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Old 01-08-2012, 10:27 AM   #1
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Trace scanned parts in AutoCAD

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I'm building an old Top Flite F8F-2 Bearcat red box kit (thread) that has been long discontinued and would like to be able to reproduce the kit for personal use and make modifications to it in AutoCAD in a format suitable for laser cutting.

- I'm using AutoCAD 2012 on Windows 7 32b, 2.5GHz Core i5, 4GB RAM
- I'm a new user teaching myself using the book Up and Running with Autocad 2012
- Inventory of uncut wood has been documented
- Parts have been scanned to PDF
- PDFs have been printed and dimensions cross-checked to actual parts

I'd appreciate any advice or help as I run into questions or problems alone the way!

I've converted my PDFs to TIFFs and have imported 12 of them into Autocad.

1. 12 is too many! I takes several minutes to open the file and the whole system is bogged down.
2. Are TIFFs the way to go?
3. I'd like to use Imperial units (1/64") because the loose wood is all sized in inches, but am more comfortable with metric. Does it matter which I use?
4. When I measure dimensions of scanned parts in AC with UNITS set to mm, they are correct (e.g. 135mm), but with units set to inches, I get huge dimensions (e.g. 9' 5"). I imported with units set to mm and scale set to 1 -- is the units setting at import irreversible, or can I scale somehow to switch between Imperial and metric?

More questions to come as I start tracing and managing the information.
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Old 01-08-2012, 12:13 PM   #2
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Re: Trace scanned parts in AutoCAD

I can't claim professional level expertise with Autocad but do use it for similar purposes to yours so will give you my thoughts.

Re. TIFFs - I believe the TIFF graphic format is very close to raw data using very little, if any, compression. It gives very large files but low information loss. I always use .jpg which does use compression algorithms to reduce file size but I've never noticed any loss of information that has affected anything referenced into Autocad.

Re. Units - I believe you have to choose one set & stick with it. When you switch from mm to inches I believe each mm becomes 1 inch & therefore everything is 25.4 times larger. You could select everything & rescale down by a factor of 1/25.4 but then later you would have to reverse the process & things could get messy. Ultimately, all that's important is that everything is the right absolute size when sent to a plotter or laser cutter. You can adjust that at the plotting stage if you need to.

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Old 01-08-2012, 03:48 PM   #3
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Re: Trace scanned parts in AutoCAD

TIFF's are likely way to big & I really can't see any advantage to them over a jpg for what you're doing. A Tiff has ZERO compression so every single pixel has been saved & will need to open to restore the full file.
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Old 01-08-2012, 04:26 PM   #4
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Re: Trace scanned parts in AutoCAD

Are you going to trace the images in Autocad or use the images directly? I assume you are going to trace the part outlines and create cut files from these tracings. If so what is the issue with multiple images? Just turn one on at a time, make the traced parts from that sheet, then either turn it off or better still remove the image from the file. Once you have captured the info in the traced component the original image is no longer needed. If the problem is each time you move the view port to trace the next section of the image it has to load etc. then try turning the images off except the one you are working on. Hope this helps. I have been using AutoCad to enlarge 3 views etc. for some time now and have done some tracing to get better airfoil data etc. but have yet to do a full laser cut set. Good luck.


BTW who and where are you getting the laser cutting done at?
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Old 01-08-2012, 05:34 PM   #5
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Re: Trace scanned parts in AutoCAD

if you have nice clean scanned pdf files there is a program called pdftodwg converter which does an excellent job of converting into autocad .dwg files.

you might have to scale the size when you get it into autocad but that's it.

there are one or two sites online that offer pdf to dwg conversions as well. for free. have not tried these myself.

one here

and another
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Old 01-08-2012, 05:57 PM   #6
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Re: Trace scanned parts in AutoCAD

If it's slow to load you may want to think of getting more ram, that's typically the issue with really larger files.
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Old 01-08-2012, 09:28 PM   #7
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Re: Trace scanned parts in AutoCAD

Appreciate all the replies - thanks.

I've uploaded one of the 17 8.5x11 or 11x17 parts scans (file size constraints here mean it's a down-sized jpeg of the original pdf scan) so you have a better idea what I'm working with. I've verified that the scanned pdf doesn't have any measurable distortion and that the dimensions are correct after importing to Autocad.

I did look into a few different raster to vector conversion tools but in the end I think the shapes are simple enough to trace manually, and that accommodating the edge shadows and varying degrees of brightness are better done by a person. I also felt that tracing by hand would be a good introduction to Autocad so that when I want to make changes, for example to formers, I'll have the ability to do that. It would probably make life easier if I traced the parts with a pen to get a more solid outline.

I've started again with units in inches, importing jpegs. Yep, they have more than enough definition, and at 3MB each are easier to work with than the 40-60MB tiff files. The mouse scroll zooming seems to have slowed down with the switch from tiff to jpeg, need to check that.

Once I'm comfortable with the basic tracing, the real issue will be how to manage all the information: 17 pages of scans, about 100 parts, all at random orientations with info like material, thickness and part number to be recorded. I'm just starting to learn layers, so some advice on the best way to implement them would be helpful.

I'm thinking of maybe sending the files to GDH Planes in Whitby, ON. He's posted some useful customer file setup information. I'm not ready to start looking yet really.
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Old 01-09-2012, 11:47 AM   #8
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Re: Trace scanned parts in AutoCAD

too bad you don't have illustrator. it will auto trace your images.
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Old 01-11-2012, 12:32 PM   #9
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Re: Trace scanned parts in AutoCAD

I agree with the above. Jpgs work better because of smaller file size, if the resolution of the image is sufficient enough. Tracing one sheet at a time saves computer resources>software delays>time.

You can set up whichever units you like best. Inches is great because that is the way wood stock comes but I don't like trying to input fractions or weird decimal numbers. If my own design, I will draw in metric (especially for plotting airfoils) and make whatever conversions I need. There are usually not too many. Like the others said, you can always draw in one unit, then re-unit the drawing when done.

You can also configure your dimension style to show both measurements. I often use this during planning/design because I still "think" in inches.

As far as managing parts...

Lets say you have a wing rib drawn. I will use a text command to label the part and write whatever other info is required (number of duplicates, material, etc). Then I will use the block command to make the part and all text a single entity. When you manipulate the block, all info stays with. You can also take this feature into 3D and the text still remains.

Another advantage for doing this is your laser cutting. My laser cutting guy (MR Aerodesign) has one colour for cutting and a different one for engraving. For instance, cyan for a cut, white for an etch. That way the parts get cut and the part number is also on it.

Layers: Often I'll use one layer for each type of component (former, rib, etc), a couple layers for generating full size construction plans and one no-printing layer in some harder-to-see colour (like dark green) for planning and working lines.

Hope this helps. Have fun with AutoCad. It is a powerful tool!
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Old 01-11-2012, 11:50 PM   #10
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Re: Trace scanned parts in AutoCAD

Thank you very much for the pointers - it is daunting to be grinding through a 700 page book not knowing what I should be looking for. Layers seem simple enough now, and I'll skip to blocks next. I like the idea to use different layers for different types of components. I suppose it might be useful to also separate balsa from ply with layers, or is there a more efficient way to 'tag' parts (or is that the purpose of blocks)?

I was wondering about etching and am glad to hear it's possible.

If I trace one sheet at a time does that mean I'll have 17 dwg files? Or do I bring in the scan, trace it, move the data aside, delete the scan and repeat in the same file? I might be hesitant to lose the scan/trace alignment so quickly, worried that I might want to go back and do it better after learning something new.

Again, thanks for the timesaving tips!
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