To build a stretcher frame yourself, you need suitable mouldings. These are characterized by two special features:
- their special profile
- their plug-in connection at the corners
The profile of a stretcher frame has a rounded elevation at one edge, which protrudes by approx. 2-4 millimetres. This round ridge forms the outer edge of the frame over which the screen is stretched. Thanks to the raised edge, the tightly stretched picture support does not rest on the wooden strip - otherwise the pressure of the brush would create a disturbing edge on the picture surface when painting.
Wedge frame corners
The corners of stretcher bars are machined in such a way that they can be pushed tightly into each other.
The stretcher frame then gains stability through the covering. The frame can be retensioned with the help of hardwood wedges. The wedges driven in with a hammer push the strips apart.
Different ledge types
There are a number of different profiles for wedge frames that are not compatible with each other. Depending on the manufacturer and region, different types of wood are used. But above all, the profiles of the slats differ both in terms of their dimensions and the height of the tongue and groove at the corners.
The quality of a wedge frame ultimately lies in the quality of the wood. Wood works (reacts to humidity) and can warp over the years. The longer the wood is stored, the greater the probability that straight mouldings will remain straight.
Often two wooden strips with opposite grain are glued together. This neutralizes the natural tension of the wood. In 90% of the cases this also works quite well, but if you buy or order strips for stretcher frames, you will notice that sometimes one or the other is not really straight. The larger the format, the stronger the effect. A warped canvas simply stands at a corner from the wall.
It is recommended to have your own stock of stretcher bars and to store them dry for at least one year. If you then select suitable strips for a new picture, you can separate the wheat from the chaff and only use the really good strips.
Read on: How to build a stretchers frame (construction instruction).