If I had access to such a laser cutter, I would cut them from a single sheet of aircraft plywood. You can get aircraft plywood as thin as 1/64" in 3 plies. It seems like 3/32" in 7 plies would work out to scale and be more than strong and stiff enough.
The cross section trussed ribs you're looking to fabricate will be about 20" across by 10" high in HO, with struts about 0.10" square. In the scheme of things that is not too big at all. Michael Rose could cut them as a single piece on his home shop desktop laser. Your laser most likely has a much greater capacity. Cutting them as two half-pieces would be, well, half as big.
There are two large bridges on my N scale layout. Both are similar in nature to your proposed structure, and both are larger. The smaller one has a 30-inch clear span; the larger, 60 inches. The web struts and girders on each measure 0.10" by 0.10", about the same as what you propose. Photos posted on my layout build thread.
Good luck.
Robert
LINK to SNSR Blog
Hi Dave,
I'm really excited about the project. Grand Central Station was torn down not long after I was born and about 10 years before my family moved to Chicago, so I never got to see it. I have done a ton of research on this project. I'm figuring the contruction of the station and train shed should take me close to a year. I have a lot going on these days.
I am very lucky to have the job I have. My job is in steel fabrication for a multi billion dollar company and includes running a cnc laser, cnc press brakes, cnc horizontal band saw, cnc plasma machine, cnc horizontal and vertical milling machines, cnc lathes, and I do some welding as well. Unfortunately, not much of this is applicable to model railroading!
If I were to make the trusses out of steel, they would be out of 12ga (.104") or 14ga (.075") material. I really don't want to thicken things up too much and get out of scale.
I am going to make the trusses out of strip styrene. I will laser cut a jig to help assemble the trusses. I will make a cad drawing of the jig template this weekend and get started on the trusses next weekend. I will post pictures of my progress as I go.
The other thing I will fabricate at work is my turnout contol boxes. The switch panel will be laser cut and etched. Should be fun.
Ed
Semi newbie HO scale modeler coming from the O scale world
Hi Ed,
That will be a neat project! I can't imagine having a tool like that and the knowledge to use it for modelling.
You mentioned that making the trusses out of steel might not work because of the delicacy. Do the truss components have to be exactly to scale? I doubt that too many modellers will be putting a micrometer on them to see how accurate they are. Perhaps increasing the width by 20% - 30% might make them strong enough while still maintaining the basic look.
Just curious - how thick would the steel be?
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
You might want to look up an article or series of articles Eric Bronsky did for Model Railroader years ago - his task was to built the elaborate and somewhat lacy looking catenary towers that the Insull interurbans (North Shore Line etc) used. But they also had to be structurally strong. His solution was a shape of clear acrylic or plexiglass (can't recall which) with the structural shapes etched in and painted. So in a sense it was an optical illusion. But it was very convincing not only in person but in photographs.
True those were catenary towers, not trainshed supports. But the elaborate and complex look was similar and the need would be similar for greater structural strength than you might get from a totally accurate model built of plastic, metal or wood.
Dave Nelson
Sounds like a plan!
I would maybe use a mold release or silicone spray in your jig before gluing up since the cement is going to seep through and cause enough sticking to make removing the truss tricky. Probably some careful slicing and prying with a #11 and a chisel-type Xacto blade.
Depending on your final thickness I think several layers of, say, .030 would probably do the trick. Looks like .040 is as thin as they go in the 24" length.
I believe Evergreen has bulk packs of the common sizes, too. (.040 x .100, 50 pieces, 24")
Good Luck, Ed
as you found out evergreen has 24 inch strips . for gussets if needed try tichy https://www.tichytraingroup.com/Shop/tabid/91/c/ho_nbw--rivets/p/8216/Default.aspx
gmpullman I don't think balsa has the strength or flexibility you would need. I would lean more toward Evergreen styrene using the laminated method and cementing the laminations with very thin solvent. Then fit the diagonals in using your truss pattern. You could get fancy and use gusset plates at the major joints to help add strength.
I don't think balsa has the strength or flexibility you would need. I would lean more toward Evergreen styrene using the laminated method and cementing the laminations with very thin solvent.
Then fit the diagonals in using your truss pattern. You could get fancy and use gusset plates at the major joints to help add strength.
mrrdadI'm thinking of making a jig and gluing 3/32 x 3/32 square balsa or basswood rods together.
I like the idea of the jig. I would probably make half-arches then at final assembly bring them together at the center.
I seem to recall a M-R article about an arched train shed that was laser-cut a few years back. I'll see if I can find the issue.
[edit] It was september 2015, p. 26 Scratchbuild With 3D Printed Parts and it showed a fancy arch end wall. 3D printing may also be a logical solution especially since you need repetitive parts. Again, I believe making them in two halves would be a good way to go and if needed you could have a short filler section in the center if you needed to adjust the width at any time.
Meanwhile, take a peek at the train shed the folks at NAPM have built.
Zephyr at Union Terminal by NAPM Model Railroad Club, on Flickr
A little something for inspiration!
I am working on scratch building the train shed from Chicago's Grand Central Station. The shed contained 14 or 15 (I can't recall off hand) arched steel trusses. How would you make these?
I run a 1.5 million dollar fiber laser at work, but I think the detail is too fine to cut them out of steel. I'm thinking of making a jig and gluing 3/32 x 3/32 square balsa or basswood rods together.
What are your thoughts?
Here is a link to a drawing of the trusses:
http://cdn.loc.gov/service/pnp/habshaer/il/il0100/il0117/sheet/00003v.jpg