TECH NEWS Some Theory: Efficient Polishing Is Dependent on Surface-Feet-Per-Minute This Marks My First Issue As Technical Editor Forsnag News
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The Society of North American Goldsmiths TECH NEWS Some Theory: Efficient polishing is dependent on surface-feet-per-minute This marks my first issue as Technical Editor forSNAG News. (SFM), not pressure applied to the polishing wheels. Excessive I want to thank Sean for all the work he has done for SNAG pressure mainly produces excessive heat. Of course, even when News in bringing us these articles in the past. These articles using proper polishing supplies and techniques the piece is have helped our community share the wealth of knowledge gonna get warm; ya can’t fight friction. Speaking of SFM, the housed within its members. choice of buffing motors and wheel size selection naturally fol- I have hit the ground running with e-mail and phone solicita- lows. In my shop the smallest wheel I spin is a 6", the largest is a tions for articles. It is my intent to bring you as many views of 10". My polishing motor is 1 HP and spins at 1725 RPM. A quick our chosen medium as possible. Sometimes the experts I con- look at Rio Grande’s catalog reveals that their wheels range in tact will lie outside of our field. size from 8" to 2". Their motor choices are 1725 and 3450 RPM; some dual speed motors range in horsepower from 1/4 to 1/2. So Other times they, like the author today, are metalsmiths who if you think about motor speeds with respect to wheel diameter, have learned a great deal about a technique from another it just makes sense that if we run small diameter wheels we occupation and have applied it to their artwork. want to spin them at a greater speed than if we were using large I hope that all of you take a look at the vast knowledge you wheels—the SFM thing. A large wheel spinning at a slower have accumulated over the years and make the decision to speed could have the same SFM as a small wheel spinning faster. share with the broader metals community. Articles from all We could go into tables and math (ugh!) but I’ll spare you. Of levels are encouraged. course a larger wheel requires more HP to spin it. Someone T.J. Fejka writes about a technique most of us take for granted: working on large pieces, such as hollowware, should consider a machine polishing and buffing. T.J. has an easy to read writing motor that can handle 6" to 8" wheels. Those sticking to typical style, injected with humor. Enjoy. jewelry items will find smaller wheels and HP motors sufficient. —Jim Bové Wheel selection is another matter altogether. Looking at the selection in Rio’s catalog boggles my mind (not a hard thing to do, some say). I’ll readily admit that I haven’t tried most of the Machine Polishing and Buffing wheels, I do most of my polishing with two wheels, a 6" diameter x 1" face soft felt and a 10" diameter x 2" face loose muslin. I Since this is my first article for SNAG, let me briefly introduce charge the felt wheel with bobbing compound and the muslin myself- Hi, I’m T. J. Fejka. OK, maybe some more detail… wheel with tripoli. I finish my pieces off with a Sunshine Cloth, available from Rio. If a customer wants a “more shiny” finish, I My metal working life began in earnest when I entered the finish with a 6” loose muslin charged with red rouge. Pennsylvania Gunsmith School after a stint in the US Navy. After graduation I was a “self-unemployed” gunsmith for five Probably the most common wheel types I see in jewelry studios years. A good gunsmith needs to be a bit of a jack-of-all-trades. are stitched muslin, loose muslin and felt. Personally I think Woodworking, machining and steel polishing are just a few of that stitched muslin wheels are a cheap and inferior alternative the skills one should possess to be a good “gun plumber.” to a felt wheel. A soft felt wheel charged with bobbing compound When I first started working silver I was pleasantly surprised will remove relatively deep file marks from your piece, without at how easy it was to obtain a nice finish versus doing the same prior sanding. If used correctly, the flat surfaces of your piece with steel. My time spent at the wheel, and with tiny bits of will remain flat and it will retain its crisp edges. The same can- abrasive paper, felt bobs and a flex shaft, diminished greatly, I not be said for a stitched muslin wheel. Even though one can could spend more time creating and far less polishing, cross remove file marks with a felt wheel, I would not recommend it polish ing, buffing...ad nauseam. The skills I developed from for most pieces or for the polishing neophyte but it can be a real the many hours spent polishing steel crossed easily into the art time saver when needed, and when the piece allows. metal realm. My hope in this article is to be able to pass some Some Technique: of that knowledge on to my fellow metalsmiths. I will discuss a bit of theory, technique, some tools and supplies and introduce Let the wheel do the work! Though you should always be mov- a supplier that you may be unaware of. So, “nice meeting you.” ing the piece when it is on the wheel, you don’t want to just do a Let’s get started! “touch ‘n’ go.” You want to keep the piece moving but moving slow enough to allow the abrasive compounds to do their job. The intent of this article is to cover polishing precious metals using a stationary polishing motor. Hand and flex shaft polish- Save all of your polishing until your piece is basically finished. ing methods are out of the scope of this missive and will not be There are exceptions. Stone setting: you set any stones after you covered. have polished. Riveted pieces: unless you are using flush rivets, polishing over set rivets is not advised. Cold forged pieces: 7 The organization for jewelers, designers and metalsmiths depending on the piece you may want to pre-polish your stock. described for wheels with an arbor hole should work, although I Of course your forging hammer has a mirror finish so it imparts have not personally done so on a pinhole style wheel. its smooth, shiny finish to the piece being forged. Polishing Once the wheel is running true, charge it with polishing com- after the piece is forged is usually not needed. If you feel you pound. “Charging the wheel,” means to coat it with polishing must polish a cold forged piece, keep it light and brief or you’ll compound. You will want to charge the wheel with just enough blur those beautiful forging marks into oblivion. Finally any compound to evenly coat its edge. The tendency is to over areas you will not be able to reach once the piece is “mechani- charge. This not only wastes compound, but, in the case of a felt cally” finished, should be pre-polished. Other than those excep- wheel, tends to produce an uneven coating. This unevenness, tions, I do all of my polishing on fully finished pieces. high and low areas of compound, will produce ripples on your A few words about prepping the piece prior to “hitting the finished piece—which you want to avoid. You are now ready to wheels” are in order. First make sure that the piece is properly bring the piece to the wheel. pickled. There should be no traces of flux remaining on your Where you look when addressing the wheel is very important. piece. You will not be able to polish flux off; your wheel will ride You need to have your head above the piece, looking behind it at over it and polish away the metal around the flux. When you do the desired contact point between wheel and metal. This is the finally clean all of the flux off, you will have a raised island of initial view you want to have prior to touching the metal to the untouched metal where the flux was. Don’t ask how I know this. wheel. Once you see where you plan to start the polishing opera- I said I would not cover hand finishing, and I won’t, but suffice tion, put your piece to the wheel and make initial contact. This it to say that fire scale is more easily and thoroughly removed first contact should be brief and done with minimal pressure. by filing and hand sanding than by polishing on the wheel. I liken this step to a golfer taking a practice swing or a pool Filing the appropriate areas and then sanding with 400 grit player a warm up stroke prior to actually hitting the ball. We paper is my first finishing step. White carding* at this point is take a light stroke on the wheel and then check the piece to see a good idea so you won’t be bouncing between file, paper and if the wheel is actually contacting the metal where we thought wheel. Once the majority of the fire scale is gone (some can be it would. If all is as you expected, you no longer need to look removed with the wheels) you will need to thoroughly clean the behind your piece but keep your position stable and begin pol- piece with soap and water.