Fitting Glass in Leading

Even though you think you have cut the glass exactly to size, it always seems that some adjustment is needed to areas of a piece to fit both into the lead came and be within the lines of the cartoon.

The temptation is to trim the glass to the amount of overlap of the cartoon line.

Note the extent of the overlap of piece #7 on the right.

In the above photo it would seem to be easy to just trim the straight line off the piece.  If you look carefully at the left side of the piece, you will see a gap between the glass and the lead came.  This means something more is happening than just being too large.  If you were to cut the glass down to fit within the cartoon line at this point you would find it too small in the end.

To find out what is going on underneath the lead came, you will see that I have made a line with a felt tip pen at the edge of the came.

When pulled out from under the came the line shows there is more glass under the came at the lower left than the middle left.  This indicates that the lower left needs to be adjusted rather than the right edge.

Groze or grind the glass to an even amount of glass between the felt tip line and the edge of the glass. This may have to be done several times to get the proper fit.  In this case I used the grinder because of the extreme texture of the glass.

This photo shows the glass fits at the bottom right, but needs more adjustment at the top right.  But it does fit under the came at the left side now. The amount of adjustment can be judged by marking the glass and grinding a portion away to fit.

An alternative example of the advantages of checking the glass is fully fitted within the came is shown here.

Here the blue piece shows it is slightly too large at the top.  The temptation is to refine the edges and reduce the size slightly.  Before doing that, it is advisable to check on how the glass is fitting into the came.  Again, run a felt tip marker along the edge of the came before pulling it out to adjust the size.

This shows there is a little bit of glass not broken off at the left side of the bottom tip.  Also, there is a larger space between edge and felt tip mark on the right than the left.

The first thing to do is to take off the excess glass on the lower left of the bottom tip and try the piece again.  That may be enough to allow the glass to fit into the came and match the cartoon.

The excess glass was ground away and a little taken from the bottom right side too.

This shows that just removing that small piece of glass has allowed the blue piece to fit correctly into the came and to fit the next piece of came to be placed without causing the panel to grow in size.

When a piece of glass is too large in leading, you need to check that it is fitted properly within the came, before adjusting the outer edges.  A method to do this accurately is described.

Fitting the Glass to the Cartoon

Often you find that the next piece of glass does not fit properly. Possibly it rocks a bit in the came’s channel. Possibly it is simply just a little too big.  Wait! Don't adjust the piece just yet. It may not be the problem.

The first thing to do is to take the too-large piece of glass out and remove the came it fits into, to ensure the previous piece of glass is not too large. The glass should not overlap the cut line. If you have drawn your cut lines to 1.2mm (1/16”) you should see only the faintest line of paper between the glass and the dark cut line. 

If the glass seems too large, check that it is firmly in the channel of the previous came, as sometimes the glass catches on the edge of the came and does not go into the channel.

If that piece seems too large, the next check is to determine whether the apparently too large piece of glass really fits the cartoon cut lines. Place the glass inside the cut lines. You should see a faint line of paper between the glass and the cut line.

When you are sure both pieces of glass are the correct size, put the came back between them and check again. If the glass is still too large, check the length of the came. Make sure the came butting onto the came separating the glass is not too long. This is a common reason for lead panels to grow beyond their initial dimensions.

If the glass is the correct size and the butting cames are correct, replace the came. Put the too large piece of glass into the came and position it so it has the best fit to the next cut line. 

Do not be tempted to start reducing the glass at the visible portion.  After all, you cut it to the right size. It may be that the fit under the came is not very good.

To check use a felt tipped pen (Sharpie) to run along the edge of the came, marking the too-large piece of glass. Take it out and check on where the line is farthest from the edge of the glass. That is where you need to reduce the piece.

The nail points to the area that needs adjustment

When you have reduced the "high" spots on the glass so it fits under the came evenly along its length, you can begin to adjust the outer edge, if necessary.

Leading Procedure

Cut the leads exactly as the cartoon indicates. In other words, where one line runs into another, that is generally a stopping/starting point for the came.

Always lead to the cartoon line, not the glass. This ensures accurate completion of the panel. If the glass is slightly too small, the cement will take up the gap (assuming the flange of the came covers the glass – if not, you need to cut another piece of glass that fits). If the glass overlaps the cut line, it needs to be reduced.  A description of the process is given here.

This shows the use of a guage to determine where to cut the horizontal lead came.

Cut the ends of the came shorter than the glass. The best way to determine this is to place a piece of came of the dimensions being used for the next edge on the cut line. Use it to determine the length and angle for the cut. The object is to have each piece of came butt squarely against the passing came, to make a strong panel and to make soldering easier.

Grinder Bits

Extending the life of your grinder bits is a matter of recognising that you should not force the glass into the grinding head. Excessive pressure against the head heats the bit and allows the diamonds to become free of the binding material, so reducing its life. If the motor slows as you press the glass to the bit, you are applying too much pressure. That kind of pressure also puts a lot of wear on the bearings of the motor.

If the grinder is not taking glass off fast enough for your purposes, you should put a coarser bit on the grinder, rather than pressing harder. The bits do come in a variety of grits. Try out some different grits to find the one that works best for the speed at which you want to remove the glass.

You can also buy a additive for the water – often called a diamond coolant – which is intended to provide a kind of lubrication for the diamonds. This may also extend the life of the bit.

Grinding to Shape

There are lots of ways people use to keep marks on the glass while grinding.

Paint markers will stand up to a lot of water if allowed to dry before being taken to the grinder.

Covering the marker line with Vaseline or lip salve will preserve the line longer.

Sticking down a water proof pattern piece on the glass will allow grinding up to the edges of the pattern piece without it breaking down. But of course, it can be ground away or pushed aside by the grinding head.


All these methods assume that there is a lot of grinding needed.

If you cut accurately, only a small amount of grinding will be needed and permanent felt tip/marker on glass lasts long enough to do the job.

Finger Protection While Grinding

Various methods of protection are used:
Finger stalls,
Taped fingers,
Altering the fingers used to press the glass to the grinding bit,
Gloves – but they have to very tight fitting to avoid getting caught in the spinning bit.
Duct tape,
Grinders' Mate.

Prevention
The sore fingers are usually caused by tiny cuts from the glass. So, all these methods are ways of putting something between the glass edges and your fingers. More importantly, you need to think about your practice if you are getting sore fingers while grinding.

The first thing is just to lightly grind all the way around the piece first. This can be quick, and should use minimum pressure. This will remove any sharp edges.

If you have to press hard to achieve the effect you want, it may be that your grinder bit is badly worn. It may also be that you need to have a coarser bit to achieve the amount of grinding that you need.

You should not be pressing hard in any case. This will wear out bearings on the motor and reduce the life of the bit. You should use medium pressure and allow the diamonds on the grinding bit to do the work. Fine work requires a fine grit, removing a lot of glass requires a coarse bit, not more pressure.

If you have to remove large amounts of glass, you need to review the accuracy of your cutting. You should not be relying on the grinder to do more than tidy your cuts.

Remedies
There are several remedies to relieve the soreness:

Cucumber melon antibacterial hand lotion
Vitamin E.
Tea tree oil
Germolene

Glass Grinder Use

Glass grinders are very handy tools. They mainly consists of a spinning diamond coated cylinder (the bit) extending above a grid surface that can rapidly and accurately grind glass to the desired shape.

Don't purposely cut glass large with the intention of grinding. Ideally no grinding would have to be done. It should be used only for minor adjustments or for grinding tough-to-cut inside curves.

Bits
The diamond bit must be kept wet in order to reduce wear on the diamond and prevent glass dust from developing and being inhaled. There are several grits available. "Fine" grinds slower but leaves fewer chips in the glass. "Coarse" grinds very fast but leaves larger chips. "Standard" is a central compromise.

Water reservoir
Ensure there is water in the reservoir before starting any grinding. Empty the reservoir daily. This keeps the water from producing a smell, and allows you to clear the glass residue from around the grinding bit.

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.

In Situ Leaded Glass Repairs

Here you are, just beginning leading and some one asks you to repair their leaded glass window. But they don't want you to take the window out of the frame. They want you to do it in situ. There are some general guidelines on how to go about it:

• Gently remove the cement from under the came leaves. You can use most any kind of stiff blade. You don't have to get it all out at once. Just work round the whole piece of glass.
• With a sharp lead knife, cut diagonally into the solder joint until you are almost halfway through.
• With a stiff blade gradually work the leaf of the came upwards. A stiff oyster-type knife (properly called a stopping knife) works really well. Apply the pressure to the leaf of the lead came.  Try to avoid levering against the glass.
  
  
  
• Continue to gently lift the leaves of the came until they stand vertical almost back to the heart. This obviously is much easier on thicker came than thinner. I try to avoid doing any less than 6mm, and that is difficult. It is also more difficult to do with half round came than with flat came.
• With grozing pliers gently lift the solder joints. Be careful of the surrounding glass, so that you don't have to replace more glass.
• If you haven't already now is the time to tape the broken glass together.
• Work out the cement between the came and the glass. This should provide you enough space to work the glass out.
• In some cases the glass won't come out in one - taped together - piece. Now is the time to take a rubbing of the opening so you know exactly where the leaves of the lead came are. It provides a pattern piece.  Smash the glass out. Wear safety glasses and gloves.
• If the glass has come out in one taped piece, use it as a pattern. You can trace round it with a felt tip pen and cut inside the lines. Alternatively, put it under the new glass and cut, using the edges as the cutting lines. You can also make a paper pattern from the glass.
• Insert the replacement glass into the opening. Most likely it will not fit in some places. See if the lead came leaves can be opened a little more. Also mark where the glass is too large. You can groze the glass, or if you are near a grinder, grind off the "high" spot.
• Remove the glass one last time, and spread a film of putty on the outside came leaf.  Use a very little, because you can't get outside to remove the excess.
• Clean the glass and handle it so that no finger prints are left on the outside.
• Now that the glass is in the opening, begin to gently smooth the came leaves toward the glass with your stopping/oyster knife. Start by only gently changing the angle of the leaf. Any large movement of the leaf will greatly deform it and might split it.
• If the solder joints are still standing up, take your stopping knife and gently tap the end of it with a hammer. The stopping knife should be parallel to the glass. Any hard hitting will tear the solder joint from the lead. (If you were doing this on a bench rather than on a vertical window, you could heat the solder joint and re-solder without all the tapping.)
• Push stiff black lead light cement under the leaves of the came from both sides if possible. Clean off excess. Polish with a soft brush.

If there are lots of broken pieces next to each other, repair one at a time, as each piece of glass supports the other. Alternatively, take the whole panel/window out and do it on the bench.

revised 26.4.24