When raster engraving both small surface areas and larger surface areas the engraving result can differ slightly even when the same laser settings are used. Minor fluctuations can occur in depth and in some cases tone of engraving. This is based on the power distribution principle.
Typically if we are engraving a small surface area, the laser power is more concentrated because the strokes of the laser head (the movement from left to right) are in a smaller more focused area. As soon as the size of the engraving increases the stroke size i.e. the distance the laser head travels increases, meaning the power distribution of the laser becomes slightly less. All engraving has a variance tolerance for this reason. The variance is very minor, in terms of depth we are talking 10s of microns, but it can affect the appearance of the engraving on a variety of materials.
When your artwork is staggered between differing sizes, the laser completes portions of the artwork a stage at a time. To demonstrate what we mean, have a look at the following example.
The laser will begin to work it’s way down the artwork. To begin with, the stroke size is fairly thin in relation to the artwork meaning the laser power will be more concentrated. As soon as the laser reaches lower down, the stroke size will increase dramatically corresponding to the larger width. This can have a impact on laser power distribution causing a minor variance in the engraving depth and strength between the horizontal and vertical strip:
To get round this, we sometimes need to use a special “high quality engraving” setting. This will calculate the entire width of the engraved area of your artwork and apply the same engrave stroke width consistently over the entire job (indicated in grey.) This does make the engraving more time consuming and more expensive but ensures a more consistent power distribution.
This example is quite an extreme case. Not all materials require using this setting. Typically it is also only when your artwork is quite expensive.
If we are engraving multiple sheets of the same material with artwork of a varying size, bear in mind that there can be subtle variation in depth / tone for the same reasons.
When arranging artwork for engraving that has a few components on one sheet, it’s best to keep all of the raster engraving as close together as possible and in a horizontal row.
With this artwork, the laser will engrave the components each row at a time with different stroke widths. On some materials, each row may therefore have a slightly different appearance in engraved tone unless we use the “High Quality” setting.
If we apply the “High Quality” Raster engraving setting to this artwork the stroke width will remain consistent however the total engraving area will become quite large:
It’s best to arrange your components more economically to keep the stroke width consistent and to ensure the total surface area is as compact as possible. As a general rule of thumb, arrange your components in line horizontally (along the X-axis) to fill the width of the sheet or until you have laid out the total number you require. Only begin a second row when you have no more space on the sheet horizontally. Also keep the rows as tight together as possible on the Y-axis and avoid redundant space between components where possible: