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Floating Arm Trebuchet Plans Download

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The parts list has now been added in Page 5. General construction steps coming soon. Please contact us with questions or corrections!
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Parts List / Cut List

Dimensions are in actual size, not rough cut pre-milled. Some parts were ripped 2x4's down the center. Most of the wood was cheap scrap 2x4 or 2x6. So when you see 1 1/2 x 3 1/2 that is really just a 2x4 as you would purchase it if you go with a soft wood. For those people that work with wood all the time I know it doesn't need explanation, but for some this is their first foray into working with wood, and milled sizes for soft woods and hard woods don't always match. For this whole project you can pretty much use cheap straight pine 2x4's with the exception of the wood guide wheels. If you want to spend a lot of money you can use oak. Regarding the wheels... You really don't need to make wood wheels and make the grooves and guides because you can subsitute plastic lawnmower wheels. You can always add more 2x4's to guide the wheel if it tends to get off track. We just wanted it all wood, metal, rope, and fabric.The best advice during assembly and construction is to make everything square. Have a good flat surface to assemble parts and use a carpenter's square during each stage.

In the parts list the "action end" will refer to the end where the guide wheel is.

Any parts listed as optional either add a little bit to the strength, guiding, or to the prettiness. You can make lots of substitutions for just about anything.

This list of parts hasn't been tested yet, so let common sense dictate.

Parts Laid Out.

These are all the guts for the trebuchet
Parts Laid Out

Full List

PartQuantityNameDimensionsRequiredDescription
A4Uprights72" x 1 1/2" x 1 3/4"YesThe uprights function as the vertical guides for the dropping counterweight. These were ripped 2x4's from another project. You could also just use 72" 2x4's instead and adjust parts D, E, and P.
B2Base Supports62 1/2" x 3 1/2" x 1 1/2"YesThese are the base horizonal supports for the trebuchet.
C2Stabilizers24" x 3 1/2" x 1 1/2"YesThese go on the ends to ensure the trebuchet doesn't tip over on its side. They are simple horizonal stablizers. If you wanted you could attach wheels to them for easy transportation.
D4Outer Guides12" x 3 1/2" x 1 1/2"NoThe outer guides keep the wheel on the rails so it doesn't hit the uprights. Cut at a 45 degree angle on one end to match the upright supports. If your arm drops without any side to side motion on the wheel these aren't necessary but they are advised.
E4Upright Supports33 1/2" x 1 1/2" x 1 3/4"MaybeCut at a 45 degree angle on both ends. These are best saved until the latter part of construction and can be used to 'true' the squaring of the trebuchet, particularly the uprights to compensate for any warping or mistakes.
F4Vertical Ends32" x 3 1/2" x 1 1/2"YesThese are the four vertical supports on each end of the trebuchet. They connect the horizontal base to the horizontal rails.
G4Horizonal Rails30 3/4" x 3 1/2" x 1 1/2"YesCut a hole in two of them that is 5/8 inch in diameter with the center 1 3/4 inch from the top of the piece, and 1 1/4 inch from the end. The 2 pieces with the hole through them will be used along with the 5/8" steel rod for the guide wheel.
H2Upper Spacers5 1/2" x 3 1/2" x 1 1/2"YesThe spacers provide the proper separation between the two sides of the trebuchet. The spacer on the action end will be lower than the spacer on the other end.
I1Trough Base30" x 5 1/2" x 1/4"YesThe trough base provides a platform for the sling and projectile.
J2Trough Sides30" x 2 1/2" x 1/4"YesThe trough sides provide the 'U' shape of the trough to help guide the sling and projectile during firing.
K4Upright Spacers1 1/8" 1 1/2" x 1 3/4"YesThe spacers provide separation for the 4 uprights. 1 1/8" allows the 1" black pipe to travel down the uprights with enough play.
L2Lower Spacers2 1/2 x 3 1/2 x 1 1/2YesThese spacers are used in the base of the trebuchet. They provide separation for the two horizontal base supports.
M1Guide Wheel4 1/2" x 1 1/2"YesThis guides the throwing arm as it falls during firing. The trough in the wheel is not absolutely necessary. It is also not necessary to manufacture one. Lawnmower wheels can work too. If you notch the throwing arm router a 1/2" deep trough in the center of the wheel edge that is 3/4" wide. You should end up with about 3/8" of material left on each side of the trough but can modify either this or the throwing arm so it has enough play.
N2Arm Wheel4" x 1 1/2"YesThese two wheels go on each side of the throwing arm. As with the guide wheel, lawnmower wheels can be substituted. If going with wood you can use a Forstner or Spade bit to drill a 1 1/2 inch diameter hole on one side of each wheel that is 1/2" deep to countersink the rod.
O1Throwing Arm83 1/2" x 3 1/2 x 1 1/2" YesYou will need a 1" diameter hole on one side for the black pipe that will travel down the uprights. This hole is centered in the 2x4 3" from the end. You should have another hole for the arm wheels that is also centered. This hole's center from the end should be about 27 5/8" from the end closest to your first hole. Your measurements may vary. Ensure you look at the section where it goes over laying all your parts out and manually moving the arm through all stages firing. If you use the guide wheel with the trough you should router out the arm so it fits in the guide wheel. The notch in the arm should be about 11/16" or 5/8" wide and 7/16" deep depending on how accurate your guide wheel is. If you are using lawnmower wheels just just the 2x4 as is.
P2Action Guide11 1/4" x 3 1/2" x 1 1/2"NoThis will be the piece that acts as the wheel guide on the tracks on the action end of the trebuchet. It has a 45 degree cut on one side to meet the upright supports. Optionally, on the end that does not have the 45 degree cut, you can cut a triangle into it that is 6/8" wide, 1 5/8" long with a height of 1 3/4". This cut and the piece is optional. It does add some strength and emergency guiding but is mostly cosmetic.
Q2Wood Spacer Washers1 3/8" outside diameter, 5/8" inside diameter, 3/8" thick.NoThese keep the guide wheel centered. You can substitute washers, drill and put in cotter pins, or use whatever you have.
S139Screws#10 x 2 1/2"Yes
S271Screws#10 x 3"Yes
S310Screws#6 x 1 1/4"Yes
S42Screws#8 x 3/4"Yes
S54Screws#5 x 3/4"Yes
N16NailsCabinet nailsYesUsed for the trough plywood.
H14Lock Rings5/8"MaybeFor the lock rings we hacksawed triangle cuts in the 5/8" steel rod. If we were to do it again we would have just used washers and drilled for cotter pins. The lock rings look cool but they took too long.
W13Washer1 1/4" outside diameter, 11/16" inside diameterYes
W24Washer1 3/4" outside diameter, 11/16" inside diameterYes
W31Washer5/8" outside diameter, 3/8" inside diameterYes
H21Release Bolt6" long eye boltYesThis was just an eye bolt that had the threads ground off and was connected to the release rope to pull out of the uprights. You can use whatever you want or put your release mechanism at the bottom action end of the trebuchet.
H31Sling Mount2 1/2" x 3/8"MaybeThis can be anything you have. We had some old rectangular metal and bent the U-Shape. You just need something to anchor one side of the sling rope.
H41Counterweight Bar1 1/2' x 1" Black PipeYesWe were able to get about 100 pounds of large cast iron weights using this length. You can extend the length of the black pipe to get more on.
H51Guide Wheel Axle7 1/2" x 5/8" Steel Rodyes
H61Arm Wheel Axle4 3/4" x 5/8" Steel RodYes
H72Arm Reinforcement6" x 1 5/8" x 1/16" Sheet SteelNoThis reinforces the counterweight bar. Although ours was only 1 5/8" wide we could have made it wider and went all the way to the cut out notch on the throwing arm.
H81Sling Rope9' x 3/8" RopeYesThe rope that attaches to the sling is about 44" on one side and about 46" on the other but that doesn't include the knots. So 9 feet is a pretty good estimate. See Page 2 of the guide for more information.
H91Release Rope11 1/2' x 3/8" RopeYesThe release rope length can vary.
H101Sling (Projectile Pouch)12" x 15" DenimYesThis was made out of doubled over denim and we sewed around the holes we cut through. When adjusting the rope make sure it is even from the release nail and the other fixed side. The finished sling is 3" x 11" with a little over 1 3/4" fold over on each side before it was sewn. I think the original size of denim before folding and sewing was 12" x 15". The 12" side was folded in the shape of an 'M' and then the sides were folded in and sewn on the edges and a sewn circular pattern where we put the rope through.
H111Counterweight BoltAnyNoWe used an eyebolt to go through the top of the arm, through the black pipe, and out the other side with a washer and a nut on it. The original intention was to incorporate this into the release mechanism but it is not needed. If your weights on the outside are even and clamped on
H121Release NailWhatever you haveYesThis was just a nail with the head cut off and bent to our desired angle. We also put a washer on the end of the sling rope for easier release.
H13?WeightsCast iron free weightsMaybeYou can use weights or build boxes that hang off of the counterweight bar so you can fill the boxes with sand or whatever if you are going for accuracy shooting.
H142Weight ClampsStandard dead weight clampsMaybeWe did have to grind down the outside diameter of the counterweight bar so that the clamps would fit on. In a pinch you can just use a large vise grip on each side.

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