I can see it in my head. I just can't see it in real life.
If there's one common difficulty the plagues the process of creating a new design, it must be that of visualizing ideas that exist only in the imagination.
For most of us, it's simply hard to see what isn't there yet.
One of the best ways to form a mental image of an idea or design is by drawing. Not everyone thinks they can draw, but the skill of drawing can be learned. Even the simplest drawings will be a great help in learning how a finished design might look.
If the general shape of your design is somewhat rectangular, it's fairly easy to sketch a view looking straight on at the object. If you like to use graph paper, you'll be in good company; but with the purchase of an inexpensive architect's scale, you can do without it, and you will be able to see the finished drawing without the graph lines.
Place a dot near the lower left corner of a sheet of paper. Place another dot above it, at a distance that corresponds to the scaled measurement of the height of your design. Now place a dot to the right of each of these, at distances that correspond to the scaled width of the design. Then just connect the four dots. Here's a good technique:
Place the tip of the pencil on one dot, but don't look at it; instead, keep your eye on the next dot as you move the pencil toward it. Continue connecting the dots, always looking at the dot you are headed for rather than at the pencil. Let your arm complete the movements by itself. You can practice this technique on scrap paper, just randomly placing dots on the page and then connecting them. Do it at all angles: up, down, right, left, and diagonally; soon drawing a straight line will become more natural.
It helps the eye and hand learn to work together -- plus, we all loved dot-to-dot games as children.
Once your four dots have been connected, you have drawn a properly scaled rectangle with proportions that are identical to those of the design. Often this is enough by itself to identify the general shape, and begin to get a sense of whether it matches your mind's vision.
A view of the design straight-on like this is commonly called an elevation, and you've just drawn the front elevation. By the same method of measuring and drawing, the side elevation is easy enough to produce, and by convention it is usually placed to the right of the front elevation.
These two views together display enough information about most designs to do the trick, but the plan view, or view from above, is also helpful to sketch. (In some designs, such as tabletops, this would actually be the more important view.) This can be drawn the same way, and is usually placed above the front elevation on the page.
Of course, some designs--such as a kitchen full of cabinets, or a piece of furniture with multiple components--can best be represented as a group of rectangular shapes. In this case, draw each individual rectangle in the approximate positions they will occupy in the design, making sure each is the correct scaled size.
The inside of the rectangle or rectangles can be filled in with the details of doors, drawers, shelves or trim using the same scaling and drawing skills. The dimensions of some of these details may not be known yet, but that's what the drawing is for. If the proportions don't look right, erase or start over with different dimensions and try it again.
Orthographic drawing is a way of combining two-dimensional drawings to produce a three-dimensional view. Here, the three separate views of front elevation, side elevation and plan view are joined into a single drawing. The point where the three views meet is made of three 120-degree angles; the resulting composite represents the object as viewed from the corner. It can be a quick way to spot shapes and forms that don't look right from an angle, even though they might look great in the all of the two-dimensional views.
To construct it, draw three lines radiating from the center of the page, each 120 degrees from the others, that form a "Y". Then, scaling from the central point, draw one of the three views as a flattened rectangle in between each pair of lines. Measure the height down from the center point on the vertical line, measure the width on the right-hand line, and measure the depth from the center point on the left-hand line. Each view will share two lines with the other views. To find the fourth point of each of the three views, measure out from the two adjascent points on the line.
By changing the placement of the measurements on the three lines, the drawing can be made to represent a view from any of the eight corners. For example, the drawing shows a view from the top left front corner; by exchanging the width and depth lines, the drawing will show a view from the top right front corner.
Again, fill in the details, this time on all three views.
This type of drawing has the advantage that it is all correctly scaled: any measurement of the drawing will accurately represent the dimensions of the piece. But it does have a disadvantage: to the eye, it appears somewhat distorted. Objects in real life have the property of perspective, or a change in apparent dimension with increasing distance from the observer. You can apporoximate this look by using perspective in the drawing.
In the case of the orthographic view, the addition of two vanishing points at the sides of the page will enable you to draw a roughly accurate perspective drawing.
Begin with the same "Y" as for the orthographic drawing. Measure the height on the vertical line, the width on the right-hand line, and the depth on the left-hand line, just as you did in the orthographic drawing. This time, instead of meeting the lines at 120-degree angles, complete top two lines by joining them to the right and left vanishing points. Now as you draw, all the vertical lines will remain vertical, but all the lines representing the width of the piece will point toward the right-hand vanishing point, and all lines representing the depth will point toward the left-hand vanishing point.
Measure from the center point to define the height, width and depth as you did with the orthographic drawing. From that point, though, you cannot measure: you must simply orient each line towards its corresponding vanishing point: vertical for height measurements, right-hand point for width measurements, and left-hand point for depth. Since the dimensions appear to shrink with distance in such a drawing, the dimensions will change at different points on the page. This makes it a useless tool for conveying accurate measurements, but the resulting drawing will look much more realistic.
Placing the drawing higher on the page in relation to the vanishing points creates a view that appears lower on the piece, and vice-versa.
Moving the drawing to the right on the page will make the view appear to be from farther to the left, and vice-versa. Moving the vanishing points farther from the center makes the drawing appear to recede. (Actually, a good view is usually achieved by placing the vanishing points well off the page to the left and right. This requires a large table surface and a straightedge.)
Have fun with drawing!