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How can I machine that logo?

This page consists of an article written by Bill Elliott, President, Northwood Designs, Inc., Antwerp, NY, in the early 90's. For some reason, it's still applicable today.

CNC user's who have tried to machine logo's and lettering have found the process to be time consuming and nearly unworkable, yet there is a solution to this problem.


The Problem.

A number of years ago our company became aware of the growing number of artistically oriented drawing packages available. This software was able to help the user design logo's, create lettering, and generally produce artistic images with an ease that was unmatched in the CAD world. Smooth flowing curves and text manipulation was refined to a high degree in many of the available software packages.

About the same time, the idea of scanning original artwork and using these scanned images for other purposes was coming into its own. Excited by the possibilities of using this software and/or a scanner to create files which we could then machine, we quickly purchased a scanner and some illustration software and set to work.

Many frustrating days later we came to the realization that this wasn't going to be as easy as it seemed. There were a multitude of problems we encountered when attempting to machine these images. These problems included: open contours with endpoints that didn't meet, extremely large files composed of thousands of short line segments, and inappropriate geometric entities such as bezier curves which both our CAM software and our control were unable to manipulate.

These were only the most glaring difficulties, there were many other aspects of the process which kept this from ever becoming something we could look forward to doing on a regular basis. The underlying complication with all of the problems was that the software that was good at producing these artistic files, assumed you were going to print them. As you can guess, the accuracy necessary to produce acceptable printed output falls far short of what is required to machine an image.

A closer look at the above problems showed us that the open contours made it difficult to "chain" the geometry we wished to cut with our CAM software. When we attempted to define the contours we wished to cut, the software was stopping at small gaps or endpoint mismatches and we would spend hours zooming in on these areas and inserting lines. Even after all of these gaps were closed the sheer number of small lines required to approximate a curve, often produced block transfer problems with the machine's control. This would cause the machine to cut slowly and often stutter as it was cutting. If we told the software to produce less short lines on each curve, the finish of the part suffered from flat spots on the curves. The third major problem was files with inappropriate entities, primarily Bezier curves. These files were simply impossible to import directly into our CAM software, and any software we used to convert these bezier curve files lead back to the first two problems. In spite of all of these problems -and others not mentioned above- we weren't ready to give up just yet.

We Need Help!

The next stage in our saga involved researching the software market for other products that might alleviate the obstacles we were encountering. It would be inaccurate to say that we made no progress, in fact we were able to machine most of the images we wished to machine, but this was in spite of any additional software we purchased not because of it. In fact, we were only able to machine this artwork after spending inordinate amounts of time and effort manually fixing the problems. One and one half years and many software packages later, we were essentially no closer to a quick and easy solution. There was a good side to this however, we were becoming real experts on the problems!

If You Want Something Done Right, Do It Yourself.

Eventually we came to the realization that there were no real solutions available to the problems we were encountering. Even software that claimed to help, never really met with our expectations or appreciably shortened the time we spent to machine these images. The only possible choice was to develop the solution ourselves.

In November of 1990 we took our first small step. The original idea was to use the HPGL (plotter) files we could export from some of the software and to translate them directly to our CAM systems toolpath format. After running the post processor on these files we were able to force the machine to jump over any gaps in the geometry. This worked reasonably well for engraving type operations but we still had problems with slow cutting and finish quality, and this method still produced files of an enormous size. It was not unusual to start with six lines of lettering and wind up with 10,000 lines of machine code.

What we really wanted was a geometry file which could be imported into our CAM software that consisted of lines and arcs. We reasoned that if the file had lines and arcs the total entity count would be much lower and the block transfer problems would go away. In addition, if we could import this file into our CAM software, without the problems, we would be able to use this geometry to produce contours with a tool offset and even pocket areas of the file!

We soon found out why we were not able to buy the software we wanted from someone else. The software we wanted had to be able to analyze a series of points which might make up a letter "A", and then intelligently fit lines and arcs while determining which point should be a corner, what should be an arc, where one arc should stop and the next should begin, whether the meeting point of two entities was smooth or pointed, ad infinitum. This turned out to be more difficult than we had anticipated, but we gradually started to obtain the results we were hoping to see.

As the entity count was reduced and endpoints matched, we started to address some of the other problems we had encountered over the previous years. We added a facility to check for gaps in contours and close them. Soon we started to import the Bezier curve (EPS and AI) files which were typically produced by illustration software. Once imported, we were now able to fit the lines and arcs to these curves. At this point we finally had a software solution which addressed the major problems we had encountered.

In The End...

Over the next several months we continued to add features to the software which helped us to make the entire process quicker and easier. Three years after our first attempts to machine artwork we were able to machine virtually anything we received in a small fraction of the time it had previously taken us. This was not to say that 10 minutes after receiving a logo we were starting the spindle on our CNC. The time from starting on a new piece of artwork to actual cutting still varied greatly from as little as 10-15 minutes to as much as five or six hours of preparation. It all depended on where we started from. If we received a perfect piece of camera ready artwork at a relatively large size, we often were able to scan the artwork and machine it in very short order. If on the other hand we received an enlarged, faxed logo with complex script lettering on an arc, the processes took many times longer.

In the real world, the artwork you are likely to receive from a customer is usually somewhat less than perfect. In fact it's been our experience that poor originals are the rule rather than the exception, and, unfortunately, even at this point in time there's no software able to make a silk purse out of a sow's ear.

The Solution.

The solution was to assemble the best software tools to handle the artwork we were typically receiving. During the years we were working on this problem, we tried many different software packages, some helped us in one way or another, but none solved the problems in their entirety. Our current recommendations for a complete hardware/software solution to machine artwork and lettering includes: 1- A full page flatbed scanner, 2- Raster to vector conversion software, 3- Illustration software, 4- Our own software "InterFlux", and 5- Your current CAM software. A discussion of each of the above follows.

Item 1- A Flatbed scanner.

A flatbed full page scanner will always produce the best scanned images. A scanner produces what is know as a "Bitmapped" or "Raster" image. In its simplest form this is nothing more than black dots on a white background. Bitmaps cannot be machined, but a bitmap is the beginning of the process when you receive hardcopy (i.e.- an image on paper) from a customer. In the best case scenario this hardcopy would be large, crisp edged, camera ready artwork. In reality, it's often of very poor quality.

The quality of the original artwork determines the direction to proceed after the initial scan. If the original is one of the rare "perfect" originals you may be able to perform what is known as a "raster to vector conversion" on the bitmap, run the resulting file through InterFlux and wind up with an easily machineable file in a matter of minutes. More commonly, all, or part of the image will be less than adequate for machining purposes and you will need to further manipulate the file. It's important to realize that there is no magic involved in machining artwork, it still requires the operator to analyze each job and determine the most appropriate method to reach the desired result.

While on the subject of scanners, it should be pointed out that most scanners have a scanning resolution of 300 dpi (dots per inch). We use a 300 dpi scanner ourselves. Currently it is possible to purchase scanners which have resolutions up to 1200 dpi or more. The cost does increase accordingly. The resolution of the scanner is mentioned at this point because a higher resolution scanner will produce better results. The penalty of a high resolution scanner is twofold, cost and file size. An image scanned at 600 dpi is four times as large as an image scanned at 300 dpi. In practical terms, this means that you will probably want a more powerful computer with more RAM to manipulate a file with a higher scan resolution, but you are likely to spend less time fixing a file scanned with a higher scan resolution.

Item 2- Raster to vector software.

The purpose of raster to vector software is to produce a vector file (lines, arcs, or curves) from a raster or bitmap file. This is often referred to as a tracing.

There are two primary types of raster to vector conversions; outline tracing, and centerline tracing. During the outline tracing process the software "looks" at the dots on the bitmap image and attempts to fit vectors along the edges of the black areas. This produces an outline which gives this method its name. The second type of raster to vector conversion, a centerline trace, is usually used when the original image is composed of lines of a consistent thickness. This method attempts to find the center of the original scanned lines and fit a vector through the center of the original lines.

There are many different raster to vector software packages available on the market. We have had the best overall success with "Streamline" from Adobe systems, Inc. Streamline is quick, will perform both types of conversions (even at the same time) and has given us, by far, the best centerline conversions. Streamline will show the original scan, as well as the finished vector file. It also has the ability to smooth the vector file before you export it. Streamline will export both DXF files and AI files. The DXF files have the same problems we started with and are not a good export option. The AI files are the most appropriate export.

Item 3- Illustration software.

Good illustration software when applied to the machining process should allow you to edit bezier curve files, generate drawings from scratch and produce and manipulate lettering. The best software for these purposes is less clear than in the raster to vector software. Two good choices are Adobe's "Illustrator" and Corel's "Draw!"

An obvious question often asked is, "What is the difference between illustration software and CAD software". To answer this question we must look at the purposes for which each of the two classes of software were designed. CAD software was designed to mimic a draftsman, as such, it's very good at drawing and manipulating geometric entities, if you need to draw something easily defined with precisely placed lines and arcs, CAD software is by far the best tool available. Illustration software was created to mimic the graphic artist. While it is true that some graphic art is very geometric, most artwork and lettering is composed of smooth, flowing curves which are very difficult to manipulate with the tools typically found in CAD software. Although these two types of drawings are not mutually exclusive, there is no doubt that each type of software is more proficient within its respective category.

We use Corel Draw! as our clearing house for problems. For instance, it's not uncommon to scan and trace a logo only to find that the artwork looks good but the lettering is less than adequate for quality machining. In this case we select the closest lettering style available within Corel Draw! and then use Draw's! text handling ability to stretch and move the text to match the original text without duplicating the problems. There are times when we are given artwork that is unsuitable for raster to vector translation. Corel Draw! has the ability to import the original bitmap scan as a grayed out image. This image is then used as a template to recreate the artwork using the drawing and text tools available within the software, (this is, essentially, "on-screen digitizing"). We also use Corel Draw! to produce our own artwork and lettering from scratch. If all we need is a few lines of lettering to engrave on a part or sign, we can start to cut the lettering in minutes.

Using the first three hardware/software items just discussed, we are always able to find a method to produce the artwork and lettering, regardless of what we are given as a starting point.

So far so good. However, this much we were able to do years ago. There is still a problem when we want to machine the artwork, none of the previous software packages produce machinable files, and now we come to the final part of the solution...

Items 4 & 5- InterFlux and your CAM system.

We had experience with the artistic files and their manipulation, we also had experience with CAD/CAM and machining. There was still the problem of going from one to the other. This is exactly the purpose of InterFlux. With the ability to import the files produced by the artistic software and change these files into a machinable form, while retaining a high precision and reducing the entity count, InterFlux proved to be the necessary link in the final solution. Internally, InterFlux works with a double precision database which gives us the ability to export files which are completely accurate 12 places after the decimal point. This virtually eliminates problems with endpoints not matching.

InterFlux was designed to be interactive so the user could visually check the results produced within the program prior to exporting to a CAM system. Many other facilities are included which apply specifically to easing the transition to a CNC machine. Artwork can be easily and accurately sized, placed in relation to the machines origin, rotated, duplicated, mirrored, etc. If the final intent is to engrave with a centerline cut, InterFlux allows the user to assign up to eight different depths and feedrates to the image and will even show an animated tool and cutter path based on a tool diameter entered by the user. With an appropriate post processor InterFlux can then produce centerline NC code.

Speed is of the essence when dealing with artistic files, the sheer size of the files slows down most CAD/CAM systems. We have often worked with files that started with 50,000 or more lines. InterFlux was optimized to redraw these lines at a greatly accelerated rate. Once the files are converted to lines and arcs in InterFlux it is common to reduce the entity count by over 90%.

If more advance cutting operations are necessary such as contouring with cutter compensation or pocketing operations, InterFlux will export to common CAD/CAM formats in the form of high-precision lines and arcs. These formats include *DXF, *CDL, and *NCI. There are plans to continue to add additional file formats in the future.

After using InterFlux and importing these files into a CAM system the files are either free from problems or at least, very nearly so. Complex pocketing is easier due to the low entity count, and the finish quality is improved because curves are cut with arcs instead of linear segments. The low entity count also produces a faster cutting file without the associated block transfer problems.

Perhaps our biggest surprise was the number of different industries which have found InterFlux to be useful. Currently InterFlux is being used as an integral part of the machining process in industries such as: roll die manufacturing, engraving, laser cutting, water-jet cutting, guitar manufacturing, church pew and alter manufacturing, jewelry, signage, and more. Typically these users are able to produce machinable files in 10 to 20 percent of the time it previously took them to generate usable files.

Conclusion

This article was intended as a brief overview of the problems surrounding machining artwork, and to demonstrate some of the possible solutions. In today's competitive market, more companies are trying to bring together all of the necessary processes to produce their work within their own facility. Machining complex lettering and artwork has been one of the more difficult operations to implement within the machine shop. It is only recently that the technology to machine this artwork has begun to catch up to the machine shop operator's need to machine it.

For more information about machining artwork and InterFlux, Mr. Elliott can be contacted at Northwood Designs, Inc.

ABOUT THE AUTHOR

Bill Elliott, is the President of Northwood Desings, Inc. and started as a consultant to the CNC industry in 1991. HIs original exposure to the CNC world was as a light manufacturer using a CNC router. Currently, Northwood Designs, Inc., develops CAM related software, and provides specialized consulting services to the CNC industry.

*NOTE: DXF is Autodesk's- Drawing exchange format , CDL is Cadkey's- Cadkey Advanced Design Language, NCI is MasterCam's native toolpath format, Corel Draw! is a trademark of Corel Corporation, Illustrator is a tradmark of Adobe Corporation

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