A common question regarding our machine is “How much excess canvas do I need past the bottom of the stretcher bar?” We require only 1.5″ past the bottom to ensure a tight clamp, this is the least amount required by any canvas stretching machine currently on the market. Too much canvas also presents a few issues also by “bunching up” when fed into the clamp. Pictured below is a cut-away section of our custom extrude angle bar. Please note that the contour of the groove matches the shape of the rubber grip on the clamping bar.
Although our machine can conduct a stretch with as little as 1.5 past the bottom of the stretcher bar it can still be impacted by other variables that we cannot control. The first variable is the canvas itself, some canvas has more grip than others. Spray laminates also can prevent the angle bar from holding and can actually build up a slight coating on the surface; cleaning the angle bar periodically with alcohol helps. Increasing the stretching force past 30 psi is not recommended when there is only 1.5″ past the bottom of the stretcher bar because there is not enough canvas “trapped” beneath the rubber grip. One indication that the stretching force is too great is when the canvas slips out of the clamp.
Gallery Stretcher vs. Competition
The clamping bar is internally regulated by us to 50 psi and should not be tampered with. We determined that this was the safest and most efficient setting to produce a tight stretch while protecting the canvas.
The Tensador II is designed to slip during a stretch for this reason it requires about 2.5″ of excess canvas to ensure that the canvas remains in the clamp.
Even the high-end Fast Frame operates on the same principle only with rubber grips that “slip” over the canvas in opposite directions. If there wasn’t “slip” built-in to this design the canvas would be held so firmly in-place the canvas would not have the chance to stretch.
Working toward a solution
One of the most important factors for an efficient stretch is dependent on the profile of your stretcher bar. The more pronounced the radius on the top the easier the canvas will stretch over and around the sides of the stretcher frame. It is worth noting that we are attempting to pull a section of canvas 180 degrees in the opposite direction around two wooden edges, the smoother the edges are the more likely it is to move. We recommend a stretcher profile with at least a 1/4″ radius on the top and ideally a slight radius on the bottom, about 1/8″. The results are amazing and require much less stretching force.