Model Steam Locomotive

My Home Made  16 mm NG Dacre Locomotive

I have now started to build a steam loco.  This will be a 16 mm narrow gauge model.  I chose this scale for several reasons;

• it is relatively inexpensive compared with larger scales, mistakes won't hurt too much,
• I can make nearly all parts of the engine myself, 
• I can run it indoors awaiting a possible future garden railway, 
• and I can achieve a result in a relatively short time to overcome my short application span.

I originally thought about doing this about a decade ago but work and other projects got in the way but since I have finally retired from teaching ( I have been supply teaching since official retirement in 2006) I have some time to get more involved in my little workshop.

I chose a model based on a 'Homemade Dacre' designed by Dick Summerfield and Erik-Jan Stroetinga which was designed in the 'Dacre' principle of Peter Jones who originally built a self designed Loco using parts from the model company Roundhouse.

Unfortunately Dick Summerfield passed away some time ago and most of his website which originally inspired me has been lost.  However the drawings for most of the parts are available freely from several sources on the Internet, including for members of the 'Steammodelloco16mm' Yahoo group.  There is some information missing and some of the drawings are in Dutch (an internet translation or Dutch/English dictionary soon overcomes this problem) but there is enough to be able to build a working loco.  There is also a booklet published by the Dutch Stoomgroep modellers as a special publication number 5, again in Dutch.  Probably worth the €20.00.

The loco wheels are fixed to the axles with grub screws in a machined boss on the wheel and as the loco has outside frames the wheels can be adjusted to run on 32 mm 0 gauge or 45 mm gauge 1 track

Frames 

I started the Loco by building the Frame which consists of:

• side frames, 
• buffer beam support plates, 
• cross members ('stretchers'),
• buffer beams and 
• simple 'top hat' bushes for the axles.

Side Frames

For the side frames the drawings call for 2 mm steel sheet but I only had 2.5 mm sheet so I used this.  The sheet I used was rusty and had to be cleaned up but that only took a short time and I soon had the basic blanks for the side frames.  

Three Rusty Blanks Ready For De-Rusting

These rusty blanks were cleaned with a belt  sander.  They were then cleaned with acetone (not nail varnish remover which contains lanolin)  and glued together with cyanoacrylate - superglue - so that they could be machined together to ensure that both sides were identical.  This ensures that the axles are aligned accurately which is essential.  the edges were then milled parallel to width.

Apart from the dimensions between the axles no dimension is actually critical so I marked out the position of the holes and recesses using vernier calipers after 'blueing' the parts with permanent marker, I chose one side and one end as datums and made all measurements from these.  This prevents cumulative error.

All holes except the axle bearing holes were drilled on my drill press.  The axle holes were drilled on the milling machine using the handwheel dials to position them as accurately as possible.

The  sides were then laid flat in the milling vice on parallels and the recesses milled with appropriate end milling cutters.

 After drilling and profiling they were pickled in citric acid to remove any residual rust.

Residual Rust Before Pickling in Citric Acid

Frames After Pickling in Citric Acid for Several Hours and Scrubbed in Alkaline Solution (Washing Soda)

Cross Beams and Buffer Beam supports

Buffer beam support (left) and the 3 frame stretchers

The cross beams (aka 'stretchers') and buffer beam supports (Buffer beams hereafter) are relative straightforward to make involving mostly cutting and drilling work.  However the buffer beams need milling the reduce the thickness in places however these beams are not really essential and strips similar to the sides can be fixed at the ends using angle brackets and bolts or rivets.  I milled the cross beams to length as a group to ensure consistent accuracy, the same went for the buffer beams.

There are three cross beams and two Buffer Beams.  The later are identical but the cross beams are each drilled differently - two of them are used to fix the footplate and smokebox plate later and are drilled and tapped as per the drawings.  I used the 4 jaw chuck to centre and hold stretchers  for drilling of the ends and tap M3.  The  pin vice was used for tapping while the stretchers were held stationary after drilling, the pin vice was twisted while supported loosely in the tailstock chuck. This is a very sensitive method of handling very small drills and  taps.

I always support small taps when using them.  In the lathe or milling machine I use a pin vice supported loosely in a tailstock chuck or sliding on a suitably sized pin held in the said chuck.  On the bench I use a simple guide block made from a piece of bar stock with ends carefully turned parallel then drilled to suite the range of Metric taps I use (below):

Tapping block (ready to tap cylinder cover fixing screw holes)

Tapping block in use

The method of use is obvious and it has two major advantages over free tapping,  the tap is held in line with the hole and ensures accurate work and also it supports small taps and prevents them being bent sideways which is a major cause of broken taps.  The tap here is an M2 first taper into brass (note the protective masking tape on the workpiece) and I am confident of an accurate tapped hole with no tap breakage. I continue using the guide for the second and plug taps to prevent sideways force and possible breakage.  Since using this device I have not had a broken tap and ruined work despite tapping many holes from M1.6 upwards in brass, steel and stainless.

 It was a valuable odd hours work in making it.  In use if the job is too small to support the guide I hold the work in the vice and align the face to be tapped accurately in line with the top of the jaws. I usually hold down the guide with two fingers of the left hand and gently rotate the tap with the centre section of the tap holder.  With larger taps I use the same technique until the tap is aligned and cut a few threads and then use the tap holder by the normal method,