Polishing Stainless Steel

Stainless Steel Polishing

Machined stainless steel parts typically have sharp edges, burrs and a matte surface finish. Vibratory tumbling can be used to get a polished finish sometimes even down to just a few Ra surface profile. This is often a multi-step process.

The part on the left is the 'raw' part ready for deburring and polishing. The first step is to deburr and round the edges. This was accomplished using a KM general purpose Ceramic Media. This was a wet process using a solution of Kramco 1010 General Purpose Compound. The result at this point (not pictured) was a matte, tumbled finish with rounded edges.

The second step needed to get the pictured polish (on the right) involved tumbling with a Precision Ceramic Sphere and a solution of Kramco 2020 Burnishing Compound. Generally, a rounder media will produce a smoother finish than an angular media.

This part could be further polished with other tumbling media or hand buffed to a near-mirror finish.

Heavy Deburring - Small Parts

Deburring Small Parts

Often times, the machining of small parts can lead to very heavy burrs and difficult areas to finish. The steel gear pictured above has a diameter of about 1/4". The machining to make the gear teeth left very heavy burrs on the edges (see part on left). The burrs can be seen as the excess material that is hanging off the edges and rolled into curls. All this steel needs to be removed before the part is functional.

The two primary criteria for finding the proper media are (1) small enough to get into the area between the teeth and not get stuck and (2) aggressive enough to remove the extraneous steel and burrs without overly changing the dimensions and tolerances of the part.

This part was deburred (see part on right) using a general purpose, deburring Ceramic Cone in a vibratory tumbler. This shape was chosen since the tip of the media will get between the teeth to remove the burrs. The general purpose bond or formulation (KM in this case) provided the best balance of deburring without being overly aggressive.

While this process did remove nearly all of the burrs on the gear teeth in only 1 hour, looking closely at the finished part will reveal some material still left on the edges. In some cases this metal needs to be removed as well and would require longer cycle times, more aggressive media and/or additional grinding steps.

Polishing Stainless Steel

After heat treating and laser cutting stainless steel parts, the edges generally need to be deburred and the surface needs to be cleaned from scale and discoloration prior to polishing. A two-step vibratory tumbling process is normally used to achieve a uniform surface finish.

The part on the far left in the picture shows the burrs and slight discoloration on the edges. The first step was to tumble the parts with a Ceramic Media to get a the uniform, tumbled, matte finish shown on the part in the center of the picture. For this particular part a 2 hour cycle time with a general purpose tumbling compound resulted in the finish seen.

The second step (far right in picture) was also a 2 hour vibratory tumble with a Precision Ceramic polishing (porcelain-type) media and a high lubricity tumbling compound. The surface is improved to a more uniform and brighter finish and the part is ready for a clear coat or further polishing as needed.

Two-Step Polishing

The far left in the picture shows a laser-cut, stainless steel part with sharp edges and heavy burrs. The goal is to clean up the edges and leave a smooth, polished surface finish. The part will need to be deburred and then polished. This will be a two-step process as an abrasive process like deburring will typically leave a smooth but matte surface finish.

In this situation, the part was first vibratory tumbled with a moderately aggressive Ceramic Media to remove the burrs and discoloration. This process took a couple of hours to result in the smooth, rounded edges and tumbled, matte surface finish shown in the middle part.

The second step used a polishing Precision Ceramic Media to improve the surface finish and brighten the part. The part on the far right have a smooth, polished look after about 2 hours in the tumbler with the polishing media. Overall, a good result without any hand deburring and polishing or manual labor.

Deburring Steel Parts

Machined steel parts often need to be deburred. For large quantities of parts, both barrel tumbling and vibratory tumbling can accomplish this task saving labor hours and increasing throughput capacity. The specific details of the process must be chosen carefully to ensure that the parts are not only properly deburred but that the other surface finish specifications are met as well.

The machined part on the left in this picture has a bright surface and sharp edges. The goal was to deburr the edges with minimal impact on the surface finish. The initial result (part on right) of tumbling with Ceramic Media and a general purpose compound did deburr the part but it also resulted in a dull, matte surface finish.

This part will need to be tumbled in second step using a polishing media and a different compound to bring the desired finish back. Having a clear understanding of the ultimate surface finish required and that multiple steps are often needed is the first step in finding the best solution to finishing parts.

Wet Barrel Tumbling Guidelines

Below are some quick guidelines for wet barrel tumbling for both deburring and polishing operations: 

• Fill the barrel about half full with media and parts.
• Use a ratio of 3 or 4 to 1 (by volume) of media to parts.
• Dilute the tumbling compound to use a solution of about 2 ounces per gallon of water.
• Add enough solution to level of the load.
• Change the solution with each batch to keep the parts, process and media clean.

Of course, these are strictly guidelines and modifications based on any specific application or process is often needed (and recommended). 

Glass Bead vs Aluminum Oxide for Deburring Steel

Machining and work-hardening steel creates burrs and scale that needs to be removed. The part in the middle of the picture above shows the 'excess' material in threads as well as the darkening caused by scale formation in the heat treating process. While barrel or vibratory tumbling can be used to remove these burrs and create a smooth surface finish, threaded areas often need to maintain the square edges and dimensionality on the part.

The other two parts were blasted with different types of abrasive blast media to show how each media can accomplish the deburring task but create a totally different surface finish. The part on the left was blasted with a Medium Glass Bead (70-100 mesh) and resulted in a satin-like surface finish with clean edges. The part on the right was blasted with 120 Mesh Aluminum Oxide Grit and has a more matte, gray surface finish.

While Glass Bead can often result in a more aesthetically pleasing finish, the micro-profile achieved with Aluminum Oxide Grit is often required for future processing of the parts (i.e., coatings application).

Complex Part Geometry

There are often many tumbling media options for deburring or polishing parts. Different shapes and sizes of media can be used to round edges, polish into corners and provide a uniform and consistent surface finish. Part shapes and sizes that are relatively 'open' make the media selection much easier.

Sometimes parts are so complex that there may be only one option for tumbling media. Finding a media that will be small enough to get into tighter areas of a part but not get stuck in other areas can seem like an impossible task. Selecting a shape that will pass through holes without getting caught in interior areas of the part are a frustrating task. It is amazing how intelligent tumbling media can be and how it seems to always find a way to gang together and cause problems. Simply evaluating a part based on a drawing (or even holding with various media on hand) is not enough. Testing the part with different media options is critically important.

The picture above shows a milled slot on the interior diameter of the part. While this type of geometry can be challenging enough, there is a small interior hole at the end of the slot. The media selection to deburr the slot without getting stuck in the hole can be maddening. The pictures below show different features such as exterior threads, small channels and slots of varying widths and depths. While any of these features can be a challenge, all this geometry pictured was located on a single part. For this particular aluminum part, it worked out that an angle cut tristar shape deburred all the critical areas.

17-4 Stainless Deburring

Ceramic Media is the most commonly used tumbling media for deburring and surface finishing on steel. This is due to the fact that Ceramic Media is heavier and more aggressive than most other tumbling media and that steel is harder than many other metals (i.e., aluminum, copper, brass, etc.).

The 17-4 stainless steel part on the right in this picture has sharp edges and machining lines that need to be removed. In as little as 1 hour, a general purpose Ceramic Cone in a vibratory tumbler resulted in a uniform, matte surface finish and slightly rounded edges.

Ceramic vs Plastic Tumbling Media

The selection of tumbling media for a particular application depends not only on the type of material/metal being tumbled but also on the finish required for the next step(s) in the processing of the part. While less aggressive medias such as Plastic Media or Synthetic Media are typically used with softer metals like aluminum, the results above show a comparison of a Plastic Media versus a more aggressive Ceramic Media.

The picture shows the machined part on the far left followed by a part tumbled with a general purpose Plastic Triangle (middle) with a different part tumbled with a Ceramic Triangle on the far right. Both tumbled parts were vibratory tumbled for 1 hour with the same Kramco 1030 mild acid compound.

The machined part shows heavy burrs and machining marks on the surface. Both media types removed the machine marks and the burrs on the edges. The differences show up when looking more closely at the 'roughness' of the surface finish and the amount of edge rounding after the 1 hour cycle time.

The Plastic Media tumbled part shows slight edge rounding and a matte but uniform surface finish. This is a good finish for anodizing the aluminum part to a matte, smooth finish. The Ceramic Media tumbled part has noticeably more edge rounding and a more tumbled, 'rough-looking' surface finish. This finish is better for accepting paint or powder coating.

Machined Magnesium Parts

Similar to aluminum, lighter weight magnesium metal parts are often machined to create the required shapes and features (see picture above). The machining process leaves burrs, sharp edges and (most noticeably) machining lines and swirls. These imperfections in the surface need to be removed prior to further processing of the part.

As similar to aluminum and other reactive metals, magnesium is subject to oxidation. When vibratory tumbling the part, using the proper chemistry is important. This part was deburred and made smooth using a Ceramic Angle Cut Cylinder tumbling media and a solution of Kramco 1030 Mild Acid Compound (see 2nd picture above).

Ceramic media was used to keep the cycle time to a minimum with maximum surface finishing. The Angle Cut Cylinders removed the machining marks all the way into the interior corners of the machined areas as well as provided an even deburr and edge rounding across the entire part. The slightly acidic pH of the Kramco 1030 prevented the part from oxidizing during the tumbling process and resulted in a clean, white-metal finish.

Tumbling Frustration

A question about deburring, cleaning and polishing brass, copper and aluminum parts.  It's worth reading through the entire question as it provides an excellent description of what may small shops are doing and the frustrations they have.

Question: I primarily machine small parts out of 6061 aluminum, a small amount out of C360 brass and a handful out of C145 copper. I currently use a small vibratory tumbler to finish my parts. I use a small (about .25" square base) green plastic triangle to do the deburr and initial cleaning cycle. The problem with this, is it takes two to three days to run to get satisfactory results. I have tried running dry, but it takes even longer to achieve the results I want. I usually add a small cup of water to add some lubrication. But I have to take the tumbler bowl off and rinse it out and wash off the media every 6-8 hours because I get a thick black foam that fills the bowl and turns the media into a solid mass that just moves around the bowl. After this step, I clean out the tumbler and add a relatively fine red corn cob media to do a polish. But that also takes two to three days of tumbling to achieve a decent finish. I never add rouge or other polishing compound because I have no idea what to use. I just use the pre-treated corn cob media and replace it every 3 or 4 months. I am hoping to add a new machine to my shop and expect to produce several hundred parts a week that need polishing (I do not need to polish to a mirror shine, I merely need to deburr after the machining operations and provide a nice level of shine). Obviously, I would like to find a better way to accomplish this over what I have been doing. My parts are typically small - 1.2" diameter x 0.12" thick discs, 0.75" diameter x 0.25" thick slugs, 0.8" x 0.375" x 2" bars. Many of the parts have threaded holes and small slots (1/16" wide). I spend a lot of time hand cleaning the corncob out of the slots with a small pick. I have tried to do research to find a better solution, but it is one of those ask a dozen people, get 2 dozen answers types of questions. Some people tell me I need flow through on my first step. Some recommend ceramic some plastic and some steel shot. Corn cob and walnut shell seem to be recommended for finishing - some say pre-treated and others say to add rouge. I am at a loss now as to which direction to proceed so I figured it was time to seek more professional advise. Would you be able to help me find the best solution to my problem? I do not have a large space to set up multiple large tumblers, I need a compact solution with at most, two tumblers.

Response: I will try to address your questions and offer a simple and reasonable recommendation.

1. Plastic Media, Ceramic Media and other types of deburring media like this require a wet process using an appropriate tumbling compound (i.e., soap/lubricant). Assuming the proper shape and size of media is being used, the cycle times on the types of metal you noted (aluminum, brass and copper) should not be more than a couple of hours. The cycle times could be longer if you have very heavy burrs or need to get a highly rounded edge. The foam is probably a result of not using enough water and no compound. This is common with Plastic Media with no flow-through system for the solution.
2. Given the surface finish requirement of a 'nice shine' and parts descriptions, I would recommend using a 3/8" x 3/8" KSV Synthetic Cone Media and a solution of Kramco 1030 Mild Acid Cleaner. This media is a light, deburring media that will result in a smooth, pre-plate finish. The Kramco 1030 will leave the metals you are using with a bright finish. This media choice may require a slightly longer cycle time than a more aggressive media (i.e., Ceramic Media) but the surface finish will be much better. In addition, a flow-system is recommended for the best results.
3. The polishing media you are using - treated corn cob grit - may be treated with a rouge or something similar. Cycle times with dry tumbling like this are often long, 24 hours or more, but can produce excellent, near-mirror finishes. Of course, if the parts have holes or slots that are similar in size to the grit, it is common for the media to get stuck. Using the recommendation in #2 above may eliminate the need for a second polishing step (depending on the specific finish desired).
4. An alternative polishing step could be with a polishing Ceramic Media or Precision Ceramic Media instead of the dry process. While this may not result in the near-mirror finish achievable with a Corn Cob Grit, the finish can be a smooth, polishing, bright surface. A solution of Kramco 2030 Neutral Burnishing Compound would be used in this step.

Polishing Machined Aluminum

Taking machined aluminum parts and polishing to a smooth, uniform surface finish is often a multi-step process. Each step is designed to accomplish a different task. The part above has burrs, sharp edges and clear machine marks. Vibratory tumbling is the preferred process.

Step 1 - The edges are softened and the machine marks are removed using a Plastic Cone tumbling media. This media is selected due to it's lower density (vs. Ceramic Media) and lesser aggressiveness. The resulting surface finish is smooth and uniform. This part could be anodized to a matte finish, powder coated or painted with excellent results.

Step 2 - In order to brighten the part and prepare for anodizing to a higher luster, the part was tumbled with Polishing Precision Cearmic Spheres. While the finish is bright and smooth, the proper shape must be chosen to ensure that a uniform surface finish is achieved based on the geometry of the part.

Deburring Stainless Steel

Deburring stainless steel parts is a well established process that can be accomplished in a variety of different ways. Vibratory tumbling with a ceramic media is a common method. Cycle times are typically 1-2 hours or less. The challenging aspect (read: art) begins when the parts don't want to behave nicely.

Flat parts or stubborn burrs or scale or oxidation can all create problems when trying to deburr and surface finish a part. The part pictured above (left) is a hardened stainless steel, laser-cut, flat part. Sharp edges, burrs, heat scale and oxidation were all present on this part. Testing in a vibratory tumbler and in a barrel tumbler with a general purpose ceramic media did not provide the necessary deburring and edge rounding. The geometry of the part also lead to the parts sticking or sandwiching together in the tumbler.

In order to get the clean surface finish and proper deburring and edge rounding (right), the part was barrel tumbled with a fast cutting, dense KDF Ceramic Media. To prevent the parts from sticking together, an additional fine media was needed to break the surface tension between the parts and allow them to tumble freely in the barrel. The cycle time for this part was 4 hours.

Increasing Tumbling Abrasiveness

There are a number of strategies that can be used to increase the abrasiveness of both barrel and vibratory tumbling operations. These can be used when a boost to more aggressive surface finishing. deburring or edge rounding is needed.

• Increase the rpm (barrel tumbler) or the amplitude (vibratory tumbler).
• Use a denser/heavier media (i.e., switch from Synthetic Media to Ceramic Media).
• Switch to a more aggressive bond/formulation of tumbling media.
• Reduce the amount of water and/or compound in the process.
• Add an abrasive such as Aluminum Oxide Grit or similar (best with a barrel tumbler).
• Adjust the load level for a more aggressive tumbling action.

Identifying the critical issues with your part will determine which strategy(ies) are best to employ. Of course, all these strategies work just as well in reverse to decrease the abrasiveness.

Precision Aluminum Deburring

6061-T6 Aluminum

Machined aluminum part that needs to be deburred prior to the next production step. The critical areas include the tab (right side of picture) and the swirling machine marks in the center of the part. The overall size of the part is less than two inches so a small media is needed to get into all the inside corners and holes on the part.

The most successful media was a 1/4" ceramic triangle media (see picture below) in a vibratory tumbling process. This media was able to remove the burrs and tabs on the edges as well as leave a uniform, matte finish on the flat surfaces.

Deburred aluminum part

Extruded and Cut Aluminum Tube

Extruded and Cut Aluminum Tube

The picture above shows an extruded and cut aluminum tube that requires both deburring and removal of the extrusion lines along the sides (inside and out). These 6" long tube sections were vibratory tumbled with a Ceramic Angle Cut Cylinder for 1 hour to produce the clean, rounded edges and surface finish seen in the picture below. A fast cutting (KSF Bond) media was used to minimize the cycle time needed to remove the heavier burrs and extrusion lines. This part is now ready for a variety of secondary steps including coating, anodizing or polishing.

Vibratory Tumbled Aluminum Tube

Water Spots on Copper

Copper is a soft metal that is easily oxidized and stained (note previous post re: green color of Statue of Liberty). Stamped copper parts need to be deburred and cleaned prior to further use in most manufacturing processes.



This picture shows a portion of a copper component of an electronics part. The stamping and cleaning process (part on the left) shows light burrs and clearly visible water spots and staining.

In order to get a clean part for proper electrical contact, the part on the right was vibratory tumbled. The customer wanted a short cycle time and was not interested in a polished or bright surface finish. A Ceramic Angle Cut Triangle was used in order to deburr the outside edges as well as the ID of the holes and other features. The media and parts were tumbled in a compound solution of the Kramco 1030 Mild Acid Cleaner to remove the oxidation and water spots. The end result was a clean, smooth surface finish that met the customer's requirements. The total cycle time in the tumbler was only 15 minutes.

Polishing Pewter

Molded pewter, rough surface finish

Pewter parts can be cast into a large variety of shapes. The casting process often results in a rough surface finish along with burrs and flashing on the edges. Surface finishing is often done by hand to produce a smooth finish and especially a high polish on the parts.

2-step polishing process

Mass finishing can be used to achieve all of the required deburring and edge rounding and often can result in a bright, smooth polished surface finish.

The part on the right was vibratory tumbled with a Ceramic Media to remove the molding marks and soften the edges. The second step to polish to surface (part on left) involved barrel tumbling with Stainless Steel Media with an appropriate burnishing compound. You can even see the camera reflection. Additional polishing can be done by hand if necessary.

The mass finishing process will significantly reduce the amount of hand work required. Vibratory and/or barrel tumbling will also allow for difficult-to-handle small parts to be deburred and polished successfully.

Deburring Aluminum Slots

Selection of media shape and size is critical when trying to deburr slots and holes. The material type (i.e., aluminum, steel, plastic) is also important in identifying the proper type of media. The part pictured above (machined on left; tumbled on right) required complete deburring of the part, decent edge rounding and a uniform surface finish. The customer's next step in the process was to create a dull, anodized finish.

The part contained a variety of geometric features including approximately 1/4" wide x 1/4" deep slots, both large a small holes, square interior corners and radiused edges. The finished part was vibratory tumbled with general purpose (KX bond) 1/4" x 1/4" Plastic Pyramids. This shape and size of media was selected in order to get into the corners of the slots and result in a uniform surface finish across the part including interior corners.

The general purpose media resulted in a dull surface finish ideal for creating a matte, anodized final surface. If a brighter anodized finish was specified, a secondary polishing step in a vibratory tumbler would be improve the results.