Architectural Details and Ornaments

[Laurence Finston]

I had a couple of ideas regarding the plaster slab: In order to prevent the plaster from sticking to the bottom plate of the spring form, I could pour in a thin layer of wax. This would also serve to cover the rim of the bottom plate which causes the cast to have a sudden change of diameter.

One way to do this would be to pour some wax into the form while the latter is in a basin filled with sand, to prevent the wax from leaking out. Then, after it's hardened and the bottom of the form is sealed, I could take the form out of the sand and pour a little more wax in, which would then be level.

However, yesterday I looked for and found my level and also went to the building supply store and picked up some shims, so I could try getting the form level while it's in the sand basin. I'm curious to see how this will work.

If I add a layer of wax, I will no longer know in advance what diameter the surface of the plaster cast will have. I have therefore revised `center_finder.mp' and `center_finder.txt' so that they produce plans for center finders in increments of .25cm. The plans for circles with diameter < 16cm are now arranged with two on each page.

[Laurence Finston]

I transferred more of the drawing to the plaster slab. However, the latter is still giving off a lot of moisture and is still somewhat soft so I will wait until it dries and hardens completely before doing any more.

I figured "in for a penny, in for a pound" and changed `center_finders.mp' and `center_finders.txt' so that the circles are in increments of 1mm (from 100mm to 290mm). I've attached the updated PDF file.

[Laurence Finston]

Started transferring the pattern to the plaster and wood blocks. I decided to extend the pattern to the edges of both blocks.

The next thing to do is to patch up the plaster block with spackle. There are a couple of places on the surface close to the edge that need this.

[Laurence Finston]

I wasn't satisfied with increments of 1mm for the center finders so I've made a version with increments of .25mm.
I've made a new "Technical Drawing" webpage and put the source code and the generated PDF file there (DIN A3 portrait): The GNU 3DLDF Technical Drawing Page

The PDF file now has 642 pages so I didn't want to upload it here.

Of course, it's not really possible to cut circles out of cardboard by hand with a tolerance of .25mm and probably not with a cutting plotter, either, unless there are high-precision, industrial versions of these machines. I don't know what the minimum would be for hand cutting. My guess would be between 1 and 5mm.

My guess is that if anything like this would ever be needed, it would be stamped and out of metal, not paper, and would cost a fortune to get set up.

I think it would be good to make versions for circles of diameter < 10cm, but I would probably have to change the guidelines and crosshairs to account for the smaller size.

[Laurence Finston]

Originally Posted by Laurence Finston

I think it would be good to make versions for circles of diameter < 10cm, but I would probably have to change the guidelines and crosshairs to account for the smaller size.

It occurred to me that this isn't necessary, at least for a selection of sizes.

The radius template is nice, because the circles down to 2.5mm radius, have holes in the middle for the pen point (.5mm).

There's even a template for isometric ellipses.

I don't know if all of these templates are still available. It seems like a lot of these products have been discontinued. For plain technical drawing they're obsolete, except possibly for teaching purposes, but for transferring drawings to fine paper or working in wood, plaster or other materials they are still very useful, as well as being aesthetically pleasing.

[Laurence Finston]

I repaired the edges of the plaster slab with spackle. It needed two coats. When it was dry, I scraped off the excess with a chisel. Then I finished transferring the drawing using the stencils.

After all of the tedious preparation, I've gotten to one of the fun parts, namely carving out the pattern, and made a start.

The alabaster plaster carves very nicely, more easily than the linoleum or the lindenwood. It has no grain and the particles are so fine as to be unrecognizable. I'm pretty sure the slab isn't cracked anywhere and so far, I've found no air bubbles or even pores. It doesn't split, as linoleum tends to do.

I don't have quite as many tools for carving in plaster as I do for wood. In particular, I don't have any chisels or gouges with blades less than 2mm in width for plaster and I don't want to re-dedicate the ones I have for wood. Of course, I could hone them, but I think they'd never be the same and I just plain don't want to do this. When my tool budget allows, I'll buy ones for plaster.

Of course, I always use a dust mask when carving plaster and, like clay, plaster and drains don't mix.

[Laurence Finston]

I was out of town for two weeks so I couldn't do any work.

I made a start on carving out the plaster slab. At first, it was hard to distinguish the white surface with the equally white carved out parts but now the pencil and chalk marks have smeared so much that that's not a problem anymore.

I'm using pencil to reinforce the lines, which needs to be done constantly, and chalk to mark the carved out parts. I think it will be easier to get rid of the chalk marks than the pencil marks at the end and I don't want either to stain the paper, when I get to the embossing stage.

I'm carving a little deeper than would be needed for embossing because I want to make a positive plaster cast in order to try printing from it and to make it possible to make additional plaster negatives.

The carving is very enjoyable. Plaster is a wonderful material, chemically identical to the gypsum from which it originally came. You couldn't come up with a material with better working properties.

The little black and red bellows is a piece of photo equipment for blowing dust off photos.

[Laurence Finston]

Finally finished transferring the pattern to the lindenwood block. It was extremely tedious and now I can't wait to start carving.

It would have made it much easier to have made a stencil for the full block, but I had originally planned to use only a small part of it.

[Laurence Finston]

I originally made the graphic with the pattern from the Alhambra from page 207 of Owen Jones' book using MetaPost. The reason I used the latter rather than 3DLDF was because I used a feature of MetaPost that I haven't implemented in 3DLDF: The wavy lines are done using "hints" to the program that indicate what direction of the paths at particular points. Around the same time, I was working on a way of achieving this effect by calling MetaPost from within 3DLDF, but it may not have been finished at the time I made the graphic. Or I may have just felt like using MetaPost, I can't remember.

At any rate, it was always my intention to convert the MetaPost program to 3DLDF in order to be able to use the pattern in 3D graphics. I've now done this. I plan to add more units and a rectangular border, but it's time to take a break.

The first image shows the pattern (5 units) in parallel projection onto the x-y plane. The second image shows it in perspective, lying in the x-z plane with the focus at the position with the coordinates (0cm, 10cm, -20cm) and pointed in the direction (0cm, 10cm, 10cm) and at a distance from the plane of projection ("picture plane") of 20cm. The image is then scaled down slightly in the original PDF file, but I have no control over what size it's displayed at here. The third image shows the pattern in a plane parallel to the z-y plane but shifted by -10cm and using the same focus.

This may be useful to anyone who wants to redecorate their house in the style of the Alhambra.

[Laurence Finston]

I've attached the source files, alhambra_207_1.ldf.txt and alhambra_207_1.txt. The former should be renamed to alhambra_207_1.ldf. The forum software won't allow files with the extension "ldf" to be uploaded. The same applies to alhambra_207_1.mp. This file contains the original MetaPost code.

It's fairly straightforward to convert MetaPost to 3DLDF and the differences may be instructive:

1. In MetaPost, points in 2D space are represented by the data type `pair', which doesn't exist in 3DLDF. The corresponding data type for 3D is called `point'.

2. The operation `point x of y' (where x is an integer and y is a path) doesn't work in 3DLDF because point is a data type, as just stated, and the name can't be used for an operation as well. The corresponding operation in 3DLDF looks like this: `get_point x y'. However, if x is a (numeric) variable, it must be surrounded by parentheses, e.g.,
`get_point (i) q'. The word `of', which is just "syntactic sugar", isn't needed in 3DLDF.

3. In MetaPost, rotation without any qualifiers is about the origin in the x-y plane. The operator `rotatearound' may be used with a `pair' argument for rotation about another point. In 3DLDF, rotation without qualifiers is rotation about one of the main axes, i.e., x-y, x-z or z-y. Rotation about one of these axes must be specified by a list of two or three numbers (or numeric variables), surrounded by parentheses, along with the angle of rotation. Rotation about a different axis can be specified using two points or a linear path.

4. In MetaPost, labels can be typeset using TeX in two ways, either with btex ... etex or TEX(...). The latter method makes it possible to include string values resulting from evaluating string expressions whereas the former only accepts raw text. However, using TEX(...) is quite slow so it's not suitable for programs that generate a lot of labels.

In 3DLDF, labels are always typeset using TEX and all evaluation takes place within 3DLDF, so the label commands accept either raw text inside double quotes or any `string expression'.

5. Some arithmetical expressions might need to be rearranged in 3DLDF. I wanted to give an example of this but I just tested it and what I thought didn't work, actually did.

So it's normally not very difficult to convert MetaPost to 3DLDF and in this case it didn't take very long.