Over the past 7 years we have received valuable input from customers that use our canvas stretching machines. We have heard from small custom frame shops that stretch only a few dozen canvas and from the large print-on-demand companies with as many as (10) machines stretching 4000-6500 stretches a month. Many of our design improvements were initiated as a result of this input. We want your experience with our canvas stretching machines to be a pleasant and productive experience and so we want to share our findings with you. This Newsletter addresses the topic of slipping canvas during a stretch.
These are some the most common causes for slipping canvas.
Excessive Stretching Force
All of the Gallery Stretcher models are purposely designed to slip slightly when the “stretching pressure” exceeds 45 psi. This preset pressure is set by us at our facility to reduce the chance of damaging the artwork. This setting should not be changed by anyone unless instructed by us. However, there are conditions that may allow the canvas to slip even when the stretching pressure is not greater than 45 psi.
Excess Build-up of Canvas
Cutting Canvas
No Cutting
We have always recommended that the excess canvas on the corners of the artwork be cut-away to reduce the unsightly build-up of canvas. There are a couple reasons for this but the primary one is that it allows the clamping bar to come in contact with more of the rubber grip reducing slippage. When the excess canvas remains in-place it creates a slight void on both sides, this is very prominent on thicker canvas and can be seen from the top. Cutting excess canvas is also recommended for the sake of appearance.
First Generation Angle Bar
Several years ago we introduced an angle bar that employed a course-textured finish to grab the canvas. This change was a vast improvement over earlier versions but that was before we discovered that the finish would wear down after several thousand stretches. This led us to develop our own extruded profile that conformed to the shape of the rubber grip. There are still a few Gallery Stretchers out there with the older style angle bars and we urge you to consider our “Rebuild Program” to bring your machine to today’s standard and you renew your warranty for another full year.
Pushing Down on the Art
Artwork Rises Slightly
This one technique is probably performed by more operators than any other and should be avoided at all costs. We designed our machine to flex and conform to the shape of the canvas. We also intended for the artwork to rise slightly, about 3-4″, to facilitate a stretch. It is easier to pull a canvas across the edge of a wood stretcher bar at something less than 90 degrees. When the artwork rises it is slightly less and it tends to travel across that edge because there is less friction. Pushing down on the assembled frame to keep it flat actually creates two problems. The first problem is that you have just increased the stretching force mechanically and the artwork will slip. The second problem is that you are torquing the frame on one side. Please allow the artwork to rise slowly about 3-4″.