Wood Panel Cutting Introduction.
Sheet - rectangular piece of wood, veneer or plywood also are known as panels or stocks.
The sheet is used to cut smaller pieces called parts.
Part - rectangular piece of wood, veneer or plywood that is required to be cut from the sheet.
Part can be considered as output of the whole cutting process. Sometimes the part orientation is important
to preserve the pattern or for other reasons.
Cut-off - rectangular piece of wood, veneer or plywood that is the rest of the sheet after
all parts have been cut. The cut-offs also are known as remaining parts or waste.
Layout - arrangement of the parts on the sheets that doesn't allow the parts overlapping each with
others or with the edges of the sheets. The optimal layout doesn't produce any cut-offs and therefore
the whole sheet is utilized.
The special computer software usually generates the layouts. It takes in account the available number of sheets
and their sizes and tries to arrange all required parts with minimal cut-offs.
If the part's orientation is important then the part cannot be rotated during the layout generation,
otherwise parts can be rotated. Part rotation allows producing better results because it gives more freedom.
The primal objective of the wood cutting is to get all required parts from the available sheets and
produce as fewer cut-offs as possible. Ideally there shouldn't be any cut-offs after the cutting is done,
but it's not the case in the real world.
There is another objective of the wood cutting - reducing working time. The biggest difference between
wood cutting and for example glass cutting is a possibility to cut several sheets simultaneously by placing
them in a pile one on the top of another. It dramatically improves the productivity and reduces the
working time. If, for example, you can cut five sheets at once then the overall cutting time gets
reduced in five times!
In the most cases the wood cutting uses the guillotine cuts when the cut is done from one side of the sheet
completely to another side. Guillotine cuts can be done in several ways depending of the purposes of cutting,
material used and the type of the cutting machines used.
The simplest way to cut the sheet is called "XY-cut", that is done along
X-axis and then in Y-axis as shown on the picture.
The X-cuts divide the sheet by several stripes and Y-cuts finalise the process by cutting the parts from the stripes.
Generally this cutting type produces the layout with the biggest amount of cut-offs and can be used for the
simplest cutting machines with restrictive functionality.
Also this cutting type is suitable to cut a big number of the parts with the same dimensions.
The improved version of the XY-cut is called "two-stage XY-cut" and consists of the two stages of
the cutting as shown on the picture.
On the first stage the sheet gets divided along X-axis into the stripes.
On the second stage each stripe is considered as a separate sheet and gets cut using simple XY-cut.
This method produces better results but requires more operations to perform the cuts.
The next type is "XYZ-cut" that allows one more level of cutting in horizontal direction.
As in simple XY-cut the whole sheet is divided by stripes then the stripes get cut by smaller pieces and
if required these pieces get cut as well.
This type is similar to two-stage XY-cut but more than one Z-cut is allowed on the same piece as shown on the picture.
XYZ-cut is more complicated then previous ones and therefore cannot be done by the simple cutting machines.
Introducing one more level of cuts produces "XYZW-cut". The example of this type of cuts is shown on the
picture. XYZW-cuts are used if there are many different part sizes required and better material
utilization is desirable.
The last cutting type doesn't imply any restrictions on levels of cuts and therefore results in the best
material utilization than any others.
However this cut type is the most difficult to use in the practice. The only reason one may want to use it is
to cut many parts with different sizes from expansive material.
The example of this cut type is shown on the picture.
The wood cutting uses the different types of saw to cut the sheets. But all of them have one common
feature - they cut the sheet by taking out the wood between the parts and therefore all of them make
gaps between the parts. These gaps may be considered in some cases when the high cutting precision is required.
The cutting machines have the hardware restrictions on the maximum cut length in X or Y directions.
Due to this limitation the first cuts that are the longest ones should be done accordingly. The layout
shown on the first picture demonstrates no limitation on the maximum cut length. But if there is limit on the
cut length then the long cuts are not allowed and first cuts should be done in vertical direction as
shown on the second picture.
The wood sheets sometime come with rough edges that are not acceptable for the resulting parts.
In that cases all rough edges should be trimmed off. The trimming sizes are specified from Left, Top,
Right and Bottom sides of the sheet as shown on the picture. Some of the trim sizes can be zero that
indicates no trim required on that side.