Picking a CNC router – Part 3

In the first two blogs in this series about picking a CNC router I discussed learning about router specs, picking the ones we needed and then selecting a manufacturer and dealer to supply our machine. I hear a great deal of talk about routers and how much they should cost. Some of my friends have bought routers from China. Service isn’t part of the package. When something goes wrong there is a steep learning curve to get the necessary parts and get things going again. I know people who want to do it all themselves, including building the router. I have no doubt they save money but they trade this money saved for the amount of time they invest. I maintain that time equals money and time is my most valuable resource. I don’t want to fiddle with my machine. I don’t even want to think about it. Other than greasing it as necessary and blowing off the dust I don’t do anything other than running it. Once or twice each year I’ll have a little maintenance done and occasionally the bearings need replacing. I let a knowledgeable and experienced factory tech do that work. I keep busy doing the work I love.

Choosing a top end router with top notch service didn’t come cheap. You get what you pay for. I didn’t endlessly haggle nor beat my guy down. I wanted a long term relationship with a friend that would take care of me over the long haul. And that I got.

Once we had negotiated a price it was time to figure out the terms to make sense of our purchase. My business plan indicated we could pay for the machine over two years. To be safe we decided to finance it over four. To be able to write off the machine quickly, we opted to lease the machine for four years with a small buyout at the end. Delivery, installation, setup, training, software and two years of service were negotiated into the deal.

The price of the machine worked out like this…

My math includes everything. Please notice that even though we purchased one of the top machines (read that expensive) out there it amounted to only 28% of our total cost. 
Delivery, duty and taxes amounted to another 10%. A good screw compressor with an air dryer added 5% more to the cost. Hooking up the electrical added 2%. The software was 4%. A good dust collector added 4%. 
When we make a big addition like the router it is time to seriously rethink the production of the shop. We literally tore apart the whole shop, cleaned and rearranged everything to fit it in right. We spent the better part of a week at the task. At shot rate this added up to 6% of the cost of the router.
Most shops would total up the cost at this point. But we weren’t done. We could do little more than turn on the machine. We had to learn to use it to it’s best advantage. We also had to create samples of the new work we would do. Unless customers can see it they don’t buy it.
Learning the software meant investing time, starting with the basics. I had never operated any type of computerized equipment previously. We had to invest in ourselves. And that we did.
For two months we only produced samples on our machine. We started with the alphabet. This meant twenty six samples – all different. I learned about creating reliefs, making shapes, adding textures and a whole lot more. While we were at it we explored finishing techniques including paints, glazes and gilding.  I filled our dumpster multiple times with things that didn’t work, and each time learned something new in the process.
Having one of the best machines in the world and not being able to use it is a poor investment. So we invested properly and counted all of our costs in the process. This meant we went in with our eyes wide open knowing we would come out the other side equipped to do anything imaginable. It worked!
Next time I’ll begin a discussion about software. Stay tuned…

Published with permission from precisionboard.blogspot.com. Source.

Picking a CNC router – Part one

I witnessed a CNC router for the first time at the International Sign Show back in 2006. I was amazed to see the machine going back and forth cutting so very fast. The machines I saw at that show were all doing cuts and not 3D. Few people were doing 3D back then. Over the course of the three day show I looked at many routers and talked with the software folks at length about what these machines were capable of. In a word – ANYTHING. Anything I could think of the machines could do.

Keep in mind that I have never owned a plotter of printer, had never even built vector files to this point. The language and terms I heard at that show were all foreign. I had so much to learn. By the end of the show I only knew one thing. I had to have one of these machines in our shop.
When I got back home the work began. A cnc router wasn’t to be a small investment. After the purchase of my building it was the next biggest number. As I got into my research I quickly discovered that the router alone was only part of the cost. I also needed a good sized compressor, an air dryer, a dust removal system, and software. Then there was the electrical needs and the time to learn how to use it as well as build a market to sell the work I would produce on the machine.
I first had to educate myself about the specifications and options available on the routers. As I stated before the terms I heard to this point were confusing. 
Stepper motors were common back then, servos only came on the more expensive machines. Through talking to many owners of machines across the continent I learned that steppers were slower, and if pushed too hard would lose their way. Servos were closed loop and were better. That was a no brainer in my book for I tend to push my equipment hard. Steppers have improved since then but based on my experience I would still only consider servos if I had to do it again.
Gantry height was the next thing to consider. I learned that the higher the gantry the more shake was possible. I also learned that by beefing up the structure and bearings this movement can be eliminated. Heavy duty wins the day here. While the height of the gantry was important the limiting factor was more about the length of the tool. The longer the tool, the more deflection was possible. This translates to less accuracy, chatter, and tool breakage. There is also what I term the cone of death. This is a triangle defined by the tool length and collet size. If your tool is only two inches long you can’t cut deeper than that (vertically) without bumping the collet. In the end I settled on six inches of gantry clearance and it proved to be right. I got a very stable machine that could be run at high speeds. I’ve never cut material thicker than four inches.
Table size was the next question. I had to think about what I would be cutting. All of my substrates come in 4′ x 8′. This included high density urethane, MDF and plywood. Shop space was also factored in. I never planned for a router when I built it and space was at a premium.  I decided a 50″ x 100″ router would work just fine. You also have to plan how you are getting the router into your building. I know people who have had to take out walls to locate their machine. We had to hire a heavy duty forklift for the task.
Electrical needs will have to be addressed and this adds up in a hurry. We only had single phase power in our shop with no option to upgrade to triple phase. This meant we had to have our router built with an inverter. It takes 60 amps of power to run the machine. Then there’s the vacuum pump and the dust removal system. New heavy duty wiring had to be run for all of the components. 
There has been a great debate for many years about the construction of routers. Is heavier steel construction better than lightweight aluminum? In one camp weight is your friend. Heavy duty castings and I-beams absorb the forces and vibrations. Strong servo motors allow for quick changes in direction. In the other camp everything is lightweight aluminum. The thought is that everything can change direction quicker if it takes less force due to less mass. When a machine is cutting a true 3D file it changes direction quickly and often. This produces a lot of force and vibration which affects cutting quality. I like to do what I call the nickel test. With the machine going full speed I place a nickel on the frame rail. A properly designed machine will allow the nickel to stand with the machine in operation. If it continually falls over you are pushing the machine too hard or the machine is not rigid enough. That means slower cutting speeds and much longer machine run times. That translates into more electricity costs and slower production times. I much prefer a heavy duty steel machine.
Then there is the matter of equipping the machine with an automatic tool changer or not. With our 3D work we typically use three tools (or more) per job. The work is first roughed out using a 3/8″ ball nose bit with a high overlap. A fine pass is then done using a 1/8″ ball nose bit. And finally I use a cutter to cut out the pieces. All this tool changing meant an auto tool changer made sense for us. It added a considerable cost to the machine but has paid for itself in the long term. There are also two options in auto tool changers. Linear style tool holders have the spare tools arranged in a holder at the end of the machine. A rotary tool changer is bolted to the gantry which means quicker tool changes as they are closer. I prefer the linear tool changer and there are less moving parts. Having the gantry travel to the end of the table to grab a tool doesn’t take very long.

Vacuum hold down was another option to consider. I quickly determined I didn’t want to fiddle with clamps or screws to hold my work in place. A quality vacuum hold down system was a must.
Spindle size (horse power) is another option to consider. I knew I would push my machine hard and so I needed five-eight horse power. Because we have single phase power and have to run an inverter I effectively lose up to thirty percent. So we opted for a twelve horse power spindle. Run times on 3D projects tend to be very long and so durability was a major factor. We opted for a spindle with four ceramic bearings. Air cooled versus water cooled is another option. Because we live in a temperate climate an air cooled spindle was deemed adequate.
Familiarizing myself with all of the terms and options for a CNC router took me a couple of months and many phone calls to both router manufacturers and owners. The internet also helped a great deal. After I had completed my research I knew the type of machine I needed. 
Our new CNC router would have the following specifications:
Heavy duty steel construction throughout. Steel gantry with 6″ of clearance
All servo drive
Four foot x eight foot table
6″ minimum gantry height
12 hp spindle with auto tool changer – linear style tool holder.
Vacuum hold down
Once I knew what I wanted it was time to actually start shopping. That’s for the next post…

Published with permission from precisionboard.blogspot.com. Source.