Important Note
These plans should be considered “beta” quality at this point. The cross I currently have built was made before I figured out all of the trig displayed below, and some fudging was necessary… I think the numbers all come out correctly, but I’ll want to build another cross strictly following these measurements before I’m comfortable calling them correct.

The Saint Andrews Cross is a popular piece of hourglass shaped furniture for attaching submissives for BDSM play. The submissive is attached in a staked-out position either facing towards the cross (thus back side “out” to the room) or facing away from the cross with front side to the room. The open-frame nature of the design means that most of the side of the submissive facing the cross is still accessible.

Attachment to the cross can be accomplished using cuffs made of leather or other materials clipped, locked, or tied to the corners of the cross or via rope wrapped around the structure of the cross or anchored to optional anchor points running the length of the sides of the cross.

This cross design is simple to build, light weight, attractive, and easily disassembled for moving & storage. The St. Andrews Cross can be customized depending on size & space requirements and on the desired position (how much stretch) of the attached submissive.

Materials

Materials requirements for the cross are fairly basic. You’ll need some lumber (how much depends on size calculations), some wood glue, and bolts to hold the assembled cross together and to serve as attachments points.

For lumber, you’ll want to use a thin, wide hardwood board. 5/4"×6" cedar is nice if you can get/afford it. 1"×6" pine boards will work as well, though you’ll want to spring for a higher quality pine if you intend to urethane rather than paint the cross. The design uses glue to bond two layers of these thin boards together which gives fairly good stiffness to the finished product at a more reasonable weight. The two-board sandwich also makes the cuts necessary to create the interlocking board design much easier as you need only cut individual boards rather than cut out grooves in a single thicker board.

You’ll also need various grits of sandpaper to sand before finishing. Paint brushes, tack cloth, and paint or urethane to protect the wood when finished.

Four or five sets of eye bolts with with nuts and two washers each hold the corners together and provide attachment points. ⅜" hardware is a good choice for sturdiness.

If you want to build a tilted stand (tri-pod design) for your cross, you’ll need a heavy duty hinge and some heavy chain to secure the legs as well as additional lumber for the leg itself.

Tools

At the very least, you’ll need a tape measure, a drill (power screwdriver will do in a pinch) with a bit to match your eye bolt harder (IE ⅜), and a saw. Ideally a miter saw or a table saw with the guides necessary to cut at various precise angles. A skillsaw can be made to work, but measuring & cutting the angles will require extremely careful attention to detail.

Some wood clamps will come in handy when gluing the pieces together. Be careful that any clamps used don’t leave indentations in the wood (use a scrap piece of lumber on either side to protect the boards).

While it’s possible to sand the finished cross by hand (or perhaps have a sub do it), an electric sander would be a huge time saver.

Design Parameters

Two main parameters determine the size & shape of this design and influence all of the measurements required to build the cross:

Total Height
Amount of stretch (angle of the “arms”)

The height requirement of your cross will depend on the height of submissives you expect to attach to it and to available vertical space in the area where your cross will stand. Ten foot ceilings are nice if you’ve got them, but lower rooms or basement dungeons might call for a more modest design.

The amount of stretch that an attached submissive feels is a result of the angle of the arms of the cross. A narrower angle leaves the submissive’s arms and legs closer to straight up & down whereas a wider angle leaves them spread out more.

In cases where a cross will be used in a low-ceiling area, you can trade vertical height for a wider stretch and likely still accommodate a submissive of a particular height without requiring as much vertical space. You may also choose to mount your cross at an inclined angle (leaned back slightly) in order to gain additional length for the cross arms without increasing the height requirements in the room where the cross will be used.

Basic Math

The hourglass shape of this cross means that all of the math is based on triangles. The Pythagorean theorem plus some basic trigonometry is required to derive the various lengths and angles of the cuts necessary to build the cross.
Start by figuring out which of the two design parameters is more important to you. If you’ll only use the cross in an 8’ ceiling room, then a 10’ tall cross wouldn’t be much good. Likewise, if your sub is 7’ tall, building a cross with only 6’ long arms would be counter productive. Conversely, if vertical space isn’t an issue, you should decide how widely spread the attached submissive should be. Compared to other cross designs, this one trades adjustability for simplicity of design, a streamlined look, and minimal material costs. Once the arm angle is selected, it can’t be changed.

The design in these instructions uses 108" length for the cross arms and has a 55º spread for the arms. Angles from 40º to as wide as 60-70º may make sense depending on your tastes.

The basic design of the cross looks like an hour glass:

\==========/  ---
 \        /    |
  \      /     |
   \    /      |
    \  /       |
     \/        B
     /\>b      |
    />a\       |
   /    \   C  |
  /      \     |
 />c      \    |
/==========\  ---
     A
Note that total arm length = 2∙*C* and total height = *D*.

The above diagram labels the three sides (capitals) and angles (lower case) of the lower triangle as well as the total height of the cross and the outer angle of the arms (*B* & >b). The measurements on the top triangle are identical in this design (the hourglass is symmetrical), and the left & right sides are mirrors of each other.

All of the lumber cuts for the cross use two angles which both derive from >a. The arms of the cross must be cut at an angle so that they set flat on the ground when attached diagonally to form an X. The angle of this cut at the bottom & tops of the arms is ½ >a.
At the place where the two arms intersect, the top & bottom boards are alternatively cut to give a criss-cross pattern. This angle is the complement of >a or 90º - >a. Where the horizontal boards meet the arms at the top & bottom of the cross (at either end of A), this same angle cut is used.

Selection by total height

If the total cross height is the more important attribute, you’re starting with B and working back to figure out the triangles.
The easiest way is to also select an arm angle and use that to figure out the outer angle of the arms (*>b*) which is the supplement of the inner angle (*>b = 180º - >a*). Each half of the hourglass forms an isosceles triangle (two equal sides & angles), so based on the selection of >a, >c is the same in all four “corners” which is (180º - >a) / 2.

Example: Given *>a* = 55º, *>c* is 62.5º

From there, you form an imaginary right triangle between the lower half of one arm and half the total height of the cross. You know >a’ (½ of >a), >c’ is 90º, and >b’ is the same angle as >b in the original diagram.

     /|\ <-- >a'
    / | \
   /  |  \ C
  /   |B' \
 /    |>c' \
/=====|=====\
         A'

The vertical side of the new triangle B’ is ½ B, so now you have an angle-side-angle problem on a right triangle:

cos(a') = B' / C
cos(a') ∙ C = B'
C = B' / cos(a')

Assuming >a=55º and desired height D=8’ or 96":

B' = ½ ∙ B
B' = ½ ∙ 96" 
B' = 48"

>a' = ½ ∙ >a 
>a' = ½ ∙ 55º 
>a' = 27.5º

C = 48" / cos(27.5)
C = 48" / 0.887010833178222
C = 54.1143"
armLength = 2∙C
armLength = 2 ∙ 54.1143"
armLength = 108.2286" ~= 9' ¼" total arm length

Now that two sides of the base triangle are known, you can figure out the length of A’ using the Pythagorean theorem:

A'² + B'² = C²
A'² = C² - B'²
A'² = 54.1143² - 48²
A' = sqrt(2928.3610 - 2304)
A' = sqrt(624.3610)
A' = 24.9872"
A = 2 ∙ A'
A = 49.9744" ~= 4' 2" total width

Selection by angle

If you have plenty of space and care more about the angle of the arms, you’ll calculate B after everything else is figured. Starting with about 9’ for the arm lengths is a good idea assuming you’re starting with 10’ lumber (some gets cut off to make the base angles).

Once >a is selected, the other angles are calculated based on each hourglass half being an isosceles triangle. As with selection by height, an imaginary right triangle is formed by bisecting the bottom half of the hour glass. One half the arm length gives the hypotenuse of the right triangle.

C = ½ ∙ arm length
cos(a') = B' /  C
B' = cos(a) ∙ C

Given an arm length of 9' or 96" and an inner angle of 55º:

C = ½ ∙ 96 = 48
B' = cos(27.5) ∙ 48
B' = 0.887010833178222 ∙ 48
B' = 42.5765"
B = 2 ∙ B'
B = 85.1530" ~= 7' 1 ⅛" total height

Now the length of A’ can be calculated using the Pythagorean theorem as above.

A'² + B'² = C²
A'² = C² - B'²
A'² = 48² - 42.5765²
A' = sqrt(2304 - 1812.7600)
A' = sqrt(491.2399)
A' = 22.1639"
A = 2 ∙ A'
A = 44.3278" ~= 3' 8 ⅜" total width

Board width adjustment

All of the lengths calculated using the trig above are lengths for the full sides of the hourglass or triangles measured from the middle of the width of each board and don’t take into account the overlap of multiple pieces inherent in the cross design. Because of this, the actual cut pieces are shorter based on where in the overlap pattern they fall.

The lengths of cuts are affected by the actual widths of the boards that you use to make the cross. For 1"×6" standard planed lumber, the actual width of the board is 5 ½". For other board widths, you’ll need to adjust the cuts lengths accordingly.

Each board is cut on an angle (either ½ >a or the complement of >a) either to lie flat against the ground or to meet flush with other angled boards which meet on a diagonal. The piece removed in the initial angle cut forms another triangle which we can use to calculate the actual cross-section of the boards for adjusting other lengths.

For the cut-off triangle, we know one length (the width of the actual piece of lumber) and two angles – one is a 90º from the corner of the board, and the other is the cut angle of the lumber IE ½ >a.

   /    /
  /    /
 / X  /
/----/ <-- Cut line
\>a'/
W\/ <-- 90º

With respect to >a’, the original width of the board (*W*) is the adjacent side. The unknown length X is the hypotenuse.

cos(a') = W / X
cos(a') ∙ X = W
X = W / cos(a')

Assuming 1"×6" planed lumber (5 ½" actual width) and >a = 55º, the cross-sectional width of cross arms is:

X = 5.5 / cos(27.5)
X = 5.5 / 0.887010833178222
X = 6.2006" ~= 6 ¼"

This width is used for where the arms meet the horizontal cross sections at the top & bottom of the cross. The same width applies for shortening both the horizontal bars as well as the legs where the horizontals overlap.

For the middle section of the cross, the boards are cut at a different angle (complement of >a rather than ½ of it). We’ll call the width Y in this case to differentiate, so again assuming 55º and 1×6 lumber:

Y = 5.5 / cos(35)
Y = 5.5 / 0.819152044288992
Y = 6.7142 ~= 6 ¾"

Example numbers

For all the lengths quoted below, the following system of angles, lengths, and lumber will be used as a basis:

108" long cross arms (*2∙C*), 55º arm angle (*>a*). This yields a cross which is about 9’ ¼" tall and 4’ 2" wide. The angle of the arms to the ground is 27.5º (*½>a*), and the angle of the arm overlap in the middle is 35º (complement of >a). Standard 1"×6" planed lumber will be used. 10’ board length is suggested.

Measuring & Cutting

Building the cross requires a total of 10 pieces of wood (excluding the optional tripod stand). Of these pieces, there should be five pairs of identical cuts. Most of the variation in the remaining pieces comes in the two cut angles and whether the piece is on the “top” or “bottom” of the cross’ criss-cross pattern. Note that while some of the pieces are physically interchangeable in terms of length and cut angles, it’s still preferable to cut the pieces specifically for their intended position in the finished piece in order to ensure the “good” side of the lumber used is always facing outwards.

For the first cuts, start with the long arms of the cross. One should be the calculated length of your cross arms exactly (*2∙C* 108") and the other must be shortened by the width of your top & bottom boards (*2∙C* - *2∙X* 108 - 12.5 = 95.5").

All four ends of these boards will be cut to a 27.5º angle. The direction of the angled cuts must be such that when the boards are joined in the middle in an ‘X’, the angled cuts lie flat on the floor (not with a point touching the groups) and the tops are parallel to the ceiling. For the cross arm boards, the angles should both go the same direction:

    /===/
   /   /
  /   /
 /   /
/===/

When you select the direction for cuts, ensure that when the boards are crossed the “good” sides of each board will be opposite each other – that is pointing away from the point where the boards touch in the middle. The other side of each board will be covered with a smaller laminated piece, so placing the “bad” side of the lumber at the inside of the intersection ensures it won’t be visible in the final piece. Positioning the good & bad sides will influence which direction you make your angle cuts.

To start, set a miter saw to 27.5º and make the first cut on the end of one board. Just snip off the minimal amount to leave a cut the full width of the board. You’ll waste a bit less than 2" at the widest and perhaps only ¼" for the saw blade width on the narrow end. Once this angle is cut, measure from the center of the width of the board to a point 108" down the board & mark this point. If you’re using a miter saw (especially if it has a laser guide), this single center point may be enough to make the cut. If not, and especially if you’re using a skillsaw, you should make additional measurements at the two ends of the board & rough in a guide line for another 27.5º angle. The two angled cuts should run the same direction, so you’ll slide the board straight down through your saw as you position it for the second cut.

For the shorter cross arm, repeat the same procedure with the shorter (95.5") measurement. You should flip this board before making any cuts so the “good” side is pointed the opposite direction from the first board so that both “bad” sides will be inside when the boards are finally put together. As a sanity check, lay the two boards together in an X on a flat surface to ensure the base & tops are aligned properly and that when the boards meet roughly in the middle, you have about the size cross you’re expecting.

Next up, you’ll need to cut the four shorter pieces which will laminate with the two arms to give a stiffer final product. Each of the boards will cover one half the length of one arm. The “outer” cuts on these boards (the ones that lie against the top & bottom of the cross at the floor/ceiling) are cut at the same 27.5º angle (*½ >a*) as the cross arms. The inner cuts are instead cut at 35º (complement of >a) so that they will meet flush against the crossed arms. Like the longer arms, the total lengths each pair of boards will be the same as the cross arms, but parts of that length are “cut out” by the overlapping pattern of the cross. Two of the boards need to be (2∙*C* - Y) / 2 or 50.625" ~= 4’ 2 ⅝" long. The other two must be (2∙*C* - Y - 2∙X) / 2 long or 38.125" ~= 3’ 2 ⅝" long. Remember to cut the boards so that the good sides are out when the boards are glued together.

Finally you need to cut the horizontal braces for the top & bottom of the cross. These all have 27.5º angles on the ends (*½>a*) with the angles pointed opposite each other to give an arrow-like appearance. Two of these boards should be the length of A or 44.3278" ~= 3’ 8 ⅜". The other two must be shortened by the amount of the arms which will displace them so A - 2*X* or 31.8278" ~=2’ 7 ⅞" long. Again, the angles are cut to 27.5º pointing inward.

Assembly

Once all the pieces are cut, it’s time to glue things together & start assembling the cross. The tolerances on the various glued angles are relatively tight, so you’ll want to lay everything out dry on a nice flat surface before gluing anything. It pretty much only works one way, so make sure all the points where pieces meets are perfectly tight before you glue anything. If you need to make adjustments, this is your only chance.

If you have enough clamps, clamping everything together dry, then unclamping, glueing, and reclamping one piece at a time will give the quickest, best results. If not, drilling & bolting the corners & midpoint first will at least give you some fixed points of reference to work with when glueing everything together. The order pieces are glued together doesn’t much matter, so do whatever seems to work the best for you. As more of the pieces get locked together, you should see the rest of the parts start fitting only one way.

Once all the glue has set, you should drill the boards at the corners and the middle (if you didn’t already before you glued), and fit eye bolts with a washer on either side to each corner and a carriage bolt or two in the middle to hold the cross arms together. At this point, the cross is structurally complete and could be used leaned (or preferably attached via chain or rope) to a wall or ceiling.

To finish your cross, you’ll need to sand and apply some sort of coating. Depending on the quality of the wood used and your tastes, you could either use an opaque paint in any color you like or apply a clear or tinted urethane to allow the natural wood grain to show through.

Optional extras

Once the basic cross is completed, numerous options exist to customize it to your own tastes and uses.

Attachment Points

The basic cross contains four-point attachment at the corners to hold the cross together. If you prefer to tie submissives down to the cross instead of using cuffs, you might attach a series of tie-down points on the edges of the cross to zigzag rope back & forth across their limbs and body. Leather or nylon straps might be attached to the cross to strap the submissive down at various points along their body. Use your imagination (and post pics to FetLife!) =)

Extra chains

Being cuffed to a cross can get tiring for the submissive’s shoulders and back. Using suspension cuffs with built-in hand holds can allow the submissive to redistribute weight in a more comfortable fashion.

If normal cuffs are to be used, one option is to run a length of chain or rope between the two top attachment points on the cross arms. The chain should droop low enough to be within the submissive’s reach and provides a handle to pull up some of the weight making longer periods on the cross more comfortable.

Foot rests

While I’ve not (yet) attempted to adapt foot rests to this design, Douglas Kent’s excellent Better Built Bondage Book strongly recommends ensuring that any furniture be designed in such a way that the submissive cannot exert force against the ground or anything other than the furniture itself. Firmly attached foot rests would allow the submissive to struggle significantly without being able to apply force to the ground which might result in the cross tipping over and causing injury.

Tripod legs

The safest, most secure mounting for this design would be to attach it to a ceiling or wall using chain run to hard restraint points, over floor joists, etc. Be certain to take into consideration that a thrashing submissive may generate a fair amount of force (particularly if they can touch the floor), so your attachment points must be sturdy. Ideally, consider using points that would be adequate for a full suspension.

If the cross is to be used freestanding, a tripod leg assembly can be added to allow use in the middle of a room (or a field…). When used with legs, the cross should be carefully monitored to ensure the submissive’s movements won’t tip the cross over.

Adding the tripod is fairly simple. An additional piece of heavier lumber is required (2×4 or even 2×6) along with a heavy duty hinge. The hinge is bolted to the back side of the cross at the middle and runs backwards to stand the cross. For stability, bolt an additional piece of lumber at the bottom of the leg perpendicular to it. This provides a wider base instead of just a single point.

In order to keep the leg in place, add additional eyebolts to the sides of the leg base and attach the bottom sides of the leg to the bottom of the cross using chain. The angle of tilt can be controlled by adjusting the length of the chains.

Recommendations

Given that the lumber and other materials to build the full-size cross can cost a couple of hundred dollars, it’s highly advisable to build a prototype of the cross first to ensure you understand how the overlaps work.

For the most basic first attempt, cutting strips of paper and taping them together can show how the various angles must be oriented to each other. If you’re more confident to start (or as a second step), use basic ½"x1" furring strips to build a small mockup, perhaps 12-18" tall. This will allow you to practice making & measuring the angled cuts. When you’re done, find an appropriate sided doll or maybe a Bondage Bear to mount to the cross, and you have an interesting conversation piece, to say the least…

The End…

Hopefully the above is useful in building your very own dungeon furniture. If you have any questions or run into trouble or especially if you’ve noticed any errors in my math, feel free to email me at [pendor at pendor bound dot com] or message me on FetLife. And definitely consider posting pics of your cross, either during construction or in use!

Calculator

A JavaScript based calculator which applies the math below is available here:

Saint Andrews Cross Calculator