What is CNC?

CNC stands for Computer Numeric Control. The movement of the machine is controlled by a computer, which reads a computer program. The written language the computer uses is called a G code, and writing this language requires intensive training and computer knowledge. Fortunately, most of today's CNC machines have the G code pre-written in the software, and knowledge of G code is not necessary. In simple terms, a CNC is a robot that is controlled by a computer.

Most people in the stone industry relate CNC with a CNC router, however, CNC technology can also control bridge saws, waterjets and laser etching machines - to name a few. For the purposes of this article, I will focus only on CNC routers.

What can a CNC do for your business?

When properly programmed, a CNC can produce a finished piece in less time than manual labor. The quality of the finished product is consistent, and in many cases, better than manual labor.

The finished piece will match the template exactly. A CNC does not need a day off to go to the dentist or to go to court or take the kids to the zoo. It also doesn't complain or need three or four cigarettes or coffee breaks during the day. For that matter, it doesn't even need lunch.

Many CNCs will also calculate the total time to fabricate a certain job. This can be difficult to do with a manual operation. A CNC can also save time on slab layout and templating if incorporated with one of the many electronic templating systems.

With all of this said, keep in mind that a CNC is a machine and will at times break down and need repair and maintenance. Human error is not totally eliminated, since a programmer must enter the information into the machine. However, there are many checks and simulations that can be performed so that errors are less frequent.

Can I afford a CNC?

This is a question that many fabricators don't look at closely enough. Before you can answer this question, you must first ask yourself if you have enough work to fully utilize a CNC. If you are only doing one kitchen a day, a CNC may not be for you. As a matter of fact, if you are only doing one or two kitchens a day, a CNC may cost you more.

It is important to examine what type of production can be expected from a CNC, the time it will take to pay for the machine and how much production is needed to make the machine worth the investment.

CNC machines will vary from model to model and from manufacturer to manufacturer. The following example is based on one of these machines and information from the manufacturer, but these figures are based on my personal experience with CNC operation and cost. Production rates and payback can vary.

Let's say you purchase a CNC for about $210,000 and decide to lease it. Your lease payment will be somewhere around $4,200 per month. If the machine works for eight hours a day and 21 days a month, that translates to 2,352 lineal feet processed per month (based on a average production rate of 14 linear feet per hour). Of course, this is assuming that the machine is running constantly for eight hours a day. Loading and unloading the machine can take from 10% to 20% of the time, which would reduce the lineal feet per month to 1,881 lineal feet at the 20% range.

In addition to the machine cost, you also need to calculate operator and tooling costs as well as power, water, etc. For the purposes of our calculations, let's assume that a set of tools for one profile costs $3,000. The life of these tools is approximately 2,500 lineal feet. This translates to a tooling cost of about $2,500 per month. CNC operator rates can vary considerably from state to state. I have seen rates as low as $16 per hour and as high as $40 per hour or more plus 20% burden for benefits, etc. In addition, you must calculate the labor rate for loading and unloading the machine. On the low end, you are looking at about $3,300 per month on labor, and on the high end about $8,064 labor.

So overall, your cost to operate the CNC for one month - based on 1,881 lineal feet per month - will range from $10,000 to $15,000. Broken down further, the cost of operating a CNC machine should range from $5.31 to $7.97 per lineal foot. I did not include power and water consumption into the calculation or the labor involved for computer time, etc., but this will serve as a guide and a starting point to help calculate costs. On the supply side, if you are charging your customers $20 per lineal foot processed, then you will be generating about $37,000 per month.

Another factor to bear in mind is the set-up cost as well as the learning curve. Don't expect to be up and operating your CNC to full production for at least three months. This, of course, will depend on the type of machine as well the quality of the training. It also depends on how good your operator is.

There are also numerous techniques to make a CNC run more effectively. In future articles, I will discuss some of these methods that even the manufacturers may be unaware of.

Do I have to hire a computer geek to operate my CNC?

This is a tough question because it depends on the operating system and the type of CNC you purchase. In some cases, it is a good idea to hire someone with good computer skills. In other cases, computer skills can be learned. The most important prerequisite is that the potential operator be open to new technology and not to be afraid of the machine.

Unless you hire someone with prior experience, it is going to take time to get someone up to speed. I have found that the best operators can be found coming right out of high school or a technical college with a computer background. This is not to say that the average fabricator can't learn, but the right person needs to be chosen.

What to look for when purchasing a CNC

As mentioned earlier, there are many CNC manufacturers out there, and the number is growing. There are also many options available. You will need to decide which options you will need. Some of the CNC options may not be necessary for your specific fabrication needs. I have seen dozen of shops that are only using their CNC for sink cutouts. This can be a large savings when set up properly, since sink cutouts can be a major bottleneck in your shop. On the other hand, it can also cost you more. How you will use your CNC and what type of work you are doing all need to be considered and evaluated before you purchase a CNC.

In addition to the options, there is one very important question that needs to be asked when you purchase your CNC. That question is: “How quickly can I get my CNC repaired, and is someone available to answer my question or solve my problem?” I can't tell you how important this is. Let's say it is Friday afternoon, and you have a job on the CNC that has to be done that day because it is getting installed on Monday, and the CNC shuts down for some reason. You get on the phone to find out how to resolve the problem, and the supplier's office is closed and won't reopen until Monday. Now what do you do? To avoid this issue, ask in advance about a CNC supplier's service policy. Are they available at night or on weekends? How quickly will they return a call?

Service is one very important requirement, but you also need to know if replacement parts are readily available for your make and model. Imagine the same scenario above, and you find out that you need a new spindle that will take four to six weeks to receive.

Can you afford to wait that long?

It is also important not to buy a CNC based solely on a “test drive.” The best way to get feedback on a make and model of a particular CNC is to visit someone who has one. Ask the dealer for three to five references, and check them out. The dealer is not going to give you any customers that are unhappy with their machines, however, if you ask the right questions in the proper way, you will get the answers you need. The following is a list of suitable questions to ask:

  • How long have you had the machine?
  • How long did it take to get comfortable operating it?
  • How many service calls did you have during the first year of operation? How many do you have now?
  • When you have a problem, how long does it take to get a return call or to get a technician onsite?
  • Would you buy this same machine again? Why or why not?
  • Did you find this machine helped with your productivity?
  • Was the machine hard or easy to learn?
  • How was the training offered? Was it worth it?
  • Did the dealer follow up once you were up and running?
  • How many kitchens or lineal feet are you getting per day?

    Of course there are dozens of additional questions you could ask. I would also ask if it is possible to visit the shop and see the machine in operation. I have found that many fabricators are open to this and will be glad to help. It doesn't hurt to ask and may be worth a trip or two. You can also go to several of the stone forums online and post your question there. One such forum can be found at www.ntc-stone.com. Some of the trade associations, such as the International Stone Institute (www.internationalstoneinstitute.com) and the Marble Institute of America (www.marble-institute.com) may also be able to help you with some additional information.

    Author's Box

    Fred Hueston is founder and president of The National Training Center for Stone and Masonry Trades, a successful marble and stone consulting and training company. He is recognized as a nationally known consultant and has written over 28 books on the subject. If you have any questions for The Technical Forum, please e-mail Fred Hueston at fhueston@aol.com.