Author Topic: Ah ha!  (Read 198 times)

M.E.

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Ah ha!
« on: March 21, 2018, 10:09:22 PM »
Ah ha! In another post I explained a problem I have with passing drawings on to be plasma cut for to build boats (skiffs, actually). It's been driving me nuts. The cutter has the latest, greatest AutoCad (which I cannot, nor ever will throw the coin down for) and he relays the hitches in my drawings to me. I know through research that AC has a function to both identify and 'fix' those problems but that is both time consuming for him and unacceptable to me for obvious reasons. So, I began to study and going through my work procedures and found at least ONE of the main culprits:

I import into DC lines from a surface modeling program specific to boats called ProSurf. It has the ability to take 3D shapes and lay them flat in order to be cut on a plasma, router or other methods cutting table. These imported lines, even if they are staight are comprised of MANY points; it's the nature of the program to do so.

In order to be economical with material use, I need to chop up some of these generated shapes to achieve that. For example, a skiff can have long curved elements such as sheer/chine 'flats' and other lengthy longitudinal scantlings that because of their curvature would eat up a lot of expensive real estate if not parsed.

I discovered, by experimenting with the 'combine lines' command that these chopped up parts did not have joined ends to lines where the were sliced. To be specific: If I took one of these shapes and bisected it with a line, then, after making copies used 'section trim' command to make  two pieces of it I would then use the 'trim' command to remove the tails. BUT! after zooming in at these trims a bazillion percent, sure enough, they did not come clean - there are gaps. Thereafter by using the 'point select' command I'm able to heal them. I prefer that to 'join end points' because I don't know why!

I suspect this problem has to do with the numerous points generated by the parent program.
Anyway, I haven't sent off the lastest set of drawings so, we'll see...

What are the chances of DC having a function to detect these gaps?   

bdeck

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Re: Ah ha!
« Reply #1 on: March 22, 2018, 01:09:21 AM »
If you are trimming Curve entities, DC cannot slice precisely. The iterative interpolation routine used for trimming curves seems to have been written in the 1980s, and optimized for speed, not accuracy.  If that is the problem you are having, there is no precise solution unless you write your own. A few years ago DC added one extra iteration to the routine.

If you are trimming Line entities, on the other hand,  the trim will be precise to the mathematical limits of the program. 

For a faster trim without gaps, you could Vector Convert prior to the cut, and then convert Line To Curve afterward. Or just leave the shape as a multi point line entity. If converting back to curves, make certain to add an extra point to each corner in point select mode.

But this method may not be as accurate as your present method, even if the trim line goes through two existing points on the curve.
« Last Edit: March 22, 2018, 01:17:41 AM by bdeck »

Dr PR

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Re: Ah ha!
« Reply #2 on: March 22, 2018, 09:33:23 AM »
Be cautious when using the functions to cut and combine lines and curves. DesignCAD has a habit of changing a simple line or curve into bazillions of points. In the past the huge number of points would overwhelm some other program a file was being exported to - I don't recall which program.

There are functions to reduce the point count, but these can also change the shape of lines and curves.

I have found that it is much easier and faster to use existing lines and curves as templates, and start over on a new layer and draw new lines and curves by tracing (gravity snap) over the original lines. Then I can make the desired edits while I am drawing the new objects.

Phil
DesignCAD user since 1987

M.E.

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Re: Ah ha!
« Reply #3 on: March 22, 2018, 12:36:57 PM »
Thanks Phil and bdeck, I just got word from my cutter that he is thrilled with the 'new' work product. He's CNC software digested the test drawings without a single snicker.

I cannot use the point reduction edit because the original surface modeling software matches point-to-point along the edges of NURBS. I don't want to even consider what might happen should I monkey with that monkey! 

"I have found that it is much easier and faster to use existing lines and curves as templates, and start over on a new layer and draw new lines and curves by tracing (gravity snap) over the original lines. Then I can make the desired edits while I am drawing the new objects."

Phil, I don't understand exactly what you are describing above. The principal parts (sides, bottom) produced by the surface modeling program have hundreds of points when imported without any further manipulations. When I 'combine lines' in the original, nothing is added or subtracted as far as I can tell. It seems that the slicing, dicing and addition was the progenitor of all my problems.

Thanks again, you folks are terrific!

Mark