Are there any guidelines for selecting optimum engraving depths?
Engraving at the proper depth is an important factor in achieving high quality engraving with a good visual appearance.
This is one of those cases where more is not necessarily better. If for example, you are engraving black material with a white core and you want a .030" line width, you want to see a black plate and a white line that is .030" wide. That will only occur at the bottom of the cut where the cutter tip just enters the white core color. If you go deeper, you will expose more of the core color, so your line width will appear to be broader. Along with ruining the desired visual effect, engraving deeper than necessary can increase engraving time and result in less than perfect cuts.
On multi-layered engraving materials where you engrave through a cap layer and expose the core, you want to engrave just deep enough to expose the core. Since there can be irregularities in the thickness of the cap layers, you will want to set the cutter depth to penetrate the core layer by two or three thousandths of an inch. This will ensure cutting completely through the cap layer across the entire surface of the plate.
Since there is such a wide variety of materials available from several manufacturers, it is difficult to offer hard, fast rules that will apply in every case. There are some generalities we can offer, however, that should give you an understanding of what is required and get you started in the right direction.
Laminated materials typically have a cap sheet that is about .010" thick. Engrave to a depth of .012".
Coextruded materials have a cap sheet of about .005" and need to be engraved to a depth of approximately .007".
Microsurface materials which encompass many of the woodgrain and metallic products have a very thin layer and only need to be engraved to a depth of .002"-.003".
Multi-layered acrylic products for both front and reverse engraving need be engraved to a depth of about .012" to clear the cap layer.
When engraving materials other than the multi-layered products, there are a few other aspects to be considered. If you are engraving materials that are going to be color filled, it is important to have sufficient depth to hold the paint or other fill material. On small characters - up to 1/4" high with a .030" stroke width - a depth of .008"-.010" is generally sufficient. As the letter height and line width increases, the engraving depth should be increased so the paint won't be pulled out of the letter during the cleaning operation. For more information see "Color Filling Fact Sheet".
On coated or anodized metal, it's only necessary and desirable to engrave just deep enough to expose the bare metal.
Since cutter width is defined as the width at the bottom of the cut, the top of the cut (assuming you are using a conical cutter) will measure some amount larger depending on the angle of the cutter.
For normal engraving of multi-layered products and surface engraving on coated metals, use the prescribed cutter width that corresponds to the character height and desired stroke width. If, for example, you are engraving with a .010" cutter in microsurface material, you will see a .010" line because you are essentially seeing the bottom of the cut.
If on the other hand, you are using a cutter with a .010" tip (assuming a standard 30 degree cutter) and are engraving to a depth of .010" on a plate that gets paint filled, the line width you will see will actually be closer to .020". The reason is that after it is filled, you will actually be viewing the top of the cut. (A 30 degree cutter with a .010" tip will actually produce a cut that is .020" wide at the top).
Given the above scenario, it is generally a good idea to reduce the cutter width in order to achieve a good visual appearance. The following information on widths versus depths for various cutter angles should help in selecting the proper tip width for your particular application.
Cutter Angle
Tip Width
Depth
Width at
top of cut
Width increase per 1 thousandth (.001") of depth
15° (30° Inc.)
.010"
.010"
.015"
0.5 thousandths (.0005" )per each 1 thousandth of depth
20° (40° Inc.)
.010"
.010"
.017"
0.7 thousandths (.0007") per each 1 thousandth of depth
30° (60° Inc.)
.010"
.010"
.020"
1.0 thousandths (.0010") per each 1 thousandth of depth
40° (80° Inc.)
.010"
.010"
.027"
1.7 thousandths (.0017") per each 1 thousandth of depth
45° (90° Inc.)
.010"
.010"
.030"
2.0 thousandths (.0020") per each 1 thousandth of depth
The width at the top of the cut can be determined by using the above chart and entering it in the following formula:
Tip Width(cutter) + {Ratio(width:depth) × Depth(of cut)} = Cut Width(top)
Example 1: Assume that we are using a 30° tool (60° Included angle). If the tip is .010" and we engrave to a depth of .010", the width at the top of the cut is .020". See picture at right.
.010" + {1.0 × .010"} = .020"
Example 2: Assume that we are using a 30° tool (60° Included angle). If the tip is .020" and we engrave to a depth of .010", the width at the top of the cut is .030".
.020" + {1.0 × .010"} = .030"
Example 3: Assume that we are using a 40° tool (80° Included angle). If the tip is .010" and we engrave to a depth of .010", the width at the top of the cut is .020".
.010" + {1.7 × .010"} = .027"
By using this chart and inputing the tip size, depth, and ratio (given above); you can figure out the width at the top of your cut.
