I started with Model CAD software, and progressed through MICROCADAM, to Design CAD 2D, and  upgraded through Design CAD 2D  to DesignCAD 97. Apart from learning to control the CAD software, the main challenge has been getting an existing three view or pattern in raster format into a CAD vector file without drawing it from scratch. If you enlarge a raster image from 8 1/2 X 11 to say 48 X 62 on a copy machine, the line widths will also be enlarged proportionately making your enlarged plan useless for building model airplanes. In the beginning, I started by experimenting with manual transfer of three view drawings using a pair of dividers and a scaling ruler. The manual method is very time consuming, and prone to error. One note on the use of copy machines to enlarge airfoils or other patterns is that a great deal of distortion will be introduced. Copy machines do not enlarge accurately. One way to minimize distortion that I have used is to rotate the enlargements 90 degrees each time. You can verify the copy machine distortion with a ruled grid sheet.

I next worked with taking pictures of three views using a Canon Digital CCD Camera, RC-250, and a SNAPPY video input device. The images produced with the camera are in Raster or bitmapped format, and the CAD program is looking for Vector mathematical format. Therefore, the raster images must be converted to vector format, unless the three view or magazine size plan is OK as is, and your CAD program will scale and print raster images. DesignCAD97 will scale and print raster images. There are many pitfalls in the raster to vector conversion process ( I fell into all of them), not the least of which is the resolution of the CCD camera which proved to be inadequate to resolve the three view lines to the degree needed by the conversion software. Lighting of the three view during the picture taking is very critical, with shadow gradients and loss of outline in random places which also confuses the raster to vector conversion software.

I purchased an ACECAD 12 X 12 Digitizer tablet, and had fun inputting vector drawings with it. It is a snap to trace an airfoil and size it for example. Results are adequate for the type of model hobby work I do.  Next,  I turned to scanning the three views on a flat bed scanner.

DesignCAD 97 does have a monochrome 'autotrace bitmap' feature, but will only trace in "Outline Mode" which is not useful for line drawing purposes. "Centerline Mode" must be used to generate vector plans.

Scan Vector demo software works very well, but is limited in size of the area to convert. I get around the size limitation by dividing my raster image into small elements and then putting them back together in DesignCAD.  Bitmapped images can also be reduced in size to fit the Scan Vector demo window.

VP raster to vector conversion software is OUTSTANDING, but again, is limited in size in the demo mode, but has many very useful features to support cleanup, skewing, merging, and a raft of others. It has CAD capability built in!

KVEC raster to vector shareware is another program worth trying. The demo version seems to perform well, although I had to run it under DOS, using the exact syntax specified in the help file. I have not tested it well enough, but its' low price makes it a good bet for starters.

Once the raster image has been converted to vector CAD there is usually a lot of "clean up" required to change line widths, connect short line segments, and fill in missing details, unless you have VP conversion software; and of course the structure of the model must be built up if you started with just a three view external outline.

I have used HIJACK Graphics Suite from Quarterdeck raster to vector conversion software . I selected this software because it supports "over 75 graphics formats". I have had moderate success with scanned images saved in .PCX format converting in "centerline mode" into .DXF format, importing them into Design CAD 2D and saving in the Design CAD 2D format. The DXF format is Autocad and is supported by most "other than AutoCAD" software as a transport medium, but there are many versions of .dxf, and I have had lots of problems emailing .dxf files because they turn up with missing entities.  One solution to this problem is to send the .dxf file in zip format.

DesignCAD 2D and 97 both are supposed to import autocad xxx.dwg files  A good friend of mine who is plotting model plans  sent me a Loening m-8.dwg file which I could not load into DesignCAD even tho the book/manual says they will import directly.  I sent a message to viagrafix asking for help and was advised that DesignCAD will import directly Autocad .dwg files up to version 13 of Autocad.  Autocad v14 gives the option of saving  xxx.dwg files in either v12, v13, or v14 format.

Dana Hague of HAGUE AUTOMATION, an engineering consulting firm in Clinton, Ct., a professional CADKEY user suggests zipping the files for sending over the internet as a way to avoid unwanted additions in headers etc.
" ............. dxf is actually a text format; if you try to email it as an attachment the mail system treats it as an ordinary message and may mess with the formatting, etc. It'll work much better if it's zipped; then the email system _knows_ it's a binary file and won't mess with it.

Q.  I have exchanged files with several people via email, and find the .wmf extension works most of the time, whereas the .dxf does not, because there are so many different versions of autocad.

A.  " Wmf files, though, aren't that useful to most CAD packages; although they're "sorta" vector, they're really a bunch of line segments _approximating_ a curve, not the actual curve. This scales better than a bitmap if all you want to do is print it, but it's not much good for editing."

Q.  What extension/s do you recommend?

A.  " Well, of course it's not just the extensions per se that matter; it's the actual file format.

IGES (Initial Graphics Exchange Standard) is the industry standard for file translation, but many low end CAD systems can't read it (even AutoCAD won't handle unless you pay extra for the translator).

DXF (Drawing eXchange Format) is actually owned by AutoCAD, but almost every CAD system and many paint programs can read it. It's probably the best choice if you're making model plans available, as anybody can download a shareware copy of Paint Shop Pro, which reads DXF. One issue with DXF is version-- most current programs (including PSP) can read version 10 or 11/12, many (but by no means all) can read version 13, and very few can read version 14. I don't really know what the specific differences are.

WMF (Windows MetaFile) is mainly useful one-way-- that is, from a vector program (like any CAD program) to a paint or word processor that handles graphics. The problem with WMF is that although it's a vector format (and thus scales better than a bitmap), all the CAD intelligence is lost, i.e., an arc becomes a series of line segments approximating the arc. Therefore it's useful if you need to past something into, say, a Word document and then scale it afterwards, but you really can't modify it. It should give fairly good prints, though.

HPGL (Hewlett Packard Graphics Language) is understood by some of the word processor and desktop publishing programs, though it's mainly intended for sending information to pen plotters (and no longer used (I think) by HP). It's similar to WMF in that it's a vector format consisting of many little lines, but always at an angle divisible by 45°, drawn point-to-point on a grid equal to the plotter step resolution (usually .001"). There are some shareware programs that will convert HPGL to DXF or CADL (a format used by Cadkey and some CNC programs)."

Q.  You mentioned that you "stripped off the headers" on the file I sent you, what does that mean? Can I strip off the headers and read my own file and possibly yours?

A.  " The headers I mean were the transmission and routing information added by the email system, as well as your note. When you send a binary file (i.e. a zipfile), the email system recognizes it and keeps it as a seperate attachment, but when you send an unzipped IGES file the email system things it's just more text ('cuz that's all an IGES file is) and adds it to the body of the message. However, the IGES translator doesn't understand email routing, etc., so it has to be removed. This isn't necessary for an IGES file that is zipped before mailing."

ModelCAD and DesignCAD printer drivers work very well, and when using fan fold paper, the paper size can be specified long enough to print the full wing span.

MicroCADam's printerdriver sucks!

As to producing building plans, except for the 1/7 Scale Fokker DR-1 which I have had blue prints made up for, they are printed in strips on a Star 15 inch wide carrage printer and are then taped together on index lines for parts that are wider than 14 inches. This does not create any problem as long as the strips are aligned carefully.  My 60" wingspan DR-1 can be printed without taped strips.

I have been playing with an ENCAD SP1800 D size plotter.  It is an older pen style plotter and ENCAD has discontinued ALL support for the pen plotters they manufactured and sold effective September 1997.  Makes a fellow want to rush right out and buy an ENCAD product, right?   I have it working but not to my satisfaction yet.  I do not have an instruction manual but have figured out most of the settings and am using the HP7580 plotter driver that comes with Windows98 and was supplied by HP.

The following email exchanges took place on what is known as the "small net"  a subscription serviced web site devoted manily to the very small models.  I thought this would be of interest because it describes how to take your cad files to get them plotted by a comercial business.  I asked my comercial printer that has a large plotter what file extension they would require to plot a master plan that I could use to have them print blue prints.  They said they needed a "plot ready file" , and I did not know or had not heard of a plot ready extension.  I have since found out that AutoCAD will produce a plot ready file that has an extension of  xxx .plt .  Doing it this way, your cad file is protected as it is not loaded into the computer but just read by the plotter driver program directly into the plotter.

From the Small Net web site............
             SMALLnet's Web Site address is:
           < http://www.eskimo.com/~smallnet >.

> Help!  I recently found a free version of Turbocad (Turbocad 2D v6)
> that I used to draw up my latest airplane design.  It is an abso-
> lutely great CAD tool.  Once I had learned the basics of how to use
> it, I zipped through the creation of a moderately complex design.

> The problem is I don't have a plotter, and the local print/copy/
> plotting shop can't get my file to plot correctly.  The latest
> attempt looked correct, but the scale was off so the plot was
> unusable.  I think the problem is that I set up the paper size at
> 22"x34" and the Autocad program they loaded it into thought the
> paper size was 24"x36" and scaled the drawing appropriately.

> Turbocad doesn't have a 24"x36" option, so I am at a loss as to
> what to try next.  The file format I am using for the file is DXF,
> which (except for the scale) seems to load fine into Autocad.  I
> have also tried saving the file as a DWG (which is supposedly
> native Autocad format) with the same results.

> Anyone have any ideas on what else I can try, or a recommendation
> for another free or low cost CAD program suitable for model
> airplane designs?

> Can you force Autocad to use a specific paper size?

> Thanks,  Adam

Adam, a while back I drew up a plan for a 120% Lazy Bee, for use with
an OS 25 I had laying around.  So many people wanted a copy, I took
the file down to an engineering outfit running Autocad with a plotter.
But before I did I took a minute out to include a ruler in the plan,
so the scale could be checked when loaded on Autocad.

It's not a big deal for them to adjust the size if necessary, but this
way the onus is on them to get it right.

Nick from New Zealand, where summer's almost starting!

Carl  adds to that:

I have the same issues with DXF and Autocad.  I have used TurboCad and
now use Drawingboard.  Both are much easier to use than Autocad and
both do not transfer well via DXF.  Fonts get screwed up, layers,
lines, colors, etc usually get crossed.

If you are trying to get a service bureau to plot for you, simply ask
what type of plotter they use.  If it is a strange brand, ask if it is
compatible with a particular HP plotter (i.e. 750C, etc).  Then, go to
HP's website and download that Windows driver.  Install it and set up
your plot for that print driver.  Set the driver to print to a file,
not LPT1.  This will retain all the formatting, etc in the file.

Then take the file on a diskette to the bureau.  They simply COPY the
file to their LPT1.  You should get exactly what the software intends
to plot out on that particular plotter.  Hope this helps.

PS:  once you set the print driver to the plotter driver, you should
have appropriate paper sizes.  Right now you are stuck with whatever
comes out of your personal printer and Turbocad is scaling to fit
that paper.

Carl

Jack  mentions:

A SMALLster was having problems printing his Turbocad drawings full
size.  I just wanted to mention that the program has the capability
of printing on multiple pages with register marks for taping the pages
together.  This method would work for building models, since builders
usually tape the plans down anyway.  The menu for printing is
"file/print preview", which will show a mosaic of the drawing on
the multiple pages.      Jack

Larry  also replies to Adam:

Your "paper space" dimensions shouldn't affect the dimensions of the
objects you've drawn.  You might ask your plotter people which version
of ACAD they're using.  I don't think it would make any difference in
this instance, but TCAD saves in the latest version of ACAD unless you
tell it otherwise (you can change the settings when you save).

I own TCAD, ACAD, DrawingBoard and DesignCAD2000.  TCAD is, by far,
the most flexible.  Truth be told, you can simply save everything you
do in ACAD format; TCAD doesn't care.  There's no other CAD system I
know that can work seamlessly, with the native formats of other CAD
software.  (Yes, most can import them, but TCAD allows you to keep
working copies in those formats.)

What I'd do to solve your problem, however, is to draw a line on your
drawing.  Make it the length of the wing or any dimension that you
know.  Take your file to the plotter people and tell them you want
the drawing scaled so that the line is "Length X".  If they can't
do that for you, find another plot facility.  It's really hard to
understand why they didn't just ask you how big you wanted it and
scaled it for you.

The 22" x 34" size you've got set up is a standard paper size.  I'm
not sure what causes you to think that ACAD is set for 22x36 as that
would be very odd indeed.  The paper size in question is ANSI D and
that's what should show up on the ACAD side of your problem.  If it's
not, again, you've got an ACAD user who doesn't know what they're
doing.

> P.S. If you are interested in the free version of Turbocad, go to
> < www.turbocad.com > and follow the links for TurboCad 2D v6.
End of Small net web page.................
 

Dana Hague has answered several of my questions, and extracts of our email question and answer sessions have been provided courtesy of Hague Automation. Dana draws everything in 3D to avoid having to redraw. His advice is:
 

Q.       How do I learn to do 3D CAD?

A.   " Just do it!.  OK, not really trying to be facetious.  When I was
     working for the Navy at the Naval Air Engineering Center about 17 years
     ago, they got a brand new expensive (well, they all were, back then) CAD
     system (Computervision CADDS 4X) without knowing what to do with it
     (typical government).  Then they chose one person from each section (I
     wasn't one of them) to go to training-- they chose whoever wasn't busy (I
     was).  I wanted to learn to use it, so my boss said, "Just borrow a manual
     and get somebody to show you how to log on".  I did-- there were two
     training books, the 2D and the 3D one-- you were supposed to start with 2D.
     I got about halfway through the 2D book and discovered how to change views
     and project flat geometry up the z-axis, and never looked back."

Q.  My  BIG question is how to generate profiles.  Which comes first, the cross section 
    or the profiles.  I cant slice till I can generate the shape can I?

    OK, lets take a wing with a constant taper.  I drawn the root rib and
    the tip rib and loft a surface over it.  I can cut it anywhere and get
    the intermediate ribs.  BUT, what if you have a NON LINEAR surface like
    the Mystery Air Ship body,or better yet an elliptical wing?  If I
    generate the root and tip and try to loft a surface over them without
    intermediate ribs how do I control the shape (plan form) of it?  How
    many intermediate ribs do I need to get a smooth curve?

A.   " Well, you have to have something to start with. A straight or straight tapered wing, for example is easy. An elliptical shape is tougher. You can loft a surface over as many intermediate sections as you want. For an elliptical wing, assume you have the basic airfoil section and the wing planform (the elliptical shape). You place the basic airfoil section at the wing root, parallel to the y-z axes (side view), and perpendicular to the planform (wing top view outline, which is parallel to the x-y axes). (X is usually the axis parallel to the fuselage, with 0,0,0 being the point where the x axis crosses the front of the firewall.) Anyway, you put lines where you want each rib to be (or enough to control the surface), and trim them to the planform curve. Then copy the airfoil section to the front (leading edge) of each line, and scale the section to the proper length. Now you have a series of sections that you can loft the surface over. If the resultant surface doesn't match the planform curve closely enough, you can delete it and add more sections, and try again."

A.  "Splines are a smooth curve going through specified points, the closest analogy is a flexible wire passing through those points. In addition, you can optionally specify the slope (angle) at the beginning and the end of the spline. Polylines are a collection of individual (though the collection is treated as one entity) straight line segments connecting the points, with sharp corners at the points. If there's enough segments and they're short enough, they start to _approximate_ the spline, but it's still an approximation. Some CAD systems define splines differently, with the spline tangent to each of the polyline segments (though the p-line itself is not actually created) rather than passing through the points. Parametric splines are the most common type of spline, and a Parametric spline surface is a surface defined by the splines. "