Materials

Adhesives

This advice comes from a long series of failures: Use a spray adhesive (available arts/crafts stores, likely hardware stores too). If you are building flat slide rules with paper and/or cardboard it produces excellent results. I had less happy results using spray adhesive with cylindrical rules, but believe that to be pilot error, not a problem with the adhesive properties of the glue. The glue gets everywhere, and rolling the cylinder requires a bit of finesse.

Do avoid any full-on liquid glue (white glue clear "school" glues, e.g.). Your paper will surely stretch, buckle and bubble. I haven’t tried any paste glues, but suggest you keep away from them as well. It’s likewise wet, just thicker.

You can use rubber cement (a thin coat on both surfaces) . I do use that method today for all my testing. I'm not sure if just being careless but I do find it seems to lift on some prints after a period of time. The collective wisdom of the internet seems to be that this should be permanent.

I recommend that you coat the paper with a spray varnish or paper protector, available from craft or art supply stores. This has two effects. It helps waterproof the surface so that the paper will not expand or discolour when glued, and it keeps you from messing up the scales as you work.

This technique may not work on scales printed on CDs! I have found that my paper protection spray did a fine job of dissolving the scales printed on a CD. I would expect there are formulas that will work; I suggest that you test it out first.

Cardboard

Cardboard materials are great for stiffening a paper slide rule scale. If you are making your own slide rule using printed scales, the extra rigidity usually gives a good result. For the casual maker, any type of cardboard found at home will almost certainly be fit for use.

If the material is too thick, it becomes difficult to cut. The ideal would be something that sturdy scissors can cut through. For the Sexton Omnimetre prototype, I used some artist mat board (2. 75 mm/0.108 in thick). Mat-board is that stuff used to put a border around paintings. That led to a very ragged circumference, easily observed in the photo. That's because Mat-board is generally cut with specialized tools.

If the material is too thin, cardboard is subject to too much flexing. For the Sexton Omnimetre, I used 1.5 mm cardboard from the back of a writing pad to back my inner scale. That was much easier to work with - about the right thickness.

In fact, I recently found some nicely dense material of 2 mm t thickness at an art supply store. I found it too thick to cut with scissors, but thin enough to be worked easily with a blade from an 'exacto knife'. I used it as the base plate for one of my models.

Foam-Core

This is a material I use a lot for prototyping. I suppose foam-core is a modern substitute for styrofoam. It is a lamination of two layers of heavy paper surrounding a foam core and comes in a variety of sizes, and is available at hobby stores.

The kind I buy is a bit larger than a printed sheet of paper. I test circular models by gluing a printed page onto a page-sized foam-core piece. I use a push pin through my cursors and the foam core, to check that the scales with the cursors are correct.

Push-pins often are not enough for testing purposes, because a lot of cursor bodies are too narrow to have enough friction to naturally lock them together.

When that happens, I can easily trade up from a push pint to a small bolt, washers, and nuts. Foam-core is very soft; it's easy to widen holes.

Wood

Any paper representation of circular SR would work well on a wood backing.

Had I any woodworking skills, I'd have been making and using them ages ago.

Recently, I hit the internet for the various ways one makes a circle from wood. The usual prescriptions either to drill a pivot hole for the center and rotate the piece through a stationary cutter or say OR put the cutter in a jig and run it around the circumference. I made my own jig for that. It failed miserably, so I bought a commercial version and failed with that one, too. I decided to give up and search the internet for a ready-made solution.

It turns out that these days you can buy 1/4 inch disks from Amazon in useful sizes: e.g.:, 8, 10, 12 inches. I would prefer 1/8 inch (3 mm), but I don't see that on the market yet.

I found them accurate easy to work with. You need only prime the surface before gluing onto it.

Paper

Generally, I print on ivory paper and laminate it to a cardboard backing. The ivory is a nod to the off-white hue old slide rules often have. Lately, I've been adding a background tint to the scales, and print on white background.

If your printer is rated for thick enough paper, you can try directly printing scales on Bristol board or card stock. I have used card stock, so I can confirm that some printers do handle that thickness.

I print on my B/W Laser printer, but now own an Inkjet, which works as well. I'll be using colour more often in future projects, although I'm not sure that using a colour background is a wise idea. The consistency of the exact hue varies by printer; I suppose that this would not matter for things such as red and green lettering, but it might be a bit disturbing if the background hue was too yello.

Some of my replicas are too large to fit on the page sizes available to most home printers. In my location, it's generally easy to have prints done at a stationery store, or specialty print shop; not too expensive.

Transparency

This used to be popular for overhead projectors and therefore may become extinct soon. I can still find transparency at local stationery stores. . CAUTION: Use materials made for printing on the printer you use. Transparency materials are made either for laser printing or for inkjet printing, and they are not interchangeable.

Transparency paper has a few possible applications:

• It can directly be used for cursors. The material is too thin for a rigid cursor, but good enough for testing or playing with scales.

• Transparency sheets can be used with an acrylic substrate, e.g., if you are putting a clear window with a hairline over some inner scale - glue the hairline on the bottom surface to prevent any issues from parallax. Transparency sheets work where rigidity is not important.

• I am confident that it'll work well for scales that require transparent windows under an opaque layer. I once used it for the bar cage on cylindrical models, those based on the Loga style, and it worked well for a prototype.

Acrylic

As mentioned above, transparency can be used for cursors, particularly for prototypes. It has the advantage that you can print on it; the hairline and shape of the cursor are simply cut from the paper with scissors.

Acrylic is a soft transparent plastic available from hobby or art supply stores. I use it for cursors on circular slide rules. I generally cut a rough-sized piece with 'tin snips' - giant workshop scissors, intended for cutting sheet metal, then cut the exact shape with a Coping saw. I then use a file to smooth it to shape. In my experience, hobby power tools like a Dremel are not good for cutting this material, as it heats up and melts. A Dremel can be tried for grinding the edges; you need to watch out for over-heating.

The material I find locally is 1.5 mm acrylic; I find it at art supply stores. It's also terrifically easy to scratch, so I best to keep it covered. The kind I get is usually protected on one side by a thin sheet of plastic material. I print templates and glue them on the material with rubber cement before cutting.

Cylindrical Materials

For cylindrical models cardboard tubes of various diameters are relatively easy to obtain. In fact, I used to bring them home from work; I'm not sure what they originally contained, but were often in the printer room bin. They aren't terrifically easy to cut to size, but it's in the realm of home tools

Cardboard Post office mailing tubes are inexpensive, come in a few convenient sizes and also have end caps.

Hardware stores offer ABS or PVC pipes, again with a couple of convenient diameters.

When I attempt cylindrical replicas, I most often use cardboard. I just pick a cylinder with the closest size to the model I'm building and re-size the scales to fit .