TREVOR GIBBS MODEL RAILROAD PAGE 6
USING A LATHE FOR MODEL BUILDING Pt 3
MAKING A "SMOKE STACK"
As a Rider - Please ensure that you are wearing Safety Glasses and that you are not wearing any loose clothing such as sleeves where they can be caught by the machine. I make no pretence about the final shape being what you as a reader may finish up with or require. However I believe that the basics are essentially correct.
We are going to make a Smoke stack with a tapered funnel shape using the compound or taper cutting capability of our lathe. Your variations will depend on the profile of your funnel so alter your tooling and techniques to suit your required shape. The steps to the astute reader will look remarkably similar in some aspects but like many functions in life, there are always a few repeated activities...
Select a piece of round stock a diameter slightly larger than the finished product will be.
Face off the surface at the end of the stock
Using the centre drill, (usually a double sided drill bit with a short cutting bit and relatively thick shank), drill a countersunk hole into the faced off end
Depending on how your lathe has been supplied, replace the Centre Drill with a live (rotating) centre or a dead centre. With a dead centre, use plenty of lubrication to avoid burning either the centre or your work and tighten the centre into the countersunk hole in the stock
Up to this stage, the carriage/tool rest has been used solely for parallel turning. However the carriage/tool rest has three adjustments. One of these is for horizontal movement along the bed of the lathe and is usually the largest wheel. This is the wheel we turn for parallel turning. The second provides for movement of the tool rest across the bed of the lathe at 90 degrees which is the main wheel we use for facing off the lathe.
The third is a little more complicated but not that hard. On larger lathes there is a third control, again a wheel which moves the tool rest. However the angle of this control can be changed by loosening the tool rest. This is usually by Allen Key loosening on the main carriage or a top screw loosened at the top of the tool post, (depending on the lathe) and rotating th
On some smaller lathes, it appears that the tool rest itself has only one cross way adjustment which can be rotated relative to the horizontally travelling carriage.
So in fact the Tool Rest is more correctly a "Compound Tool Rest" which we can use for Taper turning. By setting at an angle .
A NOTE ABOUT CUTTING DISTANCES
Most tapers are noticeable but very slight. Remember that because you are turning the taper, you only need to set to half the figure on any gauge or measure on your lathe. That is if you want a 10 degree taper you only set your machine at 5 degrees because you are only tapering one side. The two 5 degrees make a total of 10 degrees total taper... which in any terms is fairly pronounced.
This "doubling" effect is worth keeping in mind. If you want to reduce a diameter by .010" you only need to turn your carriage in .005" because you are similarly turning half the distance from both sides of the stock as it rotates.
Set your taper angle to half of what you require. Introduce the cutting tool to the work a fair distance down the shaft and start turning in the compound tool direction. As you cut further, you are placing more load on the cutting tool so be receptive to any problems which may occur and ease off the cutting pressure if necessary.
If you have two adjustments on your lathe (such as a model lathe), withdraw the cutting tool move the carriage right very slightly (about one eighth to a quarter of a turn) towards the Tailstock. If your lathe has three adjustments ( Horizontal carriage, Cross Carriage and Compound), withdraw your cutting tool, wind in your cross carriage .001" (or .04mm) towards the theoretical centre of the stock. Repeat your cutting action.
The shape which is being shown here would make a very pronounced diamond stack for an older locomotive. The centre could be drilled out further and the length parted as such after the live or dead centre is removed. .
Take care when parting your finished item that you take your cutting lightly. You should by now have an acceptable shape for your funnel
More to come...