Corruption of existing drawing

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crowhurst
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Corruption of existing drawing

Post by crowhurst » Mon Sep 11, 2017 12:27 pm

QCAD v. 3.17.3.0 Windows 10
Yesterday I pulled up a .dwg file from a year ago in order to make an alteration to the drawing. (Free open source plans for a sea kayak at http://www.cnckayaks.com) I found that the drawing was distorted at many points, particularly showing bulges where splines meet lines. All my back-up copies are similarly distorted, including those on Dropbox and on a separate back-up hard drive.
I originally made a "PDF export" of the original perfect drawing. I have attached this, and the current distorted .dwg file. Any help and advice would be greatly appreciated.
Nick.
Attachments
nodots25%scalealternatecontinuousfullformsprint.dwg
(48.46 KiB) Downloaded 38 times
pdfnodots25%scalealternatecontinuousfullformsprint.pdf
(41.61 KiB) Downloaded 38 times

crowhurst
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Re: Corruption of existing drawing

Post by crowhurst » Wed Sep 13, 2017 11:07 am

Just for information of anyone faced with the same issue, I've used Inkscape to convert the PDF back to .dxf. It converted nicely, and just required re-scaling, but layers beyond 0 and 1 are missing. The missing layers include all the text. I'll keep trying. Ultimately I can recreate the original document with a couple of hours work, but I'd prefer to understand the issue.
Nick.

crowhurst
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Re: Corruption of existing drawing

Post by crowhurst » Wed Sep 13, 2017 12:23 pm

Just to confirm that within Inkscape and the "layer export selection" menu I selected "All (default)"
Nick.

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Husky
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Re: Corruption of existing drawing

Post by Husky » Wed Sep 13, 2017 8:34 pm

Hello Nick - I thought you are already on the water ... :wink:

Honestly I don't know what is going on and I don't have a one click solution! It looks to me that the Points for the splines are Ok but the calculation isn't as expected. Maybe Andrew has an explanation for this ...

However - here are my two cents:
If you use the same Points for redrawing the splines it will come much closer to that what you are looking for. In this example I selected the "wrong" existing spline to see the points so that I can use them to draw a new yellow spline (SL). That doesn't takes hours to fix this issue.
Husky-2017.09.13-01.png
Husky-2017.09.13-01.png (19.52 KiB) Viewed 2424 times
crowhurst wrote:Just for information of anyone faced with the same issue, I've used Inkscape to convert the PDF back to .dxf. It converted nicely, and just required re-scaling, but layers beyond 0 and 1 are missing. The missing layers include all the text. I'll keep trying. Ultimately I can recreate the original document with a couple of hours work, but I'd prefer to understand the issue.
Nick.
Note: Layer 2 and Layer 3 are empty - everything is on Layer 0

As I already wrote - with my suggestion it comes much closer but I also remember this topic from last year and I recall that the drawing wasn't perfect regarding the splines. Maybe now is a good time not only to fix it but also to come closer to a "perfect hull spline". Yes I agree - perfect is relative but it could save you time and headache in the built. What is your plan for cutting the parts? CNC or manual with Hand power tools?
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crowhurst
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Re: Corruption of existing drawing

Post by crowhurst » Wed Sep 13, 2017 9:29 pm

Husky, many thanks for the information. I'll have a try at that procedure tomorrow evening.
As regards the sea kayak kayak plans, we (my son and I) supply them to the world, open source and free of charge. So far, in the past three years, 4,000 copies of the plans have been downloaded, from Russia to South America and everywhere in between. I've built five, and 135 people have been kind enough to send me photos and/or details of their completed kayaks, and you can see many of these these in the Gallery of our website at http://cnckayaks.com/shrike/build-gallery/
These have been mainly of our Shrike design, but we have a new design this year, Vember, and the corrupted file is of the cross-sections of Vember.
Thanks again for your help.
Best wishes, from Nick.

crowhurst
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Re: Corruption of existing drawing

Post by crowhurst » Thu Sep 14, 2017 8:16 am

Husky, I neglected to answer your query about the method of cutting out the panels. The free plans download at http://cnckayaks.com/shrike/downloads/ is provided in PDF format for those that wish to cut out the panels by hand, in .dxf for those who wish to use a CNC device, and in .dwg for those who who wish to modify the design. (However, the design is already hugely adaptable and scale-able, as described in the Build Manual in the download)
Cutting by CNC has an obvious attraction in speed and accuracy, but I prefer to use a hand saw for the main hull longitudinal panels. My reason is that the hull is over 5 metres long, and this necessitates the very accurate alignment of three sections cut by CNC out of a standard 2440 x 1220 mm plywood sheet. It is far easier to cut three rectangular strips from the plywood, glass tape and epoxy glue these end to end, and then cut the long thin panels from the assembled long piece of plywood. I cut within a couple of mm of the pencil line with an electric jig saw, and then hand plane to the pencil line. One of my granddaughters built a Shrike by this method as her first ever woodwork project. Here she is pictured with her Shrike: http://cnckayaks.com/project/shrike-lv/
Use of CNC to cut the panels, coupled with incorrect alignment, has resulted in gross distortion of the hull in a couple of unfortunate cases. There are ways to ensure alignment, but for me it's far simpler and more accurate to cut by hand.
All the best, from Nick.

crowhurst
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Re: Corruption of existing drawing

Post by crowhurst » Thu Sep 14, 2017 7:15 pm

Husky, that works as you describe, thank you. I now have to check the shapes against the original curves.
Nick.

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Husky
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Re: Corruption of existing drawing

Post by Husky » Thu Sep 14, 2017 7:28 pm

Glad to hear that and thank you for the "How to built a nice Kayak" explanation! :wink:
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crowhurst
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Re: Corruption of existing drawing

Post by crowhurst » Fri Sep 15, 2017 9:02 am

After some origami this morning I found that the re-constituted curve does not sufficiently replicate the original. I suspect this is because I created the "apparently curved lines" from a combination of straight lines and splines, and the software will now attempt to create a single spline from these points. I've used the "divide" command to separate the splines from the straight lines, and tried to select just the splined points, but this ends up being messy, showing a spline as more than one spline in series, which is not what I created.
Reluctantly I've decided that I have to re-create the original document, and I hope the same corruption does not recur. It would be very helpful if you could find time to do the detective work to discover what's causing this feature.
Many thanks for your efforts, from Nick.

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andrew
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Re: Corruption of existing drawing

Post by andrew » Fri Sep 15, 2017 9:15 am

The start and end tangents of splines are not correct in this file. I've loaded and re-saved the file ignoring start and end tangents (not something you can easily do on your end).
Attachments
nodots_scalealternatecontinuousfullformsprint_no_tangents.dwg
(47.95 KiB) Downloaded 34 times

crowhurst
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Joined: Fri Nov 11, 2016 4:56 pm

Re: Corruption of existing drawing

Post by crowhurst » Fri Sep 15, 2017 11:00 am

That's perfect, thank you. You've saved me a load of time and aggravation.
Nick.

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