1 SPOT and 1A booster,  scroll down and click on pictures to enlarge

Finished models (has to be done by yourself): RTR, painted, decalled, glazed, connected.

Bulldog 1 Spot, primed, handrails and new truck sideframes

 Bulldog 1 Spot, primed, handrails and new truck sideframes

Bulldog 1 Spot, primed, handrails and new truck sideframes,      Bulldog 1 Spot, primed, handrails and new truck sideframes, American Limited diaphragm added                                                  American Limited diaphragm added      

1A booster, primed, handrails and new truck sideframes,              1A booster, primed, handrails and new truck sideframes,       American Limited diaphragms added                                                 American Limited diaphragms added      

1A booster, primed, handrails and new truck sideframes,               1A booster, primed, handrails and new truck sideframes,      American Limited diaphragms added                                                 American Limited diaphragms added      

Shortened and adapted frame for the 1 Spot.

Trucks frame sides have been removed (couplers still have to be removed).

Original Kato E8/9 frame. Areas to be removed painted black.

Original (below) and adapted/shortened (above) Kato drive shafts 

1 Spot completed chassis: decoder (in oiltank), 13x8 mm sugar cube speaker with custom made baffle above rear truck, capacitor + LED + resistor above front truck, Kapton tape to hold wires in place.

Truck assembly template (left) with sizes in mm.

Short couplers used between 1Spot and 1A booster.

only 1st hole is used; last hole (end) is cut off.

Shortened and adapted frame for the 1A booster.

New truck frames have been added (couplers still have to be removed).

Kato truckframe sides grinded/filed down to about 0,5 mm thickness. New 3D printed sideframes shown.

1A booster completed chassis: wired + connectors + side skirts, Kapton tape to hold wires in place

1 Spot completed chassis underside: Soundtraxx Econami sound decoder in place of oil tank, two 0,5 mm styrene sheet skirts to conceal decoder.

Click on the above buttons to see the movie


N-441 EMC 1 Spot, 3D printed engine shell only, cleaned, Air Eraser treatment, primed.

          EMC 1 Spot, printed and ordered directly from Shapeways (ATSF EMC 1 spot bulldog) in TAN Fine Detail Plastic

N-442 set of four 3D printed truck sideframes for 1 spot only, cleaned, Air Eraser treatment, primed.

           printed and ordered directly from Shapeways (ATSF 1 spot set of truck sideframes) in TAN Fine Detail Plastic

N-443 EMC 1A booster, 3D printed engine shell only, cleaned, Air Eraser treatment, primed.

           EMC 1A booster, printed and ordered directly from Shapeways (ATSF EMC 1A booster) in TAN Fine Detail Plastic

N-444 set of four 3D printed truck sideframes for 1A booster only, cleaned, Air Eraser treatment, primed. 

           printed and ordered directly from Shapeways (ATSF 1A set of truck sideframes) in TAN Fine Detail Plastic


In 1934 the Santa Fe ordered their first two passenger diesels from Electro Motive Corporation: the Twin Spots or Amos and Andy, powered by two 900 HP Winton 201A engines each. They were delivered in August 1935 and were intended for the then heavywheight Super Chief.

There were numerous (smaller) changes to the looks during the first years, skirting partially removed, extra cooling equipment on the roof, different paint schemes.

In 1937 the engines pulled the then new lightwheight Super Chief.

In 1938 the were rebuilt into the 1 Spot and 10 Spot, with 1 raised - bulldog nose - cab each, better cooling systems and painted in warbonnet style. Also the lead truck was changed to 6-wheel, with the lead axle unpowered.

The units were now used primarely on Eastern Lines passenger trains. Very shortly afterwards the rear trucks were also changed to 6-wheel, with again the lead axle unpowered.

In 1941 the 10 SPOT was converted to booster 1A by removing the raised bulldog nose cab.

In 1948 this 1A booster was converted to transfer/road switcher 2611, riding on 2 EMD FT trucks. It was first used in the Los Angeles area but later transferred to the Eastern Lines.

Both units were returned to EMD in 1953. They were rebuilt into two EMD E8m engines, numbers 83A and 84A.\

Al lot of useful information can be found in THE ONE SPOT TWINS by Larry E. Brasher, published by the Santa Fe Railway Historical and Modeling Society. Also IRON HORSES by E.D. Worley (the motive power handbook) and SANTA FE's EARLY DIESEL DAZE by John B. McCall and searching the internet provides much information.


The chassis for this shell/engine is the Kato E8/9: it is quite easy to modify, runs very well and pulls many cars with ease.

It needs 2 major modifications: shortening the frame by 6 mm and new truck side frames.


The prototype total axle spacing on the E8/9 trucks is the same as on the 1 Spot or 1A trucks (after the addition of the 3rd idler front axle): 14 feet 1 inches. Only difference: on the E8/9 trucks the spacing between the 3 axles is equal, on the 1 Spot or 1A the spacing is 6 feet 7 inches between the 2 motorized back axles and 7 feet 6 inches for the idler front axle. That creates an offset in the center of 5 1/2 inches on the prototype or 0,87 mm in N scale. Given the thickness of the side frames that offset/difference is invisible under normal operating/viewing conditions.

I choose to remove/replace the side frames only and not make/print a complete new 3D truck frame because of the flexibility of the E8/9 trucks. You can easily remove and reattach the modified truckframes many times without risk of damage to the 3D printed sideframes.Complete new 3D printed sideframes would not have that flexibility and would be prone to damage/breaking.

The outside of the E8/9 side frames has to be removed and the remaining "wall" made as thin as possible (about 0,5 mm) using a metal cutting blade and/or grinding disk in your Dremel combined with filing/sanding. The cupholes of the axle contact plate should just "open up". See picture above.

The 3D printed new sideframes must be cleaned first(Bestine, strong degreaser). I also give them a blast with my AIr Eraser using aluminum grit to smooth the surface and remove all remaining support material. I would also recommend to have these frames printed in GREY FINE DETAIL PLASTIC by Shapeways. Attach the new sideframes to the filed down E8/9 truckframes using CA glue (Zap A Gap medium is my favourite). Added advantage: if it turns out the new frame is not positioned perfectly you can still very carefully insert a sharp hobby knife between the 3D print and the plastic frame and seperate the two parts. Remove the excess glue gently with a file and start all over. 

To position the new 3D printed sideframes correctly I made a small template using 1,0 and 0,5 mm styrene scrap pieces. The underside of the axle pots of the new 3D printed frames should be 0,5 mm higher than the bottom level of E8/9 frames. Be careful: the short drop equalizer extends below the underside level of the axle pots, therefore a small "interruption" in the side frame support of the template. Click on picture above to enlarge to see sizes of the template.

Also check the orientation of the new 3D printed sideframes on the Kato trucks: the distance between the idler front axle and the center axle is a bit more than the distance between the center and back axle..... so "long end" forward on BOTH trucks.

This way the steps on the trucks will line up with the side doors and end handholds. The steps had to be on the trucks because the swiveling action and position of the trucks prevented attaching to the carbody.

When the CA glue has dried clean out the contact plate/axle cup holes with a small drill a little (carefully) to remove excess glue.

If the tops ofthe ladders are a bit high to your liking for free movement of the truck, very gently remove a little material from the top using rail nippers or the cutting/grinding disk in your Dremel (almost no pressure on the ladders, they are fragile).


The prototype center truck spacing on the E8/9 is 43 feet and the center truck spacing on the 1 Spot or 1A is 40 feet.

That means shortening the Kato frame by 6 mm: trucks centers on the shortened frame should be 76,2 mm.

I solved this as follows: the blade thickness of a metal miter saw is usually about 3 mm (or a little more).

I went to a local blacksmith/metal working company and asked if they could make 2 cuts just in front and behind the motor (see picture above - the black vertical stripes). The exact location is not really critical and it is even not critical if the cut is not at exactly 90 degrees: mark the 3 pieces beforehand with a permanent maker and glue together in the same sequence.... everything will stay in line perfectly. I had 2 frames cut for €10 = $ 11....... a couple of minutes work only.

If the cutting blade is a bit thicker that 3 mm you can opt to add/glue a styrene shim in the cut first to regain the 76,2 mm truck center distance. Glueing is done with CA glue (I use Zap A Gap medium).

The 1A booster needs also some metal removal at the front.Total length of the 1A booster frame should be 111 mm now, with the top of the back end slanted inwards a bit.

I also added 4 thin scrap brass strips over the cuts (see pictures above) to strengthen the modified frame: it is rock solid now.

Before glueing the 3 pieces together you should also make possible other cuts to make room for an optional decoder, sugar cube speaker and capacitor if you go for DCC/sound.

Because of the removal of quite a bit of wheight on the 1 Spot due to my DCC/sound wish, I opted to operate the powered 1A booster permanently coupled, all wheel (both engines connected) pickup and both motors on 1 decoder (no problem due to the low current draw).Than means running 4 wires between the engines with micro connectors (see pictures above).

If you want to run the 1Spot by itself only on DCC/sound that is still possible, but some pulling power is lost.......

If you run your 1 Spot on DC you will only have to remove a little bit of metal from the back end, probably only the small ridge.

If you want DCC with sound some more cutting is necessary: remove a block of metal from the back end to accommodate the speaker/baffle and also shorten the frame a bit (about 1mm), remove the "oil tank" under the motor to accommodate the decoder and remove part of the nose to accommodate the capacitor. I did all cutting with the most simple metal hand saw and coarse metal file, clamping the frame part in a vise....... it only takes some time and a little sweat but cuts are not really critical.

I also grinded a slot (about 3 mm wide and 1 mm deep) on both side off the frame near the middle/motor to guide the decoder wires from the decoder down under to the top. To conceal the decoder I CA glued two 0,5 mm thick styrene strips (6 mm wide) as a dummy oil and water tank.

If you run DC you can just keep the brass contact strips on top, just shorten them 3 mm on both sides. With DCC I suggest to discard them. I like to solder everything, also the leads/contactstrips from both rails. To make room on top for all wiring I removed these strips.

A warm white 3 mm LED and resistor are attached with double sided sticky tape to the front end. Bend the LED leads a little downwards to line up with the front light hole in the nose.

Last point: take some 2 mm scrap styrene sheet to make a U shaped attachment to the front bottom of the chassis following the curved nose contour (see pictues above). With some trial and error you will be able to make a snug fit between shell and chassis, eliminating the need for extra fastening methods or risk of the chassis dropping out of the shell when handling/lifting the model. 


If you order directly from Shapeways you will need to clean the shell first using Bestine, naphta or a strong degreaser (see the internet for various discussions/solutions). I give the shell an extra cleanup using an Air Eraser with aluminum grit. That removes all remaining support materarial (the white fuzzy stuff) and also diminishes the layering/surface roughness of the 3D print. Using a 0,5 mm drill clean out all preprinted holes (nose, sides and backend). All hand grips are formed from 0,15 inch phosphor bronze wire (Tichy Train Group 1102) and glued from the inside using CA glue. Grind of all protruding wire on the inside after drying.

An American Limited diaphragm has to be added to the back door of the 1 Spot and 2 in case of the 1A booster.

Coupling the 2 units and the end coupler posed a bit of a problem...... The trucks on the prototype are placed so close to the body end that in N scale close coupling is difficult. To accommodate a coupler there are pads at the shell end facing outward, designed to accept a MTL 1015 (screw hole must be predrilled with a 0,9 mm drill).  If you run both 1 Spot and 1A booster together I suggest a shorter coupler (see picture above). In that case you can remove part of the coupler pad lip. I used a MTL coupler screw to attach these couplers. The diaphragms will hide the pad/extending coupler quite well.

Grind or cut away as much as possible of the back end of the truck, just barely behind the gear on the last axle, to create enough clearance.

Now clean/degrease the completed shell in warm soapy water or a dgreaser. Let dry and airbrush the shell with diluted Mr. Primer Surfacer 1000. This will also help covering printing irregularities.

Next airbrush the shell with your favourite aluminum paint (I use Vallejo). When thoroughly dry mask the area to remain aluminum with masking tape (I use Tamiya tape in different sizes). The template for the curved warbonnet is made by copying the decal sheet, covering the complex curved warbonnet stripes on that paper copy with masking tape and cutting down the middle of the line using a fresh no 11 scalpel blade. Gently lift the masking tape from the paper and apply to the shell. You can easily reposition several times till you are satisfied with the result. Airbrush your favourite ATSF red paint (I use Tru-Color).

There is no dedicated decal set for this model so some improvisation is needed.

The nose sigar band of the PA is almost spot on, both shape and length are OK. Can be found on Microscale N 60-72 (Santa Fe PA diesels). All other decals can be found on Microscale N 60-1072  (EMD E1, E3 and E6 cab units). It will take some cutting and pasting. The only tricky decal is the vertical part of the cigar band, around the headlight up to the window front. There is no decal fitting that contour. I ended up masking the little area with Tamiya tape and brush painting the spot ATSF yellow (Tru-Color). With all other decals in place I did not dare masking everything and airbrushing that little area, but it turned out OK anyway. Adding all the little black striping (wide and thin) was a challenge....... but succesfull.

I repaired small blemishes in all 3 colours with a 0/5 brush and a steady hand. A short airbrushing with Dullcote sealed everything.

The last job is window glazing. Personally I am very happy with Kristal Klear from Microscale, applied with a steel needle, but clear styrene could also be used. The thickness of the walls is a bit more obvious then.