Small HCW trebuchet plans

height to top of arm when at rest

about 465mm

height to pivot

195mm

drop of counter weight

114mm

counter weight

500 to 650 grams lead shot

projectile

5 grams

ratio of counter weight to projectile weight

100 : 1

upper arm/lower arm length

268mm / 67mm

base dimensions

315mm long, 220mm wide including buttresses

sling length

260 mm

The start of the frame.

The base (middle) is added.

The uprights are added.

The front, rear and side buttresses are added.  You might like to leave the side buttresses until after the cross members are glued in place later.

Cap glued to top plate.

Make 2, one for each side of the treb frame.

Gluing top plate and cap assemblies to top of uprights, the bucket of shot is there in an attempt to ensure that the assemblies are glued 'true' to each other.  It seemed to work!

Top plates glued to inside of uprights and cap assemblies.

Cross members glued to side of frame.  Note that each cross member has a channel in it to accommodate the other cross member - see this picture for a view of the cross members mated together.

Track supports glued in place on bottom of frame.

Track glued in place.

Track sides glued in place.

Trigger mechanism attached to underside of track.

Frame complete.

The start of the counter weight carrier.

Ends added.

Side added.

Hole drilled through side plates at same time (using a bench drill).

Dowel added to support the bottom of the carrier.

The start of the throwing arm.

The arm with the tube fitted for the axle and the pin lashed to the end.

The tip of the arm, sling not yet attached.

The arm, and all of the gear needed to mount it to the frame and make it pivot.  The cartridges are on the outside, then pieces of tubing that go in the cartridges are between the cartridges and the arm.  The axle is shown in the tube in the arm.

The completed arm/axle assembly.

The cartridges mounted in the cap pieces on top of the frame.  Note the holes in the cap pieces.  These were drilled through the cap pieces with the cartridges in place to be sure that the holes in the cartridges lined up to allow me to hold the cartridges in place with pins.

The pins are pushed into the holes, securing the cartridges.  This took a fair bit of patience and mucking about but it was worth it because it keeps everything nice and straight and square whilst allowing me to remove the arm should I need to.

This is a close up of the trigger mechanism, it's really quite simple but is only suitable for small trebuchets.  Larger trebs would exert much more force on this type of trigger mechanism, probably to the extent that you might not be able to fire the treb.

Another view of the trigger mechanism, with no sling attached.

A view of the pouch suspended while the arm is at rest.  The pouch is folded from a piece of plastic carrier bag, with a small piece of cord sewn to either end.  The sling is completed by attaching a longer piece of cord to each piece of cord on the pouch.  The longer pieces are attached to the pouch using a lark's head knot, with one of the longer pieces looped through an eyelet on the under side of the throwing arm to form the fixed end of the sling.  The free end of the other long piece has a small ring affixed to it, the ring going over the pin on the tip of the arm.

A side view of the loaded pouch when the arm is cocked and ready to fire.

A top view of the loaded pouch when the arm is cocked and ready to fire.

A view of the loaded pouch from the business end of the track.