Creating nesting and NC cutting files

I have minimal CAD/CAM and no design experience but would like to create nesting and NC cutting files for an existing, proven design, the Alan Pape Ebbtide 33; 33'LOA, multi-chine steel. (Sadly, Mr. Pape recently passed away but plans are available through Fay Marine) It would seem that MaxSurf could be used to create the files from the plans and table of offsets but buying the program and additional software modules would be relatively very expensive since I wouldn't be doing any "design' work, as such. An alternative to creating the files myself would be to contract it out but I would prefer to have the experience of creating the files myself (and to save the cost). So, can anyone suggest an economical software package for creating the nesting and NC cutting files from an existing design. Thanks.

 

Airtoad - it would be simpler if you just produced a flat drawingof the plates. Anyone with the capability to cut them on an NC machine will also have the necessary software and experience to do the layout, toolpathing and nesting.
Also, they will have software that talks to thier cutter, which may not necessarily be the case with some other system.

Steve

 

Since you have minimal CAD skills, I would offer a single word of caution: ACCURACY. This aspect of lofting can never be overemphasized. Even professional lofters make mistakes and as an amateur you are likely to make more than your fair share.

These mistakes can mean the ruin of hundreds, if not thousands, of dollars. The first step toward this accuracy is to create a three-d model. What software to use is a matter of considerable and ongoing debate, but I lean heavily towards Rhino, since it is less expensive than most of the hull-dedicated software and can model anything any of them can.

Once you've mastered the use of this software, then I would recommend getting more than "minimal" CAD skills in order to tackle the job of turning your model into 2-d parts for cutting. A very important facet of this endeavor is to make sure that all your cutting lines form a closed loop. Whatever you draw is what the torch will cut. If it is confusing, then you will have confusing results off the table, assuming the torch can even follow your instructions.

Before creating your drawings, talk to the steel guy who will cut the project. He will more than likely have specific suggestions on how to format the drawings so they will make sense to him and his machine. If the steel guy won't discuss the project with you, then find another who will. Don't go on price alone.

If all this sounds daunting, that's because it is. The professionals spend years working on their craft. What you spend having them do the job can be more than saved in the cost of ruined plates and rework.

Good luck.

 

Computer lofting Ebbtide 33

PhotoBoatGuy, SailDesign, et al:

Thanks for the helpful replys. I recieved the study drawing of the Ebbtide 33 a few days ago and my enthusiasm for the design has not ebbed (if you'll excuse the lame word play). As I climb the steep learning curve of CAD/CAM capabilities, NC cutting files, and steel boat construction in general, I am struck by a recurring thought: "this ain't as easy as I imagined". With regard to computer lofting I am coming to suspect that there is -in addition to the need for accuracy that PhotoBoatGuy mentions- some judgement that comes into play when lines are faired in the computer and this would lead to subtle (or not so subtle?) differences in the final product depending on who lofts the plans. Please correct me if I am wrong on this point, but it would seem that even if the computer lofting was contracted out to a professional, I could get a materially different boat -even with identical plans and table of offsets - based on who I chose to do the lofting. If this is correct, then employing someone who is "just" a CAD/CAM software jocky would not be good enough. I would need someone that also had solid naval architecture and design savy to inform his/her judgements throughout the computer lofting process. In a nutshelll, it would seem that accuracy is a necessary but not a sufficient criteria for optimum results. Comments, please.

As you may suspect, right now I am leaning toward having a professional do the computer lofting and producing the NC files ... I think because of the potential for costly errors that I might (would probably) make not to mention the investment in hardware and software required, the economics strongly favor contracting the work out. Any suggestions as to folks that could bring the requisite experience, skills to bear on a relatively small project such at computer lofting the Ebbtide 33?

Also, since I have not yet purchased a set of plans for the Ebbtide, I thought I would solicit comments from the forum regarding the design and possible alternatives applying the following very general criteria.

a.) steel - collision survival
b.) primarily singlehanded by a 50-70 year old (read, crew fatigue avoidance)
c.) cruised primarily in Gulf of Maine - cold water, fog, rocks, lobster trap buoys everywhere! protect that prop and shaft!
d.) capable of atlantic crossing - no plans; just like to know that I could
e.) boat takes care of itself if the crew can't
d.) suitable for big adventure but NOT suicide
e.) would be nice if it sailed well (but I recognize that heavy displacement and large wetted surface are are going to harshly penalize light air performance. The literature that I can find on the Ebbtide, however, claims better then good performance in F4 and above)

Note that my selection of the Ebbtide 33 was made through the lense of three readings (OK, I'm not the sharpest tack in the box so it takes a bit of re-reading and thought to "get it") of C.A. Marchaj's "Seaworthhiness: the Forgotten Factor" . Was wondering if there is other science that debunks, supports, or otherwise updates Marchaj on the subject.


Thanks.

Airtoad

 

Hi Airtoad:

Choice of lofter is a matter of whom you trust. If a lofter is any good at all and the design drawings are adequate, then the end product will be quite close to the drawings.

The lofter's job is not to design or improve on the designer's work, but to faithfully reproduce it in steel. His only mandate with respect to improving the designer's work is in the area of fairness. When the designer did his work (at least back in the middle ages before the rise of computer aided design), He did not have the benefit of full-scale drawing, so the lines were done at small scale. Additionally, the designer would do his lines to "stations", which were needed for calculations, whereas the lofter needs the shapes of the hull at frames, bulkheads, etc.

When the lofter fairs the hull, he is charged with taking out any unfairness inherent in these small scale lines. In modern times, most if not all designers are using computers and have the same capability of removing unfairness, so this function is less important to the lofter. However, the good lofter will still make dead certain that the hull from which he cuts parts is fair, before beginning the bulk of his work, which is the generation of parts.

This process involves using his modeling software to cut frames, bulkheads, stringers, decks, shell plates, etc., which are usually exported to drafting program or module for refinement. Here, each part has openings, intersections with other structure and other novel features added. The lofter also makes certain the burning torch will follow the path of the part and its openings faithfully. Also added in this process are all the labels, which make it possible for the builder to know what part he has and where it goes.

The lofter then either a) Passes the drawings off to the cutter; b) nests the parts onto plates and passes these off to the cutter or; c) generates "tapes" from these plates and passes these to the cutter. He then works with the cutter to assure proper delivery of the parts and with the builder to assure proper assembly.

All of this sounds quite complex to the uninitiated, but to a lofter, because of years of experience, it is quite natural. If it sounds like I've been thru this before, I have. I have lofted somewhere north of 100 boats in my capacity as a marine designer and lofter. I've only recently become a sailing photographer.

For more information, you can visit my site at http://basline.com/baseline.shtm. I would gladly entertain private emails to discuss your needs, also.

 

TouchCAD enables you to both imports coordinate points and 2D or 3D DXF drawings/models and in scale high resolution background images (seperate for the Front, Top and Side views) if you just have access to scanned in paper drawings.

TouchCAD also enables you to unfold the panels and generate a cut layout in the Unfold view without loosing the dynamic link to the 3D model. The cut layout can be exported as DXF (and many other commonly used file formats) to be used for cutting or with automatically generated coordinate measurements to be used for manually plotting full scale cutting templates. TouchCAD does not have a limitation in the number of panels that you can use so you can essentially design all major panels in the boat.

More info at www.touchcad.com