Wednesday, 18 July 2012

Installation of Glazing Bars

There are a few tips that concern the installation of glazing bars into wood frames. An important element to understand is that the purpose of the bars is to protect the panel from horizontal wind pressures on the window, not to lift the panel or in any other way strengthen the panel vertically.

Glazing bars are normally round. The diameter depends on the span of the opening. For openings of about 600 mm a bar of 10 mm will be sufficient, up to 900mm needs 12 mm at least. Of course, the depth of the rebate will be a major factor, as there needs to be some wood remaining on the frame to hold the bar secure.

In some cases a large bar is indicated, but there is not enough depth in the rebate to take such a diameter. These are the cases where the bar is heated and flattened so it can be inserted into a slot, rather than a round hole.

The holes on one side should be at least 5mm deeper than the other. For a really secure attachment one side should be at least 15mm deep and the other 10mm. This allows a significant amount of wood to seat the bar. The bar should be at least 10mm longer than the opening is wide. And the deeper hole allows the bar to be slipped deeply into one side and then slid back to seat in the more shallow hole.

The hole you drill should be 1mm larger than the bar diameter. This will make moving the bar easier. Additionally, the ends of the bars should be filed to remove any roughness. Also, greasing the ends of the bar with tallow or candle wax will ease the movement of the bars.

If the bar is to be installed inside sash windows you can ease the installation by determining the height of the hole to be drilled. Present the panel to the opening and mark the frame where the bar is to be attached to the panel. Drill the hole so the edge of it is flush with the rebate but no deeper than the outside of the opening. This allows you to use a chisel to open the hole enough to allow the bar to be placed in the socket now prepared from the outside. In these cases the bar needs to be no longer than the opening.

The installation should be completed by forcing putty into any gaps left between the bar and the hole. This will stiffen and help to firm up the bar’s attachment to the frame.

Tie wires for glazing bars are to keep the panel from rebounding due to wind pressures on the window. There also is some pressure created within the house by the opening and closing of doors, although this is minor in comparison to the weather.

The tie wires should be securely soldered to the panel at solder joints. Placing ties elsewhere leads to the tearing of the lead. The soldering of the tie wires requires more heat than simply soldering the lead joints. The tie wire needs to be heated enough to melt the solder of the joint to which it is being attached. Then an additional dot of solder needs to be added so that the wire cannot simply pull out from the joint by being only sweated to the joint.

When installing tie wires for panels that are to sit on top of one another, the wires should have a small loop created where it is soldered to the joint. The wires should be soldered at the loop end to the panel joints and extend down or up along the panel. On the other panel which meets it, the same procedure should be followed. In these cases the minimum amount of solder should be used to avoid making the panel too thick at the point where the upper lead comes down on the lower.

At installation, when the panel is fully seated in its opening and fastened by nails or sprigs, pull the tie wires out at right angles right at the edge of the solder attachment before twisting the wire. Do not use any more than firm pressure. Then you are ready to cross the wires over the glazing bar. This ensures there is no excessive give in the copper tie.

On panels sitting on top of one another, the wires on the lower panel should be passed behind the bar and up before turning over the bar. The wires of the upper panel should be passed below and behind the bar before turning up over the bar. The protruding wires should then be twisted as for single panels.

Do not over tighten the tie wire twist. Only twist until snug against the bar. Then continue to twist the loose ends until you have them a satisfactory length. Cut off the twist rather than the tail ends to provide a neat finish. Then tuck the twist under or over the bar, just as you desire.

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