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milos_gajic

I have a little problem. I need to draw an arc and only know the radius. so I need help how to find where is the center if there is any way to do in autocad. I am using autocad 2010 for a while now and I'm pissed of ... I 'm posting a pic of problem so any suggestions is helpful.

arc_problem.jpg

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BIGAL

Just use snap center and pick arc ?

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Jack_O'neill

Your diagram gives you enough information to get this far. The small circle is the D10 hole, the half circle above it is the R13 fillet above it. You know by adding the 17 and 26 dims that your center line is 43 away from the center of the D10 hole. The width of the piece at the horizontal area is shown as 26, so you know that line is 13 above the center line of the piece. Construct this as shown then go to the second image.

 

FILLET.PNG

 

 

once you have that, use the fillet command with a 72 radius. Pick the half circle and the horizontal line. Presto, one R72 arc, no center location required.

 

fillet2.jpg

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Jack_O'neill

Dunno what happened to the colors in the second one, sorry. Hopefully you can see what's going on there.

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nestly

I'd basically use the same method as Jack described, however I do think the drawing is insufficiently dimensioned to recreate the part without guesswork.

 

It is incorrect to fillet between the R13 and a "horizontal" line 13 units above center, because the arm tapered. You'd have to create the tapered line first, however I'm not sure how that can be done from the given dimensions.

Edited by nestly

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milos_gajic

fillet command worked. never thought of that. nestly you are right, I did used guesswork at the end.First draw the R72 then R35 and joined those two lines some where that looked nice :D. Anyway thanks for the tip.

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SLW210

All the info is there.

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Jack_O'neill
I'd basically use the same method as Jack described, however I do think the drawing is insufficiently dimensioned to recreate the part without guesswork.

 

It is incorrect to fillet between the R13 and a "horizontal" line 13 units above center, because the arm tapered. You'd have to create the tapered line first, however I'm not sure how that can be done from the given dimensions.

 

If you look very closely (or do like I did and pull the image out into a viewer where you can zoom up on it) you'll see that there is a very short horizontal area right behind that big arc. It runs from the bottom quadrant of the arc to approximately half way to that 26 dim. The tapered area begins at the right side end of that straight area. I agree with you though that there is not enough info to accurately reconstruct the taper. Where that straight portion ends and an angle would have been very helpful. The rest of the thing is doable with what's there, but the guy in the machine shop is going to have bad things to say about who ever drew this originally.

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nestly

Ok, I see that now Jack. My initial assessment assumed that the taper extended to the tangent point of the arc(s) on both ends, but I see now that it doesn't on the wide end, and may or may not on the narrow end of the taper. If that's the case, then it's impossible to reconstruct it accurately.

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Jack_O'neill
Ok, I see that now Jack. My initial assessment assumed that the taper extended to the tangent point of the arc(s) on both ends, but I see now that it doesn't on the wide end, and may or may not on the narrow end of the taper. If that's the case, then it's impossible to reconstruct it accurately.

 

I thought so too at first, and it may be an illusion created by the dimension lines, but it does appear to be there. The other end is pure guesswork. That 18 dimension is pointless since there's no way to know where that dimension was taken. You can't just throw a dimension on a taper somewhere and expect it to be measurable at the exact spot you picked. That one doesn't even appear to reference the quads of the arc. I'm sure if you measured up and down the taper carefully you'd find it to be 18 somewhere along it's length!

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eldon

I read the 26 and 18 dimensions to be the distance apart of the tangent points (wherever they might be).

 

If you take an angle of 1¾ degrees for the taper, you are not far out.

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nestly
I read the 26 and 18 dimensions to be the distance apart of the tangent points .....

 

Yeah, I did as well, but as Jack pointed out, upon closer examination, it's pretty clear there's a distance of ~25 units that's un-tapered between the R72 and the tapered line.

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eldon

I looked at it closely, but it is all a bit pixellated at that scale. It is not logical to have a untapered section after a tapered section, so I presumed that it was an extension line from the 26 dimension.

 

But a few more dimensions would remove all doubt.

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Jack_O'neill
It is not logical to have a untapered section after a tapered section, so I presumed that it was an extension line from the 26 dimension.

 

But a few more dimensions would remove all doubt.

 

Admiral Leonard H. "Bones" McCoy: [looking at both sides of Data's head] I don't see no points on your ears, boy, but you sound like a Vulcan.

 

It wouldn't be logical, but when did that ever venture very far into what humans do?

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paulmcz

Closest I could get (attached) - no guesswork.

arc-problem.dwg

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Jack_O'neill
Closest I could get (attached) - no guesswork.

Congrats! You win the prize for today's cleverest user! Very nice indeed.

 

 

Have a cookie!

cookies.jpg

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paulmcz

Thanks, cookie was good. There certainly is a solution for drawing this accuratelly but it involves some calculus to find the distance of the center of the larger yellow circle (R72) from the main center line.

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Jack_O'neill
Thanks, cookie was good. There certainly is a solution for drawing this accuratelly but it involves some calculus to find the distance of the center of the larger yellow circle (R72) from the main center line.

 

Actually, what you did will place it about as accurately as could reasonably be expected. I guarantee, no cnc mill could work any closer than that and there are few devices capable of measuring it that close. A pair of 6" calipers and a protractor ain't gonna cut it.

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qball

I had a slightly different take on it. I drew a R72 yellow circle and rotated that around Point C, from the the intersection of Point A to Point B - dimension.

Doing the same thing at the other end creates a little kink (not smooth transition).

Drawing2.dwg

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Jack_O'neill

I still think that flat spot is there :lol:

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