Polishing on the CNC Router

   That depends on several variables, including machine stability and rigidity, the type of tooling used, and – of course – the competency of the operator/programmer.
   Let’s touch on the customer side of the question for a moment. Will your customers accept a CNC polish on their jobs? (That may depends on the market you’re in.) Is your company known for high-quality work? Are your customers’ expectations higher than the local competition clientele?
   And, do your customers expect perfection on each and every job? Mine do. And so do I.
   I get paid to expect perfection in every detail of every job. That’s why, after all, clients return to us for repeat business. They know what to expect, and in turn, rely on us to perform the same on every job. Many high-end custom shops have the same customer expectations as mine.
   On the other end of the spectrum, there’s the high-volume production shop. The same questions above apply … although in a different arena. The clients of many production shops have expectations as well: a fast turn-around and the same standard of quality the shop’s produced since the beginning. They’re not as concerned with polish quality as they are with speed and price.
   So, with the customer aspect taken into consideration, let’s move on to machine marketing.  Many machine manufacturers and dealers will try to sell you their machine based on speed and quality of the finished product. As stated above, quality is in the eye of the beholder. (More on this later.)
   Speed is another aspect to consider. Do you think that your machine can outperform experienced polishers? Many shops employing experienced help don’t depend on the machine to polish for them. In fact, they believe that hand polishing is faster and of higher quality.
   Take this scenario into consideration: While the machine is running the hard part of the job in the shaping, your polishers could be putting the best bling-bling on the piece that just came off the CNC.
   After many hours of running the latest in stone-working technology, I’ve come to the realization that it’s more-productive to polish by hand. Think about it; the average edge still has to be touched up in one sense or another anyway.
   Take the ogee; it needs to have the top and bottom lines rolled. So, you have to set the job up on tables to do so. Since you’re already going through the motions, why not just polish the edge after the final metal diamond from the CNC? Take it from 800 grit up to buff, and you’ll end up with a beautiful edge comparable to the surface of the slab. And that, after all, is what many of our clients want.
   Now, back to the machine polish issue. The inherent problem with CNC tooling is that the tools rotate. In the process of machining an edge and polishing, the tooling spins on a single plane. In short, current stone-machining technology is limited to tooling designed to spin in one direction. This tends to leave lines in the edge.
   That lack of dual motion is why I see hand-polishing as superior. The hand-held polisher cuts small lines in different directions; each small line cancels out the other. As the polisher moves from one side to another (left-to-right, for example), the small lines left are cut out by the next move. Therefore, no lines are left behind for the next grit pad to remove. As you progress up in grit, the polish gets better and better.
   Machine tools tend to leave lines from one bit for the next bit to remove. As the tools wear, this becomes more of a problem. The lines left from one bit to the next get deeper and deeper as tooling wears. That’s why the average CNC will produce a great polish at the start, and get worse as time goes on.
   Tooling manufacturers are always coming up with new ideas to improve the machined edge; products have come a long way in just a few years. In fact, some tooling companies are getting very close to hand-polish quality.
   Some machines are capable of managing tool wear. The systems keep tool tolerances within manufacturer specs, reducing wear and excess lines.
   Some CNC machine companies are also combating the tooling issues with other methods of shaping and polishing edges, taking stone work to the next level in quality utilizing standard flat diamond tooling (similar to hand tooling) in a manner similar to C-arm-type machines for straight edges. This type of CNC machining appears promising, but only time will tell.
   So, it’s back to the first question. Will you and your customers accept a machine-polished edge? You decide; only you can control your quality and production. It all depends on what you expect as a stoneworker and business owner, and what your current clientele expect in each job.
   Until next time – Donny Taylor.
   Donny Taylor is a proud member of the Stone Fabricators Alliance. To ask him a question, or find more info, visit www.stoneadvice.com.

This article first appeared in the January 2007 print edition of Stone Business. ©2007 Western Business Media Inc.