A Home-Built Glass Working Lathe

Version 1.00

Copyright © 2000
J. Lega and Samuel M. Goldwasser
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Corrections or suggestions to: papalega@swbell.net or sam@stdavids.marconimed.com

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Introduction

A commercial glass-working lathe is a fairly expensive device for sporadic and limited hobby work.

This is a short description of a home built glass-working lathe which has helped in the manufacture of glass tubes for pulsed argon and other lasers.

Although I was able to make hand supported butt seals that were functional, they looked uneven and were difficult to lineup in the laser tube support so that the capillary would be centered. I then decided to manufacture a device that could reduce my lack of skills in this area.

Description of the Glass Working Lathe

I came across a microwave measurement device manufactured by Measurements Corporation that had a couple of carriages riding on two parallel rails. The carriages used linear ball bearings, which made their riding very smooth and accurate. This was the starting point for the lathe. However, this could have been manufactured using parts from W. M. Berg Incorporated. They have a web site with catalog information. They specialize in hardware of the type needed for this project, such as timing belts, machined rods, linear bearings, pulleys etc.

There were several items, which I could not manufacture at home due to lack of proper machinery. I located a machining shop and had them made to order. Those were the two pieces of stainless steel schedule 160 pipe and the key on the driven shaft. The other pieces and components were readily available or were purchased from W. M. Berg.

The carriage end plates were leftover pieces of aluminum from a previous project. This limited their size and therefore the rotating clearance. The thickness of the rotating pipes was selected so that the radial glass holding screws would have enough "meat" without the need to attach nuts to the internal diameter of the rotating pipe. A much lighter rotating pipe can be used if screw nuts are soldered to the inside or outside of the rotating pipe. Make sure that the screws are radial to the longitudinal centerline of the pipes.

The reader is encouraged to replace components and to find alternatives to the design and parts shown in this article. The principle should be maintained: two glass tube holders which run concentrically, can hold the glass tube centered and one of the holders needs to move horizontally, maintaining concentricity.

In lieu of the Measurement Corporation carriage, one could use a dovetail rail if it can be made to ride smoothly in the horizontal plane. Getting fancy, one could install a rack and pinion drive to the movable carriage.

Possible Improvements

Here are some suggestions for changes to the basic design:

A higher throat or tube-to-rail clearance height would be a welcome addition, if "refurbishment" of broken laser tubes were contemplated. This would allow, for instance, replacement of the capillary on tubes, which are already equipped with electrodes. (NOTE: This would affect the length of the belt) I do not plan to perform this retrofit, since it requires major re-work.
Variable speed motor. The original model uses a constant speed motor that may be too slow for some work, since some glass pieces tend to droop when heated to high temperatures. I do plan to perform this retrofit.
Use of a metal working lathe chuck on one end. This allows supporting short pieces of glass, such as the end pieces of the pulsed Argon tube and sealing electrodes to Pyrex glass etc. This is shown on the pictures. For a lower cost, a standard 3-jaw drill chuck can be used. Either can be supported by the radial screws on the carrier pipe.

The Drawings

The original drawings were developed in AutoCAD and converted to GIF files. Although the GIF files are adequate, if someone is interested in the project and benefits from the original drawings, they can drop me an email and I will attach the drawings to my response. The only addition to the final product, which is not shown on the drawings, is an idler pulley on the timing belts. This was required due to a small amount of slack on the belt, yet not enough to allow the next standard smaller size belt to be used. The idler is shown on the pictures but not on the drawings.

Here are the drawings:

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