Having the right tools and using the correct process to cut stainless steel on the job site can make the difference between a rough cut that takes forever and a normal clean cut.
This may sound obvious, but you should first see if you are able to have the pieces cut to the right size by your fabricator. Your fabricator likely has the appropriate equipment and experience to do this for a fraction of cost vs. the labor it would cost to be cut to size at the job site. We know this is not always possible as some measurements are always going to need to be taken on the job site.
This article is geared towards cutting stainless steel for architectural applications on the job-site, so we will skip a discussion of shearing, laser cutting, water-jetting, cold sawing and flame cutting and focus on cutting sheet, structurals and bar less than 1/8 inch thick. The tools for these applications include chop saws, abrasive saws, hack saws and band saws.
Stainless Steel Properties
If you are new to working with stainless steel, you should be aware of its fundamental material characteristics.
First, you can mechanically cut stainless steel and retain the corrosion resistance on the cut edges. Some materials, such as galvanized steel, simply have a corrosion resistant surface coating of zinc. Galvanized steel will corrode when you expose the underlying material. However, stainless steel is consistent throughout and when it is mechanically cut it will naturally form a corrosion resistant passive film.
Another property to be aware of is that stainless steel work hardens, particularly in the 300 series. This means that as the material is penetrated, the material will harden making it more difficult to continue with the same pressure and speed.
Fundamentals of Cutting Stainless Steel
The fundamental considerations outside of the tool are (i) feed/pressure, (ii) blade speed, (iii) lubrication and (iv) blade pitch.
The feed/pressure is almost always going to be heavy with stainless steel. Stainless steel is very hard material and can dull your blade quickly, which makes it important to keep pressure on the blade into the material. Feed speeds vary by the alloy of stainless steel, but for Austenitic grades (300 series) the proper feed is 1.7 to 2.3 surface feet per second for material 1/4 inch to 1/2 inch, 1 to 1.7 surface feet per second for 1 to 3 inch and 0.7 to 1.2 surface feet per second for 4 to 12 inch.
The speed of the blade should always be slow; slower than cutting aluminum or non-ferrous materials and much slower than cutting wood. For Austenitic grades of stainless steel, an appropriate speed in strokes per minute would be approximately 80 with 0.006 inches of feed per stroke. If you are using a sawing method with a backstroke (hack saws) it is critically important that the blade be lifted clear of the surface to avoid work hardening and dulling the blade. One common overlooked way to change the blade speed is to change the diameter of the blade. The larger the diameter the blade, the faster the outer perimeter spins when you hold the RPM constant.
As for lubrication, an emulsion of soluble oil is most often used as a cutting fluid to dissipate heat and aid in transferring material chips away from the work area. Small pitched blades should be used for cutting thinner gauge materials and as the material increases in thickness the tooth spacing should also increase.
For thin gauge material, it can help to place a scrap piece of 1/4 inch plywood or something similar beneath the material to stiffen it and prevent bending and prevent the blade from grabbing the material.
For the material of the blade, the tool companies seem to continually introduce and improve upon the materials available. While you would want to use a high speed steel blades at a minimum, there are also cermet, cermet / carbide blends or an advanced carbide / tungsten carbide.
Cut Off Saws
In the past ten years, a new generation of portable metal cut off saws has become available to make job site cutting easier. Some examples of these are the Morse metal devil, Dewalt metal working chop saws and import knock offs at stores such as Harbor Freight. These tools have become possible because the the blade metallurgy advances that are designed to transfer heat away from the work piece and improved shape and hardness to facilitate cutting. These cut off saws can be used to cut angle, structurals, rebar, joists, studs and more and are 5-10x faster than using a cutoff wheel on a grinder, while offering a cleaner cut.
These newer cut off saws are generally the exception to the rule regarding lubrication. You should clearly review the user manual for your particular model, however most manufacturers recommend operating these saws dry (without lubrication).
With any of these saws, it is important to take appropriate safety measures. These include properly clamping the material being cut, wearing a face mask to protect your face and wearing hearing protection as the operation creates an enormous amount of noise. Also, these metal cutting circular saws are designed for carbide blades which can not be replaced with high speed steel blades.
The operating cost of these tools can be an issue. Many of these blades can cost $100 for a replacement blade, have a limited life of 800 to 1,500 cuts and can not be resharpened.
Power and Hand Hack Saws
Hand hack sawing of stainless steel is not ideal and should only be used on light gauge bar, and small diameter bar, tube and pipe. For thinner gauge material (such as up to 16 Gauge or ~1/16”), a wave set blade of 32 teeth per inch would be appropriate and for heavier gauge a wave or raker set blade of 24 teeth per inch would be more appropriate. There should be two teeth in contact with the material at all times.
The operator should use long, smooth strokes with light but constant pressure at 30 to 50 strokes per minute. To avoid work hardening, on the back stroke the blade should be lifted clear of the surface to avoid riding over and work hardening the surface, particularly when cutting 300 series stainless steels.
An emulsion or soluble oil / cutting fluid should be flooded onto the work area to maximize the cooling.
While it may be more difficult to have a band saw set up with the appropriate blade on the job-site, it can generally save time on the cutting. The considerations for operating a band saw are similar to that of a hand saw. The cut should be adequately lubricated (a minimum of 30 drops per minute). Finer pitched blades should be used for thinner materials (32 teeth per inch for up to 16 Gauge or 1/16”) with tooth spacing increasing as the material thickness increases (24 or 14 teeth per inch for 1/4” to 3/4” thick, 10 teeth per inch for 3/4” to 1 3/8”).
Abrasive saws or cut off wheels are one common way for cutting thicker stainless steels, even though they can be messy and leave an imprecise cut. An abrasive saw needs to rotate at high speeds for this application. Cut off operations would use a soluble oil emulsion lubricant and a rubber based. It is important that the disc selected is a dedicated disc and is not contaminated by other materials. For example, if the same disc had been used to cut steel the material from the steel could be imbedded in the stainless steel and give the appearance of rusting, requiring the refinishing of the part.
All of the major distribution houses (McMaster Carr, MSC Industrial and Grainger) carry cut off wheels designed to be used with your 4 1/2 inch grinder. Just such at their sites for “cutoff wheels” and select the arbor and wheel diameter for your grinder.