A great timesaver when designing and building a model railroad is the use of templates. Some of these devices are commercially available but sometimes it is easier to make them yourself. When drawing a track plan a set of radius guides made to your drawing scale are much more convenient than having to use a compass for every curve you draw.
The above drawing shows a 36” radius curve pattern at a scale of ¾”=1’. The radial arms show the circumference of a 36” radius circle in 1 ft. increments. As shown, the distance from 0 to 180 degrees of this circle is 9.4 ft. You will need to make separate patterns for each radius you intend to use in your track plan.
The construction of these patterns is fairly simple. They can be made of thin wood, plastic, or cardstock. Using a compass, draw a semicircle of the scale radius desired and (using the above example) mark a length of wire in ¾” increments(or your chosen scale), bend the wire to conform to the circumference, and mark the semicircle using the wire increment markings. These are your scale 1 ft. sections. Use a sharp #11 knife or a new razor blade and carefully cut out the drawing. Now when you draw your track plan you will also know how much track the curve will require.
If you enjoy doing the math, here is the formula for the circumference of a circle: C=π x D, D = 2R, C=3.14 x 6’ for the example above. C=18.8ft. A complete circle with a radius of 36” has a length around of 18.8ft.
When laying out curves for track installation a collection of templates of the proper radius will make the task much easier and accurate. These can be easily fabricated from either heavy cardboard, plastic, or thin wood sheets. I use 1/8” masonite to make a variety of patterns for tracing curves on roadbed and to maintain the correct center to center track spacing. The following illustration shows one of these curve guides:
I have curve guides for radii of 42”, 40”, 36” and 24”. The following procedure explains how to make a radius arm drawing guide. The illustration shows a strip of scrap wood which is 41” long 2” wide and ½” thick but any available size of scrap can be used provided it is long enough. For simplicity, the example shows a guide for 36” radius-but additional nail anchor holes can be provided on the same arm for other radii.
Keep in mind that the patterns created with this instrument are guide lines for tracklaying and not precise gauge measurements. The guide shown was designed for HO scale which has an approximate track gauge of 5/8”. If you model in another scale the distance from R1 to R2 will be your track gauge and the distance from R3 to R4 will be your tie length. Remember that track radius is measured to the track centerline. Be sure that the anchor nail and the material that is used for the curve template is firmly held at the proper distance for the desired radius.
This fixture can be constructed from any material such as plastic or wood since nothing will be glued but the base material should be soft enough to accept push pins for the masking tape. The space between the upper and lower spacing strips only needs to be wide enough for the masking tape to fit. The jig can be as long as desired but a 12” length seems to work well as a good size for handling the tie string.