Taking the strain

After looking at the steps to build a simple polariscope in Straining the point and Strain in the neck, this time we’ll run through the use of the device to visualise and recognise strain in typical neon bends, as well as some basic annealing techniques that can help to reduce strain and lessen the chances of breakage.

Scientific and industrial polariscopes can be used to make numerous accurate measurements of strain and its properties in a wide range of transparent materials. In this post we will concentrate on using the kind of simple polariscope shown in the last two posts to make fairly simple determinations of the level of strain in glass. For typical neon work this is more than adequate (although scientific and industrial glassworkers may want something more refined).

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Strain in the neck

In the last post we looked at the steps to build a simple strain viewer, or polariscope. In this article we’ll try to improve on that design to produce a more robust, smaller, and more usable device.

The principals are exactly the same – the light source and two polarising filters to produce plane polarised light, and to filter out the light that passes directly through the sample. The only difference is that this time we’ll use a larger stage area, and a more sturdy case to house the unit.

img_20181014_1517411 — Finished 150mm² polariscope

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Straining the point

Welcome back to another home-brew neon equipment post. This time we’ll take a look at techniques for visualising strain (or stress) in glass.

Stress develops in glass when it cools unevenly from a softened or molten state. This often happens when the glass is cooled or heated rapidly or when the glass itself is uneven (perhaps because the thickness of the heated glass is not uniform). Mechanical forces that exist between the different parts of the glass cannot be resolved since part of the glass has already cooled back to the solid state. These forces remain trapped in the fabric of the material and may cause unpredictable breakage at some future time.

Very rapid heating or cooling may cause glass to immediately shatter from the stress – especially if some pre-existing strain is present.

Viewing strain fringes in transparent polycarbonate with the polariscope

In this post we will look at the construction of a very simple optical tool for examining stress in glass that can be built cheaply and with simple parts and materials. The total cost is under £20, and a simple device can be built in just a few minutes.

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Cutting Crew 2: Electric Boogaloo

In the last post we looked at a range of manual techniques for cutting glass tubing. Most of these rely on creating a scratch in the glass surface which then allows controlled cracking and separation of the ends.

It’s always easy to apply these methods to straight, unbent tubing and for this type of job these techniques are all that is needed. Sometimes however, it may not be possible to break the tubing in the conventional manner, either because it is awkward or impossible to get good leverage on the tube to snap it, or because the length of glass to be removed is just too short to be snapped. Trimming electrode doublebacks, or to make welds for continuation tubing are common cases where a different approach might be required.

In this post we’ll look at the design and build of a simple hot wire tube cutter for the neon workshop using common off the shelf parts. hwtc-1

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Cutting Crew

Glass is a tough material that shows excellent strength and resistance to breakage, but this all depends on the integrity of the outer surface. An imperfection, scratch, or other break in the continuous surface of the glass can be made to spread and eventually cause the glass to break: the difficulty is in making this a controlled process that yields a clean, square cut without jagged edges, cracks, or chips.

Cut glass will typically need to be welded, either to an electrode or another section of tubing and this is most reliably performed when both pieces of glass have cleanly cut surfaces.

Many tools are available to cut glass in various forms. In this post we’ll concentrate on tools that are useful for cutting the types of tubing used in neon work. Diamond styli and wheels are common tools for cutting glass sheet but these have little use in the neon shop. We’ll run through the different types and their use, and the proper technique for splitting the glass.

: Tools for glass cutting (left-to-right): mill bastard file, laboratory glass knife, plastic glass knife, diamond file, circle scorer

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Control freak

Welcome back to part two of this series on control systems for neon workshops (and apologies for the slightly longer than planned hiatus over the winter break!).

In this post we’ll look at the details of putting a system together, and the parts and circuit elements involved.

After looking at the requirements and high-level design in Standing in the way of control, we have an idea of what we are trying to achieve and the requirements for the finished system: now it’s time to choose parts that meet those goals and figure out exactly how to hook them all up together.

Front panel with start/stop buttons, voltage select and status lamps,

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Vacuum cleaning

I realise we haven’t really gotten into the details of the diffusion pump on the blog so far (or any vacuum pumps at all to be honest), but since I needed to dismantle my pump for a service this week it seemed like a good time for a post on the subject of the care and feeding of these clever little machines.

While the pumps were down I also took the opportunity to change the oil in the mechanical pump so we’ll look at the steps involved in that job too.

We’ll have a quick look at how the pump system works and what it’s doing for us in the bombarding process and then run through the steps to clean and re-install a glass bodied pump in an existing set up, and a typical oil change procedure for a rotary pump.

I’ll quote details for the SVP standard flow pump that I use (also valid for Precision Neon Labs pumps), as well as my Vacuum Research rotary pump, but the procedures are largely the same for any glass diffusion pump or mechanical roughing pump used for neon work.

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Standing in the way of control

A neon workshop contains a number of electrical systems to support the glass work and processing equipment: electricity powers the bombarder, air blowers, mechanical vacuum pump and the heating and cooling equipment for the diffusion pump, as well as a host of minor auxiliary loads such as gauges and the spark tester.

In this article we’ll take a look at some of the components that go into the controller for a neon workshop as well as some of the high-level design and practical considerations involved in putting together a working system. Continue reading “Standing in the way of control” →

Burn baby burn

“You’ve worked hard, and you’ve saved and earned, but all of it’s going to burn”

It’s a little known fact that Arthur Brown wrote these lyrics while setting up his first neon shop: he’d just read the quotation for the necessary gas torches and was feeling the heat in his wallet.

It’s a truer fact that the burners, and the equipment needed to run them, are one of the two chief expenses in setting up a working neon shop. Getting the right kit and understanding when and how to use it is key to setting up and staying within budget.

Arnold 141aPLS torch

6″ ribbon burner

Flame bench two

Arnold 103PLS Bench Burner

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Pipe down

This week I thought I’d take a brief detour from electrical matters and take a look at another fundamental topic for the neon shop: pipe work. Standard industrial fittings can be used to make air and fuel gas pipework and manifolds, and are cheaper and more flexible than off the shelf equipment.

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