Building the Baldwin 50hp, step by step

In the First World War, the War Department Light Railways used Baldwin 50hp petrol tractors to haul supplies behind the lines. Our 16mm scale kit lets you build your own, in 32mm or 45mm gauge. This guide takes you through the whole build in order, with tips from our workshop and George Williamson's two-part video series to follow along.

What's in the box

• 3D printed body, chassis and detail parts

• Laser-cut steel chassis frames and coupling rods

• Laser-cut acrylic parts and wire mesh

• A ready-built gearbox with a 6–15V MFA motor and a 20:1 worm gear

• Wheels, axles, brass bearings and bushes

• All the screws, nuts and bolts, including 2mm and 3mm sizes

• Rivet heads and detailing parts

  
  

What you'll need

• Superglue, and liquid poly for the rivets

• Wet and dry sandpaper and a small file

• Filler such as P38 (optional, but it improves the finish)

• Grey primer and your top coat colour

• Small screwdrivers and spanners for the 2mm and 3mm nuts

• Batteries and a switch to run it: disposable batteries and an on/off switch, or rechargeable batteries with radio control

  
  

Step 1: Prepare the printed parts

Time spent here shows in the finished model.

1. Sand every part you plan to paint to remove the printing marks. A small file gets into the tight spots.

2. Fill any marks that remain with a body filler such as P38.

3. Give the parts a coat of grey primer. We use Halfords plastic filling primer.

4. Rub the primer down with fine wet and dry, then prime and sand again until the surface is smooth.

5. Glue on the rivet heads at 5mm intervals with liquid poly. Let them dry, then give one last coat of primer.

For more on sanding and priming, see our post How to paint 3D printed kits.

Step 2: Build the chassis

The chassis is the heart of the model, so take your time and get it running sweetly before anything else goes on.

1. Fit the brass bearings into the axle holes in the frames, flange outward. Press or glue them in. Now and then a frame needs a little adjustment for the bearings to fit.

2. Attach the chassis frame spacers to one side of the chassis frame with 2mm countersunk screws, with the nuts sitting in the slots. Don't overtighten them.

3. Fit the wheelsets and gearbox so the motor drives the front axle, then fit the second frame and the motor cover.

4. Fit the brass tube through the dummy gearbox, centre it so both ends stick out equally, and glue it.

5. Fit the cranks to the axles and tighten each one with its grub screw. The 2mm bolts through the cranks are the crank pins that the rods run on. Set the crank pins on one side at 90 degrees to the other side.

Workshop tip: check the movement as you add each part, from the moment the wheels go in. If it doesn't roll freely, you can unscrew the motor from its housing so you can find where it's tight.

Step 3: Fit the coupling rods

1. Open out the holes in the rods until the brass top-hat bearings just fit. A dab of superglue holds the bearings in the rods.

2. Fit the two short rods to the cranks, held with a 2mm nut at the front and a printed washer at the rear.

3. Test run the chassis. If it binds, check it through methodically, one part at a time. It usually comes down to the cranks not being quartered properly.

4. Once the short rods turn freely, fit the long coupling rods:

   • Put the front drive crank onto its axle, but don't tighten its grub screw yet.

   • Fit the long rod, with a top-hat bearing at each end, and secure it with 2mm nuts.

   • Use the long rod to set the quartering. The cranks on each side must sit at 90 degrees to the cranks on the other side, and match the other cranks on their own side.

   • Once the rod is on and the quartering is right, tighten the drive crank's grub screw.

   • Do the same on the other side.

5. Test run it again.

George covers the chassis in Part 1 of his series:

PDF Models 'Baldwin' 16mm SM32 Build Pt 1: Chassis!

Step 4: Build the bonnet

1. Fill and paint the bonnet, then fit the louvre panels.

2. Fit the radiator cap into the hole on top of the radiator, and glue the grille inside with superglue.

3. Fit the exhaust with a 3mm bolt.

4. Fit the bonnet to the chassis, then glue the radiator to the front, using the chassis to line it up.

5. Glue the fuel tank support to the top of the bonnet.

   
   

Step 5: Build the cab

1. Paint the cab parts before you glue them together. It's much easier than painting inside a finished cab. Remember to sand a little paint off where the parts join, so the glue can bond the acrylic. Or mask off a small strip before painting, so it stays bare and ready for glue.

2. Glue the control panel inside the cab. Extra cab detail parts are included if you want to go further.

3. Fix the cab with three 3mm bolts and nuts: one at the front and two on the floor at the rear.

4. Glue the roof on last.

Workshop tip: you can paint parts as you go if you want them a different colour to the main body. It saves a lot of masking later.

Step 6: Paint and weather

These machines worked in mud and all weathers, so a bit of dirt makes it look right. George shows his painting and weathering in Part 2:

PDF Models 'Baldwin' 16mm SM32 Build Pt 2: Body & Paint!

Step 7: Power it up

Fit your batteries and switch, or your radio control gear, and it's ready for its first run.

Want the extra detail?

The kit is also available with the SLR detailing pack, for an even more finished model.

Get the Baldwin 50hp kit. The build instructions are on our Building Instructions page.

Happy building, Stan