Photo Chemical Machining Requirements

photo etched metal parts

Vaga Industries provides high precision photo chemical machining of thin metal parts for customers in a broad range of markets. The photo etching process is effective with numerous metals and alloys—we stock a large inventory of materials to meet the needs of our customers. We can also work with customer-provided materials, as needed.

Our chemical etching services can be used to fabricate precision parts from nearly any design, no matter how simple or complex. However, there are a number of specific photo chemical machining requirements, characteristics, and tolerance considerations. Many are presented here, but if you have questions about how these chemical etching requirements will affect your parts, please contact Vaga Industries for assistance.

Undercut

As the etchants used in the photo chemical machining process cut through the material, a certain amount of side erosion or undercutting occurs. This is the main factor governing the tolerances that can be held. As the thickness of the material increases, so does the undercut and, in turn, the tolerances that can be held

Hole Size & Metal Thickness

As a general rule, the diameter of a hole created via photo etching cannot be less than the thickness of the material. This relationship varies with the thickness of the metal to a certain extent.

Material Width Between Holes &  Metal Thickness

The thickness of the metal being used in the chemical etching process puts limitations on the possible material width between holes. Minimum widths are shown in the table below.

Thickness Space Between Holes
< 0.005" At least metal thickness
> 0.005" At least 1.25 times metal thickness

Center-to-Center Dimensions

Center-to-center tolerances are dependent upon the photo tool used in masking the part. These tolerances are proportional to the linear distance involved, as shown below.

Center-to-Center Dimensions (Inches) Tolerance
1.0" or less ± 0.0002"
1.0" to 3.0" ± 0.0004"
3.0" to 10.0" ± 0.0008"

Inside Corner Radius & Metal Thickness

Minimum inside corner radius is generally equal to the thickness of the metal. If the metal is 0.005” thick, the inside corner radius will be 0.005”

Outside Corner Radius & Metal Thickness

The normal radius of a sharp outside corner allowed by the photo etching process is 2/3 of the metal’s thickness. Special adjustments can be made if a sharper corner is required.

Edge Bevel & Metal Thickness

A small amount of lateral etching/erosion does occur during photo chemical machining. In most instances, the metal sheet from which parts are fabricated will be sprayed with etching acid from both sides. The resulting edge profile will resemble the drawing below. Bevel “A” is approximately 10 percent of the material’s thickness.

Edge Bevel and Metal Thickness, Photo Etching Requirements

In certain applications, etching from only one side is preferred. In these cases, “B” will be approximately 40 percent of material thickness.

Tolerances on Prototypes & Short Run Production

Approx. flat size Thickness (inches)
0.002 0.005 0.010 0.020 0.040 0.060 0.080
2" x 2" ± 0.0005 ± 0.001 ± 0.002 ± 0.004 ± 0.005 ± 0.006 ± 0.007
8" x 10" ± 0.001 ± 0.002 ± 0.003 ± 0.004 ± 0.005 ± 0.006 ± 0.007
12" x 18" ± 0.001 ± 0.002 ± 0.004 ± 0.005 ± 0.005 ± 0.007 ± 0.010
18" x 24" ± 0.002 ± 0.002 ± 0.004 ± 0.005 ± 0.006 ± 0.007 ± 0.015

Bend Radii

The table below shows minimum internal bend radii for different types of metals used in the photo chemical machining process. Though the radii shown are generally accepted throughout the industry, prototypes should be made to ensure structural integrity. (SB = sharp bend; T = thickness of material.)

MINIMUM RADIUS FORMABILITY -90°
Material Alloy Temper Across Grain
Direction
45°
Parallel
Low Carbon Cold-Rolled Steel No. 1 Hard 2.0 x 3.0 x T Flat
No. 2 1/2 Hard 1.0 x T 1.5 x T 1.5 x T
No. 3 1/4 Hard SB 0.5 x T 1.0 X T
No. 4 Soft SB SB SB
No. 5 Dead Soft SB SB SB
Stainless Steel 301/302 Annealed SB SB SB
1/4 Hard SB 0.5 x T 1.0 x T
1/2 Hard 0.5 x T 1.0 x T 1.5 x T
3/4 Hard 1.0 x T 1.5 x T 2.0 x T
Hard 1.5 x T 2.0 x T 3.0 x T
Beryllium Copper 25 Annealed SB SB SB
25 1/4 hard SB SB SB
25 1/2 hard 0.5 x T 0.7 x T 1.1 x T
25 Hard 1.0 x T 2.0 x T 2.2 x T
Brass No. 6 Annealed SB SB SB
3/4 Hard SB SB SB
Hard SB SB 0.5 x T
X Hard SB 0.5 X T 2.0 x T
Spring SB 1.0 x T 3.0 x T
X Spring 0.5 x T 1.5 x T 3.5 x T
Phosphor Bronze Grade A Annealed SB SB SB
1/2 Hard SB SB SB
Hard SB SB 1.0 x T
X Hard SB 0.5 x T 2.5 x T
Spring SB 1.0 x T 3.0 x T
X Spring 0.5 x T 1.5 x T 3.5 x T
Grade C Annealed SB SB SB
1/2 Hard SB SB 0.5 x T
Hard SB 0.5 x T 2.0 x T
X Hard SB 2.0 x T 4.0 x T
Spring SB 3.5 x T 5.5 x T
X Spring 0.5 x T 4.0 x T 7.5 x T

Edge-to-Edge Dimensions

There are a number of parameters involved in determining dimensional tolerances. Among the first should be cost: if a tolerance can be opened up to production parameters and not affect fit, form, or function, it should be used. In some cases, this option is not available, in which case additional quality control measures must be employed to guarantee acceptable parts. This, of course, increases costs.

Tooling Holes

In many instances, photo etching is a practical method of manufacturing formed metal parts. Tooling holes can be located very accurately in relation to the part for secondary forming.

Hand Forming

Bend lines as shown below can be etched into one side of a part. This allows for easy hand forming of sharp bends. However, this does result in the loss of some structural integrity.

Hand Forming, Photo Etching Requirements


Request a quote for your project, or contact Vaga Industries for more information on our photo chemical machining requirements.