!*!* DCG - Before and After!! *!*!

Jason_H

Hey guys, what are yous studying for DCG?

I'm hoping for interpenitration, perspective and oblique plane

Sxcshoes

I'm ready for pretty much anything bar certain points in conics that I need to brush up on. Positive bit is that I've a week between last and second last exam. What C-Section questions are ye guys doing? I'm doing road and surface geometry. Hoping for an A1

Ag_science2015

Hoping for perspective,co-ord geometry and my c options are surface and geologic geometry. what you expecting for short questions. skew lines appear regularly

ajguy97

Section A Skew lines prob , still have to look for any trends in it
Section B really hoping for axonometric and any question with dihedral angles
Section C probably doin surface geometry and dynamic mechanisms

dazzadazza

I love surface geometry. I also do structural forms and dynamic mechanisms. Im looking for an A. It's going to depend on what short questions we get. Fingers crossed.

liverpool1997

Anyone have any predictions

Ag_science2015

Hoping for skew lines in short questions

ajguy97

What do u guys think will come up in section B
Its sad to think that axonometric wont come up probably gonna have to suffer with interpenetration

examstress

Quick question :
When u are given th pitch of a surface , where do u go from there when u have to draw the elevation ? Can anyone explain this to me simply ? (If reference needed use 2012 c-3) would really appreciate it !!

Also what does determine the traces of the plane mean ?(with reference to 2010 b-3?)

I would be so grateful if someone could help me out !

ozymandiusm8

Anyone know how easy it is to simple pass on the part A's and B's of a question?
I never done TG and my teacher for the past two years was incredibly inept, which sounds like a cop-out but he seriously never taught me a thing, everything I know I learnt myself or from friends in the class but there's still a lot I can't grasp and unlike most other subjects it's difficult to find much aid online for DCG. I'm confident my project has gotten me at the minimum 20-25%, would it be much harder to get the last percent to push it up to 40%?

skewedfingers

Anyone know how to get the height of C and E for 2012 B3?

Solid_Shepard

examstress wrote: »

Quick question :
When u are given th pitch of a surface , where do u go from there when u have to draw the elevation ? Can anyone explain this to me simply ? (If reference needed use 2012 c-3) would really appreciate it !!

Also what does determine the traces of the plane mean ?(with reference to 2010 b-3?)

I would be so grateful if someone could help me out !

Okay, regarding the first part, the pitch of the surface is the angle the it's sloped at. In 2012 C-3, please see this image: http://imgur.com/iAzPvbu. Each line on the elevation is an entire surface in the plan in this example. To assist, I've colour coded, so you can see how this is. The white surfaces in the elevation are the black rectangle which encompasses the shape in the plan. We want to start off this drawing, so first, ask yourself what we know.

Look at what we need to draw. We know need an elevation, plan, the dihedral angle between B and E, and F knowing a dihedral angle. We're going to need a few auxiliary views here, so you need a good bit of room.

In any DCG question, the first thing that you need to draw are boxes, boxes which will contain the entire elevation, plan, and if needed end view. With these, you'll know that your drawing fits on the page, and you'll easily know if you've gone wrong if it goes outside your box.

So, Start off by drawing a light horizontal line the entire way across the page, which will contain the bottom of your elevation. Somewhere here, draw a light vertical line the entire page. This will be the extreme left of your elevation and plan. What do we know from these two lines? Well, we know they'll contain the height of the drawing, the length of the drawing, and the width of the drawing. We also know the width is 9 metres (90mm), and the length is 220mm. We do not know the height. So work with what we know. Drop down ten millimetres and put a pencil mark, drop three millimetres and put a mark (these will be for any text), and drop ten more millimetres and put another pencil mark for the top of your plan. We know the width is 90mm, so step down 90mm and put another mark. Do we know anything else about the drawing at this stage? We do, but nothing of use, so draw all of your horizontal lines first (from the marks which are along the vertical line) starting with the top (so it doesn't smudge the page), and then draw all your vertical lines, from left to right. These should obviously be light lines, and should extend heavily.

With what you have drawn, what do you have? Why do you need this? How will this be of benefit? If you're not doing the question with me, at this stage you have a rectangle that will contain your entire plan. You don't have the height, so you can't get the box for the elevation yet. Now, it's time to fill in the box of the plan given the measurements. Step down 20mm, 25mm, 15mm, 10mm, 20mm, and step over 70mm. Draw your lines.

You've the skeleton of the question, and you've everything which you know for a fact is correct down. Now it's time to look back at the question to see what else you can put down. A and C have a pitch of 60*, B and D have a pitch of 40*. Ask yourself, what could a pitch possibly be? Look at the elevation and plan you have what do you think it could be? Please do not read the spoiler unless you've thought about it for awhile. Look at the drawing, consider what you're looking for, and what you have.

Pitch = The angle of the surface in relation to the horizontal plane
Side note: What does this definition actually mean? What is the horizontal plane? How do you know which angle it's referring to?

So, the pitch uses the definition above. Now, we need to know how to use this. Surface A is the yellow line in the picture above. If this surface is inclined at 60 degrees, it means that the entire surface is at an angle of sixty degrees to a horizontal plane. Do we have a horizontal plane? We do, in an elevation, any horizontal line is a horizontal plane, for example, the XY line. We know, for a fact, that A is from the bottom left of the elevation. We know this by what's given, and more importantly the plan, so draw a line at 60* here. The surface A must be somewhere on this line, because the line is at an angle of 60*, and A is at an angle of 60* to a horizontal plane. Similarly, at the 70mm mark in the elevation, we know that C starts here, so go 60* up right. C must be somewhere along this line. What else do we know? Well, we know B and D are at 40*. We know where D meets the horizontal plane because it's in the plan, and the bottom right of our elevation. So from here go 40* up left. It has a pitch of 40*, so it must be contained on a 40* line in the elevation (think of looking down on a cereal box when the side is the elevation: if you look down on it when it's standing up correctly, you see a rectangle. When you start tilting it, looking down, you see a larger rectangle as it's tilted more and more, but you can only see how much it's angled against the horizontal when you look at the angle from ninety degrees). What happens? the lines C, and D, intersect. We now know where the surfaces intersect. Draw a light horizontal and vertical line from this point! Now we just need B. What do we know? We know B and D are contained on the same horizontal plane (they're the same height). We know that B ends when it intersects with surface A. Therefore we know that when this horizontal line meets the 60* line containing surface A, that this is the end of surface A, and it also is a point/line on surface B! So what do we know now? We know B is inclined at 40* to the horizontal, so go down 40* (to be specific, it's 40* south of east). What do you know? This line contains surface B. Surface B intersects Surface C. We have Surface C. We have a line containing surface B. We have a point on surface B. Therefore, where this line meets the 60* line containing surface C, that's the end point of surface B! But wait! We have more! Because we're attentive, we see that the 70mm line, containing where Surface B meets the horizontal plane containing the XY line, also contains a point on Surface E in the plan, so mark where this meets the line B and draw a horizontal and vertical line because it'll be important later! But wait! Where this horisontal line meets D is also an important point as we see in what we're given, because it's a point containing F, so mark this too and bring it horizontal and vertical.

Now we've made good progress. Draw horizontal and vertical lines through any new points you have! Now we focus on the plan. Because we have where surfaces A and B meet, we have that line on the plan. Because we have where C and D meet, we have that line on the plan. We can put in a little more detail on the plan, but first, let's ask what we have, and what we need. We have A, we have B, we have C, we have D, we don't have E, we don't have the little rectangle intersecting E on the plan, we don't have F, we don't have the bit behind F.

The rectangle behind E is interesting. We know that in the elevation, the line of intersection between E and the rectangle is horizontal. We also know it is horizontal in the plan. If a line is horizontal in the elevation, then the line in the plan is a true length. This means that by bringing across the point where the 70mm line meets B until it hits C, and bringing down both, into the plan we have the entire line of intersection in the plan, (because we also know that this line of intersection is down 20mm). Now in the plan we have a point containing E and the line of intersection, and we can connect these to get E in the plan (NOT THE TRUE SHAPE OF E THOUGH) and we can also connect the lines in the elevation to get it in the elevation. While we're working on E, we know we need to get the true shape. How do you get the true shape of something? What do you know about the true shape of any surface?

For flat surfaces: To get a line view of a surface, you need to look along the true length. This is intuitive, if you look along something that's not a true length, that line is at an angle in some way, so when you look along it like this it's going to be of little benefit. When you look along a true length though, you know that that line will be represented as a dot in the next view, and the entire surface will be a plane between that dot and the end of the surface.

To get a true shape of a surface, you need to look perpendicular to a line view of the surface. This is because it isn't at an angle tilted away or towards you in any direction. You're looking directly at it and everything is a true length and angle on the surface

From the true length in either the I like working in the plan, extend this to the left or right of your plan and draw an auxiliary elevation (EASY TO REMEMBER: If you project from the plan, it's an auxiliary elevation and you take measurements from the elevation. If you project from the elevation, it's an auxiliary plan, and you take measurements from the plan). When you project the surface E, you'll get a line view. Then, go at 90* from this to get the true shape. Done.

Now, what do we have, and what do we need? Well, we have A, B, C, D, and E, but not F. We have a point on F. We have the dihedral angle between D and F. We know that the dihedral angle is the angle between both surfaces. We have two points on the line of intersection D and F. We do not have the true length of the line of intersection of D and F. So, what do we do? We need to get the true length of the line of intersection. Looking along the true length of the line of intersection between two planes will give you the dihedral angle (think about it: if you look along the true length of a line on a plane, you get a line view of the plane. If you look along the true length of a line which is on two planes, you get a line view of both planes). If you want the true length of something, you have to look at it at 90*, so in the plan, do that, go 90* to the line of intersection between F and D (it's the bottom left line on the triangle).
NB NOTE: Here we can do something clever. You can take the entire surface D, or you can do something really witty. D is a surface. That means you can take planes from it which will have the same dihedral angle. so, if you make a triangle on surface D, say this: http://i.imgur.com/NspG9Yg.png (the blue triangle, I've labelled the points) it'll be easier to bring the points up.
Then it's just a matter of auxiliaries. Do your auxiliary elevation looking ninety degrees at the line of intersection in the plan to get the true length of this line. Then look along that to get an auxiliary plan showing you the line view of D and F. Use the information you have regarding the dihedral angle to draw surface F, and keep bringing points on surface F back to find F and finish the drawing in light. Finally, draw the drawing in heavy, label the XY line, X2Y2 line, X3Y3 line, and so on. Also put in labels stating "Elevation" (when you went down ten three ten, between the ten and three line you can write elevation, go do the same at the bottom of the plan), mark in A, B, C, D, E, and F, and label what the true shape is for full marks on presentation.

In general, your approach to a DCG question should be
Step 1. Determine what you will need to draw in the question, and how much space it will probably take.
Step 2. Set up your box for your elevation and plan (if relevant, an end view too). Start with the horizontal plane (the XY line). Then put in a vertical plane (a vertical line that'll be the extremity of your elevation). On the vertical line, step up the height, then from the horizontal line again, step down ten, three, ten, and then the width of the drawing. On the horizontal line, step over the length.
Step 3: Fill in the boxes using all of the measurements you have. Mark down all of the measurements at the exact same time, then draw lines through all of the points.
Step 4: With all of what you have down, assess what you have.
Step 5: Ask yourself what you know, and what the question is asking you to do.
Step 6: Again, ask yourself what facts you know about the question.
Step 7: Look at the question for any further information once every measurement is down.

I might go through the plane question later, but for now, the traces of the plane are where the oblique/simply inclined plane intersects the ground horizontal and back vertical plane on your elevation and plan.

Note, always take a systematic approach; it'll speed you up immensely. Put on all of the measurements you can at the exact same time. Next, draw all of the horizontal lines you can starting from the top. Next, draw all of the vertical lines you can from left to right. This will save you so much time in moving the equipment, and you'll become automated in how you start up a question. If you put down a measurement, draw a line, put a measurement, draw a line, etc., you're going to waste so much time, and time is your biggest enemy.

Solid_Shepard

skewedfingers wrote: »

Anyone know how to get the height of C and E for 2012 B3?

Consider what you have, something like this I believe: http://i.imgur.com/v0QLvAa.png (I just sketched it). What do you know about the question?
You know they are two planes. You have the line of intersection BA (not the true length). You know point D is on the ground, and is on one plane. You know point C is on the ground, and is on the other plane. Therefore, you have two planes. Because you have the line of intersection already, you can find the true length of the line of intersection. Because you can find the true length of the line of intersection, you can get an edge view of both planes. Because you have the two points in the plan, you can bring them onto your auxiliaries. Because you can bring them onto your final auxiliary as a line view (you know their distance from the datum line in the plan, so you can get a line that they have to be on in that auxiliary. However, they must also be on the line view of the surface. Where the two lines intersect is your point, and then you bring them back onto the previous auxiliary to get their height in the elevation), you can get their height (remember, if you project from the plan, you have an auxiliary elevation, and you take heights from the elevation).

Rough sketch I just did of it: http://i.imgur.com/tovCyiT.png. It may come out slightly different for you because I didn't use any measurements, just sketched it, but that's roughly how to do it. DCG questions aren't generally done linearly (i.e. you do part a, then part b, then part c, etc.), you can only work with what information you have. Only become concerned if with all of the information you have there is no way to progress on anything.

EDIT: Apologies for the double post as I believe I was cutting close to the character limit in the previous and still have to update it with the solution to the Skew Line question

examstress

Solid_Shepard wrote: »

......

Thank you so so so much ! Will have a look at it in 5, studying economics atm. Im really grateful !

dazzadazza

Anyone know how to get the door in part c of 2012 c-2? I know it's a hyperbola but there is no rectangle to put it in.

dazzadazza

How did everyone get on in the paper? I though the higher level paper was beautiful. I left out a whole part b of a question though due to not seeing it until the last minute. (The Pringle question). I'm expecting an A2/B1 because of that.

Chickennuggets

Was that test really easy or did I get everything wrong

Doctorhopeful

Absolutely delighted with that exam, couldn't have gone any better. Did all the short Qs (actually managed them for once :P ) B-1 B-2 C-1 C-2, and i'm in confident in all finished with about 45 minutes left to have a good look over, considered doing the perspective too but passed on it. Finally one exam went really well haha!! Did everyone else find that really accessible?

dazzadazza

Doctorhopeful wrote: »

Absolutely delighted with that exam, couldn't have gone any better. Did all the short Qs (actually managed them for once :P ) B-1 B-2 C-1 C-2, and i'm in confident in all finished with about 45 minutes left to have a good look over, considered doing the perspective too but passed on it. Finally one exam went really well haha!! Did everyone else find that really accessible?

What did you do in that Pringles question for part c? Where it asked for the curvature of the surface when intersected by a vertical cutting plane?

Bah_Humbug

In the Skew Likes Q what did people get for the true angle between the horizontal line and the VP?

ajguy97

That was an ok exam
I did all short qs

B-1
B-2

C-3
C-4 (a) (b)

and i think i got an A1 there well it all depends on the project now

Doctorhopeful

dazzadazza wrote: »

What did you do in that Pringles question for part c? Where it asked for the curvature of the surface when intersected by a vertical cutting plane?

1. Went perpendicular to the slice in the plan

2. Drew lines through each element that crossed the slice in the plan, perpendicular to the slice. (the elements overlapped perfectly on the line)

3. Took the heights of where each element crossed the slice in the elevation (once again the elements overlapped perfectly)

4. Marked out the heights i measured on the corresponding lines that i drew in the plan

We did a similar question in class, simple enough if you know it (now wait for someone to tell me i actually got it wrong lol :P)

Bah_Humbug wrote: »

In the Skew Likes Q what did people get for the true angle between the horizontal line and the VP?

The short Q? Wasn't too sure about that, I got 58°. I did all 4 though so i have some leeway thank god

Hydrocerium

Paper was quite nice but I did preetty bad
Only was really able to attempt one of the short questions and spent ages trying to figure out the others. Started B-2 but didn't finish it. Did C-4 which I actually managed to get all done and then did C-5 but didn't get to finish it fully.
Was going to do B-3 but I didn't have enough time.
Was around 10 minutes late too haha

Hon the Dubs

Honestly didn't seem a hard paper for anyone who was prepared
Pity i wasn't... :pac:

eman129

does anyone know how many marks the part c of that structural forms question would be worth? I completely skipped it by accident and only realized now after reading this thread

dazzadazza

eman129 wrote: »

does anyone know how many marks the part c of that structural forms question would be worth? I completely skipped it by accident and only realized now after reading this thread

I skipped it by accident too. Hopefully we only lose like 6 or 7 marks.

Farmer1234

Anyone wish to hazard a guess at how many marks I'll lose for getting the Aux. VP wrong in the perspective question? I joined S to VP1 and went at 35 degrees off S, but I accidentally joined them where VP1 goes perpendicular to S so it hits the horizon line. Just hoping I don't lose enough marks to take the A1 off me, thanks.