How to Cut a Flawless Mat for Picture Framing

How to cut a mat for picture framing
How to cut a mat for picture framing

To cut a flawless mat you must let go of the idea that there is anything automatic about mat cutting. To the extent that a “machine” provides a predictable result, flawlessly, without the know-how of the operator, a mat cutting machine doesn’t exist. Cutting a mat is, to a great degree, a craft, requiring an understanding of the material as well as the know-how to use the tools properly. A mat cutter is an instrument in the hands of a knowledgable user.

Mat board is a dense stack of paper. It is several laminates thick and held together with glue. The blade used to cut it is very thin. It must be, because if the blade was too thick it would tear the paper. But because the blade is so thin it has a tendency to flex as it drags through the mat board, and if the blade flexes, the line of the cut will waver.

Blade Flex

This common flaw is most evident at the beginning of the cut where the blade first penetrates the mat and is seen as a slight dip or “hook” near the corner. To help alleviate the problem some mat cutters are designed so the blade passes through a narrow slot which keeps the blade rigid to the point of penetration. Others have a tiny screw that can be tightened against the face of the blade to stiffen it. Despite these helpful features, blade flex can still occur if the cutting head is twisted, rocked or torqued during the cut. It is ultimately up to the operator to make sure consistent directional pressure is applied to the cutting head throughout the cut.

Even with that precaution, the blade flex can still occur if the cut is too deep. In mat cutting, a scrap piece of mat board called a backing sheet is used under the mat when cutting. When the cut is too deep, the blade penetrates through the subject mat board and halfway or more through the backing sheet. This puts excessive drag on the blade, leading to blade flex. Adjusting the depth so it just scratches the surface of the backing sheet will alleviate the issue.

Once the backing sheet has a lot of scores in it, it should be replaced. Otherwise the blade can catch in previous scores and track on them, flexing out of line. Any left over remnant of mat board can be used as a fresh backing sheet. A dull blade can also lead to blade flex. When the blade is new it passes through the mat board with little resistance, but as it becomes dull it drags more and more. The more it drags, the more it flexes.

If blade flex occurs, three steps should be followed to eliminate it. Change the blade depth, change the backing sheet and change the blade.

Rough or Ragged Edges

Rough or ragged edges are another common problem in mat cutting. Different manifestations of the problem can be detected by different feels in the cut. If the cut feels crunchy, the blade is dented or chipped and must be changed. If the cut feels like it’s pulling or tugging slightly, you are cutting repeatedly in the same score on the backing sheet and the backing sheet must be moved slightly one way or the other to find a fresh place to cut into.

Patchy Cutting Through

Patchy cutting through or failing to cut through consistently over the length of the cut indicates a chipped blade (you’ve lost the last little bit at the tip that allows consistent penetration). Change the blade. Alternatively, the problem could be the result of a depth setting that is too shallow. Adjust the blade depth. Proper blade depth is the key to eliminating many of the common flaws seen in mat cutting.

Over Cuts and Under Cuts

Unbeknownst to most novice framers, mat board varies in thickness. Even within a so-called line of “standard thickness” mat board, minor variations are common due to the different thicknesses of the face papers. These different thicknesses are largely responsible for the most bedeviling issue in mat cutting, a seeming inability to stop precisely and consistently in the corners, leading to over cuts and under cuts.

All mat cutting blades penetrate the mat at an oblique angle, meaning that they penetrate the back of the mat at a point further back than they emerge from the face. If the mat board is thicker, it takes the blade longer to emerge, leading to under cuts. If the mat board is thinner, the blade emerges earlier, leading to over cuts. On most mat cutters, it is possible to set the blade depth precisely so the blade emerges precisely at the corner each time. However, everything changes when you change to a different color or style of mat board, as it may be thicker or thinner.

Rather than struggle to readjust the blade depth each time, most framers employ some form of visual compensation to cope with the issue. The most common approach is to simply watch the point of penetration relative to the pencil lines, moving the point of penetration forward or back slightly to compensate. On mat cutters where the blade cuts through a slot before penetrating, the same adjustment can be accomplished by moving the cutting head’s indicator line forward or back of the pencil line.

The trick, of course, is in knowing how far to move it. Is it a sixteenth of an inch? Is it a thirty-second? Well, that depends on the degree of the over cut (or under cut). So what’s called for here is a test cut to diagnose the degree of the over or under cut. If you are willing to make six cuts rather than just four, you can get perfect corners on your mats fairly consistently. Here’s what you do…

If it’s your intention, for example, to cut a mat with 2 inch borders, start out by drawing your borders slightly wider, say 2½ inches. Mark out all four pencil lines but only make two adjoining cuts, starting and stopping on the lines you’ve drawn. Then turn the mat over and diagnose the over cut / under cut situation. Now readjust to the borders you actually want and use the diagnosis from the test cuts to move the cutting head slightly forward or back to achieve the best possible corners.

Mat cutters with automatic production stops provide a third way to compensate for over cuts / under cuts. Automatic production stops are metal blocks that lock down on scales. They stop the cutting head automatically at the point of contact. If you are using automatic production stops and see that you are getting a 1/16th inch over cut, you will naturally move the stop by 1/16th inch on the scale to eliminate it.

Eliminating Common Problems

Cutting a flawless mat is more of a craft than most people assume. Understanding the materials and tools are the key. But if you can cut a mat that doesn’t exhibit over cuts or under cuts, a mat where the edges are sharp and clean, and a mat that has a consistent 45-degree beveled edge without any wavering in the line of the cut, you have, by definition, a flawless mat.

And that’s how to cut a flawless mat for picture framing.

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