Geometrical Problem Solving?

[Strix]

Ok, thanks

you didn't answer my question :wink:

 

do you know what the construction lines are there for?

[dbroada]

BTW Spider, both me and DB do electrical schematic draughting so we've both got an excuse for not doing 'proper' drawings :wink:

while that is true my apprenticeship and training was actually mechanical and spent on a drawing board.

[Strix]

Try this

Project const lines up from the end of the 017 dimension to the 15R circle;

draw an arc Start, End, Radius from the intersection of the circle and the const line to the 017 line with a radius of 12.5

are you defining that 'end' with a TANGENT snap?

[lpseifert]

are you defining that 'end' with a TANGENT snap?

Nope. The arc and circle aren't tangent using my method (close tho)... Upon further review I don't believe there's enough info on the image to draw it correctly if the intent is to have the arc and circle tangent. Maybe I'm wrong...

[Strix]

if the smaller circle HAS to touch two other elements, then that's as much info as you need lpseifert - you just need to decide how to position it

 

I would just have thought there'd be an ACAD method of positioning it rather than using the OFFSETs of the other two elements

 

(there's another command which may be useful Spider :wink: )

[lpseifert]

Nope. The arc and circle aren't tangent using my method (close tho)... Upon further review I don't believe there's enough info on the image to draw it correctly if the intent is to have the arc and circle tangent. Maybe I'm wrong...

I take that back, there is a way... good thing the boss is Mr. BigPockets.

It involves drawing a R12.5 circle tangent to the R15 circle; draw a const circle center of R15 circle thru end of 017 line; rotate reference R12.5 circle. Illustrations would be an easier way to explain if anyone's interested.

[Strix]

yes please

[lpseifert]

Colors got mucked up in the translation

[eldon]

What tells a draughtsperson to draw a "construction circle" with r27.5, and another construction circle with r12.5, on the far RHS of the horizontal line?

 

What you are trying to do is to find the centre of a circle that is a) tangential to the circle R15, and b) passes through the right hand end of a horizontal line. From geometry the centre of a circle which is tangential to another circle is at a distance away from the first circle equal to the radius of the second circle. Hence you draw the circle of radius (15 + 12.5) = 27.5, and you know that the centre of your required circle is somewhere on that. Also you know that for a circle to pass through a point (end of line) the centre of that circle is a radius away, so you draw a second construction circle on that end point. Where the two circles intersect is the required centre point. (The circles intersect in two points, but you chose which intersection gives the required result).

 

I would draw things slightly differently.

1) line 17 long

2) line from mid pt of 17 line, 30 upwards

3) circle R 15 from end of 30 line

4) offset this circle 12.5 outwards

5, 6, 7 & 8 ) circle R12.5 from each end of 17 line

9) circle R12.5 centred on required intersections

10) offset the 17 line by 44

11) erase construction lines, and trim all unwanted bits.

The advantage of drawing the four circles of R12.5 together is that when you draw a circle with a radius, Autocad remembers the radius and the next three circles can be drawn very quickly without entering the radius.

 

I would say your tutor gave you an efficient way, but everyone sees the construction differently.

[Strix]

I think you may also have learned something else in this thread Spider...

 

... in AutoCAD, there's always more than one right answer :wink:

[CAD_Spider]

I think you may also have learned something else in this thread Spider...

 

... in AutoCAD, there's always more than one right answer :wink:

 

That's a good thing!

 

I'll have a go at some of these methods .... I was busy last night

[CAD_Spider]

I would say your tutor gave you an efficient way, but everyone sees the construction differently.

 

Thank you for your time, Eldon

 

The tutor insisted that I solved the problem his way. He would have failed me on the spot if I had done it any other way

[CAD_Spider]

Colors got mucked up in the translation

 

Thanks anyway

[CAD_Spider]

you didn't answer my question :wink:

 

do you know what the construction lines are there for?

 

Yes .... to help position the objects that you are trying to draw

[CAD_Spider]

What you are trying to do is to find the centre of a circle that is a) tangential to the circle R15, and b) passes through the right hand end of a horizontal line. From geometry the centre of a circle which is tangential to another circle is at a distance away from the first circle equal to the radius of the second circle. Hence you draw the circle of radius (15 + 12.5) = 27.5, and you know that the centre of your required circle is somewhere on that. Also you know that for a circle to pass through a point (end of line) the centre of that circle is a radius away, so you draw a second construction circle on that end point. Where the two circles intersect is the required centre point. (The circles intersect in two points, but you chose which intersection gives the required result).

 

This is precisely what I wanted to know . It's as clear as day ... staring me in the face

 

I've worked through everybody's examples, and I understand them. Thank you for your time!

[Strix]

Yes .... to help position the objects that you are trying to draw

or more specifically - the smaller circle - which is why all the 'maths' is equal to the radius of said circle

 

Your tutor sounds like the ones I fell out with at Poly

 

The department head (who was the youngest tutor in that subject) brought me into the office at the end of the year and sat me down for a chat

 

It was strange - wayward students are supposed to get a talking to, but he wanted info from me!

 

I'd taken the course I had as I wanted to be a designer, so 'engineering design' should have been my favourite subject, but these guys were making it hell by doing what your tutor is doing - refusing you room for working things out for ourselves, creativity, etc, and it was sucking the enthusiasm out of the whole course group

 

The department head was also involved in Institute projects outside of the Poly, and was dismayed at the transformation which was taking place - it was evident that secondary school children were more creative an innovative than those in higher education - so what was higher education doing to bash this innovation out of students?

 

He wanted to know what my analysis of the course was and where I thought it could be improved!

 

Anyway - for now - do as your tutor says, get your marks, and we'll see you back here if you really want to lean how to draw :wink:

[skipsophrenic]

I remember that "Practice" drawing from college myself - wish i knew about cadtutor back then, it took me an 3 of my m8's 2 days to figure it out (no sleep)

[CAD_Spider]

I remember that "Practice" drawing from college myself - wish i knew about cadtutor back then, it took me an 3 of my m8's 2 days to figure it out (no sleep)

 

The college should explain the geometrical concept of the problem, but oh no .... let's make things awkward for the students .

[skipsophrenic]

true true, but at least now u know it's do-able.