$25K sounds like a lot to convert files to DXF. Most CADD can be saved as DXF. The only problem would be if the design is not based on developable surfaces.
OK, let me justify the costs of producing a cutting file for metals (or even plywood). First off, as a full disclosure, I worked for a company in the UK that was a water jet cutting company as a CAD technician/production manager, general dogsbody and chief cook and bottle washer ... you get the idea. My job was to turn customers drawings (either paper copies or DXF's) into a cutting file.
First off, the computer file had to be adjusted for the width of the cut itself and the toolpath had to be offset by half the expected "kerf" of the cut otherwise the part would be undersized by that amount. Not significant on a 44 foot yacht but still needed to be borne in mind.
Secondly, you cannot start the cut on the line - ALL cutting devices need to be offset from the line on the scrap side of the part as the initial hole that the cutter punches into the plate or material inevitably wanders and forms a ragged hole. Think of an artillery shell crater effect. This needs to be somewhere in the region of 1/2 to 1 inch away, depending on the thickness of the plate - the thicker the bigger the size of the dispersal of the cutting medium. Next you need to command the program to move to the line and then follow the line to cut out your part, bearing in mind that you need to know your machine and cut in one direction (clockwise/anticlockwise) to avoid problems with backlash.
But wait! If holes (lightening holes, access hatches, port lights etc.) need to be cut too then you need to cut those out before the main outline of the part because the part might move and the holes would then be cut in the wrong place. Work from the inside out.
No doubt the client will want the most efficient use of the plate being cut so you need to nest the parts manually (SOME, but not all CAD programs have a nesting function) and then work out the cutting sequence - holes first, then the smaller parts cut into the "scrap" from the bigger parts then the bigger parts etc. and all need to be toolpathed properly. To cut down on machine time and costs, the CAD technician will look for ways to share cuts. Imagine you are cutting sheet material to make a picket fence around your house. The top of the panel might be a simple point or a Fleur De Lys which needs to be cut but the planks themselves will be parallel and straight. The CAD technician will have them "touching" and adjust the DXF drawing file to make them wider by the width of the kerf. The price you will pay will be based on the length of the cut and the dwell time (that is, the time it takes to cut the part). So in that simple example, the CAD technicians time and cost is more than saved by not making two cuts to each plank as the cut separating one plank from another will be the cut of the next plank - if you follow my meaning (except the first and last in line). OK, it is unlikely that many parts for a yacht could share cuts (you might want to cut a dozen or so access plates to tanks which could use this idea) but it is a factor that needs to be understood and taken advantage of if possible.
But wait! There is more! Aluminium has a "grain" caused by rolling at the mill and parts must be orientated to take advantage of the different strength properties. The CAD technician must take this into account when laying out the parts and this may mean that not all the plate is used as efficiently as a steel plate would. In other words, the cutting files for steel and aluminium will be different.
Since the yacht will be constructed of different thickness materials then the parts need to be sorted according to their thickness. The paper plans will simply state "All frames to be from 1/4 inch plate, keel sides from 1/2 inch, keel base from 3/4 inch" etc. The builder then toddles off and cuts the parts as necessary but our CAD technician must make sure that the separate cutting files specify the parts for that thickness and account for this.
Now, Tony is looking at a 40 to 44 foot yacht which will have a beam of somewhere in the region of 12 to 12.5 foot so the frames cannot be cut out of a single 8 foot x 4 foot plate but most likely be cut out, as a minimum, in two parts and welded at the keel junction, perhaps in three of four or more parts and that means that the designers CAD drawing of these parts needs to be "cut up" in the CAD program to form these parts, then they are nested, taking account of the grain of the aluminium and the cutting file created, of course.
Since the finished kit will have a LOT of parts, then it would be handy to mark them. Not a problem, any CNC cutting machine can engrave the part with an identifier such a F4U (Frame 4 upper) and while we are at it, we may as well engrave the waterline, centreline and any other marks that will help the builder set up the frames etc. and ensure that the parts are correctly aligned. This is a separate file from the cutting file (you will not want the text to be cut through the plate) and again, this must be manually done - the paper plans will have all the waterlines drawn as one line superimpsed on all the sections and it would be up to our builder to mark these when lofting from the plans and transfer them to the frame, stem etc.
Next the work must be checked. Recall that there WILL be various sizes of material (thickness) and you do not want to cut a part from thinner material than required. It COULD be that the designer specifies 3/8 inch plate for the 6 or 7 frames above the fin keel and 1/4 inch plate for all the other frames. Using the wrong sized plate here and/or incorrectly orientated on the aluminium plate could be potentially disastrous so the checking is essential.
I wish it WAS as easy as simply typing "Toolpath" into the CAD program and it will all be done by magic but unfortunately it involves a lot of manual input, skill and judgement to successfully translate a CAD design into a set of cutting files to produce the kit of parts. You can either pay up front for a CAD technician to do the work and produce superbly accurate cut out parts that will snap together like a plastic model kit. This will save yourself from needing to loft the vessel, spend a lot of time on a dirty, boring and repetitive task cutting the parts yourself, sorting out the material and spending a good while marking up the parts from the lofting board. As usual, you can swap time for money or money for time - if you have lots of time and not much cash, then do the work yourself but if you want a hull that is accurate, to the designers weight calculation and quick to assemble, then pay the cash and specify a set of cutting files.
So don't begrudge the cost of the designer doing this extra work - it is not straightforward and is something of a black art and an acquired skill to do well.
And you wonder why I went prematurely bald! >};o)
While you are looking a the Kasten Marine website, go to this page:
Articles on Yacht Design and Boat Building http://kastenmarine.com/articles.htm
At the bottom he has two downloads - Marine Metals Reference and Corrosion, Zincs and Bonding. Both worth studying.
