Fatigued by metal clamps? Derek Jones builds a set of wooden sash clamps
Hard to believe I know, but there was a time when the workshop walls of the world were not festooned with row upon row of neatly arranged metal sash clamps. Cast your eye over ancient reproductions of period workshop images and you’ll notice a distinct lack of clamping paraphernalia save the odd twin screw and holdfast. There’s a couple of possible explanations for this, either these items were so thin on the ground as to not be thought of as important details or there just wasn’t a need for them full stop, suggesting a different approach to building the basic forms of cabinetry.
There’s a natural tendency among furniture makers and joiners towards resourcefulness and to some extent many assembly headaches are best dealt with by selecting the right style of joinery in the first place. That might be something as simple as a nail or as complex as a sliding tapered dovetail. The use of clamps to exert pressure across a joint suggests a reliance on glue and for that the woodworker needs a controlled method to deliver the right amount of force in precisely the right place for anything up to 24 hours.
In The Anarchist’s Design Book (Lost Art Press) there’s a picture reproduced from an original Roubo plate of some rather serious clamping. The image in this context is being used to illustrate the use of ‘marriage marks’ for the sequential orientation of components within a structure; fascinating stuff for sure but not what caught my eye. It was the idea of ’shop-made sash clamps that had me rifling through the leftover bin for suitable components to recreate my own serious clamping. The marriage mark is drawn across what we assume is a series of edge-jointed boards joined together to make a larger panel.
When joining just two boards together it would not be uncommon to use a simple rub joint, i.e. one that doesn’t require clamps. This is achieved by coating one of the two flat edges with glue and then rubbing it back and forth along the length of the joint onto the mating edge of the corresponding piece until the two pieces are sucked together. Once set in this state the panel just needs supporting while the glue dries. No clamps or pressure is required for this method although it will require the boards to be accurately trued
in all directions.
Add a third board to the mix and things get a little more complicated. The options now are allow the first two boards to become one panel and then add the third in the same way. Or do the plate spinning equivalent of glue-ups and join all the boards at the same time. I’m sure it’s possible but I think I’ll leave it to someone else to try.
Whether ‘T’ section, round or rectangular bar, metal sash clamps are unpleasant to use for a number of reasons. Heavy and cumbersome they typically require a means of barrier protection between their surfaces and those of the item within their grasp. For the most part this means either growing or borrowing a third hand or developing a series of accessories to mitigate the effects of an over engineered solution. Wooden, ’shop-made clamps on the other hand are a joy to use and a whole lot cheaper.
For this example I repurposed some leftover short sections of softwood from a stud wall. I spent a few minutes removing twist from two of the wide faces of each pair. I sourced a length of 20mm diameter hardwood dowel and drilled a series of holes in each piece with identical spacing to suit the size of panels
I intended to make. I found that having a tight fit on the bottom dowel and a slightly looser fit on all the rest made things a bit easier to handle when they are put to use.
Although the faces of the bars are flat and straight they are not really intended to correct defects in the panel components while gluing up. I made them like that to facilitate accurate drilling of the dowel holes and so as not to inadvertently introduce a wave into the panel.
Closing the gap
Applying pressure across the panel is done by driving a wedge between the edge of the outer board and the top dowel. There’s a little leeway here when it comes to choosing suitable material for either of these parts. Softwood wedges work better with hardwood dowels as they compress less than the dowels and are easily replaced. If your only option was to use softwood for dowels then stick to the softwood wedges. Cut your wedges with a 5–10° slope and if you’re using the clamps in pairs drive them towards the centre with a strategically placed batten between each clamp. This will help to ensure the pressure is applied at 90° to the joint. If that’s not possible then use a pair of wedges driven from opposing directions. If you struggle to find dowel of a suitable thickness then use square stock and cut square holes. If you do then the twin wedge method is your only option.
Conclusion – on wooden sash clamps
I know what you’re thinking – they look a bit clumsy don’t they? Let me tell you they’re not. They are lighter than metal clamps and also stack neater when you want to move the panel off your bench while the glue dries. They don’t fall over when you’re about to rest the panel down and you can make them to the size you
need. Oh yes, and in the winter they’re not freezing cold. What’s not to like!