Wooden Scorpion




Introduction: Wooden Scorpion

About: Hi, I'm Dave and I like to party.... No, really, I'm just a guy who likes to do guy stuff...camping, canoeing, making stuff, shooting pool, and working hard to take care of my family. I hope you enjoy my humb…

My goal for this project was to create a hand-held weapon that I could use to hunt small (or possibly large) game.   This is an original design I adapted from a tabletop crossbow (which I based on an ancient roman weapon) I made last Christmas as a gift for my brother.  I would say this project is intermediate level, but a determined beginner could do well also.  My wife encouraged me to document the process and share it as my first Instructable.  I have used my scorpion to target shoot, but have not yet had a chance to take it hunting.  It shoots as accurately as I could hope for in a homemade weapon, and I believe with enough power to kill small game.  I will update if/when I am able to use it for hunting. 

You will be using power and hand tools for this project, so of course proper safety precautions are a must!

Step 1: Equipment and Supplies

I had several board feet of red oak saw-mill grade lumber in my shop so I planed down a 5 ft board to 3/4" thickness and another 5 feet to 1/2" thickness.  You could use any hard or soft wood you have laying around the shop.  See Materials list below if you will be buying from a lumber yard.  Be careful with soft woods.  They may not hold up to actually firing an arrow.  The only other materials you'll need are some parachute chord (also known as 550), a small spring from any cheap pen,small finish nails and wood glue.  You could use some other nylon string but the small strands inside the 550 are very strong and worked great for me. 

1" x 8" x 6' hardwood board (this will actually only be 3/4" thick)
1" x 4" x 6' hardwood board (if you don't have the means to plane down to 1/2", DON'T buy a thinner board.  Use 1" x 4"  and adjust the tenon measurements as noted on the following step.  Your crossbow will be a bit heavier than mine.)
24 feet para-cord for springs
cheap click pen (for the spring) or make your own
finish nails
wood glue (I used Gorilla brand)

You'll also need...

Hand Tools
Ruler/ Tape measure
Drill bits
Box Knife
Round file
Coping Saw
Sand paper

Power Tools
Table Saw
Scroll Saw / Jig Saw
Rotary tool/ Dremel
Drill or Drill Press
Belt or Orbital Sander

You don't need all these power tools.  They just speed up the work.

Step 2: Cutting the Main Frame, Supports and Limbs

To build and accurate and functional weapon, it is important to make your measurements as precise as possible.  Take your time and double check your measurements so you won't have to re-cut any pieces.  Use proper safety measures and Let's Get Started!

Pictures 2 - 9 show the measurements of the various pieces.  Please note the drawings are not to scale.  Before cutting any pieces, you will need to make your templates using a pencil, ruler and some heavy paper.  Cut out your paper templates for all pieces. Trace onto your boards, cut pieces and don't forget to sand out the rough edges!

Main Frame pictures 2-4
Top and bottom plates CUT FROM 1/2" THICK BOARDS
** If you are using standard 1 x 4, see notes under Vertical and Main Supports **
You will cut 2 identical plates that will be the top and bottom of the frame.  You should have marked the size and location of the 3/8" square tenon holes and the 3/4" round spring holes.  I used a scroll saw to cut out the square tenon holes.  You could also use a 3/8" drill bit to drill the exact center of the holes and a chisel to square them up.  For the spring holes, simply drill exactly on center using a 3/4" drill bit.

Vertical Supportspictures 5,6,11,12
You will cut 4 identical vertical supports.  Note that the vertical supports have a tenon at each end which is flush with one side. See pictures 8 & 9 .  These tenons will fit into the 3/8" squares in the top and bottom plates.
** If you used standard 1 x 4 for your main plates, you will need to adjust the tenon length to 3/4" instead of 1/2" **

Main Bow Supportspicture  7
You will cut 2 identical Main Bow Supports.  These will fit vertically. They will not have through  tenon joints, but will be glued in place.
** If you used standard 1 x 4 for your main plates, you will need to adjust the tenon length to 3/4" instead of 1/2" **

Limbspictures 8-10, 14
** If using standard 1 x 4 boards, no adjustment is necessary **
You will cut out 2 identical limbs. They will fit through the springs horizontally and rest against the vertical supports.

Spring Tightening mechanism picture 11
** If using standard 1 x 4 boards, no adjustments are necessary **
You will cut out 4 identical tighteners.  They are rectangles  3 1/2" x 1/2" x 3/8". 
Note : make sure the grain is running lengthwise.  Since the string springs will wrap around these pieces, it is important to slightly round the corners of the middle to minimize
wear on the strings.

Step 3: Main Frame Assembly

You will want to dry fit all the pieces to ensure a tight fit before applying any glue.

Assemble in the following order:

Lay the bottom plate down with the outermost tenon holes away from you as in Picture 1 .

Insert Vertical Supports with the tenon side facing toward the outside of the plate.  The front and back tenons will face opposite directions. See Picture 2 .

Mark position of the Main Supports (remember these are shaped like an H) exactly 6 1/2" from the edges on the bottom plate.  The outside edge of the support will line up with this mark.

Gently fit the top plate onto the vertical support tenons.  Do not use the mallet to tighten down just yet.

If you tilt the main supports sideways, you should be able to slide them between the top and bottom plates.  Position according to the marks you made on the bottom plate.

LIGHTLY pound the top plate into place with a mallet and check the fit of all the tenons and the main supports.  There should be minimal gaps (and they should be even all around).  If you have pieces that aren't fitting flush, sand these as necessary.

Take the frame apart and apply wood glue to the tenons before putting back together as before.  Don't be afraid to use too much glue!!  For the Main Support pieces, DO NOT glue the surfaces yet - we will do that when attaching the stock.  After using the mallet to gently hammer the frame together, wipe off any excess glue.  Clamp frame using at least 2 clamps with even pressure, using the square or a level to ensure frame is plumb and true all around.  After checking all surfaces with the square, tighten clamps.  Wipe off any excess glue.

Allow frame to dry.

Remove clamps and sand as much as necessary to make your frame smooth and beautiful.

** You will not be adding the limbs or string tighteners just yet.**

Step 4: Cutting the Stock, Trigger

You will want to start by printing out the pictures below marked Stock and Trigger Template 1 and 2, these are scans of the templates I used when cutting out the stock and trigger pieces.  If they are printed full sized (8.5x11"), they will be exactly what I used when cutting my pieces.  Template Pictures 1 and 2 should be taped together as marked.  Don't forget to add 6" to the barrel end as noted in template picture 1.

Cut out the stock and trigger templates.  See picture notes for more information.  Trace the stock template onto 3/4" board that is 28" long. This is how I cut my pieces using the equipment I have. If you can think of an easier way for you to do it, then please go ahead.

I clamped the first board (with the traced template) on to another board of the same size and cut the bottom part of the barrel ONLY using a table or circular saw (since the top part
was the edge of the board).  To ensure a nice straight cut, be sure to use your saw guides.  See 1st picture below.   Then I removed the clamps and cut the rest of the stock using a jig saw for more control on the curves.  I first cut the top board that had the template traced onto it, then used that board to trace the final shape onto the 2nd board (so the halves would be as uniform as possible) and cut the 2nd piece also using the jig saw.

Trigger Housing
Next, I had to cut out the housing for the trigger mechanism (see picture below for finished cuts).  Refer to Template picture 1 (labeled at the bottom) for dimensions.  The correct placement is noted on the barrel template of the same picture.  Note that when cutting the trigger housing into the stock pieces, the cuts will mirror each other. The 2 stock pieces will be glued together after the trigger housing and trigger pieces are cut, drilled and the trigger pieces are set in place.

This step could be done with a router, but his is how I did it with my table saw.  I wish I had pictures, but I got too caught up in the project and forgot to stop so I will describe it as best I can. Please mark your cuts in pencil first to be sure you don't cut the outside of your boards. I  used the square cutting guide on my saw and set the blade depth to 3/8". I cut both edges of the housing groove first then made lots of cuts between the two edges and used a chisel to knock out the waste.  I then notched  the other board, again, being sure to cut the housing out of the inside of the stock so the 2 halves together will make a hole for the trigger mechanism. I used a rasp and sander to smooth the housing on both boards

Main Frame Attachment Notches
Notice in pictures 5,6 &7 there are also notches cut into the end of the barrel pieces.  This groove will fit between the Main Bow Supports in the center of the main frame when attaching the stock. I made these notches (using a square to ensure accuracy) by marking  a line 1/2" from the end of the barrel. Then I used the main bow support template from previous step to mark the width of the groove. This is important to ensure a tight fit.    The grooves on each side are only  1/4" deep.  Again, don't forget to be sure you are cutting into the outside edge or your stock piece will be ruined.

Trigger and String Release pieces
Refer to template picture 1 for trigger piece templates.  Cut out the trigger and release mechanism templates and trace onto your board.  Don't forget to mark where you will need to drill the holes for the pins that will hold the trigger and release pieces in the housing.  Cut out with a scroll saw (without cutting the grooves in the release). I cut these pieces out of a board that was 5/8" thick.  You could use a board a little thicker, as long as the trigger mechanism moves smoothly in the housing.  Use a sander to thin down your board if necessary.

To shape the trigger
  After marking my cut lines all around the trigger piece, I clamped the cut-out trigger piece into a vice with the trigger end pointed up.  Then I used a coping saw to cut away the waste around the trigger. I sanded with my Dremel, then drilled the mounting hole as marked on the template.  See notes on pictures for more details. 

To shape thestring Release
Using the template as my guide,I drew all the cut lines onto the release mechanism just like the trigger.  I again clamped the piece to a vise and used my coping saw to cut out the notches.  I finished up by drilling the mounting holes and sanding it all smooth with my Dremel.  See pictures below.

Step 5: Assembling the Stock and Trigger

Attaching trigger and string release mechanism
See pictures 1-3 for correct placement of mounting pins.  First, punch a nail into the wood at the marked spots just a bit to use as a guide for the drill.  This will keep it from dancing around the surface.  You could also use a center punch if you have one.  Drill holes into the stock at the marked locations, being absolutely certain that the holes on each side are lined up identically and  that you only drill far enough into the wood to hold the pins in place.
Once your holes are drilled, you will need to gently hammer the pins into one side. I used finish nails for the trigger and release mounting pins. I cut off the points and heads and cut nails to fit into the housing, making sure they are short enough that they won't punch through the outside once clamped together.  I used a drill bit that was the same size as my finish nails. You can use any nails you have as long as the trigger and release pieces move freely and they are cut down to appropriate length. Refer to pictures below for trigger and release assembly.  Once all the trigger pieces are in place on one side of the stock, you are ready to very carefully attach the other half of the stock.  Smother the half of the stock that has the trigger attached (do not get glue in the trigger housing). Carefully line up your drilled holes on the other half of the stock with the pins and press into place. 

Clamp  the two halves together, being sure to  wipe off excess glue with wet rag. Check the barrel with the square to get it as straight as possible. Let dry.

Shaping the stock
I used a draw knife to shape the stock, but you don't have to shape it at all.  Rounding off the corners with a sander would work just fine.  If you use a draw knife, be careful to never go against the grain as you will wind up ripping chunks out of the wood.  You could also use a rasp, but it would take a lot longer.

Now time to sand the stock and barrel.  You will want to use your square to be sure the barrel is as straight and true as you can get it.  I clamped my belt sander to the the top of my table saw (blade completely retracted of course and saw was unplugged) so I could run the stock piece down the sander.  Use whatever sanding method you are most comfortable with.

Step 6: Attaching the Stock to the Main Frame and Attaching Arrow Guide

Attaching the Stock to the Main Frame
Set the main frame down with the center most vertical supports facing you as in picture 2. You should have both main supports stuck in the frame between these vertical supports-remember they are not glued. If you haven't already, make a straight line exactly 6 1/2 inches from both outer edges.  This is where you will line up your main supports after the stock is attached. Slide your main supports outward toward the vertical supports to leave room for the stock piece to slide through. Once the stock is dead center, slide your main supports over and check for fit. If anything needs sanding or adjusting, do it now. Once everything fits flush, slide pieces apart slightly and smother in glue. Don't forget the tenon arms. Clamp lightly, then use your square and check from every possible angle to be sure every thing is straight.

Tighten clamps and wipe excess glue. Allow to dry.

Arrow Guide
Now it is time to cut and attach the arrow guide.
The arrow guide has to fit just inside the release mechanism and must be low enough for the string to catch . I used a board that was about 4 inches longer than I needed so I had a few inches to play with to get the blade depth just right. Then I cut off the end that wasn't quite right. The finished guide is 15 3/4". I used my table saw to cut the arrow guide. I set the guide to 1/16" away from blade and set blade to 1/8" depth. I then ran the board down to cut the groove in the arrow guide. Then move the guide just a fraction and make one more pass to widen groove just a bit. Then I moved the guide to 5/16" and raised the blade to 1/2". I made one more pass which completed the piece. I then had to turn the board and cut the guide out of the larger piece of wood by turning the board and making a very careful pass down the blade. See pictures below.

Now that the guide is cut out of the board, it must be sanded. To prevent the arrow or string from catching on the guide, the tops of the channels should be smooth and slightly rounded. I made several passes with the round file down the center and rounded off the edges with the Dremel. Glue the guide onto the stock along the center seam, using your square to ensure your guide is true. Pictures below show correct placement.

Step 7: Making the Springs

Next we'll make the nylon string springs.

Cut your 24ft of para-cord into 12ft lengths. 

To form the springs, you will wrap the strands of para-cord around a jig like the one shown in Picture 1 .  Using any scrap board (or your workbench), nail 2 finish nails exactly 7 inches apart.  Removing the nail heads will make it easier to slide the string off after wrapping.

I recommend doing the next steps with one length of para-cord at a time to keep the strands from falling apart.   Remove outer casing from your para-cord.  Save this for the next step.  My cord had 4 strands inside, yours may be different.  If there are more than 4 strands, you will have to shorten the length or the completed spring will not fit in the frame.  You will have to experiment a bit to find the best fit.  Be sure to keep your strands together during the next steps.

Holding all strands together, wrap the length around the jig as many full rotations as you can.  You will have a few inches left over after the last full rotation.  Cut off this extra.  Use one strand as your threading string.  See Pictures 2 & 3.   Loop the threading string through all layers of string at one nail and tie securely.  This will ensure your spring strands stay together and will make threading the spring through the holes in the frame much simpler. 
It's also a great way to keep the strings separated so you can get the spring tighteners and arms into place.

Repeat for the other 12ft length of para-cord.

Using the threading strings, hang your springs somewhere out of the way where the strands will not tangle.  We will add the tighteners, springs, and bow limbs in the next step.

Step 8: Attaching the Springs and Bow Limbs

Gather your spring tighteners, 4 finish nails, bow limbs, springs and a 60" length of para-cord casing (pulled off the springs in previous step).

There are notes on the pictures below for reference.
Attaching the limbs
Thread one of the spring tighteners into the loop of strings. Use the threading string on the other end of the spring to pull the spring through the bottom hole.  Now put the wide end of one limb through the center of the spring loop.  Now thread the spring loops through the top hole.  Thread the top spring tightener through the loops sticking up from the top hole.  Now lay the crossbow face down with the limb pointing toward you. See picture for correct layout.  Now it is time to tighten the springs to hold the limb in place.  Holding one tightener in each hand, turn them both 2 full rotations toward yourself at the same time.  Stick finish nails in the holes drilled for this purpose to hold the tighteners in place.
Repeat with other limb.

Attaching the string to the limbs
Take the 60" length of para-cord casing and the 2 loose ends together to make a loop.  Now tie the knotted end to one arm using whatever kind of knot you are comfortable with.  Be sure to leave a loop about 3/4" to 1" to loop around end of the arm. This ensures string is secure. Twist the loop of casing to make a nice tight string between the limbs and tie to other limb the same as the first.  You may have to adjust the length of the casing or the amount of twists to get a tight fit.


Step 9: A Note About Arrows

I made my own arrows as the picture below shows.  That might just be my next Instructable.

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    7 years ago

    This is awesome I'm sooooo adapting this design into a longbow size design


    7 years ago on Introduction

    Your attempt to explain the construction of the torsion springs (Step 7) is rather pathetic. It does not offer a clear explanation of how/where to begin or end the spring cords. Do the ends hang loose? That would unravel the spring. It offers little assistance to the casual reader. Please consider adding more detail.


    8 years ago on Introduction

    I love reading all these inspired projects and seeing the (mostly)supportive comments. I feel frustrated that I have a garage full of tools and wood and other supplies and no one to utilize them. Even I have a hard time getting started because there's not good organization of everything. My family would like me to just get a dumpster but I have old heart pine 2x4s and beams and bolts and hardware just aching to be turned into something in the right hands. I have tried offering a rental house I own for free to a local hackerspace but after leaving me hanging for months they rented a bigger space. I just want to expose kids and adults to doing and making that maybe don't have the place or resources on their own. Any thoughts on how to connect? ps. Organization is not my strongest suit.


    8 years ago on Step 8

    just asking, why the lever trigger instead of a roller nut?

    This is brilliant, possibly one of the best things i have ever seen. I have tried building my own crossbows before but i could never source an effective prod, well good enough to hunt with anyway. This is the ideal solution to my problem, how powerful is the crossbow?


    9 years ago on Introduction

    Hi dbull
    I'm in the process of making the scorpion , having trouble downloading the stock plans could you give the length and with of the stock and barrel . Thanks Ron

    Very cool but this is not a crossbow, it is a Roman Scorpion. A Scorpion uses rope torsion with rigid arms while a crossbow uses arms that flex when pulled back. See attached pictures. (first is a scorpion and second is a crossbow)
    Nice work anyway


    Reply 10 years ago on Introduction

    While we're getting all technical the projectiles crossbows shoot are generally referred to as bolts, not arrows. A scorpio is a type of a crossbow too so the original author was technically correct. Actual scorpios all have mount stands.

    Great article by the way.


    Reply 12 years ago on Introduction

    I didn't originally-I added that after I verified this comment was correct. I didn't want to totally change my title and confuse people. thanks though!


    Reply 12 years ago on Introduction

    I stand corrected, sir! I actually modeled my weapon off of pictures of ancient Roman weapons I have seen, but the books I had didn't say what they were called. Thanks for the info and the compliment.


    Reply 12 years ago on Introduction

    And I just looked at the instructable again and you have a very cool trigger design! I build a giant version of this a few months ago (about 10 feet long) at my friends house but we never could figure out how to make a trigger...Maybe ill try to build one like this!


    Reply 12 years ago on Introduction

    that sounds awesome. Just shoot me a message if you need any design pointers. The more I use this one, I'm sure I will come up with some tweaks to the design. I would be happy to lend a hand


    11 years ago on Introduction

    im going to make this but a dumbed down version as im a beginner.


    11 years ago on Step 9

    amazing! the trigger system helped me sooo much, iv been wanting to build a cross bow for ages, but all the triggers i could find where either to hard for me to build, or required tools/metals that i didnt have, thought i wont be using the bow that yours has, (im attaching an old fiberglass bow) everything else is awsome!!!!! thank you sooooooooooo much!!!!!!!!!!!!!!!!!!!!!! =)


    11 years ago on Introduction

    that's amazing!!

    unfortunately, i never have any money and i don't have the tools. what i might do though, is make it out of plastic, metal, and sweet gum saplings... thats about all that i have access to!