Continuing work on the gantry crane for the sawmill. Here’s a photo of the prototype for reference:
I’d gotten to the point of building the boom, and the most complicated fabrication of the model. It’s a truss, but the vertical members are inclined and some of the structure would have to be inferred because it’s not visible in the photo.
I started by scaling the boom off the mechanical house. I then marked a template on cardboard to aid in structural positioning. I suppose I could have drawn the structure, figured the dimensions of all the pieces, then cut the parts and assembled. That would have been the good engineering approach, but despite training and experience, I didn’t do that. I did what I suspect pretty much everyone does, and built the structure in place while fitting pieces individually.
And there’s a lot of pieces. I used 2 mm I-beam for the main vertical supports and the lower longitudinal beams, and 1.5 mm I-beam for everything else. I would have preferred 1 mm I-beam for the bracing, but none was readily available. I guestimated the vertical support angle at 75 degrees, and that looks about right. During assembly I used CA for initial fabrication, then applied MEK to the joints after the CA dried to ‘weld’ the styrene.
Assembling the boom:
I decided not to add gusset plates because in N-scale, it’s not worth the effort. I had thought to use modeling putty to fill in the holes where the vertical and horizontal members join, but discovered that the gaps are so small it’s hard to produce an acceptable result. I left the gaps, trusting that paint would cover those flaws.
The boom in Flat Red primer:
This resemble nothing so much as a dragster frame at this point.
And with the color applied:
Building the crane boom reminded me of building a model of CVN-65 Enterprise as a boy and masking and hand-painting the flight deck markings. Tedious, exacting, and sometimes frustrating, but the end result is hopefully worth the effort. I could certainly point out all the flaws, but most people are going to see this and think ‘Wow. That’s really cool.”
I built the boom over the space of a couple of weeks, and it took a while. Several football and basketball games were enjoyed during construction. The crane in general and the boom specifically are the most complex scratch building projects I’ve attempted, and may well be the last time I build such a structure by hand. For similar projects in the future I’m going to look into having them 3D printed. There’s a learning curve for the drawing programs, but once the time is invested producing drawings will take far less time than fabricating a structure. Printing is more expensive than styrene stock, but the time saved will more than offset the expense. And the models will be much better.
While the model is not yet complete, the really fiddly parts are. Like learning mechanical drafting prior to learning a drafting program, I’m glad I did this so I know what’s involved. But for even a small number of such structures I’m not sure that hand fabrication is the most efficient way to go about this. I enjoy scratch building, but there’s only so much time.
Next up: the trolley.