Trebuchet

What is a Trebuchet?

A trebuchet is a medieval siege weapon. Here are a few examples:

Château des Baux

Runneburg

Warwick Castle

Château de Castelnaud

Its primary use was to hurl rocks at castle walls. Think of it as a catapult on steroids. The major difference is a trebuchet uses a rotating arm, a large weight, and whip-like action to throw the projectile. Here's a YouTube video of a trebuchet in action:


Trebuchet Video

Why Build a Trebuchet?

Many say it's an interesting demonstration of applied physic. Some like the connection to ancient technology, and weaponry. But let's face it, there are very few castle walls to knock down anymore. Any reason other than "it's cool" is a rationalization.

Model Design

I choose to build a 1/6th scale model based on Dan Becker's design . I enhanced it by adding an adjustable release hook, and trigger.

Construction

The main frame is built out of four strips of pine, each 12" long. Two pieces are mortised together, forming a right angle.

Mortise Cut

Frame pieces

Cross beams are added, and secured in place with wood screws:

Frame With Cross Beams	Secured Cross Beams

Finally, the two frame halves are connected with four three-inch beams.

Frame With Connecting Beams

The throwing arm is built from a 19" piece of hard wood that is tapered at one end with a router:

Tapering Arm

Knotches are cut on each end of the throwing arm. One to hold the counter weight, and one to hold the throwing hook:

Arm (Counter Weight End)

Arm (Hook End)

Trebuchets thow in a similar manor to a hand-held sling. The projectile is held in a pouch (sling) attached by two lines. During the throw, one line remains attached; the other releases. The timing of the release is controlled by a hook at the end of the throwing arm. When the sling whips around, the line slips off of the hook and releases the projectile. The release point can be changed by altering the angle of the hook.

Hook

Hook and Throwing Arm

Hook and Sling

The counter balance weight is a 2.5lb fishing weight tied to a eye screw:

Counter Balance Weight

The sled is used to guide the projectile in the early part of its flight:

Sled

The trigger is used to hold the arm in place until the trebuchet is ready to fire. It's constructed from half a key ring with two loops soldered in stratigic locations:

Trigger

Trigger (Attached)

Trigger (Ready to Fire)

Finished Trebuchet

After some stain, varnish, and paint, here's the finished trebuchet:

Conclusions

The trebuchet doesn't throw as far as I'd hoped, but it's a toy not a weapon. And it was fun to build.

Here's a quick video of a second version of the trebuchet in action:


Trebuchet Video (280K)

Glass Fused Snowflake

Overview

This blog describes how to make a simple glass fused snowflake.

Components

Cut several strips of clear glass about 1/4" wide. Approximately three feet is needed for one snowflake.

Cut Strips

Break on score

Strips

From the clear strips, cut the follow:

• Six pieces 2 1/2" long
• Twelve pieces 1" long
• Twelve pieces 3/4" long

Cut six squares approximately 1/2" wide from green transparent glass. Remove the corners to form crude circles. Save the chips (corners) for later use.

1/2" squares

Squares, corners removed

In a similar fashion, cut one 1/2" circle from clear glass.

The picture below shows the components necessary to create one snowflake:


Parts

Assembly

1. Arrange in star pattern

2. Cap with clear circle

3. Add inner leaves

Closeup

1. Assemble the six 2 1/2" clear strips into a six-pointed star.
2. Place the clear circle over the center of the six strips. Secure with fusing glue.
3. Form inner leaves. Place two 3/4" strips on each snowflake arm about 1" from the center. One end should rest upon the arm, and the other on the kiln shelf. Secure with fusing glue.

4. Add outer leaves

5. Add green circles

6. Add green chips

Closeup

4. Using the 1" strips, assemble outer leaves. Secure with fusing glue.
5. Place one green circle onto the end of each arm of the snowflake.
6. Accent each inner leaf with a green chip (saved corner of squares). Place a small drop of fusing glue, and then a green chip on the end of each inner leaf.

Fusing

Place the snowflake into the kiln, and fuse at 1465^oF for 5 minutes. Anneal for 20 minutes at 960^oF. Flash cooling (crashing the kiln) is not necessary.

Finished Snowflake

Snowflake

Snowflake

Fusing Glass

Introduction

Let's face it, I'm obsessed with glass. I've made stained glass for years, and I built miniature studio in my garage so I can make torch-worked sculptors.

Fusing, and slumping is one of the few glass art forms I haven't yet tried.

Having no previous experience in fusing, I decided to take a class at the Bay Area Glass Institute (BAGI):

What is Glass Fusing?

Fusing is the process of heating multiple pieces of glass in a kiln to form one unified piece. Heating the glass just enough to join, but while still retaining the original shape of the individual pieces is called a tack fuse. Heating the glass enough to form one seamless piece is called a full fuse

What is Glass Slumping?

Slumping describes the processing of reshaping a piece of glass by heating it, and allowing it to fall into a mold (form).

Instructor

My instructor, Janett, has an amazing knowledge of not only glass fusing, but also torch working, glass blowing, and stained glass:

Tools

Here's the tools of the trade:

Bullseye glass

Kiln

Glass cutter

Fusing glue

Not all glass is appropriate for fusing. Glasses which expand, and contract at different rates will indeed fuse, but then crack as they cool. Bulseye glass is the most popular as it comes in a wide variety of colors, and styles.

Kilns are basically big ovens which can reach about 1600^o

Glass cutters are used to create scores, and direct glass to crack along certain lines.

Fusing glue hold the glass in place before it is fired.

Kiln shelf

Kiln wash

Applying kiln wash

Fusing is typically done on a large flat unfinished ceramic kiln shelf.

Kiln wash is basically glass Teflon. It keeps the glass from sticking to the shelf.

First Project

Glass fusing is deceptively simple: Cut out pieces of glass, arrange them, and pop them into the kiln. Here's my first project:

Red circle of glass	Cut-up circle of glass	Into the kiln
Fused circle

But there are any number of things that can go wrong. Molten glass flows -- sometimes in unpredictable ways. Fire too long, and the glass will spread out, and then contracts back leaving uneven borders. Fire too short, and you'll get lumpy glass. Some glasses melt faster, and spread out when fired; others tend to stay put. And many types of glass don't fire true -- i.e. change color when fired. To help out us neophytes, Janett created this pallet of pre- and post-fired glass:

Second Project

Here's my second project. On the bottom is a layer of clear glass. The second layer has red on the edges, stripes of black, and more clear in the center. On top of that is amber squares, and sparkling green stringers (thin rods of glass).

Before fusing

Fused, and slumped

Julie's Projects

Here's a few projects made by my classmate Julie. The piece below is made of three layers of glass, giving it great depth. Some of the squares almost appear to float.



Here's very simple, but elegant design:

Big Tools

One of the cool things about BAGI is their equipment. I grew up with a garage full of lathes, acetylene welder, and drill presses, so I found BAGI's collection of over-sized glass grinders fascinating:

Belt grinder

Bench grinder

Disk grinder

Holiday Sale Items

BAGI is a nonprofit organization, and every year they have a Holiday Sale. Artists donate pieces, and the proceeds go to BAGI. These are amazing. I guess it's always good to have something to work up to ...

Holiday Sale

Holiday Sale

Holiday Sale

Holiday Sale

Conclusion

I've seen a lot of fused glass at art shows -- much of it monumentally bad. From this I assumed any yo-yo could fuse. But it's more complex than I expected. There's a lot of technical gobbly guck: coefficient of expansion, annealing/fusing/tacking temperatures, devitrification. There are four types of clear glaze that melts at different temperatures. There's dozens of types of glass: transparent, opaque, streaky, iridecent, textured, dichroic, two types of black, and 19 types of clear!

But it's not that hard either, and it is great fun.