Nested Based Manufacturing is more productive and lower cost

Some Thoughts on Cutting Speed

Overview

Nested Based Manufacturing is the name given to machining a nested group of parts directly from a large sheet, using a CNC router. A common attribute of Nested Based Manufacturing is that each machine cycle cuts a different nest of parts rather than cutting the same nest over and over. The most common application for Nested Based Manufacturing, or NBM, is machining parts for custom cabinet boxes. In many cases using NBM, parts can be completely machined in a single cycle. Certain cabinet construction however, may require that some machining operations be preformed on the flip side of some parts.

In most cabinet shops Nested Based Manufacturing of cabinet boxes is at least twice as productive as traditional manual methods and in many it is three or four times as efficient.

Nested Based Manufacturing is rapidly replacing the prior approach to automating the machining of cabinet boxes in which the sheet is first cut into individual blanks using a panel saw and then the blanks are machined into finished parts, one at a time, using a point to point machining center.

Nested Based Manufacturing is substantially more productive than a panel saw/point to point (Details). It requires fewer steps, fewer employees for a specific level of production, improves yield, is faster, requires less capital investment and generally results in higher quality, because machining is performed in a single setup on one machine rather than requiring multiple setups on two machines or more.

Thermwood pioneered Nested Based Manufacturing, having developed much of the core technology in use today. Essential technologies, such as high volume vacuum used to hold parts in Nested Based Manufacturing and the blind dado construction method were first developed at Thermwood. Today, Thermwood continues a robust development effort and currently offers technology important to cabinet and furniture builders but not available from anyone else.

Much of this exclusive technology centers on making the overall job of programming and running nested based jobs easy for non-technical machine users. It strives to eliminate unnecessary steps and procedures, streamlining the process and improving productivity. These features address the practical difficulties encountered when trying to apply nested based manufacturing to real world requirements. Let’s examine this in a little more detail.

A common approach to NBM is to use cabinet and kitchen design software, operating on a computer, normally located in the office. This software generally offers output to a CNC machine, either as part of the standard package or as an extra cost option. The output is generally a series of programs, one for each sheet of material and still other files for operations that may be needed on the flip side of some parts. All but Thermwood have the characteristic that the nest layout and program files are created on the computer in the office. Thermwood’s approach is different.

First, it is important to realize that Thermwood’s control and machines are able to execute programs created this way, as any other CNC control can. In addition, Thermwood’s control can actually do the nesting and create the CNC program right in the control and this process is completely automatic. We will talk about how this happens, but first let’s see why this is a fundamentally better approach.

The primary advantage of nesting at the control, or “control nesting”, is that you can incorporate information about the sheet material you are using that is not available when programming in the office. For example, if you find a defect or broken corner on a sheet, it is easy to nest around it when nesting at the control. It is much more difficult to abandon the completed nest programs and return to the office with the information needed to nest around the defect. Typically people who nest in the office discard the sheet or, run the program, scrap and remake any parts that the defect affects. Even so, remaking the scrap parts may require a trip to the office to develop the new programs. Overall, control nesting is much more flexible and easy.

Another major advantage of control nesting concerns material left over at the end of a job. At the end of each job you will have one or more partial sheets of material left that are large enough to nest parts on. Nesting at the control makes using this material easy. To understand why, you need to understand how Thermwood handles the nest files for a job.

As we said earlier, most cabinet design software outputs separate files for each sheet of material and each flip operation. This means the machine operator must manage these files, loading the correct file for each sheet and matching up and loading the correct file for each flip operation. At best this requires extra time and a more technically skilled operator and at worst it leads to errors and scrap parts.

Running these jobs on a Thermwood CNC router is just plain easier. The Thermwood control handles the entire job as a single entity. The operator loads the job, the control nests it (automatically) telling the operator how many sheets of each material will be needed. It then instructs him to load the first sheet and start the program. It guides him through the loading of each material until the job is complete. It prints labels for each part and a nest diagram showing where to put the labels.

For flip operations, the label on that part has a bar code that calls the correct flip program. The operator simply scans the label and runs the part. He can run them in any order and he doesn’t even have to know what the part is. This overall approach is much faster, much easier and much less prone to error.

Now let’s see how this approach handles the partial sheets left at the end of a job. In addition to printing labels for each of the parts, the Thermwood control also prints a label for any material, large enough to reuse. When you start a new job that uses this same material, the control asks if you have any partial sheets you want to include in the job. You simply scan the sheets in the order you want to use them. The control nests on these first, then uses full sheets and then prints labels for any remaining material.

Also, to make this material easier to handle, the control automatically cuts away any protrusions or unusable outcroppings, squaring up the piece.

Control nesting was first developed for the eCabinet Systems program. eCabinet Systems is a cooperative of cabinet and woodworking shops that is described in detail in another part of this web site (Click Here). This program provides its Members with a powerful cabinet design software package for free. It is free because the program is paid for through purchases Members make through the program rather than by charging for the software.

eCabinet Systems is a powerful design tool with the ability to modify every aspect of cabinet design. Not only can you design cabinet boxes but you can design all the other components of your kitchen including drawer boxes, door and drawer fronts and face frames. You can even add carvings to cabinet parts. This brings to some new and exciting Thermwood developments that are dramatically expanding the role of Nested Based Manufacturing.

With Thermwood, it is now possible to do much more with Nested Based Manufacturing than just cut cabinet boxes. Let’s look at some of these developments.

Drawer Boxes – You can now add drawer boxes to your eCabinet Systems designs and then nest and machine the drawer box parts right along with everything else in the job. Even more exciting is the ability to specify a special dovetail joint that can be machined in the nest to make truly high quality drawer boxes, quickly and easily.

MDF Doors – Design MDF doors in the software and again send them to the machine, nest and machine them as part of the same job. An exciting part of this is that you can use a modeling technique and standard modeling tools to machine virtually and profile or raise shape without the need for special profile tooling.

Five Piece Raised Panel Doors – Five piece solid wood doors, designed in the software are sent with the same job to the Thermwood CNC. Using simple clamp fixtures and special profile tooling (all available from Thermwood) the parts are automatically and easily machined. As with machining of nests, the control guides you through each process on each part, telling you what size blank you need and how to position it. Building these doors are now really easy.

Nested Face Frames – Face frame components can now be nested and machined as any other part in the job. They can be machined from sheet stock or solid wood but the really exciting advance is a new type of joint called the “Puzzle Joint”. This joint, which looks like the joints on a jigsaw puzzle, can be machined in the nest. It makes assembly extremely fast. Without clamps, fixtures or screws you can assemble face frames that are accurate, square and true and they are extremely strong.

Carvings – Thermwood offers an extensive library of wood carving files that you can rent for a small fee. These carvings can be designed into your job, rotated and resized as needed and then, when the parts are sent to the Thermwood CNC router, they will be automatically machined in the nest, just as you designed them. These types of high-end design features can mean higher prices and more profits.

Profile Shapes – You can design almost any profile shape in eCabinet Systems, allowing you to create part edges, straight moldings, arched or curved moldings and the like. When the job is sent to the machine for processing, the control asks if you have a proper profile tool for the shape you designed. If you say no, the control creates a modeling program to produce the shape using standard modeling tools. With this you can custom make almost any type of molding quickly, easily and without a major tooling investment.

In addition to all this, control nesting can also be used to process parts from other software packages in addition to eCabinet Systems. Instead of sending a complete nest program to the control from these other packages, (which you can do if you want) you can also export DXF files for the parts needed, and send those files to the control for nesting. A DXF file is a file that defines the part geometry and is a common format that virtually every major design software program exports.

This means that you can take output from every major CAD and design software and send it directly to the Thermwood control without the need for separate CAM and Post software. This offers incredible flexibility and simplifies this whole area. You can even nest together parts that originated in different software packages. The flexibility is amazing.

There are a lot of other details in Nested Based Manufacturing that Thermwood has addressed and refined in their systems and these systems are successfully and profitably running every day. Thousands are running eCabinet Systems software, secure in the knowledge that when they are ready to move into CNC, they simply press the CNC button and send the files to the machine where they will run. This simplifies the transition to CNC and makes the move almost easy.

If you are considering Nested Based Manufacturing, regardless of how you plan to design your products, Thermwood is the best choice, offering features available from no one else, features that simplify your operation and save you money.

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The advantages of Nested Based Manufacturing over panel saw/point to point are centered on four areas:

There are fewer steps in Nested Based Manufacturing.

To produce a nest of parts using panel saw/point to point requires:

To process the same nest using Nested Based Manufacturing:

You may notice that we did not transport parts to the edge bander in this process. This is because, in Nested Based Manufacturing, the cycle time per sheet can run 6-10 minutes during which time the same operator is free to perform other functions such as edge banding. When processing parts on a point to point the operator must be involved with each part, continuously loading and unloading and adjusting vacuum pods between parts.

Overall, a process that requires 4-5 people using a panel saw/point to point only requires 2-3 people using Nested Based Manufacturing.

The yield improvement comes primarily from the fact that a panel saw can only cut straight lines while a CNC router can cut in any direction. A panel saw must cut all parts as rectangular blanks, even parts that are not rectangles. Excess material from these parts must be scrapped. A CNC router can cut the actual part shape from the sheet so parts can be intertwined in the nest with some parts inside of others. On certain designs this can result in significant material savings.

Even on rectangular parts, a panel saw requires that the edges of the rectangles be lined up in the nest along common cut lines so the saw can cut them. If the rectangles are not the same width, this requirement results in additional scrap. A CNC router allows the rectangles to be nested in the most efficient manner (it’s called True Shape Nesting) eliminating the need to line parts along cut lines and eliminating the extra scrap.

Some proponents of the panel saw point out that the kerf of a router bit is larger than that of a saw blade, which reduces yield. This is seldom true. The only case where it might occur is if the difference in kerf width determines whether one of two parts can be nested across a standard width sheet. The common cabinet depth used today allows enough clean up material around each part on a standard width sheet that this makes no difference.

In addition to labor savings, Nested Based Manufacturing produces as good, and in many cases better material yield than a panel saw/point to point producing the same jobs.

The production rate of each approach is determined by how fast parts are machined. The actual machining speed of a CNC router and a point to point are about the same, being determined by the tooling rather than the machine itself. With the point to point, however, the operator must unload and reload each part. The time required to do this is added to the processing time for each part, making the overall machining time higher. In addition, point to point machines commonly use vacuum pods to hold parts for machining. These must be adjusted for differences in parts size, so this additional step adds even more time to the overall process. Finally, since the point to point must process parts one at a time, any tool changes must be done for each part, adding extra time to the cycle. In Nested Based production, a tool is changed and then every part on the sheet that needs that tool is machined. This results in a fewer overall number of tool changes and faster production.

The panel saw/point to point approach requires both a panel saw and a point to point machining center. Combined, these two machines cost more than a CNC router equipped for Nested Based Manufacturing.

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Some suppliers of nested based machines actively promote feed speeds of over 3,000 inches per minute and claim three to four minute nests. While technically accurate, these claims are misleading. Here are the facts.

Top speed of a CNC router seldom has much effect on cycle time. Cutting speed is determined by a combination of the router bit and material being cut, not by the top speed of the machine. Once you are cutting as fast as the tool and material will allow, extra machine speed is of little value. Positioning motions between parts, however, are not limited, but these motions are typically so short that the machine never reaches top speed.

We have built high speed (over 3,000ipm) machines in the past, however, in actual operation there has been little difference in cycle times over standard machines. Customers running the same parts on both, find anywhere from no difference to perhaps three seconds per cycle. Hardly worth the extra cost.

Actually, the most important factor in cycle time is acceleration. Although cutting speed is limited, the faster you reach the optimal cutting speed and the longer you hold it before decelerating, the faster the cycle time. Proper acceleration can cut several minutes off a typical nest with no real downside. This gives Thermwood machines a real advantage over the lighter duty systems with lower acceleration rates, often promoted for nested based machining. Even here, however, there is a practical limit. At some point acceleration is so fast that edge quality is reduced and accuracy suffers.

This being said, there are other factors that affect cycle time that should be considered. Our system automatically adds a skin cut and double pass for parts that are small enough that they might move during machining. We also slow down for the last pass on each part, again to avoid the possibility of the part moving. This adds time to the cycle, however, each time a part moves, you are faced with a lot of additional effort, and time, to replace the scrap part. It just makes sense to take the extra time and be sure your parts come out right every time.

Also, the time to cut a nest depends on how complex the parts are. Blind dado assembly, movable shelf holes, KD fasteners and other details result in longer cycle times, however, these features increase the quality of the product and save valuable time in assembly and can reduce secondary operations. The extra time is well worth it. In the end, cycle time is not nearly as important as what you do with the time available.

So, the next time you hear a company claim they can blow through a nest in three to four minutes, take it for what it is, an empty marketing ploy. We can blow through a nest in two minutes, if we can pick the nest.

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