I have been asked to share some metal polishing tips that I have picked up over my many years of experience in the field.
First of all metal polishing is not rocket science. Anyone with access to some abrasives can — in effect — polish. This being said, just because you have the equipment does not necessarily mean you are ready to take on a polishing job. I am often asked to help figure out how to fix a polishing job after someone has spent countless hours trying to achieve a desired finish, or I am asked how to speed up the process because all of the estimated profit is being lost in the extra hours needed to complete what is sometimes seen as an afterthought to a job.
Before starting I feel I need to clarify a few things. I am not the last word in polishing. There are a lot of more qualified people than myself in the art of polishing. I also know that there are countless ways to achieve a desired finish and to this day I will not argue technique. I am more interested in results than method. I have tried to keep an open mind for other approaches to metal finishing. With that being said, I am going to define the common finishes I see. I am also using the finish call out designations I feel are the least confusing.
- #4 Finish is a directional grained finish created by polishing to the equivalent of 150 grit abrasive.
- #6 Finish is a directional grained finish created by polishing to the equivalent of 240 grit abrasive.
- #7 Finish is a buffed finish that is mirror-like, but has some surface imperfections.
- #8 Finish is mirror-like and has had all surface imperfections removed resulting a very smooth and reflective finish.
Always be sure to have good finish samples on hand to make sure everyone involved can see first-hand the desired finish. I believe the most common and costly mistakes are made before any abrasive touches metal. As I stated before, metal polishing is not rocket science, but it can be extremely labor intensive if it is poorly planned and executed.
- Pre-plan a polishing job before fabrication starts
A lot of money can be saved in polishing while the project is still a drawing. Always define the surface finish that is required in the quote process. Look for any areas that will pose a polishing problem, tight angles and radical changes in finish direction come to mind. Also, look for ways that can save time. If for example it is a hand rail, does the side that faces the wall and floor have to be polished to the same quality as the visible surfaces? 30% of your polishing time may be wasted on finishing part of a rail that is not seen. Sometimes a job has to be mocked up to make certain that polishing can be completed satisfactorily, if the job is going to be polished to a mirror make sure the design allows enough room for buffing. Some angles that would be easy to polish to a #4 finish cannot be adequately buffed because there is no way to get the buff into a tight radii.
- Materials to be polished should be handled with extreme care
Once the drawing has made it into production the materials to be polished should be handled with as much care as possible. All raw materials should be inspected with a careful eye keeping in mind any surface defects will have to be polished out. Sorting out any damaged material that would need extra time to repair will save considerable time in polishing. During the fabrication process remember to handle all materials with care. A few extra minutes in handling on this end can save hours in polishing.
- Before assembly, pre-polish everything
Pre-Polishing will allow you to inspect all of the components to make sure they are easily cleaned up after assembly. It will also allow you to replace any undesirable components before they are assembled.
- Weld with care
If components are to be welded together remember that welding tables will scratch the materials. Try to ground the parts without causing surface defects. A good welder can save polishers a considerable amount of time by keeping the weld bead as small and flat as possible. Excessive weld, weld spatter and porosity will add considerable polishing time. In most cases a couple of extra minutes in welding can save an hour in polishing.
- Only use as coarse an abrasive as is needed
There is no sense using a 36 grit abrasive to grind a weld when an 80 or 120 will work. Always keep in mind any polishing lines put in the material will have to be removed by the next operation until the desired surface finish is achieved. A good rule of thumb is never jump more than 100 grit at a time, an example is 120 grit can be removed with 220 and 220 with 320.
- Always use an abrasive lubricant when polishing
Be careful to get an abrasive lubricant that is compatible with the abrasive you are using. An example being tallow based grease may clog a 400 grit abrasive causing it to not cut at all.
- Use buffing compound with hand pads
When using a ScotchBrite or hand pad type abrasive, I have found that a small amount of buffing compound applied to the abrasive will help give a cleaner more uniform finish.
- When polishing to #8 Finish, care should be taken in making sure that all polishing lines are removed from the previous operations before starting to buff
A good steel compound on a sisal buff will remove 320 – 400 grit lines with relative ease, but will make a hard go of it if some 120 or 220 lines are missed in previous operations.
- When polishing to a #8, it is easier to buff warm materials
Especially in the final “color buffing” operation. The color buffing operation consists of using a very fine compound on a cotton or felt buff to bring out the true shine of the metal. It is common for the compound to pull off of the buff and get stuck to the polished surface. This can happen for several reasons but the most common I see is the polished material is not warm enough to keep the compound liquid. A solution for this that has worked for me is heating the polished material with a heat gun so that the area to be buffed is warm to the touch. Care should be taken not to get the material too hot because trying to buff overly heated material will cause the compound to pull off and burn on to the buffed surface creating an even worse problem.
- If you smell smoke, something’s wrong.
Properly lubricated abrasives should never get base materials so hot they smoke. If you see the polished materials turning blue or brown stop! Something is not working. You are using too much pressure, over running the abrasive, or running a buff dry are a few causes for smoke. At no time in polishing is this amount of excessive heat useful.
- Wrap the polished materials immediately after polishing
This will guard against accidental scratching or cross contamination of metals.
- Make sure to clean up all polishing dust daily
Pay special attention to electrical outlets that may accumulate metal dust and short out. Always have a class D fire extinguisher on hand whenever polishing.
The only way to get good at polishing is hands-on experience.