will serve as well.



    Rick Shory
    Natural Resource Ecology Lab
    Colorado State University, Fort Collins CO 80523-1499
    (970) 491-5835
    rick.shory@colostate.edu

    Page updated 9 June 2009