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Stamp Mill in O Gauge

After several years of having an empty space on my layout, intended for a stamp mill, I decided it was time to build it.  I purchased a basic set of plans from Western Scale Models.  These structures don't have to be large as fewer stamps can be used and a variety of building sizes are possible; stamps come in batteries of 5.  However, I decided 20 stamps would be more impressive.  I wanted to include all the interior machinery and equipment, not just an exterior structure.  This would require the roof to open for viewing as well.  The following is not intended as a step by step guide to building one, but an insight into elements that can be applied to any structure such as building board-by-board siding, board and batten, and so on.  Some of the weathering techniques have already been discussed in my other articles, so visit those as well.  

This image is similar to the stamp mill I am building, approximately 21" x 21" x 20" high.  The cut-away shows the basic elements from delivery to processing.

  Processing...

 The process of treating gold ore to extract gold (and silver) and, therefore, produce bullion is called milling. The building housing the process is called a stamp mill. A stamp mill is similar to a mortar and pestle. Indeed, the vessel holding the ore being crushed is called a mortar. In order to extract the gold, the gold ore was first brought to the surface of a mine, then crushed in a massive stamping mill first by a rock crusher then by repeatedly dropping heavy stamps on the ore in the mortar. To mechanize the repeated lifting and dropping of the stamps, a rotating cam typically engages a tappet on the stem of each stamp. A battery of stamps dropping in a single mortar can all be lifted by cams arranged along a single shaft. While the rocks are fed under the stamps and being stamped, water was being mixed in and the slurry fed onto Wilfley tables. The Wilfley concentrating table came into use in the late 1890's. The table is made of wood covered with linoleum. The mechanism below shakes the table and causes the separation of the quartz tailings into the "tailings" side of the table and the heavier materials into the "concentrate" end of the table. The last step was to send it to the local bank.

  The Exterior Structure

 Base

Since this will be a fairly large structure with interiors, it will be heavy requiring a very firm base, so I made one using 3/4" MDF with two basic levels.  This will enable me to carry it as required and eventually set it into place securely.

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 Scale Lumber

I estimated the lumber I would require, using the mock-up, and purchased the strip wood from Mt. Albert Scale Lumber Co.  This was followed by applying grain to each piece using a file card, dipping them into a solution of Sweet and Sour, followed by drying in the oven at 200 degrees for an hour.  These were then laid out and sorted according to size.  This light stain would be fine for interior unweathered wood.  The exterior sides would later receive another coat of darker stain.

Wall Framing 

I took each elevation drawing and glued wood blocks along the frame edges to secure all pieces while being glued together.  This also ensured all repetitive parts would be exact for alignment.  I noted deletions and additions to the drawing that my structure would have as I enlarged it.  I also attached strip of Scotch tape to all joints on the drawing so that the joints of the frame would not stick to the paper.  Here you see the framing assembled on the drawing using 8” x 8” pieces for the structural parts and 2” x 8” for window, door and intermediate frames.  The exterior will receive 2” x 12” vertical wood siding with 1” x 2” battens.  Intermediate framing is required in  places, since exterior planks should not span more than 4’ unsupported. 

Once the frames are completed, they were test fitted together and held in place with clamps.  The steam engine and boiler casting were placed in their approximate location to see how they would look.  Later on, I decided to relocate the boiler from this position to allow for more space up front as well as for a coal bin for the boiler.

Retaining Walls 

Western Scale Models had included using a timber retaining wall on their plans.  However, I felt that with all the pounding taking place in this type of structure something more solid was in order.  After all, it is holding back rocks and soil from the mountain behind.  So I cast a stone wall using Plaster of Paris and fitted the sections together against the base using carpenters glue. I sealed the plaster with clear Krylon and washed stains across the casting, applying extra stain to individual stones. With all the crushing of rock that takes place it is usual that everything eventually gets covered with fine dust so it was followed by a liberal application of pumice that had a neutral colour. 

 With the walls still in place, an 8” x 8” piece of strip-wood was glued down on the deck against the frames followed by intermediate framing to support the 2” x 12” floor boards as seen above.  This is followed by gluing all the floor boards in place.  Using a sharpened pencil, nail-heads are created on the boards.  The boiler and steam engine locations are finalized so that the boards can be applied around the base.  The concrete foundations for the engine and boiler were set on the frames and the floor boards abutted to them so that the foundation pads were flush with the boards.

 Exterior Wall Finish

The initial staining of the wood was primarily in a light base colour that would be appropriate for the interior that was not exposed to the weather.  The 12” siding boards and the battens now received another application of stain using an alcohol/shoe dye combination.  I use both a black and a dark brown colour, alternating randomly and mixing so that all the boards vary in colour.  A rag is wetted and wiped across one side only.  Note that all wood strips were rubbed using fine 0000 steel wool after the staining to remove any fine fibers.  Keeping in mind that there would be a maximum board length, cut the boards to fit the framework accordingly and glue in place using carpenters glue.

Nail heads are applied as the boards are attached to follow the frame.  The battens are attached next in the same manner.  I dilute the glue for these as the strips are too narrow for full strength glue.  When dry, these are then all trimmed off flush with the frame edges.  Now I applied dye to the bottom edge of each wall holding it upside down using dye and clear alcohol. With a loaded brush, wipe on the edge so that the dye bleeds down.  This gives the look of stains from water on the ground along the foundations.  Some of these stains bleed inside but that just adds to the overall effect.

Next I liberally applied pumice to the insides of the walls, mostly to the lower regions for dust accumulation, scrub it in with a brush and blow off the excess.  

Some windows and doors are plastic castings from Grandtline while others are scratch built.  In either case, they received a base coat of weathered gray followed by lightly dabbing rubber cement to parts with a piece of foam as a frisk.  A final coat of paint, in this case white, is airbrushed onto the surface.  I lifted the frisk off using masking tape.  This leaves the look of peeling paint.  Finally, I cut and applied cellophane glass to the insides. Here are some examples of the finished walls with windows and doors installed. 

Perfect wood blinds to make your home look unique.

Wood joists have limitations for spans so I had to decide on their means of support.  Horizontal spans would be too far, so I made wood trusses for the long spans.  There are many designs for this but I used 2” x 6” diagonal bracing with top and bottom cords on both sides as well as vertical pieces.  The ends of these sit on 8” x 8” x 4’ posts bolted through the king post posts.  The ridge has a beam above a truss.  I plan on installing joists from ridge to truss to truss. Since the inside will be detailed, we need to see it, my intention is to have roof portions hinged. 

Water Tank 

The boiler requires both coal and water.  A coal bunker was built inside the front wall close to the firebox.  A water tank could not be fitted inside so I decided to install it outside behind the boiler for more exterior detail.  A water tank is quite easy to build and makes a nice project on its own.  Here I used a section of cardboard tubing cut to length, fine nylon fishing line (to represent steel cable), strip wood and hoop fasteners.

After preparing the strip wood, mark vertical lines in pencil around the tube as a guide to keeping the planks plumb.  Glue these in place with carpenters glue after adding a top and bottom to the tube.  I liked the random lengths for interest along the top edge.  Decide on how many cable  bands you want and mark dots around the tube using dividers.  The lower ones are closer due to the water pressure. Prepaint these cables.   Press brad pins into one side so that the nylon line can be wrapped around them and on to the next loop.  A "U" shaped section of structural wood can be used to conceal the pins afterward to represent the level gauge.  I installed a small pulley at the top for the gauge marker float line.  I also installed two castings for fittings for the in/out pipes.  These were scrap parts from earlier tank car kits.

The deck supporting the tank sits on braced posts with joists across two beams.  I added a ladder on the side of the tank to check the tank as needed.  The top of the tank is recessed and was painted black and a small amount of resin was poured in.  Let this thoroughly dry before installing the tank on the deck or its piping.

With age and use of well water, the tank will eventually produce lime deposits through the plank joints.  This occurs when the wood joints open slightly as the water lowers and dries out.  I apply diluted washes of white paint to the sides, following the plank joints and mainly to the lower edges.  This will also stain the joists.  Here the completed tank sits on its deck with a water pipe coming up from a frost box and into the tank.  Presumably there is a water pump down there.  The lower pipe feeds the boiler through the wall.  I included a set of stairs from inside the mill.

Roof

I am using scribed sheet material as apposed to individual planks as the underside will rarely be seen.  It is also more stable as a unit, only the back panels will be visible and the are fixed in place permanently.  I pre-stain everything and glue the joists to the underside after locating them to sit on the wall, then add weights to ensure a flat panel while drying.  The beams were glued across the grain and weighted until dry to ensure no warping occurred.  This will happen when applying stain to one side, so both sides were stained.

The roof panels on the back side were installed permanently.  The front roofs consisted of only two pieces, one with the main gable over the entrance, the framing of this gable rested aginst the wall gable wall while the top of the roof panels sat on the cross beams. I decided that several gables would be required to allow natural light into key areas of the interiors.  I pencilled in guidelines for the 3 gables to keep them in line.  These would provide light to the stamp/Wilfley table areas, a second one over the steam engine and a larger dormer above the stamps and bins. 

Left: Sheets of scribed siding are edge glued to build up the full height and cut and test fitted to the walls.  Gable is built and glued in place on the lower roof.  The locations for the dormers are marked and cut-out made for light.  

Middle: These dormers were framed up and planked without the roof and glued in place.  Windows were built to fit, stained and weathered with peling paint.  Once dry, the ridge beam was cut to fit level, framed and roof decking applied.  The dormers are assembled and placed for a test fit.  I larger one is made for the upper roof panel.  Note the two end units on the ridge for a vented structure.  This is attached to the front panel only an hooks over the top ridge to sit in place.  The lower roof panel located itself by having the gable and joists rest against the front wall.

Right: Joists will be applied to the underside of these two roof panels to stiffen them up so that they lay flat.  Corrugated roofing will follow after pencilled guide marks are made on the roof.

 I cut strips of paper for the valley flashing, painted them a weathered silver grey and glued them in place.

The aluminum sheets of corrugated siding were purchased from Sodders Enterprises in 8' and 10' strips.  These were attached to strips of green masking tape applied to a sheet of cardstock and hung on a wall.  I wanted a weathered and rusted appearance so these were then airbrushed with Floquil rust and varied by adding some boxcar red, sprayed in a varigated fashion and then adding a little grimy black and gently over spraying.  A little stronger colour was applied to the lower edges.  There are over 400 sheets on this model.

      

      

   

   

  The Interior Structure

 The point of illustrating the various levels and further on the various pieces of equipment is to show these phases while they are completely visible.  As the assembly progresses many of the parts become partially hidden from view, but it is important to construct them as the occur in order to facilitate the structural framework... besides, there is a satisfaction knowing they are all there!

I like to use the sanding disc for most of the fitting as it can make fine adjustments quickly.  First make a "master" piece that will fit precisely.  Precut the additional pieces that are to be duplicated and tape them securely together.  The feed into the sanding disc until the rough edges meet the master piece.  Sometimes a guide will be need for angles.  In this case, I used a square since the pieces were high and wanted to keep them in line.

Here are the finished lengths with the various angles shaped.  Any rough burrs are quickly removed with a piece of sand paper.  I use a 6" nail file card with a corse and fine on each side.  I like these because the faces are flat making it easy to sand smooth.

The 6 stamp battery legs with 2 notches for cross beams were cut in the same manner with shaped notches for the cams, a hole for a steel rod was also predrilled while the legs were still taped together.  

Level 3 is framed with 12" x 16" beams that will abut to the stamp battery legs.  These legs are left off until later to access the rest of the framing since the space is tight.  The assembled stamp battery is test fitted.  The posts will be a guide all the way up with the framing following for support.

Level 4 holds the ore bin.  This is framed with 12" x 12" timbers followed by side and bottom boards of 2" x 12" planks.  Unfortunately much of this is unseen later but is instrumental in the framing.  But I know it's there.

Level 5 covers the ore bin with a delivery hole in the deck.  All decks are 2" x 12"s.  The space on the left is clearance for the belts and on the right will be stairs accessing each level.

Level 5b consists of 4" x 8" framing that will hold the rock crusher and the "grizzley" which is a grate below the ore car track.

Level 6 is the frame to support the track for the ore cars.  The posts supports are still to be installed and along with the combined grizzley and hopper combined.  At this stage the entire area was dusted with pumice and scrubbed in the blend all the stains and provide that well used and dusty appearance.  The ore feeders will be fabricated and placed below each of the openings in front of the ore bin.  These will feed the crushed rock into the stamps.

  The Boiler Room Equipment 

Steam Engine 

This image shows a various parts to assemble the steam engine provided by Western Scale Models.  Not shown is the concrete base and piping.  Note the dime at the bottom to give scale.

This is the completed model of the Ames Iron Works Twin Cylinder Steam Engine.  Aside from the cast pieces I have included wire and brass tubing for pipes.  First I dipped all parts in “Blacken-it” for a base weathered finish.  The governor balls and flywheel were polished using fine 0000 steel wool.  Various parts were painted such as the red handles and brass oil cups.  Oily portions were painted using metallic gun metal paint and gloss paint applied to the oily and wet portions.  The concrete base is a urethane casting washed with grey paint and weathered.  I attached this to a piece of 1/16” styrene for a foundation base as the engine would have been anchored to something solid and painted it a concrete gray along with washes of stain.

Boiler

The boiler also needed to sit on a concrete pad, so a piece of 1/16" styrene was again used and painted in the same fashion as the engine base.  These received washes of stain to resemble a weathered and dirty surface.

This boiler is encased in brick for insulation.  The main brick casting was first painted in a red brick colour and a gray top representing the asbestos lining.  I applied a gray mixture of acrylic paints to the joints, scrubbing them in, then gently removing the surface pigment with a lightly dampened towel.  Several wipes were needed leaving the brick face clean.  This leaves the mortar in place.  Some mortar areas are whiter and others darker for a weathered effect.  Later this was randomly dusted with pumice.  The various castings and pipes are all blackened and assembled, then attached to the boiler.  Valves and handles are painted red and brass accordingly.  The stack is a brass tube and will be blackened when extended through the roof.  This will be left until the roof section is fabricated because it will be in two sections, one attached to the boiler and the other to the outside section of roof so that it can be lifted.

Now that I have the locations of the boiler and steam engine determined and in place, we need to fabricate a steam pipe delivery.  In this case the pipe drops down from the steam dome to the floor where is crosses to connect to the engine intake.  I used flanges and elbow castings to achieve this.  The section crossing the floor will be very hot and a danger to anyone crossing it, so it was clad in an asbestos wrap.  I used a paper towel cut into narrow strips and wrapped around the pipe.  This was then painted gray, the paint securely holding it as it dried.

I had to relocate the door that ended up behind the boiler shown on the left.  The right image shows the completed boiler dusted with pumice and a ladder installed to access the top of it.

Generator

These were simple castings but required some filing to fit and then painted.  The armature casting was painted copper for the coils and the remainder painted a dull green after all parts were first dipped into Blacken-it.  The pulley was filed smooth and polished using fine 0000 steel wool.  A belt will be added to it later as a drive.  The final location was determined after all the pulley locations were determined so that they didn't conflict with each other.

Cleanup Barrel

Like the generator, this too is a very simple kits of parts.  It was first blackened then painted flat green.  This was followed with weathering using rust paint dabs and dusting with chalks and pumice.  A supporting wood frame was fabricated.  A sluice box was quickly pot together using boards and stained.  The bottom slopes and has a 1/8" dia. piece of brass tubing at the bottom end as a drain installed.  This also was weathered using stains and chalks.

 Interior Views

Some interior views of the early assembly...

  The Stamping Room Equipment

 Ore Crushers

These rock crushers were used to catch the ore too large to pass through the grizzly (grates).  These would crush the ore rocks into smaller pieces and drop them into the hopper below.  In this case I had two sets and thought it would be interesting to have a pair in operation.  The 3 centre wheels are flywheels and the outer two pulleys still to be connected to the drive pulleys above.  The pulley surfaces were polished with steel wool and the remainder painted and weathered similar to the clean-up barrel.

The hopper below the track is now framed in and the sloped grizzly installed.  The ore is dropped down and falls through the grizzly while the larger pieces are delivered to the rock crusher.

Ore Bin Gates

These castings are mainly the gates which slide into two guides on either side.  A ratchet and gear are driven by a hand wheel to raise and lower them.

Once the gates were assembled and attached to timber supporting beams, chutes were fabricated from wood and attached below.

Ore Feeders

These castings were cleaned up and then dipped in a solution of "Blacken-it" like all previous castings.  This gives a natural weathered metal finish as a base.

The wood frames were first constructed after additional staining.  The various mechanisms were assembled and the hopper glued in place.  This photo shows each side of the feeder.  I used ground rust rubbed into the hopper with a Q-tip to give a weathered appearance.  The projecting arm will attach to one of the stamp rods in each bank and as the stamp lifts and falls it activates the mechanism to deliver a little ore onto the revolving disc underneath.  As this spins it delivers the ore into the mortar where it will be stamped into dust fines.

The feeders in place temporarily.  A cat walk still has to be installed across the front of the chutes and then a deck around the stamp battery after it is in place.

Stamp Battery

Below are the stamp legs as noted earlier.  These will carry the entire stamp mechanism to crush the ore.  On the right are the base castings including pulleys, bearings, cams, tappets, lift legs, stamps and mortars.

The stamp battery is mostly completed.  Six foot diameter drive pulleys are attached on the ends of the shaft.  These will rotate the cams randomly lifting and dropping the stamps.  The cross beams have all had the nut/bolt/washers installed across their face.

On the left is the mortar box that receives the crushed ore from the ore feeders behind. These 1,000 lb weights then pulverize the ore as water is mixed with it and the fine sludge exits from below onto an amalgamating table.

On the right can be seen the tappets across the top of the rods.  These are not yet in place but will be positioned randomly at 36 degrees apart.  The cams below will lift each tappets/rod as the shaft is rotated by the drive pulley  These large 6 foot diameter pulleys were made of wood layers laminated together.  The top and bottom cross beam fillers on the back side were drilled to receive the rods freely.  Again these were mated together and drilled at the same time in order that the holes align perfectly.  Nuts/bolts/washers will be added across the face of the cross beams to clamp the two halves together.  In order to drill the stamp blocks to receive the rods, I drilled a matching hole in a block of wood like a die, inserted the stamp block and drilled it while holding the top with needle nose plyers preventing it from spinning.  After blackening all the parts, the rubbing surfaces on the cams were polished with steel wool.

Again, another test fit. More stairs have been added.  Floor boards to the ore bin have been removed to install 4 lamps over the feeders.  A sound module is also installed from Miller Models of an actual stamp mill in operation.

  Lighting

At this stage I realized I should have planned for lighting.  There would not have been a problem had I not wanted working lights.  So I had to remove some of the bin deck boards to access a place for the wiring to connect the lamps and then feed them through the back wall.  I used 1.5V lamps with shades.  I twisted the wires behind the lamp and bent them into a hoop as if it was a conduit and applied ACC to the wires.  This held them in shape.  These were fed through the wall of the bin, connected behind and the deck boards replaced.  A final application of paint would finish these.  But before closing in the bin the lamps were first tested with a 1.5V battery.

  Speaker

Naturally there should be sounds and fortunately my good friends Bill & Mary Miller of Miller Models produced a sound chip of an operation 10 stamp mill.  For now I felt the sounds of 10 stamps would do as 20 stamps might be too much to hear the individual stamps.  Besides, 10 stamps may work alone at any time.

Again, poor planning; I should have installed a speaker inside the bin behind the stamps but at this point there was too much to take apart.  So I opted to cut a round hole in the back wall behind the bin.  The red wires are from the lamps.  I glued the speaker in place using a hot glue gun.  A speaker by itself doesn't have the tone of volume required.  I cut a cardboard tube, in this case the same one I used for the water tank which fit perfectly, and capped one end with a flat piece of cardboard to create a resonance chamber.  This was attached to the back of the speaker with a full bead of hot glue.  The sound will be just as effective coming from behind the stamps.

I installed a module (SS671) from Miller Models in a control panel as I had done with several other sound units in my layout.  Once the structure is in place the lamps and sound module will be hooked up.  I turn on the sound using a SPST toggle switch.  The sound unit has a cycle of about 20 seconds.  If you flip the switch on then off, it will play one cycle, good for a demo.  If you leave it on it will continue playing.

 Belts

 There are many types of materials available to use for drive belts, but I found that drafting velum is the best, it is strong and stable in any humidity condition.  I use the type that is matte on both sides.  I mix a colour similar to weathered leather and spray both sides.  Belt widths vary so I cut excess length in each case, dab a little ACC on the back of a pulley and attach one end of the belt after cutting to length and width.  I try to have the joint at the back out of view.  Only in one case was it unavoidable. Then I pull the belt across the next pulley securing it again with a little ACC and finally back to the first one, overlapping and ACC it in place.  Make sure you have extra length and cut after final glueing.

These views show the various belts that drive each pulley from the main drive pulley.  Above left has not yet been attached to the stamp pulley.  It gets tougher to access these areas as more details are added so in this case the belt was attached before adding the stamps or else I could not reach the back drive pulleys.  The twin rock crushers now have their drives belts in place. The one remaining pulley without a belt will drive the Wilfley tables once they are installed.

Hoist

These are the castings for the hoists which are used to lift stamps that require repairs or replacements.  The pulleys are 1/8" dia. so making all fit and being able to feed the chain was quite a chore.

Below left are the two steel beams supported from the reinforced wood truss complete with the pulleys and hooks.  These are used to lift the stamps out for repair or replacement. The wood trusses also now have all the added details of NBWs (nut/bolt/washers).  The image on the right has the stamp pulleys now connected with belts.  The final stairs have been added to connect each level.  Water lines with attached hoses is in place complete with shut-off handles.  This is fed from beneath the floor in the centre from the water tank.  The cams are also now set in place at their required off-sets.  Also, the fingers are in place across the front of each stamp that will be used to hold up each stamp for maintenance.  These are pushed forward and placed under a cam in the top position to take the load.  A new deck is added across the front to access these fingers.

Amalgamation Table

The amalgamation table under construction and finally in place.   I added a tough across the ends to collect the "sludge" from the stamps that has been mixed with water.  This slurry finds its way down the table to the trough and down a spout through the floor where is will eventually find its way to the Wilfley tables.  In another process option, these tables would have been covered on copper sheets and mercury poured across it.  The gold would attach itself to the mercury where it would be separated on the Wilfley tables and extracted in a retort.

Casting Prep

All previous casting were prepared in a similar manor as these.  Below are the castings for the Wilfley tables, there are four of them.  Note the dime on the bottom right.  This is probably the most intricate assembly of the entire building.  All the casting are checked and flashing filed off.  These were wooden framed tables and were covered with a sheet of linoleum, so they will be painted, not blackened.

While some of the casting are large, they can be placed in a small dish with the Blackenit covering all pieces.  When it comes to the wire, I simply drop it into the jar and remove it with tweezers when blackened.  In the case of these parts, they are too small and can be easily lost, so I placed them in a plastic baking sieve and immersed them.  You will have to use a small paint brush to scrub and stir them around to be sure all surfaces are treated and to activate the agent.

Once I was satisfied with the treatment I rinsed the parts gently under water to stop any further activation.  

These parts are carefully removed with tweezers and placed on a paper towel to air dry. Some of the pieces can be lightly brushed to remove some of the blackened dust.  Some portions can be painted next or left until after assembly.

The following two images show the timbers for the wood frames.  They were "grained" using a file card, rubbed down with 0000 steel wool and a stain applied.  In this case I used the alcohol and leather dye solutions, randomly mixing the brown and black, wet on wet, applied with a brush.

Close-up:

Two of the frames assembled with the the table rollers, height adjustment rack and braces in place.  The final mechanism assembled in place that vibrates the table.  Pulley belts are yet to be installed once the upper drive shaft is in place.  These tables were covered in Linoleum.  Pipes for water are still to be installed.

Left: Here is a preliminary layout where the Wilfley table will finally rest.

Right: The pulleys and drive shaft in place with bearings waiting for the belts to be installed.

The stamp mill in its new location.... scenery to follow.

Written by :

lexpar