Leading Tight Curves

Sometimes it can be difficult to get the lead came to conform to the curves of the glass, especially on compound curves.  This is a method to make the leading more accurate.

When leading tight inside curves, bend the came into a tighter curve than is needed for the glass. Then roll it into the glass. Finally, run your fid or stopping knife along the heart of the came to ensure it is firmly against the glass. All this helps the came to fit snugly into the curve.

Foiling Tight Curves

Foiling tight curves often leads to splits in the foil.  This note gives information on how to generally avoid the splits and a repair method when they do occur.

Make sure the piece of glass is free of dust and oil and that there are no sharp ledges. Find the flattest part of the glass piece to begin the foiling.

To get the foil to stick to the curve and fold over onto the glass with the minimum of tears, use your fingers first to burnish the sides of the foil onto the piece of glass beginning on the outside curve.

As you move to the inside curved portion gently and progressively ease the edge of the foil with your finger toward the surface of the glass. Easing and burnishing one side of the curve at a time will give you better results toward getting the foil to stretch onto the glass without tearing the foil.

Finish by burnishing the foil down using a fid. This helps keep the foil firmly adhered to glass through the soldering.

Dealing with splits
Tears in the foil line happen. Clean up the broken foil lines with a craft knife and the solder line will look nicer when project is finished. You can also patch the tears by placing a small section of foil over the broken foil.  Place the scrap on one side, burnish it, and fold it onto the edge.  Ease the foil onto the second surface and burnish all the surfaces again.  Then trim the scraps that extend beyond the rest of the foil with a craft knife.

Cutting Hour Glass Shapes

Hour glass shapes, wasp waists, or those that are thinner along the length than the ends, should be avoided as much as possible.  They are difficult to break out from the score.  More importantly, they are an inherently weak shape. The longer the piece is with the narrow part along its length, the more likely it is to break; in cutting or in the long term, in the panel.  However, these shapes are sometimes unavoidable.

The principle to use in scoring and breaking out the glass is to remove less glass than that you are retaining at each stage of the process.

This has consequences: 

• ·         breaking the first score is the easiest
• ·         only a rough outline of the final piece should be scored and broken from the sheet
• ·         Relieving scores and breaks will be necessary.  The number will depend on the relative thickness of the thin and thick parts.
• 
  

You can make the first score and break of one side of the shape from the main piece of glass – usually with little difficulty or need for relieving scores. (1)

You then should score and break off the piece to be retained from the larger sheet.  Be sure to give a margin for the final piece. (2)

Now score the other part of the hour glass shape.  Do not tap the score. Begin gently to run of the score from each end.  Don’t worry if the runs do not meet up.  Do not tap to make them meet up. (3)

If running the score from both ends is not enough to make the run complete, you will need to use relieving scores.  These scores can be like onion rings – generally concentric curves running in the same sort of shape as the curve to be broken out.  

Or you can use the fish scale approach – overlapping crescents.  These are most useful for deeper inside curves.

Either way, each score needs to be planned.  Each relieving score should be smaller than the width of the piece to be retained.  In general, this means the outer relieving scores can be wider apart.  As you approach the final shape, the distance between the scores will need to be less and less. (4,5,6)

More information on scoring and breaking out concave curves can be found here:  http://glasstips.blogspot.co.uk/2008/08/cutting-concave-curves.html

Holding the Cutting Head

Many people hold their cutting head steady with a finger during the scoring process.  This is not necessary.

The axel of the cutting wheel is slightly forward of the centre line of the cutter.  In addition, the cutter is held slightly angled back toward the operator to be able to see the wheel and the cartoon (or marker) line.  Both of these act to ensure the wheel follows the movement of the arm or body in a forward motion. 

In cycling, the distance between the angle of the shaft of the cutter and the axel is called the “trail”.  The greater the amount of trail, the easier it is to keep the bicycle following a straight line. The same applies to the cutter. This trail is created by the extension of the angle of the cutter to the glass.  The axel of the wheel is behind that line. The cutting head has a sharper angle at the back than the front to accommodate this angle backwards. The resultant forward force is in front of the axel and so leads the wheel to follow the direction of the cutter without any need for stabilisation.

There is no need to have your finger on the cutting head. It swivels for a reason. It will follow the direction you are pushing without any angle, so there is a clean score.  If you attempt to stabilise the cutter head you risk the wheel running at a slight angle to the direction of the score.  I talk about this as a skidding score. The result of this is to give a score with forces directed not only straight down but sideways too.   This gives the glass many more ways to break.  And not always along the line you want.

Also when you want to score a tight curve, the slight movement of the head allows the curve to be slightly smoothed again without any skidding.  This means there will be fewer pressure lines sideways to the score line.

Manufacturers have put the play into the cutter heads for a reason.  The above attempts to explain it.  The manufacturers would not include a feature that costs time and effort, as well as cost if it had no purpose.  It seems perverse of us to try to run counter to that by holding the head or even fixing it solid, so it is unable to pivot at all.

Assembly of Circles and Irregular Shapes.

Leading

Circles and ovals as well as irregular shapes significant support as leading often involves sideways pressures to fit the lead to the pieces of glass. Thus there are two main methods of support for the perimeter of the panel.

You can cut supporting pieces of glass to place around the perimeter. These need to be cut to the outside of the perimeter cut line. These supports must be in at least two or more pieces to enable the came to be put in place progressively. You then assemble the perimeter lead into it and continue to lead up as normal. The perimeter support can also be made from thin plywood or similar materials. This can be useful if the shape is to be repeated.

A simple means of supporting irregular shapes while leading is to place a number of nails around the inside edge of the cut line. There need to be enough to support each piece of glass with at least two nails. So you may need to add more nails to the initial set up. Build the panel without the perimeter leads. When the interior is assembled, put the perimeter came around the panel. Ensure the fully leaded panel fits within the dimensions of the opening. Then solder as normal.

Copper foil

The above methods can be used, but are often a bit heavy duty for copper foil processes. Instead of glass, timber or nails you can use more easily cut materials. Such things as stiff double walled cardboard, foam board etc., are suitable for light duty. You can cut the complete shape from these materials, but only good if no pressure is used in fitting the pieces.

If you are likely to repeat the shape and size, you can use plywood or similar materials. Build inside the shape and remove it when the whole is soldered on the first side.

Jewellery-scale Ovals

Rather than trying to perform the difficult task of cutting small ovals, you can use the heat of the kiln to do some of the work for you.

Cut a rectangle the length and width of the oval you want. Then groze the corners to the approximate curve of oval you want. Do not worry about the little inaccuracies of the curve. If it is the curve you want, the heat of a full fuse will even out the edges into oval you want. Clean the glass, assemble and fire to your normal full fuse temperature. The result will be a smooth edged oval of the shape you grozed from the glass. Of course anything less than a full flat fuse will produce a piece with some of the inaccuracies that you grozed into the glass.

If you do not go to a full fuse, or are using only 3mm thickness of glass, this will not work.

Refining Edges

You can make the freshly cut glass safer to handle by gently wiping the edges of the cut piece with the waste piece. This removes the sharpest edges without chipping the glass.

After the glass is scored and broken, you can remove small, unwanted chips with grozing pliers. The serrated jaws of these pliers are used to gently nibble away at the jagged edges.

Rough edges can also be smoothed with a carborundum stone. You rub the stone along each edge, upper and lower, to remove any sharp edges. You can remove more glass with the stone if you wish by a little more aggressive grinding action or just a longer light rubbing of the stone against the edges.

A diamond smoothing pad removes glass in much the same way as a carborundum stone, but does it more quickly with the coarser grades. You can use a number of grades to get an almost bright polish to the edges. These pads must be used with water.

A glass grinder is used by many people. Many models of grinders are available. The grinding surface of the bit is covered with fine diamonds, which grind away unwanted glass very quickly without chipping the edges. In addition, they are water-fed which keeps the glass from cracking due to heat, prolonging the life of the diamond bit, and preventing the powdery ground glass form flying around.

A glass grinder is not a substitute for accurate cutting.

Cutting with Patterns or Templates

As a general rule, always make the hardest cut first. Glass tends to run in a straight line. This means inside curves should be done before any other cut is made.

It will be most efficient to place the pattern to be cut with the inside curve facing the raw edge of the glass. If something goes wrong, the pattern can be backed away and tried again, resulting in less glass and time wasted.

It is also hard to break very thin strips of glass away from the desired piece without getting ragged, chipped edges. Allow a 6 mm minimum distance from the edge of the glass when placing the pattern on the glass unless the edge is going to be used for the whole edge of the piece.

When scoring around a paper pattern it is necessary to steer (turn) the cutter in the proper direction. The paper will not turn the cutter for you. You should steer the cutter by turning your upper body rather than your fingers, wrist or elbow.  Failing to do this may allow the cutter to run over the pattern and so fail to score the glass.

Alternatives to using the paper pattern directly as a guide in cutting glass are to outline the pattern paper on the glass with a pen or to draw the pattern on the glass while it overlays the drawing. You follow the inside edge of the pen line with the cutter.

Directly cutting the glass over the cartoon avoids the time spent in making patterns, and the difficulties and inaccuracies in multiple transfers of the shape. Often a light source is required under the cartoon to enable the lines to be seen through the glass. There will always be times when the glass is so dark or opalescent that the lines cannot be seen and therefore a pattern is required.

Keep the pattern cutting restricted to the times when nothing else will do.

The only times I use patterns for cutting are when the glass is too dense for the cartoon lines to be seen through the glass with light behind or for repeat shapes where a pattern can speed the process.

Two pattern pieces used to draw repeats of sails on the glass and then cut out

A boat design assembled in the kiln

 I draw around the pattern pieces, as that avoids the possibility of the cutter riding up on the card that I use for templates.  This comes from several occasions when the cutter did go over the template which prevented the score and so created a bad break.  Others do score around the template stuck to the glass successfully.

Where to Start Cuttng the Glass

As a general rule, always make the hardest cut first. Glass tends to run in a straight line. This means inside curves should be done before any other cut is made.

It will be most efficient to place the glass to be cut with the inside curve facing the raw edge of the glass. If something goes wrong, the glass can be backed away and tried again, resulting in less glass and time wasted.

It is also hard to run very thin strips of glass without getting ragged, chipped edges. Allow a 6mm minimum distance from the edge of the glass when placing the glass on the cartoon unless the edge glass is going to be used for the whole edge of the cut piece.

Copper Foil Splits

Copper foil splits often occur at tight inside curves. This is caused by the inability of the copper to stretch enough at the edges to make it around in tact.

There are at least two ways to deal with copper foil splits: avoid them or repair them.

Avoidance
One way to avoid splits at tight inside curves is to hand foil pieces that have these curves. When folding the foil from the edge to the sides of the glass, gently and progressively ease the foil toward the sides of the glass with your fingers rather than a hard tool. Do not try to make the fold all at once. Give the foil the chance to stretch into the curve through gentle persuasion.

Another way to avoid the splits is to use several short strips of foil at the tight inside curve. Apply each strip from one side around the edge to the other side of the glass. Overlap each strip until the inside curve is covered. Then you can cover the whole curve in the normal way with the copper foil. When the piece is foiled, you can then take a craft knife and trim the overlapped foils to match the edge of the long strip of foil. Or you can just trim the overlapped foil pieces to match the rest of the foil. Be aware that this increases the space required between the glass pieces as the foil is now effectively twice the thickness of regularly applied foil.

Repair

To repair splits in the foil at tight inside curves that have been foiled along with the rest of the piece, you take small pieces of foil and overlap at the splits.

Then trim the overlaps to match the line of the main foil. You can do this only on the surfaces or by going from one surface around the edge to the other surface.

When tinning these repairs, you need to take care that the heat from the iron does not loosen the adhesive so much that the foil pieces move.

Outside Curves

Outside curves are usually the easiest curve to break out. You do not have to worry about breaking the piece you wan to keep.  The break, if it goes off the score line, will be away from the piece rather than into it. 

Outside curves often have complimentary inside curves. So, on the principle of making the most difficult break first and the easiest last, the outside curve will be broken out last. Unless, of course, there is a straight line on the other side of the curve when the straight line would be the last, as it is the easiest score to break out.

Cutting concave curves

There are several methods that can be used to break out extreme inside curves. In all the cases you should retain a significant amount of glass around the edges of the curve. You should make this most difficult cut the first on the piece. If it fails, you may be able to move the glass a little and score again, without loosing too much glass.

To accomplish inside cuts by using the hand breaking method and/or pliers method, you must first score according to the cartoon line. Then you can make a series of concentric scores. Gently run the primary score line so any break does not run beyond this. Remove the graduated concentric scores in sequence.

In this example the glass is placed over the cartoon and scored directly over it.

You can also accomplish this type of cut by using the criss-cross pattern of score lines instead of concentric scores. First you must run the score of the curve to avoid the criss-cross lines from running beyond the curve. Then you begin to take out the little pieces from the waste area.


Another method is to score and run the curve (1), and then score a number of small crescents in the waste area, looking like fish scales or the fan type of paving seen in some European cities. Pull out each small crescent working toward the main curve (2,3,4).

Cutting Circles

Circles can be scored freehand or with a circle cutter.

First, score the circle, making sure that you start and stop the score line at the same point.  The direction should be anticlockwise to avoid loosening the locking nut on the length bar.

Turn the glass over onto a piece of corrugated cardboard, or other surface with some give, with the score line face down. With your thumbs, press along the score line until you see the score line "run" progressively and completely around the circle. This prevents the relief scores you are going to make from running through the circle.

Turn the glass back over to the side on which you scored it. Score several lines perpendicular to the circle to the corners of the piece of glass.

Gently open these scores by tapping with the ball of your cutter, or with your hands, pliers, or other tools. The pieces should fall cleanly from the circle leaving you with no rough or jagged edges.

Measuring for size

Cutting small circles

Various methods

Revised 26.4.24

Deep inside cuts with turntable

Deep inside cuts can be assisted by using a lazy susan – a turntable affair, similar to a cake decorating turntable.

The first question you have to ask yourself is whether you should make such deep inside cuts or redesign the piece to avoid creating such fragile shapes.

OK. You have decided to go ahead with your plan in spite of good advice. Put your cartoon onto the turntable and the glass over it. If the glass is too dark or opalescent, make a template and mark the glass. Adjust the starting point, put one hand on the glass and cartoon, and turn the glass instead of yourself to get round the score with ease.

You still have the task of breaking out the glass from the score line. This is the subject of another tip.