Making Your Own Patterns
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.
Pattern for a Stack
The North American Live Steamer, Volume 1, Number 9, 1956
Perhaps one of the most pleasant lines of any engine is in the relationship of stack and domes to the graceful massiveness of the entire engine, and unknowingly to most of us is the thing that attracts us to a certain engine within a certain type. We therefore should attempt to reduce the prototype to miniature with faithfulness to keep the original grace. To do this we must sometimes build our own parts.
The following stack pattern took only 3 hours to make and cost about $1 to have cast in a beautiful bronze casting that required very little finishing as it fit the contour of the smoke box right off the bat. Since we usually only have one or two castings made, the first few are always beauties.
The first in this series of articles on pattern making concerned a simple pattern for drive wheels, whereas this pattern is a trifle more difficult, as it entails both a split pattern and one core, but no core box required, as explained further on. Let me reassure you that making patterns is simple. I knew nothing about it at all until I read a library book on the subject and talked briefly with a foundry.
Step one. Glue two pieces of clear pine, using sheet of newspaper as a separator, slightly larger than the finished cross section of your stack. The sheet of paper is necessary to separate the halves later and holds well while turning. Center in wood or metal lathe and shape as desired, being sure to leave portion parallel where flare is attached later and where stack centers smoke box. Allow 1 inch extension on each end for core print. Core print is so called as it leaves an impression in the sand mold so that the core can be layed in by the molder. Sand pattern in lathe and french polish if desired. Remove from lathe and before separating halves, drill two 1/8 inch dowel holes (see sketch) through both halves. This keeps them concentric when separated and in molding process.
Separate halves with light tap of chisel on ends and sand off any remaining newspaper. Glue dowels into one half only and permit dowel to enter only about 1/4 inch into other half. The remainder of the hole in the half without the dowels can be filled on the outside with wax, just enough to give a smooth outside finish. The two halves should be a good but easy fit as the molder has to lift them apart from the sand with little effort in order not to disturb the sand.
Step two. Glue two pieces of pine together (end grain) for ring as shown in sketch, using newspaper again as separator. Shape as shown in sketch to fit OD of stack where it enteres smoke box and OD of smoke bot itself. Separate halves of ring using care and glue halves of ring to halves of stack pattern while stack is held together with rubber bands. It is important to remember at this point that the halves of ring must be made as shown in sketch, i.e. with diving line running across the curve of the ring so it will pull from sand. Be sure to line up the works of both stack and ring exactly. When dry cut down through the rings at parting line with razor to separate any glue that might be holding pattern together. Using same method as described in article on drivers, apply and smooth out wax fillet to each half of your finished pattern.
Step three. Now that your pattern is finished you are ready to shape the core to form the internal hole through the stack casting. A core is a baked composition of core sand and oil which the foundry makes. The core fits into and is suspended in the mold by the impression formed by the core print at each end of your pattern. Ordinarily one would have to build a complex core box for making the desired shape for the stack core. I simply took a cylinder of core that the foundry supplies in many diameters and shaped it with sandpaper. Take a medium sandpaper and begin shaping your core. It cuts fast, so use care and don't attempt shaping with knife or other metal tool, as the sand core is brittle. From time to time use calipers and place core between your eye and stack pattern to 'eye up' the wall thickness. More or less choke in your finished stack is determined by your shaping of the core. The core should be sanded to length to be about 1/16 inch shorter than the overall length of the stack pattern to assure core will drop easily into mold. Next issue we will discuss building a dome pattern.