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Trouble With Hatch


Bill Tillman

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I am having the worst time with a detail we're trying to hatch. Normally, this is taken care of with a LISP routine but for some reason in this detail I cannot get AutoCAD to accept the hatch area even trying to do it manually. I've checked and double checked that the area to be hatched is closed....but...apparently I'm missing something because it keeps telling me the boundary is not closed. There are other times when I attempt it and it will hatch but it grabs the thickness of the green extrusion and I end up with concrete hatch pattern inside of the extrusion.

 

The detail on the left shows what I start out with and the detail on the right shows what it should end up as. BTW - there were all kinds of problems with the wing nut block in this one. I corrected all of those (bad drafting practices from previous staff), of course I never practice bad drafting so I can be critical :D.

HatchTest.dwg

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I got just one anomaly at the wing nut otherwise it hatched for me no problem. But first I used the FLATTEN command on the whole thing. Bad practice - all geometry on layer "0" with the color overridden. Smack that guy will you!

 

BadHatch.JPG

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I think I found the gap. It is on the back side (top) of the wing nut where the arc meets up with the green extrusion. That's probably why you did not see it.

 

WingNutGap.jpg

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ReMark, thanks man. I will double check that one but I spent considerable time yesterday re-doing that wing nut. And yes, I work for a company that insists on NDA thus I must always strip everything I submit for public consumption down to it's bear minimum...only layer '0'. I will look at that closer. And it keeps telling me that the gaps it's finding are at the upper right leg of the extrusion where it meets the slab line...and it also points to locations which are not even inside of the area I'm trying to hatch.

 

And I am seeing some other anomalies on that wing nut. I think I will have to redraw it to get it right. This is from a very old block which was drawn by someone who uses metric units...but that shouldn't make any difference. There is something in that green extrusion which keeps throwing it south. I have tried making it a polyline, left it alone, re-filleted all the corners, etc.... I have checked the properties of those lines and they all begin at the same point.

HatchTrouble.png

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So you're saying there are multiple gaps? Don't smack the guy, send him back to AutoCAD 101 for a refresher course.

 

Did you know there is a wipeout in the drawing?

 

Did you know there were seven overlapping lines in the drawing?

Edited by ReMark
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The wipeout I know about. But the seven overlapping lines...I'll have to search for those. I have found a couple of them but the results are still the same with the hatch.

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Try just moving the wing nut out of the way, that cleared up the hatch problem when I did it, the wing nut is also just a tiny bit away from the green line which looks as though it is confusing autocad.

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Okay, I'm beginning to see the light now. These blocks were handed to me by someone who did them long ago and using only 2D drafting methods. But you're right ReMark, if you flatten this drawing first, you'll get different results. Now to figure out why and how the blocks are not flattened in the first place.

 

Thanks.

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If you zoom in real tight you will see that the vertical line of the wing nut where it is against the green line is not actually touching, that line is slightly out of vertical (use properties to see) and as pointed out the upper arc of the wing nut is not closed. Once I fixed those it works fine for me.

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And yes sir, you're correct. When I double checked that wing nut it is .000000354 units away from where it should be. And as we all know, that's enough to throw AutoCAD off the trail.

 

But here's the glitch. My LISP code created the drawing below. As you can see on one side of the assembly everything went fine. But on the other side...and this thing is symmetrical, and it uses the exact same code as the one on the left used with a few variables changed to do the opposite side, it did not work. I guess I'll be hacking at this one for a while yet.

 

Thanks.

HatchTrouble2.jpg

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Ok, that green extrusion block which was given to me by a trusted source has all kinds of bugs in it. I'm making more corrections to it now and will report back. The trouble with it did not show up until I flattened all the lines in it and then .... oooof! And now I just discovered that flattening the lines in the drawing and chosing "Y" to erase all hidden lines causes the lines to foreshorten or elongate by about 1/32".... more oooof! Or should I say "Doh!"

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Okay, I learned another important lesson on this one. Never trust a drawing created by someone other than yourself. And even then be only 1/2 trusting of it. These blocks came from a trusted and experienced user. Turns out they were originally done in Metric and then someone played around with them, incorrectly I might add, to convert them to Imperial. Then a really close examination revealed lines on top of lines, lines made of straight segments instead of a single line, etc... this one was in really bad shape. So once I got that corrected and merged the detail with another related block, the problem has resolved itself. There is still something about that darn wing nut which doesn't let the hatch work exactly as planned, but it's > 99% like the boss wants and he's happy with that. So onward we go.

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The problem with CAD is everyone thinks because they drew two lines, one vertical and one horizontal, all of a sudden they are Leonardo da Vinci. Many times a close examination of drawings posted here and elsewhere reveals too many mistakes that just shouldn't be. It seems there is no discipline.

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