The desired finish of a job depends on the product application, material, and type of finish your customer requires. These tips will help you deliver just what the customer expects in terms of a surface finish.
Finishing is both an art and a science and often poses challenges for today’s welding fabricators and mechanical contractors.
Whether you are trying to achieve a linear, nondirectional, or mirror finish, you need to follow a specific process to arrive at the desired finish. Following the correct steps and using the correct power tool and corresponding consumable result in a process that is efficient and effective, reducing frustration and quite possibly production costs in the long run.
The desired finish of a job depends on the product application, material, and type of finish your customer requires. When formal training in the finishing process is lacking, it can lead to undesirable results. This includes the frustration of not achieving the required finish and the use of an excessive amount of consumables, which can have a large impact on the cost of the project. Following the required steps and processes to achieve different finishes can alleviate this frustration and help to prevent problems that fabricators may face when tasked with finishing.
An Explanation of Finishing Values
Before a discussion of a step-by-step process to metal finishing success takes place, you need to understand Ra (which is the average roughness determined by an algorithm) and the different values required to achieve a specific finish. Customers typically reference a desired Ra value when describing their finishing requirements.
This “roughness average,” which is expressed in units of microinches, is by far the most common parameter in the U.S. for quantifying the surface roughness of a material. Using a device called a profilometer with a highly sensitive diamond stylus, you can measure the so-called “peaks and valleys” of the finished surface. It is important to keep in mind that the resulting number is in fact an average of the data points that the profilometer collects, meaning that it is possible to have an inconsistent surface finish that still yields a desirable Ra. This is why it’s important to thoroughly understand and follow the steps of the finishing process.
So, after your shop is done cutting, grinding, and blending, you are then charged with performing the final step of finishing. The job instructions call for a mirror finish—an Ra of 4 to 8 microinches. How does that differ from a sanitary finish or even a fine finish? One process does not fit all, and having a clear understanding of the proper tool speed, the right consumable, and how to use those elements are critical to achieving the desired outcome.
Read more: The basics of metal surface finishes