Making Your Own Patterns
by Richard Stokes
The North American Live Steamer, Volume 1 Number 8, 1956
So many engines that we would like to build so very often have odd size drivers that are just off "store boughten" castings and we are confronted with one of two choices. Select a near size wheel or build another engine.
Here are a few simple steps to follow in building a pattern in a couple of evenings that will reward you for time spent in a good looking driver and to scale as well.
Before starting, keep in mind one thing all the time you are building the pattern and you will have no trouble at all. All patterns for the conventional sand molds must have draft or taper to be able to be pulled from the wet sand. Besides, your foundry man will not fool around with a pattern that has no draft and on the other hand will welcome a smooth finished pattern with ample draft. 1/16 inch to an inch is more than ample to allow clean removal of pattern from the sand. All draft must face toward front of wheel and any taper on rear of spokes, if you desire, can easily be filed on the finished casting.
Step 1. Select diameter of wheel and see chart to determine number of spokes. Cut ring from one piece of clear pine with hand or jigsaw with draft on inside as well as outside of ring. I generally allow more on outside to reduce amount of metal to be taken off of casting later but I still like plenty to get into heart of casting. Remember the casting shrinks so allow for it when determining diameter of ring. Spokes and hub show very little shrinkage so no allowance need be made. Also allow additional 1/16 inch thickness both on front and rear to allow for cutting under the scale of the casting. Same applies to hub but rear of spokes only as no cut is taken on front of spokes.
Step 2. next fit and glue lightest counter balance to the ring.
Step 3. Take length of clear pine and shape to cross section of spoke but with no taper on rear of spoke as it will not work in pulling from sand - remember! Also flat side of rear of spoke will let spoke stand upgright on your assembly table.
Step 4. Cut hub from clear pine and remember taper towards the front. Leave layout centering hole in hub to help you later with assembly of the pattern.
Step 5. Assembly - Place wax paper on a flat board or table and attach hub with brads, leaving heads of brads so you can pull pattern from broad later. Brad holes can later be filled over with wax. Place dividers in center hole of hub and center your ring as you swing dividers. Brad to board when wheel is concentric with hub and balance is in proper relation - ship to hub.
Step 6. Lay out positions of spokes on the rim, and at point on hub where spokes if drawn to center of hub would intersect center. Carefully measure each spoke and after all fit in correct position - glue. Exact fit is not essential as you can fill in later with wax. The wax paper prevents glueing the apttern to the table and will come off easily when dry.
Step 7. When spokes are dry remove and check wheel pattern to be sure back side is flat. Next fill in your fillets with bees-wax and a bent nail heated over a candle. I place a piece of wax in the corner and flow it into shape with a warm, not hot, nail that has bent to a curve. (See sketch) Here again be sure draft is given the wax fillet. Any rough spots in the wax can easily be smoothed out with knife and a small brush using benzine. Allow benzine to dry and shellac wheel. After dry the pattern should be smoothed up with fine sandpaper using care not to cut into wax.
Step 8. Now the real time saver. Only one pattern is required for main and coupled drivers. Have the lightest wheels cast and get an extra in case you ruin one while machining. When you get your pattern back and are happy with castings, simply notch into the front of the spokes opposite and the balance 1/16 inch at the point where the 2nd heaviest counter-balance intersects the spoke and remove 1/16 inch from notch down to original balance. Fit a piece of sheet pine into this notched out section and you now have a heavier balance. Turn over and fill up between spokes with wax. On main wheel pattern fill in sides of hub with wax as shown in drawing.
The drawing serves only as a general spoke layout. Consult a Locomotive Cyclopedia for wheel cross sections, counter balance shapes, etc.
This is the first in a series of articles on pattern making as it affects the live steam builder. An attempt will be made to give step by step construction of patterns using the simplest methods that will result in a destinctive locomotive of scale proportions without adapting an off brand stack, dome or driver to an otherwise beautiful engine. The entirety of a handsome prototype or model is due to the relationship of its components to each other. The first of this series of articles deals with the simplest of patterns. Later, patterns of split design, coring, etc. will be discussed and will include cylinder, stack, dome, pilot beam and miscellaneous small patterns.