Flat-Table CNC Versus Pod and Rail or Beam Saw

      What starts out as a question about energy usage of various equipment turns into a detailed discussion comparing CNC equipment with other choices in terms of efficiency and output. January 23, 2012

Question
Does anyone have information on actual energy usage of panel saw plus ptp versus flat table nesting of machined parts? I am interested in upgrading our pod and rail machine and always thought I would get a newer machine of the same type, but now I am thinking about a flat table router that would be more useful for a lot of the curved components we make and also for nesting sheets.

I am thinking the flat table machine would use a lot more energy per part with its larger router, dust collection, and huge vacuum pump. I know it would save us man hours on labor, but at the cost of how much energy? It does not seem to be a very green system.

Forum Responses
(CNC Forum)
From contributor M:
I had a nested flat table CNC (Thermwood) and now I use panel saw and boring machines. My old shop (with CNC) was 2,500 sqft and had relatively small machines. Aside from the CNC, the biggest motors were the 3hp saws and planer. My new shop is 7,000 sqft and has several 10 HP motors, including the panel saw that runs all the time. Not to mention the edgebander that pulls 60 amps. My new shop has lower electric bills and much higher product flow. If I make twice as many cabinets, my electric bill is still less than the CNC shop's was.

Labor, and more importantly your business model, will be more far more important factors because the electric bill difference will be measured in hundreds of dollars where the labor and overhead differences are thousands. Machines do not define the production - your business and production model will dictate the machines.



From contributor T:
I was in the woodworking business for 18 years and I have run large shops and small ones. Without a doubt a flat table nested based CNC router is the absolute best choice for any shop that does less than 100+ cabinets per day. The difference in power consumption is insignificant. The improved material yield and lower labor costs are what matters most. Anyone who says otherwise either does not really know or has a hidden agenda. If I were starting a new shop today, a nested based router would be the first piece of equipment that I put into service.


From contributor M:
Are you serious about the 100+ cabinets per day? I do not know any shops that have that kind of volume who rely on nesting. In fact I do not know even one shop that averages 50 or even 30 cabinets a day relying on nested based machining. Can you describe the shops that are doing this and how they do it? I have never heard of a shop nesting more than 7 or so sheets an hour. I think 5 is the norm for a well equipped shop with a big CNC.

By the way, I am not anti-CNC and I do agree that a small shop with a nested CNC can do very well. But it is not always the best option for a new shop.



From the original questioner:
Thanks. I am already sold on the idea of a nested router as the least labor intensive way of creating cabinets and the idea of handling the parts once instead of twice is a huge draw for me.

I know the difference in energy usage would not be significant enough to offset the labor cost of doing it the way we are now. I am not considering this as a total dollars in the pocket thing as much as building unnecessary energy into the product as far as carbon footprint goes. As we try to get greener in our products, this seems to be one of those things that would work against us. I know several of the machine builders are even selling beam saws that tout a lower energy usage for product output. I know this seems trivial to some, but I drive a 50+ mile per gallon car and think of it as a gas guzzler, and am looking at all electric with solar charging station at my house.



From contributor T:
I am indeed serious about that number. In fact we had an industrial engineering firm do very detailed time studies at the last company I was with. The number actually came in at 96 boxes, so I just rounded it. We were doing commercial cabinetry at an approximately 45,45,10 mix of base, wall, and tall. In 2007 when I left them, we were averaging about 120 units per day. Much of our product was going to another city several hours away, so we were looking into a satellite operation for that segment of the business, hence the time studies. We also did a significant amount of millwork and that did factor into the equation.

A small CNC (and Iím not talking about a ShopBot or similar - I am talking about a real industrial machine) will cost you in the neighborhood of $120,000 and it is fairly easy to cut 5 to 6 sheets per hour depending on the nests and your operator, of course. Larger, faster CNCs can produce up to 10 sheets per hour with the proper configuration; however I would probably opt for 2 smaller CNCs over one large twin table if my volume required it.

These are not theoretical numbers - I have seen it work. The tipping point comes at approximately 120 sheets per day. At this level there is typically a large enough volume of like parts that efficiency of stack cutting starts to pay off.

For me, if I were in that position again, I would start with a router and add a second should my volume require it. At my previous position we had 3 beam saws and 6 point to points. We produced commercial cabinets, commercial millwork, and institutional furniture. So donít think that I am coming from a position of ignorance about the cost/benefit of work cells. I just know that big volume is required to justify work cells. Nested based will beat work cells on small volume every time. Also, keep in mind that if you do any cuts that are not rectangles, a CNC will be an even bigger benefit. With a work cell approach, you will waste a huge amount of material when you cut irregular shaped parts. With a CNC and true shaped nesting you can nest parts inside of parts. The one and only downside to a CNC is the inability to edge bore, so if you use dowel or confirmat construction you will need to invest in a boring machine. We did use dowel construction on our casework and RTA fittings for the furniture, so we opted for a CNC bore glue dowel machine to work in conjunction with the CNC.



From contributor M:
Sounds like our numbers are in agreement. But in order to produce 100 cases a day, you would need to run a good single router 10 hours a day, non-stop. With lunch, tooling changes, and the usual CNC stuff, that is 13 plus hours a day. And that is based on a very optimistic 10 minutes a sheet. To do that you will need a loader and unloader and all kinds of production support.

A pendulum machine is only slightly faster. You might get two extra sheets an hour. So two good nested CNCs with loaders and all the expensive support systems will get you up to the 100 sheets in a 10 hour work day, barely. At the cost of $400,000.

Managing production with nested CNC is easier and that is why many shops are more successful with it. Saws, machine centers and doweling machines are much more productive (have a much higher throughput) but they are a lot more complicated to organize into a cohesive production system.

The small shop making 50 to 100 boxes a week can do very well with a nested router. But I am able to do that with a slider, bander, manual boring machines and three employees. Total machine investment 100,000 USD. Many of those machines would have had to be purchased even with a nested CNC.



From contributor K:
With environmental issues, the utilization of sheet stock is also relevant. It is unusual to achieve 90% on a beam saw. 80 to 85 is a more typical average depending of the product line and optimized run size. With really good nesting software (like Alpha Cam or others) and nested runs exceeding 15 or 20 sheets, a router is genuinely capable of 93% plus sheet utilization, even accounting for larger kerf (3/8 bit versus a 1/8 blade).

Contributors T and M both make excellent points, and I am also strongly in favor of nested base for shops that are in the small to medium range. I am very much in agreement with contributor T - have 2 or even 3 nested machines (having a backup machine for repairs or maintenance related issues can be really comforting) or extend shifts until you see the stack cutting of a beam saw pay off.

As contributor M says, it's your business model that drives the choices in the end. If you do a fair lot of furniture, maybe a point to point (or even 5 axis) makes sense. Floor space requirements alone are a huge factor. Beam saws are huge! And as you say, the versatility of a router for a lot of curved applications is very enticing. There are nested based systems that quick change to a double sided pod configuration that address this issue pretty well.

You will find a lot of people strongly in favor of point to point machines in a small shop as well, not all are wrong. For a very high volume shop making just cabinets, well upwards of 75 per day, it really may make sense to take advantage of stack cutting capabilities of a beam saw. Some product lines, like furniture or entry door fabrication argue for point to point. Bottom line is both can work well, but for the vast majority of small to medium sized shops, nested is the clear winner.



From contributor M:
Great post, contributor K.

I knew shops that had multiple CNCs, but they are job shops and did a lot of outsourcing for other shops. They never (that I know of) ran the machines in parallel for the same job. I can see the benefit, but the cost and overhead of those machines is staggering compared to saws and P2P. A shop with the same output could have as much as double the investment (we are talking several hundred thousand dollars here) and the overhead (machine, not labor) would also be a lot higher. But the CNC shop is a lot more flexible and easier to manage. In some ways the speed of a saw/PTP shop is a drawback. Things happen so fast that it is hard to keep up. A beam saw, dowel bore/insert and a good PTP will blow through 50 sheets before lunch, even with only 3 people running the cell! That is a lot of production IT to stay on top of. Running out 100 cabinets a day is no small feat. Now that I am entering the world of higher production, I am realizing that the machines are not the problem. It is the IT, job orders, reports, inventory tracking, and general business management that becomes the overwhelming issue.

Most new shops looking to gross 40 or 60 thousand a month will do very well with a nested setup. But if you are pushing towards 100 or 200K, it gets hard to make the CNC do all the work.

Another question... Do you really think the difference between 90% and 80% matters? On most jobs, that equals less than one sheet of material. The electric consumption could actually outweigh that. I tend not to worry about the material too much because I already charged the client for it. If I focus on material usage I would only get a tiny return on it. It is man hours and production time that I focus on. I can increase the profitability of a job by 1,000 dollars by focusing on efficiency of production, but efficiency of material usage might only mean $100, or less.



From contributor K:
Exactly! The machines are driven by the product, and never need to be the problem. For the vast majority of small to medium sized shops one inexpensive router will never reach full utilization. I currently keep a shop with 15 employees busy doing a mixed commercial product line stressing architectural millwork. Cases, desks, curved work, paneling, the works. With only modest changes to my setup, on my one nested machine I could keep up with nearly twice that and not even have to hire a full time operator. If I programmed all the time and had an operator run the machine 40 hours a weekÖ Well, you get the picture. That would change if all I did was boxes, but I am where most people are, in a mixed production environment.

Your points are well taken and all of them are relevant. Tooling also weighs into the mix - a saw blade will cut many times what a router bit will dollar for dollar, sharpening for sharpening. But in a very real sense, and even putting the environmental factor aside, I do think 10% of my sheet goods budget is something to consider. Perhaps less so if my main material is white commodity melamine, but if I am cutting 75 dollar pre-finished or 120 to 160 dollar 2 sided laminates, I want to think on the issue. 10 percent less of my sheets have to be carted away in the dumpster as well. Itís just another of a long list of factors that need to be put in the mix when deciding what to buy.



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