Acrylic Duck Calls

Acrylic Duck Calls

Above is an other good example of the results that can be obtained with dry barrel tumbling using Hardwood Media and the Finishing Creams. The part directly out of the milling is on the left and the final result is on the right.

There are a number of other pictures with brief descriptions of the process used located at these links:

Polishing Molded Acrylic
Polishing Machined Acrylic
Polishing Colorless Acrylic
Acrylic Button Polishing
Acrylic Knife Handles

3D Printed Parts

An interesting thread about deflashing and surface finishing 3D printed parts has been started on the ShopTalk Forum. As this 3D manufacturing process becomes more popular and mainstream, surface finishing using both barrel tumbling and vibratory tumbling will continue to be an issue. Please provide any comments and experience you have either on The Finished Part Blog here or on the Forum.

Dry Tumble Deflashing

Molded plastic parts often have flashing or excess material that needs to removed from the edges of the part (see part on left of picture). This can be accomplished in a variety of ways including a wet process using vibratory and barrel tumbling with an abrasive media (i.e., Plastic Media) or with an abrasive blasting process to blast the flash off the edges.

If the part is a hard plastic with a relatively simple geometry and the surface finish needs to be maintained, tumbling the part with a polishing media is ideal. The mass of a polishing media will knock the flash off the edges and will not change the surface finish since it is a non-abrasive media.

The part on the right was barrel tumbled with a KP Ceramic Angle Cut Cylinder that was small enough to pass through the ID of the part. These results were obtained in only 15 minutes. The parts were retrieved from the process clean, dry and ready for the next step in the production process.

Cartridge Brass - Study (Part II)

Dirty Cartridge Brass Casings

In the last post we discussed the differences in performance between vibratory tumbling and barrel tumbling to clean brass cartridge casings. A wet process using a polishing media is a much quicker method to clean brass than dry processes using Walnut Shell Grit or Corn Cob Grit. The test results indicated very similar results in both types of wet tumbling systems.

This post will focus on three different media options for cleaning the dirt and oxidation off the brass. In all three cases, the same solution of Kramco 1030 Mild Acid Cleaner was used and all tests were conducted in a barrel tumbler with a tumble time of 15 minutes.

Carbon Steel vs Stainless Steel

The first test compared the differences between Carbon Steel Tumbling Media and Stainless Steel Tumbling Media. It is pretty clear from the picture above that the Stainless Steel was much more effective at cleaning the brass. While this difference would not be expected initially, the reason may have something to do with the characteristic of the Carbon Steel Media to oxidize and possibly the transfer of iron to the brass casings. This reason will be more clear after reviewing the results of the second test.

Polishing Ceramic vs Stainless Steel

Once the Stainless Steel Media was declared the winner in the first test, the next step was to compare this heavy, burninshing media with a less dense (and less expensive) media. The above pictures compares the results of a K-Polish Precision Ceramic Media to the same Stainless Steel Media used in the first test. The K-Polish Precision Ceramic Media is a high-alumina, porcelain-type media used commonly in many different tumble polishing applications. Both of these media types are extremely long lasting with the capability for 1,000+ operating hours.

As the results for the Stainless Steel Media and the Precision Ceramic Media are very similar, the decision on which media to use will hinge on the type of equipment being used (many vibratory systems can't handle the weight of steel media), the available budget and the overall desired process.

In conclusion, these tests would seem to indicate that excellent results can be obtained in very short cycle times using either a Stainless Steel Tumbling Media or a K-Polish Precision Ceramic Tumbling Media in either a barrel tumbler or vibratory tumbler.

Cartridge Brass - Study (Part I)

Dirty Cartridge Brass

Cleaning cartridge brass (see 'dirty' brass above) has traditionally been accomplished using a vibratory or barrel tumbler with a dry media such as Walnut Shell Grit or Corn Cob Grit. Both of these medias will do a good job of cleaning the dirt and oxidation off the brass but typically require a long cycle time (12-24 hours or more).

Alternatives to this long tumbling time are available that will result in clean, bright brass is as short a time frame as 10-15 minutes. These alternatives also require a vibratory or barrel tumbling system but with different media and use a wet (chemical compound solution) process. This post and the next will review the results using different tumbling methods as well as comparisons of different media.

The basic process involves (vibe or barrel) tumbling the brass with a polishing media. A typical ratio is about 3 parts of media to 1 part of brass by volume. The solution would be added to the level of the load in a barrel tumbler. In a vibratory tumbler, the solution could be circulated through the media/parts load or could be added as a small amount (usually about 5% by volume of the load size) in a batch process. The selection of compound (i.e, Kramco 1030 Mild Acid Cleaner) is critical to achieving good results. Obviously, it is important to ensure that the equipment being used is designed for a wet process.

Vibratory vs Barrel Tumbler

This picture shows the results using the exact same media type, parts/media ratio and solution but with different tumbling system types. The parts on the left were vibratory tumbled for 15 minutes with a recirculating solution of Kramco 1030 compound. The brass on the right were barrel tumbled also for 15 minutes with the same solution filled to the level of the load.

It is clear that both tumbling processes did an excellent job of cleaning the brass and that the results are very similar. Based on this test, it seems that either a barrel tumbling system or a vibratory tumbling system can be used to clean cartridge brass. The decision comes down to the type of equipment available and the desired in-house handling process.

The next post will compare different types of media all in a barrel tumbling process.

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). 

Polishing Medical Parts

Once cut, machined and heat treated, stainless steel parts to be used for medical applications (see tweezer parts above) need to be deburred and polished to a high shine. The part in the top of the picture above is ready for surface finishing and some light edge rounding.

To remove the heat treat discoloration, the part was first blasted with a Coarse Glass Bead. This created a uniform, satin-like surface finish on the part. In this situation, a larger bead was used on the hard metal in order to keep the finish a bright as possible and make polishing a little easier..

After blasting, the part was barrel tumbled with a Steel Polishing Media to smooth out the finish, provide some light edge rounding and prepare the part for an additional polishing step. A final step such as a burnishing wheel or electro-polishing would create a near-mirror 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.

Wood Parts Tumbling vs Hand Sanding

Hand sanding wood parts can be a tedious and labor intensive process. The ability to smooth the surface, remove cutting marks and round edges on a large quantity of parts can same time and money.

The part pictured above needed to be sanded down prior to the application of a stain and coating. The part on the right shows the sharp edges and some flashing after the initial cutting of the part. A two step barrel tumbling  process was used to achieve the end result on the left.

Step 1 involved using a Hardwood Peg Media and relatively coarse White Aluminum Oxide Grit. This produced the edge rounding and major 'sanding' of the part.

Step 2 used a similar Peg Media along with a much finer grade of White Aluminum Oxide Grit to result in a smoother, sanded finish. If necessary, subsequent steps with even finer grades of Grit or a quick hand sanding to the final required surface finish can be used. Barrel tumbling the parts in this dry process can eliminate most if not all of the hand sanding often done.

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.

Mirror Surface Finishing

Achieving a near-mirror finish on many metals using only mass finishing such as vibratory tumbling or barrel tumbling can be a challenging process. The combination of tumbling media, equipment and compound will determine the results. And these results will vary depending on the type of metal being polished.

This stainless steel part has a very flat geometry with minor scratches and imperfections. Generally, the heavier and rounder the tumbling media, the better the surface finish. Additionally, a tumbling process that produces a smooth, even tumbling action will produce the best results.

The part was barrel tumbled to give a nice rolling action of the media against the part. A Stainless Steel Round Ball (Sphere) in combination with a highly lubricating, tumbling compound (Kramco 910) kept the process clean and resulted in a near-mirror finish on this stainless steel part. The total tumbling time get from the before (top picture) to the after (bottom picture) was 1 hour.

Heavy Slag on Steel

When laser cut (or saw cut), steel parts can develop heavy slag on the edges (see picture above). The slag is developed as the metal is melted during the laser cutting action and then re-forms on the edges on the 'bottom' of the part. The excess metal can be removed by hand grinding; however, if the parts are small or there are many parts to be cleaned, hand finishing is not efficient.

The finished part above was barrel tumbled part-on-part to remove the slag and excess metal on the edges. A small addition of 36 Mesh Aluminum Oxide Grit increased the abrasiveness of the tumbling action allowing the process to go from the before to the after in only 30 minutes. While the surface finish is rough after the tumbling process, the parts can be painted or sent through additional steps using other tumbling media to smooth out the finish and possibly polish the part.

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.

Polishing Firearm Parts

There are two types of finishes needed for firearms. Most (military and hunting) require a matte or dull finish to minimize reflection and give good 'grip' properties. Firearms used for show pieces or when reflection is not an issue will often need a higher polish or near-mirror finish on certain areas of the gun.

The part above is an as-produced finish. The surface is relatively smooth but dull. To process large quantities of these parts, a single-step process can be used to significantly improve the finish. The same part below was barrel tumbled for 18 hours (overnight) in Stainless Steel Ballcones and a solution of Kramco 910 Burnishing Compound to produce much brighter, mirror-like finish.

Choosing Tumbling Media

Choosing to proper tumbling media for a specific part can be challenging enough. When you are producing a variety of parts, the decision can be overwhelming. The following steps will provide a guideline for moving through this process as effectively as possible:

1. Identify the results you need to accomplish - deburring, polishing, surface profile.
2. Calculate the desired cycle time and the volume of parts you need finish per unit time.
3. Determine the type of equipment you need (i.e., barrel vs. vibratory tumbling; wet vs. dry, etc.).
4. Review the part size and geometry for all the parts that need to be finished.
5. Select the proper media and compound to achieve the desired results with these parts.
6. Confirm the process and media selections with testing.

And just to make the decision more difficult, there are many surface finishing options such as abrasive blasting, high energy tumbling, shot blasting and others that may result in as good a process or even better.

Wood Parts Tumbling to Remove Flashing

Common practice to remove flashing and sand wooden parts is by hand. Sandpaper or sanding wheels can be used to effectively clean up parts one at a time. A more efficient process (especially for large quantities of parts) is to use barrel tumbling.

This picture shows a before (left) and after (right) of a walnut wood part with heavy flashing, excess material on the edges and a rough cut surface finish. This is probably an extreme example; however, a simple barrel tumbling process created the surface finish on the right.

This part was tumbled with Hardwood Media and a small amount of 120 Mesh White Aluminum Oxide overnight. The result is a smooth surface finish with rounded edges and no excess material.

Silverware Burnishing

Previous posts about the basics of silverware burnishing (Part 1 and Part 2) described the process through which silverware and flatware are restored in a barrel tumbling process. The basic outline described the flowing of the metal to 'fill' the scratches and the removal of the oxidation on the surface. Below is a picture showing an extreme example of what can be accomplished.

Silverware Burnishing Test Results

• Far left - Before sample with heavy oxidation, scratches and some pitting on the surface
• 2nd from left - Tumbled in Steel Media and a polishing compound. Sometimes testing is required to determine if the combination of media and compound will discolor the surface even though the process removed the scratches and pitting.
• 3rd from left- Tumbled in steel media with an alternative compound. While it is difficult to tell, both the 2nd and 3rd pieces are similarly polished The proper compound (for this application) clearly resulted in a brighter, polished finish.
• Far right - Tumbled with the same compound as the 3rd part but with a Precision Ceramic polishing media. The surface is clean and bright but not quite as good as the Steel Media. This process would be best if the tumbling equipment being used is not designed for heavy media.

Acrylic Polishing

Here is another good example of the polished finish that can be obtained on acrylic plastic using a barrel tumbling process only. The part on the left had been cut and machined to the general shape and size. The machining marks and square edges can be seen rather clearly - along with the dull surface finish.

A two-step dry barrel tumbling process was used to achieve the polished results on the right. Both steps used a Hardwood Media. The first step using Shynolyte Pre-Polishing Cream provided the edge rounding and a smooth (but matte) surface finish. The second step using Microlyte Polishing Cream brought out the bright shine and gloss of the plastic. Each step was about 24 hours and the results certainly speak for themselves.

Fired Clay Parts Tumbling

Common sense would state that using a barrel tumbler for fragile fired clay parts would be inadvisable. The aggressive tumbling action would damage or crush the parts. This logic might follow for brittle parts such as ceramic tile and the like.

In fact, tumbling all types of fragile and brittle parts can be accomplished quite successfully in a barrel tumbler. The part in the picture above is a molded and fired clay pendant that is only about 1/8" thick. The project required that the excess material on the edges be removed and that the edges are heavily rounded.

In this case, a wet process would have involved undesirable absorption of water into the pendant. A dry tumbling process was used to achieve the stated goals. The parts were tumbled with Hardwood Media and White Aluminum Oxide for less than 2 hours to achieve the edge rounding as seen in the part on the right. As long as the proper ratio of media to parts (about 4:1 in this case) is maintained, damage the parts will be insignificant and batches as large the barrel will allow can be done.

Rock Tumbling

Rock tumbling and stone polishing is a popular hobby. The most important ingredient to achieving a great finish is time. Polishing is typically a 4-step process involving progressively finer and finer abrasives. Each step is done with a clean barrel, fresh water and a virgin abrasive. The Creetown Gem Rock Museum (in the UK) has a good outline for polishing stones.

The first three steps require a coarse grit (80 mesh) followed by a medium abrasive (220 mesh) and finally a fine grit (400 mesh). Aluminum Oxide or Silicon Carbide are the preferred media due to their durability and hardness.

The fourth step demands a very fine, hard media that will maintain it's 'cutting' ability for the entire cycle time. Cerium or tin oxide are the abrasives of choice as they will maintain their sharp edges as they break down over time. Sawdust can be added to this step to ease the impact and eliminate chipping of the stones.

Hobby size barrel tumblers will generally have capacities of just a few pounds of stones. Tumbling times for each step is about 1 week. Larger, industrial-grade tumblers such as the MT Series Barrel Tumblers will allow for more weight to be tumbled at one time. This often leads to reduced cycle times and higher production rates. Regardless of the equipment, patience is the key to beautifully polished rocks and stones.