1/72 Cletrac High-Speed Tractor.

[Builder 2010]

I have a colleague that asked me if I could create a 1/72 scale model of a Cletrac tractor for a diorama that he's creating. I've done other 3D printed articles for him. I first had to draw the vehicle and found enough images on line to use in SketchUp's "Match Photo" application. While not a perfect or fully detailed rendition, the model is so small that many of the details, while capable of being printed, were incapable in being cleaned up and finished. I first attempted to print larger sub-assemblies with supports, but the fine supports failed miserably and all I got were some track sets and seats. I re-designed the model and the printing approach and got some more success, but still more to do. I'm going to reprint more tracks and try a different approach tot eh tiny headlights. They're so small that some disintegrated in the ultrasonic cleaners used to remove the uncured resin that accompanies all 3D printed parts.

Here's the real vehicle.

Here's my drawing. The headlight and radiator guards would not be viable in a resin print in 1/72. They would barely survive in 1:48. Injection molding does have some advantages over 3D printing in producing viable small cross-sections.

Here's the parts breakdown that will be used in printing some of the parts.

And finally, here's the parts printed so far. I'm reprinting the tracks, seats and headlights. It costs very little to print these tiny parts… pennies… so making more than you need is prudent since spoilage is quite high.

 

[Wurger]

 

[Crimea_River]

Cool.

 

[herman1rg]

What slicing software do you use?

 

[Builder 2010]

I use ChiTuBox which came included with my Elegoo Mars Resin Printer. It's a decent slicer and it's been upgraded several times since I've owned it.

I was using the wrong scaling factor to reduce the full-sized SketchUp drawing to 1/72. I was using 0.013 and the model looked too small. Also I was having a terrible problem with the right track part. After fussing with the prints I decided to examine the drawing more closely and found that the bracket that supports the road-wheel bogies was not a solid shape. The very narrow bottom was missing. As a result the print kept failing in weird ways. I fixed the error and re-exported all the drawing STL files with a scaling factor of 0.014. 1/72 scales to 0.0138, so .014 is closer. Having it slightly oversize (very slightly!) made for better printing and gave a little more strength to some of the finest cross-sections. I split the parts up so ALL can print directly on the build plate and no supports need to be removed and cleaned up.

Here are the new parts still on the print plate. I got 100% success on all of them.

I'll have them cleaned up and assembled tomorrow.

 

[Wurger]

 

[Gnomey]

Good work so far!

 

[Builder 2010]

I'm ready to deliver these to the customer. The back tow frame broke on one so I gave him a discount. The reprinting to a more accurate size was a good choice.

 

[Wurger]

 

[fubar57]

Beauty

 

[Gnomey]

Good work so far!

 

[Builder 2010]

An update: The ones I built were probably 1/144 or smaller and basically trash (although an N-Gauge fellow who works at the hobby shop wants them) and the fellow who wanted the 1/72 scale cancelled his request, BUT… the owner of Scale Reproductions, inc. (America's best hobby shop IMHO), has asked for two of them in 1:48. To go from 1/144 scale to 1:48 required re-drawing and engineering the entire model almost from scratch. I did finally find a simple line drawing that had the correct overall dimensions of the M2 and I was able to get the scale correct. I also detailed all the subassemblies down to the bolt heads as required by a larger scale. The model came out to 15 or so parts including the detailed Hercules 6-cyllinder flat head engine that's almost invisible in the finished model. Drawing took a lot of time and studying the pictures I found of this tractor. The results are gratifying and I finished them today. I will be delivering them tomorrow.

He was the final drawings in an exploded format showing pretty much the subassemblies. The headlights were two-part affairs and my final version combined the frame, bumper and winch in one part. I suppose you could print the entire model in one piece, but not on an LCD matrix printer. The supports would be so complex and hard to remove that it would destroy the model in the process. There are other 3D printing systems that don't require supports, and they are expensive, but could do the job in one go.

Many of the parts required multiple printings or printing multiple parts in a single go based on the parts fragility and how many will get broken in the cleaning process. I printed many headlights because they were very frail and I needed many of them before I was able to get four intact ones. Luckily, the printer isn't too sensitive to quantity of small parts and the amount to resin consumed is miniscule. I printed 3 sets of treads to get two good ones. I didn't detail the track assmbly's back since I thought I would print it directly on the build plate. As it is, adding all the additional details (track adjusters, fender straps, etc.) required tilting the tracks on the machine and adding supports to make it all print.

I printed several tests of the headlight guards and the operating floor which included the steering levers and gear shift lever. I kept having to add thickness to make a part that could sustain itself. Same goes for the complex air tank system. There's a lot of trial and error in this business. The good thing is once you get a scheme that produces good parts it will continue to do so forever.

Here's the finished product.

The window glazing is 0.010" clear styrene. I then added back framing with cut strips of Tamiya tape painted Olive Drab. I used straight Tamiya O.D. for the first coat and then went back and air brushed a coat of lightened (faded) O.D. on the top facing surfaces. I lightly weathered the track area with dust colored chalk powders, and made a window mask for the wiper track. I didn't have a way to make a respectable windshield wiper since it's a good candidate of photo-etched. And I didn't add decals since I can't make white ones. I'm leaving this last bit up to Brian Bunger, the client, who is a terrific model builder besides the hobby shop owner. I tried to print the headlight guards with final detail, but it didn't work. Again. This is a good PE candidate.

 

[Wurger]

Excellent !

 

[rochie]

fantastic

 

[Gnomey]

Nice work so far!