3D printed parts for the 1/25 Peterbilt 281 from 'Duel'

The movie 'Duel' made an impression when I saw it as a child, just like 'Convoy' did in a different way. 40 years later, I have plans to build two US trucks: the 'Duel' Peterbilt 281 and the 'Convoy' Mack R700. For the Duel truck, you generally start with the AMT Peterbilt 359. It's a complicated project: cab, hood, grille, wheels, tires, engine, axles have to be changed. I started work on the front wheels and the cabin's front windows.

Front axle wheels

The front axle wheels have been identified as five hole (diamond shape), split-rim Budd wheels. First, I wanted to know whether the wheels were 20" or 22" diameter. I had heard or read that director Spielberg had bigger wheels and tires fitted, to make the truck look more menacing. On the MCM forum, Brian Smith suggested comparing the bolt pattern diameter to the rim size - an excellent idea!

I did a photo measurements of three movie screenshots, and determined the relative size of the bolt pattern diameter compared to the outer rim size. I averaged the size of the outer and inner bolt pattern diameters. The middle and right one agreed nicely at 44%, the left one resulted in 52.6%. Maybe we don't see the whirling nuts, just the the sheet metal disc? Next was finding the value of the bolt pattern diameter for US 10-bolt wheels. 11.25" / 285.75 mm kept coming up on the internet, so I used that. Using that figure plus the 44% from the photo analysis, I get 11.25"/.44 makes 25.6". Deduct two times 2 inch for the tire retaining lip, and I get ~21.6". That's close to the 22" I was guessing. The value of the tire bead retaining lip comes from a Dutch reference from 1961 (Steinbuch); it lists 50.8-51.0 mm (i.e. 2 inch) for 10.00W-20 wheels. But I have no idea whether that number is correct for US trucks. I will assume 22" wheels from here on.

Apparently wheels for the Duel truck were made by 'Griffen Designs' in resin around 2009, but they no longer active (see The Duel Truck, who makes a kit). Also mentioned are the front wheels of an AMT fire truck, likely the American-LaFrance Custom Pumper / Ladder Chief / Aero Chief series of models. What I found showed five-hole wheels, but the holes were D-shaped, and I could not find the size. Lastly, the Moluminum Tyrone Truck Mate Wheels. Also a five-holer, but with elliptical holes, and again I could not find the size. 'DoubleTake' is also mentioned, but has closed shop. I concluded it was easier to have my own wheels printed, than find and order them from the USA. Here's my first version of the front wheel in 3D. It needs to be refined. All dimensions in 'axle direction' were guesstimated from the photos, I don't have a way to measure them. Note to myself: the front wheels have different colors.

A second version of the front wheel. Wider diamond cutouts, a slightly less dished disc, slightly smaller wall thickness for the disc.

Here's the first print by club member Wim Hoogendoorn, in orange resin no less. It looks great I think! But I clearly made a mistake with the wheel width. With the tire beads on the rim, the wheel sits too deep in the tire. I'll have to redesign the 3D CAD part. The tire is from AMT's Part Pack PP028 'Semi tractor tall tires 11.00-22'. 11.00-22 means an 11" wide tire body on a 22" diameter wheel. Standard aspect ratio is (was?) 88 percent, making a 22 + 0.88 * 11 * 2 = 41.4" theoretical diameter tire. That makes 42.0 mm in 1/25 scale, and the AMT tire is exactly this size.

Shown here are the first print with the tire only half on the rim, and the second print with changes. I increased width between the tire beads by one millimeter, and increased the depth of the disc by the same amount.

I gave the parts four light coats of Tamiya Surface Primer. The wheel fitted nicely in the AMT Parts Pack tire. I think I'm done! Or maybe not? My latest analysis of movie screenshots suggests that 12.50-22.5 tires were fitted instead of 11.00-22 tires. This gives a theoretical 44.5" instead of 41.4" diameter, 7.5% larger, or 15.5% extra visible area. I have no idea whether 12.50-22.5 tires are available in 1/25 scale.

Windshield modification

The Peterbilt Spotters Guide reports: "Post-1960 Unilite cab that featured larger glass, a new instrument panel, smaller rubber windshield gaskets and a larger rear window" and "This view shows the pre 1960 cab. Note the slider rear window, the drip rail that surrounds the roof of the cab". I also found "The (Duel) cab is earlier and has even smaller windows than the California Hauler 'small window' Unilite cab 351 and AITM has the correct cab." The movie truck is a 1955, so it has a drip rail above the windshield, therefore the windshields must be decreased in height. The cab is probably steel instead of aluminum (Unilite), hence no rivets, or less rivets. The photo compilation shows these details clearly. The solution might be simple: design 3D printed wide rubber gaskets, slightly lower windshields, to be glued inside the kit's window openings. An alternative is to make the rubber gaskets with (for example) two lead wire diameters.

Here's the first version of the windshield correction piece. The radius of the pre-1960 windshield corners are much larger, so I decided to start with an insert made to fit the kit windows, and added the rubber gasket on top of that piece. On the top side I left 0.5 mm to create a bit of space to the drip rail.

On the back side I made a recess for the windows. One problem might be whether the part as designed is printable. It will require a ton of supports I guess.

The prints by club member Wim turned out fine. I was afraid that they would be too floppy to print.

I gave the parts four light coats of Tamiya Surface Primer. They fitted nicely in the window openings, with minimal sanding of the corners. I based the design on measurements the left window opening, therefore the fit of the right-hand part was a little less tight. The kit's cabin had moldings around the windows, the chrome trim. Since these were not present on the old 281 version, I sanded them all off. The 3D printed parts can be glued in now.

Needle nose grille

Another major component required for the conversion is a narrow grille. I based the design on measurements of screenshots of the movie. The exact width is a bit of a guess..

On the rear side the part has lips for the hood parts to rest on, and enough room for a radiator.

Version 2: it was narrowed a bit, rivets were added to the sides, and a simplified hood ornament was added.

Off to the resin printer now. It's always a suprise what comes out..

Club member Wim printed three examples, all in different positions. On the right one, the grille louvers failed to print completely. On the left one, the louvers are 99% right, but they are so thin they look like razor blades if viewed at the right angle. The horizontally printed one is maybe the best, but it's slightly curved. All prints have in common that multiple supports attach to the louvers, and it will be very difficult to remove them without breaking the louvers. I will probably make them thicker for the next print.

The next print is on the left. The louvers were made 0.45 mm thick instead of 0.3 mm, and still look thin enough to my eye. Each louver had about eight print supports. But I forgot to add supports to the frame above the louvers, so that came out deformed. Another problem that kept coming back were 'dog ears' at the bottom of each printed part. The next print was perfect! I added extra supports at the 'dog ear' corners, and that solved the problem 95%. A bit of sanding solved the remaining 5%.

By request: a picture of the 'pre-supported' grille. The supports were added manually, because automatically generated supports did not yield good parts. It's my own interpretation of what was required, and I went for 'safe' regarding the thin louvers, giving them 10+ supports each.

The result was a true forrest of supports. But that's mainly because this a difficult part to print. As a consequence, it was difficult to get all the supports off. I worked my way down from the grille's top, and maybe spent half an hour. I had positioned the supports on the louvers such that I could get to them with a razor blade saw from the front (as you see in the picture). I would then snip away the supports from the rear side. Still I broke three louvers, but the breaks are so brittle that they fit perfectly back together, and could be glued invisibly with thin CA.