
MODEL STEAM ENGINE PLANS BUILDING MODEL STEAM ENGINES
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THE ENGINE TOSCA
THE TWO CYLINDER MODEL STEAM ENGINE "JESSIE"
ABOUT THE ENGINES THIS SITE WILL ENABLE YOU TO BUILD TWO STURDY MODEL STEAM ENGINES,"TOSCA" and "JESSIE"
LAYOUT OF THE ENGINES CLICK ABOVE TO SEE THE CONSTRUCTION OF THE ENGINES
SAMPLE PAGE OF ENGINE PLANS CLICK HERE TO SEE SAMPLE OF PLANS.
ABOUT THIS WEBSITE CLICK ABOVE TO SEE MORE INFORMATION
SAFETY CLICK ABOVE TO SEE IMPORTANT SAFETY INFORMATION
METALWORKING SKILLS ARE YOUR METALWORKING SKILLS SUFFICIENT TO BUILDING THESE ENGINES
SCREWCUTTING CLICK ABOVE TO SEE ACCURATE METHODS FOR CUTTING SCREWTHREADS
METALWORKING HINTS AND TIPS SOME INFORMATION ABOUT LATHE WORK AND SOLDERING
MEASURING INSTRUMENTS CLICK HERE FOR INFORMATION ON READING A MICROMETER AND VERNIER CALIPERS.
LINKS OTHER SITES OF INTEREST
COMPLETED PROJECTS THIS PAGE IS DEDICATED TO THOSE WHO HAVE BUILT MY ENGINES

MEASURING INSTRUMENTS

To find out how to purchase the plans click HERE

Before taking any reading it is good practice to close the jaws or faces of the instrument to make sure it is reading zero. If not then note the reading (its called the zero error) and subtract this value from any subsequent readings you take. Good quality instruments which have been well maintained should have no zero error but over the years one might creep in.
The main measuring instruments for accurate metalworking are the micrometer and the vernier callipers. I am always surprised at how many otherwise competent metalworkers shy away from their use and resort to all sorts of strange tactics to avoid using them.
I have written this web page to encourage those who do not use these instruments to begin doing so. There are no complicated maths involved and I have refrained from going into the theory of how they work – just a few basic rules for their use.
You can if you wish buy the digital versions but I much prefer the manual instruments.

Always wipe the anvil and spindle faces to remove any dust, grit or slivers of metal as these will ruin the accuracy of the reading. The micrometer spindle is tightened on the work to be measured using the ratchet stop not the finger grip. This ensures that the correct force and no more is exerted. You can over tighten the micrometer if you use the finger grip on the thimble and this will destroy the accuracy of the instrument.
The micrometer is read where the datum line meets the edge of the thimble. The reading on the datum line (6.00mm) is added to the reading on the thimble (0.45mm) to give the result (6.45mm). These figures refer to the photograph above.
I set the micrometer to this value to illustrate a difficulty which some people experience in using this instrument – how can you tell if the thimble edge is before or after the 6.5mm mark on the datum line?
The answer is found by looking at the two possibilities and using a little common sense to eliminate one of them. If the thimble edge were after the 6.5mm mark this would result in a reading of 6.5mm + 0.45 ie a value of 6.95mm (almost 7mm) and the thimble edge is too close to the 6.5 mark for this to be possible.
The photographs below show some further micrometer readings. Run the mouse pointer over them to see the reading.

4.91mm

7.24mm

12.07mm

12.56mm

VERNIER CALIPERS

A vernier is a sliding scale placed beside a mainscale in order to achieve a greater accuracy than the mainscale itself could produce.
To read such a combination of scales you first take the reading on the mainscale where the zero of the vernier meets it. Do not make the mistake of reading the mainscale at the metal edge of the vernier – a common mistake. In the photograph below this reading is 18mm plus a small amount which will be give by the vernier scale.
Look along the vernier scale for a mark which is coincident with a mark on the mainscale and read the vernier at this point. In the photograph this is 0.34mm.
You may decide that it looks more like the mark before or after this point as human eyesight is often unable to determine the exact point of coincidence. This results in a small margin of error in the instrument.
The final reading is 18.34mm. There are some more examples in the other photographs. Place the mouse pointer over the picture to see the reading. Again a difference of 0.02mm in the result is acceptable.

READING A VERNIER SCALE

12.74mm

21.54mm

21.88mm

37.12mm

THE INTERNAL MICROMETER

The internal micrometer is read in a similar way to the more common external micrometer. You can determine any zero error by using the internal micrometer to measure a known gap eg. between the faces of an accurate external micrometer. You must keep in mind that the datum line scale increases from right to left and the zero mark will be hidden by the thimble making it a little more difficult to read. An example is shown below.
If you do not have this instrument then you can use a pair of internal callipers which are adjusted to be a sliding fit in the hole to be measured. The callipers are then measured with an external micrometer as shown in the photographs below.

READING THE INTERNAL MICROMETER

CLICK HERE FOR MORE PRACTICE IN READING A MICROMETER

SETTING THE INTERNAL CALIPERS TO THE SIZE OF THE HOLE

READING THE CALIPER SEPARATION WITH AN EXTERNAL MICROMETER

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