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Glass Blowing for Vacuum Devices

Filament Lamp C

This lamp has a blown bulb, but does not require any glass joining. It is also the first time I have applied oven annealing.

The construction methods are the same as for previous lamp designs, but the bulb is blown part way along a tube. One end of the tube then becomes the pumping exhaust and the other is for the electrical connections.

Blowing a bulb part way along a tube is possible by hand, but is extremely difficult. The use of a lathe makes the operation much easier. The lathe shown above is a Unimat 3 metalwork lathe. A metalwork lathe is not ideally suited to glass work. Unfortunately, proper glass working lathes are very expensive and tend to also be very large and heavy. The main special feature of a glass work lathe is that it has two chucks that are driven in synchronism. I have substituted this feature with a PTFE support mounted on the cross slide. The lathe is set to its minimum speed (130rpm)

The blue bulb attached to the brown tube is a 'mini-lung' made by Neon Works. It saves having to physically blow into the tube. I have found it to be very effective. The bung in the left hand end of the tube has a rotating joint.

Above is one of the better results. The support has to be aligned with the tube very carefully. Any excessive friction causes twisting of the bulb while it is hot. The orange sleeve in the chuck is a neoprene Hellerman sleeve to protect the tube and provide grip.

Above is a 7 minute movie of a lamp of this design being made from start to finish.

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