When making curved strings using horizontal laminates one of the trickier operations is gluing up the face laminates or veneers.
The difficulty is that the veneer that is between 30 and 50cm wide is placed on an angle with the vertical and has to be clamped up along the vertical.
This gives a vertical clamping length of between 80 and 120cm, where the clamping pressure has to be distributed evenly.
The same problem arises when gluing up traditional laminates on a form.
In the case of traditional laminates glued onto a form , it’s possible to put the laminates in a vacuum bag, place the packet on the form and use vacuum to clamp.
For a string built with horizontal laminates this is not possible and I have built some special clamps, I call bolt clamps, to distribute the pressure onto the string.
This curved string is being veneered with 2mm face laminates using ordinary PVA glue and custom made bolt clamps.
In this example the central cut string is veneered with vertical grained larch on the face and cross grain larch on the edges.
When the veneers are glued up parallel with the slope the string looks like a solid piece of wood.
In this example a helical stair in elm has been built using horizontal laminates for the string and handrail.
Bolt clamps are made of 3 pieces of wood:
– a fix jaw made in ash or beech 50x40mm
– a mobile jaw in ash 60x40mm
– a soft wood padding make in spruce 35x20mm
To assemble the clamp I use:
– 2 threaded 8mm rods, with a couple of nuts and washers to fix them to the fixed jaw
– 2 wing nuts to hold the mobile jaw
The other parts are:
– a 8mm pressure bolt about every 100mm
– a nut for each bolt
– strip of metal that spreads the bolt pressure on the padding
– a couple of elastic bands cut from bicycle inner tube to hold the mobile jaw together
To make the mobile jaw fist machine a 20x15mm groove then drill the 13mm recess for the nut.
Drill a 10mm hole through the jaw for the pressure bolt.
Hammer the nuts into the recceses, the fit should be tight so that they don’t turn.
Glue the veneers up with slow setting white PVA glue.
The best way to go about this is to clamp the veneer temporarily in place without glue.
Once in place un clamp half and lifting up the veneer, spread glue on the string over about 40cm.
Place a bolt clamp and tighten with the wing nuts.
Add even pressure by tightening the pressure bolts starting with the bolt in the middle of the clamp and working outwards.
Glue up another 40cm of string and repeat.
When you reach the end un clamp the other half of the string and use the same procedure to finish veneering.
This is a half turn sting rising very fast built using traditional laminates because the string is only 45mm thick.
The vertical clamping height is over 120cm and the bolt clamps are the only way to clamp this one up.
In this photo the bolt clamps are used on a traditional form to pull the laminates into shape.
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