# circumference staying the same on shape change in a software???



## MadKad (Oct 2, 2008)

Hi

this is probably the strangest question you may have seen, but I need to ask some one and I thought that some one on here might no 

OK I need to know if there is a softwere that I could say place a 10mm circle image and then change its shape to any shape I want but still keep the overall circumference the same.

 ??? :-[ I use Alibre and photoshop 7 but don't think they do it (could be wrong)

I am at my last straw on how I could do this lol

Thanks,

Karl.


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## firebird (Oct 2, 2008)

Hi Karl

Do you mean like this?







Start with a circle (the top one) then change its shape like the next two. I'm no CAD expert but if thats what you are after I did this on Coreldraw.

Cheers

Rich


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## BobWarfield (Oct 2, 2008)

I'm assuming he wants to look at that circumference like a length of string that is fixed, and if you deform the string it doesn't grow longer or shorter.

I can deform the circle similar to what Rich shows in Rhino, but I don't see a way to preserve the "total length of the string".

Best,

BW


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## Bluechip (Oct 2, 2008)

Hi

I wouldn't bother .. even if you deform a circle to something approximate, ie. an ellipse, a squashed circle, it gets really out of hand.

Try this http://home.att.net/~numericana/answer/ellipse.htm#exact

Sooner you than me : :

Dave


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## mklotz (Oct 2, 2008)

What are you trying to do that raised this question?


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## Maryak (Oct 2, 2008)

Just a thought,

What if you convert your circle to a polyline/polygon with xxxxxxxxxxxxxxx?? sides


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## Tin Falcon (Oct 2, 2008)

The ratio of a pumpkins diameter to its circumference is .........
Marv is gonna love this one ...
*Pumpkin PI* ;D
Tin


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## mklotz (Oct 2, 2008)

Tin Falcon  said:
			
		

> The ratio of a pumpkins diameter to its circumference is .........
> Marv is gonna love this one ...
> *Pumpkin PI* ;D



Yes, and a pizza of radius "z" and height "a" has a volume given by:

pi * z * z * a


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## Tin Falcon (Oct 2, 2008)

> Yes, and a pizza of radius "z" and height "a" has a volume given by:
> 
> pi * z * z * a


Love it Marv
Actually in this part of the country Pie r rectangular (Tasty Cake Pies)
Tin


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## MadKad (Oct 2, 2008)

*Firebird *thats right but with what 

*BobWarfield* said ie. the string needs to stay the same, like a squashed circle this still keeps the circumference over all and is right in what I ment to say lol.

*Bluechip*, thats the maths side of it and confuses the hell out of me lol
*
mklotz*, it because I make jewellery like this:

round: http://cn1.kaboodle.com/hi/img/2/0/0/e9/d/AAAAArwi-ZYAAAAAAOnWog.jpg

but want to do shapes like these:
teardrop
http://cn1.kaboodle.com/hi/img/2/0/0/be/0/AAAAAgnfRPoAAAAAAL4Kwg.jpg
http://www.tajarts.co.uk/shopimages/products/thumbnails/HSPth.jpg
http://www.tajarts.co.uk/shopimages/products/normal/HTP.jpg

But these go in the ear lobe, and lets say they have a round one at 10mm and 31.4xxxxxx circumfrence, well the teardrop one would need to have the same circumfrence (the square or any other shape with straght sides is easier)

*Maryak*, sorry I dont understand what you mean? 

lol and you others are mad


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## zeusrekning (Oct 2, 2008)

Cool Karl, But I bet a bunch of old farts are thinking... "WTF?"
 :big: :big: :big:
I love the old guys just givin em hell.
I have never seen the shaped ones. I used to have a zero gauge (I think) in my ear but got to be a pain. I couldn't keep up with the rings and had to use other stuff. What materials are you using?


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## MadKad (Oct 2, 2008)

zeusrekning  said:
			
		

> Cool Karl, But I bet a bunch of old farts are thinking... "WTF?"
> :big: :big: :big:
> I love the old guys just givin em hell.
> I have never seen the shaped ones. I used to have a zero gauge (I think) in my ear but got to be a pain. I couldn't keep up with the rings and had to use other stuff. What materials are you using?



They are probably thinking its not right also lol

I use

Acrylic
woods (only the safe and all have warnings)
Delrin
PTFE (virgin)
Serg steel
and my best Titanium (nice and safe)

I will use all other organic items also, if the customer knows what they are doing and asks for something (like a wood) as long as they know how there body works and I warn of the some small risks involved then I will use what they like (if its safe and its OK with there body)


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## BobWarfield (Oct 2, 2008)

This old fart is thinking much as I hate either piercings or tatoos I sure hope my kids choose the piercings.

Wince,

BW


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## Maryak (Oct 3, 2008)

Scratch my previous thought :

How about a backwards approach i.e. draw the teardrop first, work out he total length, which should be the circumference of the circle required.

See attached PDF

Hope this helps ??? ???

Bob 

View attachment Drawing2.pdf


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## Cedge (Oct 3, 2008)

Silly Tin man... Everyone knows pie are round.... cornbread are square.

Steve


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## MadKad (Oct 3, 2008)

Maryak  said:
			
		

> Scratch my previous thought :
> 
> How about a backwards approach i.e. draw the teardrop first, work out he total length, which should be the circumference of the circle required.
> 
> ...



Hi

thanks I see what your saying, I think  I will sit there trying to figure it out as I kind of have your idea.

for oval I think I have done it, I have added a pic with my idea


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## Maryak (Oct 3, 2008)

Sorry but your a little off

Circumference of circle = 31.42 mm
Circumference of oval = 33.41 mm - To get a circumference of 31.42 with a minor radius of 2.5 mm, major diameter needs to be approximately 13.9334 mm, (How accurate do you need to be?)

You seem to be still trying to work forwards from the circle to the final shape.

Try and reverse this i.e. from the final shape to the circle.

Regards
Bob


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## MadKad (Oct 3, 2008)

wow you are clever, I was reading and got the math like this (I guess wrong lol)

10mm diameter x 3.14 = 31.4

bu doing this on a oval I cant work out how, I guess you use the radius also within the math, every were I look uses that algebra and that means nothing to me 

I suppose if i can figure how to get the circumference from the R and D then I can do it backwords like you say and show.

for how accurate, I have to be to the 0.05 of a mm in the size or closer lol


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## Maryak (Oct 3, 2008)

Gee, I wish that were true,   

I didn't do the math, the computer did it with my CAD software 

Just tell me the major and minor diameters or radii and I'll put George, (my computers name), to work on it. :

Regards Bob


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## MadKad (Oct 3, 2008)

Maryak  said:
			
		

> Gee, I wish that were true,
> 
> I didn't do the math, the computer did it with my CAD software
> 
> ...



lol that maths (10mm diameter x 3.14 = 31.4) works for me lol

I will give you a standerd size idea but size could be anything when I am doing it as it depends on what the customer wants lol

so tear drop 
the fat bit 10mm wide
thin bit (top) 5mm wide
full lenth 15mm

Is that what you ment for me to do?

also did you do that tear drop in the pdf in a cad software?

Thanks


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## Maryak (Oct 3, 2008)

Yes, all done with CAD, 

Attached PDF is your answer 12.54 mm diameter.

Regards and Spokonye Noche

Bob 

View attachment Teardrop.pdf


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## MadKad (Oct 3, 2008)

Hi mate, so could I do this my self in say Alibre? (is this what you used?)

also now that you have done that part can you alter it in sizes when ever you feel like it to get the circumfrence needed?

lol and sorry if you did that in Alibre could you show me how :-[ this is sending me potsy lol


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## BobWarfield (Oct 3, 2008)

Rhino3D will tell you the length of any curve. So, to get a teardrop or other shape sized properly:

1. Draw the shape.

2. Measure length with CAD.

3. Compare vs the desired circle circumference length.

4. Scale drawn shape to get to desired length.

Might take a couple of iterations, but ought to be straightforward.


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## MadKad (Oct 3, 2008)

are right mate, I will download it and take a look.

thanks


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## wareagle (Oct 3, 2008)

Gentlemen,

This topic has been locked.

This topic fails to reflect this forum's vision; that is model engine building in a home shop environment. Due to the exercise in complex calculations, I am leaving this topic visible.

Regards,
wareagle


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