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Other side of 2 point arc (#1848)
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blowlamp  
#1 Posted : Wednesday, November 19, 2008 2:49:56 PM(UTC)
blowlamp

Rank: Senior Member

Joined: 6/28/2008(UTC)
Posts: 648
Is there any chance of you being able to make it possible to draw the other side of the arc in the 2 point arc command, by say holding down the shift key please? It really would be a very useful addition for me and others, I think.

Thanks very much.
Martin.
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ianjkirby  
#2 Posted : Thursday, November 20, 2008 3:29:17 AM(UTC)
ianjkirby

Rank: Senior Member

Joined: 6/20/2007(UTC)
Posts: 107
Hello Martin,
I'm not sure if this will help, but I had a lot of trouble with arcs until I really absorbed the fact that arcs in most CAD packages are drawn anti-clockwise. This means that the order of selection of points is important to the outcome.
Regards, Ian.
Ian Kirby
Wollongong Australia
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blowlamp  
#3 Posted : Thursday, November 20, 2008 4:17:34 AM(UTC)
blowlamp

Rank: Senior Member

Joined: 6/28/2008(UTC)
Posts: 648
Hi Ian.
Thanks for your reply but it still doesn't give me what I am after. Have a look at the attached images to see what I'm after. I find it a real pain trying to get the 2pt arc on the right. I need the option to flip which side of centre the arc appears.

The second and third images show how CamBam does it, but bear in mind that CamBam is primarily a CAM application with some CAD functions included for covenience.

Thanks for looking.
Martin.
blowlamp attached the following image(s):
arcflip.JPG (66kb) downloaded 4 time(s).
cambamarc1.JPG (62kb) downloaded 4 time(s).
cambamarc2.JPG (66kb) downloaded 4 time(s).

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unique  
#4 Posted : Thursday, November 20, 2008 6:38:17 AM(UTC)
unique

Rank: Senior Member

Joined: 6/24/2008(UTC)
Posts: 591
Originally Posted by: blowlamp Go to Quoted Post
Hi Ian.
Thanks for your reply but it still doesn't give me what I am after. Have a look at the attached images to see what I'm after. I find it a real pain trying to get the 2pt arc on the right. I need the option to flip which side of centre the arc appears.

The second and third images show how CamBam does it, but bear in mind that CamBam is primarily a CAM application with some CAD functions included for covenience.

Thanks for looking.
Martin.


Hmmmm do you know that drawing a 2pt. arc works by drawing it anticlockwise ;)

Your example should be simple enough?
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blowlamp  
#5 Posted : Thursday, November 20, 2008 7:58:14 AM(UTC)
blowlamp

Rank: Senior Member

Joined: 6/28/2008(UTC)
Posts: 648
Hi Paul.
The arc on the right of the first picture is what I want to achieve, by using the 2pt command . The important feature of that arc, is that it is bigger than 180 degrees. I need to be able to produce arcs that are larger than half a circle and it is this that I can't get the 2pt command to do. The first CamBam photo represents an arc as produced in ViaCad. The second CamBam photo shows virtually the same thing, but I have pressed the shift key. The effect is to show the first arc's complement (release shift and it reverts to the smaller arc). That, or something similar, is what I would like.

Thanks.
Martin.
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unique  
#6 Posted : Thursday, November 20, 2008 10:29:22 AM(UTC)
unique

Rank: Senior Member

Joined: 6/24/2008(UTC)
Posts: 591
Originally Posted by: blowlamp Go to Quoted Post
Hi Paul.
The arc on the right of the first picture is what I want to achieve, by using the 2pt command . The important feature of that arc, is that it is bigger than 180 degrees. I need to be able to produce arcs that are larger than half a circle and it is this that I can't get the 2pt command to do. The first CamBam photo represents an arc as produced in ViaCad. The second CamBam photo shows virtually the same thing, but I have pressed the shift key. The effect is to show the first arc's complement (release shift and it reverts to the smaller arc). That, or something similar, is what I would like.

Thanks.
Martin.


Hi Martin,

I see what you mean, but is the radius of the arc important?

The same could be said about the 3pt arc and the ability for it to hold the endpoints of the curve whilst changing the radius (within reason of course)
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blowlamp  
#7 Posted : Thursday, November 20, 2008 1:58:01 PM(UTC)
blowlamp

Rank: Senior Member

Joined: 6/28/2008(UTC)
Posts: 648
Hi Paul - and others of course.
Yes, the radius of the arc is important. Same function please, just the extra facility to invert the arc would be handy.

Cheers.
Martin.
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ianjkirby  
#8 Posted : Thursday, November 20, 2008 8:02:26 PM(UTC)
ianjkirby

Rank: Senior Member

Joined: 6/20/2007(UTC)
Posts: 107
Hi Martin,
I appreciate it is not the 2-point arc tool, but I can do what I think you are trying to do with the center point arc tool, which utilises 2 points on the arc, but must include the center point. The order of selection of the 2 points on the arc for a given center point will give each side of the arc. You said the radius is important, so it seems that the center should be a known item, or do I still misunderstand? By all means follow on with querying the 2-point arc tool, but I think this is a workaround.
Regards, Ian.
Ian Kirby
Wollongong Australia
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blowlamp  
#9 Posted : Friday, November 21, 2008 4:38:12 AM(UTC)
blowlamp

Rank: Senior Member

Joined: 6/28/2008(UTC)
Posts: 648
Hi Ian and others.
The beauty of 2pt arcs is that they are not bound by their centre location. Draw 2 parallel lines, say 40mm apart and use 2pt arc to convex cap one end at 20mm radius- it should look like a rounded slot. If you now increase the radius of the arc to 30mm the arc becomes flatter but is still bound to the ends of the lines. That's great, you can now move the point where the arc and line intersect (within reason) and they stay connected, the arc's centre moves accordingly and the radius stays the same.

The problem comes when you want to place a 2pt arc on the end of the lines that has a diameter larger than the distance between the lines to form the shape of a keyhole. A 3pt arc is no good if you need to move the line ends as 3pt arc is bound by its centre and won't move in the right way.

I have however, found a way to do what I require that I don't think the developer is aware of, using 2pt arc by utilising a quirk in its use. Using the above example and ensuring the arc diameter is larger than the distance between the lines:- Deep select the arc and grab one end. Move straight towards and go slightly past the other (fixed) end of the arc. Now sweep back towards the original intersection point, keeping away from the lines whilst doing so. VOILA!! It should look like a keyhole! That's all I wanted but it could be a little easier to do.

I should add that when doing the above you might find 2pt arc is a little buggy. This has been mentioned in another thread though, so I assume is being attended to.

Thanks for your help.
Martin.
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billbedford  
#10 Posted : Sunday, November 23, 2008 4:34:06 AM(UTC)
billbedford

Rank: Senior Member

Joined: 2/19/2007(UTC)
Posts: 186
Why can't you use the Tangent Point Arc tool?
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blowlamp  
#11 Posted : Sunday, November 23, 2008 5:42:07 AM(UTC)
blowlamp

Rank: Senior Member

Joined: 6/28/2008(UTC)
Posts: 648
Hi Bill.
I gave it a go and although I can get the correct keyhole shape I'm after, I find the arc is bound by its centre most of the time. It also seems impossible to enter an exact radius whilst keeping the lines and arc connected.

Thanks for taking the time to help.
Martin.
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billbedford  
#12 Posted : Monday, November 24, 2008 2:25:46 AM(UTC)
billbedford

Rank: Senior Member

Joined: 2/19/2007(UTC)
Posts: 186
Originally Posted by: blowlamp Go to Quoted Post
Hi Bill.
I gave it a go and although I can get the correct keyhole shape I'm after, I find the arc is bound by its centre most of the time. It also seems impossible to enter an exact radius whilst keeping the lines and arc connected.


Sorry, but I think you are on to a loser here.

I would use a line rectangle of the correct width, but longer than I needed. Then I would draw a 3 point arc centred on the midpoint of the top of the rectangle so that the ends of the arc lie inside the recrangle. I would then remove the top of the rectangle and trim between the rectangle sides and the arc to get the intersections. I can then adjust and trim the bottom line of the rectangle to get the correct length.
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blowlamp  
#13 Posted : Monday, November 24, 2008 3:05:20 AM(UTC)
blowlamp

Rank: Senior Member

Joined: 6/28/2008(UTC)
Posts: 648
Hi Bill.
Check out reply #9, paragraph 3 in this thread, as I've found a work around.

Thanks again.
Martin.
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