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When a guillotine is mentioned in reference to picture framing, it generally refers to a machine that is used to chop straight sections of frame, before they are rejoined into a rectangular shape. The reason why they are called guillotines is obvious once you see them in action, as they bare fair resemblance to the execution machines of yesteryear.
Guillotine blades are also known by the term knives, as they are simple cutting surfaces much unlike a circular blade, which is made up of teeth, and uses a sawing motion to cut mouldings.
The way a guillotine works is quite simple. Picture framing moulding is placed on the precisely machined working area situated at the top third of the machine around waist height. Once the timber is secure and aligned just so, it is slid under the blades while they are raised up in the "ready" position. The blades are then forced downward by means of a powerful pneumatic piston. On the way down the blades encounter the frame that has been placed beneath them. Because the blades are very sharp and being pushed under great pressure, they simply cut through the timber as though a cleaver is being applied to a carrot.
The blades themselves are set at 90' to each other, making an equilateral triangle with the mounting of the guillotine head. When they cut through the timber, they cut out a wedge of 45'. When two pieces of timber are joined together both possessing this 45', they combine to create a 90' corner. And when 4 of these 90' corners are made properly, they result in a complete rectangular frame.
In order to get a clean cut on a frame, it is often required to use small nibbles, instead of taking out large bites. This this requires the blades to be pulled backwards away from the operator on a specially designed sliding head assembly. Now when the blades are pushed down through the timber, they still go all the way through in vertical aspect, though they don't penetrate as far in the horizontal pane. This results in a small nibble or notch being taken out of the frame, and the moulding still being ultimately left intact. The next step is to move the blades a little closer toward the user, and chop out another little nibble while not moving the timber at all. This makes the notch grow in size. Repeat this action over again, until the nibbles span the entire width of the frame and the timber becomes cut in 2. This method is used on all but the smallest of frames and is especially important when dealing with synthetics.
The trigger mechanism for the pneumatic piston is usually in the form of two buttons linked up to the compressed air system. They are set far enough away from the cutting blades so that when an operator is pressing them and causing the blades to drop, their fingers care out of harms way and can't be cut off. Most dual trigger systems are set with a fail-safe that means you need to press both buttons at the same time. Doing this means you cant work the machine single handed, and get your other hand under the blades.
Most conventional mouldings have a rebate into which goes the glass and artwork etc. These types have a lip that over hangs the rebate, which is what holds everything in place and stops it falling out the front of the frame. When a frame is cut in a guillotine, the lip of the frame is obviously also cut. The only problem with this is that the lip has the rebate (essentially empty space) underneath it offering no support. So when it is cut the blades make a messy exit wound out the other side and can cause the lip to completely snap off. The way guillotines get around this is with a rebate support. A rebate support is a device built into the guillotine that holds up the lip and substitutes the support of the rebate. These little attachments can be either screw or pneumatic in operation, and are essential to make a guillotine useful.
Measuring several frames out by hand is a tedious and often inaccurate job. Guillotines get around this by using production stops.
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