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3D Printing and CAD techniques and questions


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Hello, I have been watching the advances in 3D Printing for some time now and having seen some of the superb model railway parts that have been produced by rmweb and demu members it has got me thinking about a possible way of making a project I have thought about finally come true.

 

Essentially, what I am trying to achieve is some OO scale models of a design of electricity transmission tower. Think of the Hornby plastic pylon kit that has been in their range since the early 1960s and is still in regular production. These are a reasonable but much scaled down version of the type of pylon that runs past the Hornby factory in the Westwood Industrial Estate in Margate. These towers are one of the earliest towers built for the new National Grid during the 1930s. What I am trying to replicate is the other version of this design of tower that only has a single circuit rather than the double circuit seen on the Hornby model. These single circuit towers have the three phases arranged with two crossarms on one side of the tower and the other one on the opposing side but between the other two, thus creating a triangle arrangment of the crossarms.

 

I did have a stab at doing these towers in etched brass a few years ago but that didn't quite work out and the project has remained on the back burner since. Having done all of the research on these towers I would still like to get them made somehow. An injection plastic tower would be totally out of the question on price alone whereas a 3D printed tower using the Shapeways process might make it a lot more affordable.

 

Now I have absolutely zero CAD skills and I have had a look on the other threads and I have noted that Google Sketchup and TurboCAD Deluxe v12 seem to be useful tools to have a tinker around with. Or it is worth asking if any members would be interested in helping me out with producing a suitable CAD model that could be used to make the Shapeways model?

 

As for the transmission towers themselves, well they come in different designs according to their function. The simplest is the S2 standard tower that has vertical hung glass or ceramic insulator strings. These towers don't usually allow the course of the line to deviate any more that 2 degrees. Next up is the S10 deviation tower with pairs of insulator strings on each crossarm to allow the line to deviate upto 10 degrees. Then further variations allow deviations upto 30 and 60 degrees and the final design being a terminal tower where the circuit reaches a electricity substation. As for drawings of these towers I haven't been able to get hold of any so far (any suggestions or help most welcome here). I can obtain photos of towers that I can access from public footpaths and I would be able to obtain some measurements from the base of the tower only as obviously it is certainly not a wise thing to try and climb up any part of the tower whatsoever. I will add that I have an interest in transmission towers, the designs and history and don't worry I am not the only one who shares this passion (and no I haven't been sectioned yet!)

 

So is it possible to make a tower shape in 3D and get models produced via Shapeways? Any comments and help most appreciated.

 

Thanks Paul

 

PS. I can post links to illustrate the tower designs, which you will have seen on your travels around the UIK at sometime or other

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It should certainly be possible, the only thing you'd have to watch is the size of the various sections, as they'd probably be rather fragile in whatever material you had them 'printed' in. From what I've done so far, I don't think it'll be that difficult to draw up in a 3D package.

 

I'd suggest downloading Sketchup and completing a few of the online tutorials, to give you an idea of how the program works and whether you can get on with it. The style of Sketchup and TurboCAD are quite different, with one being designed as a 3D package for animation and that kind of thing, the other being designed for making engineering parts.

 

HTH

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Thanks Martin, I will give them a go and see how I get on. Just so rmwebbers know what I am on about here is a photo of the kind of tower I am looking to do.

 

http://i195.photobucket.com/albums/z231/paulsrailphotos/UK%20Pylons/2009%2007%20Hartford/DSCF0259.jpg

 

That should give you some idea of what I would like to try and do. Obviously some of the metal latticework would need to be beefed up and this might be the only area where such a model would be too fragile. But no harm in having a go at it.

 

Cheers Paul

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No harm at all. I guess the only other suggestion I'd make (apologies if this is an egg sucking moment) would be to see what parts are similar in the various designs of tower that you want to do, and split the model in those areas, cutting down on the design time.

 

Best of luck, I look forward to seeing how you get on.

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There are two restraints, apart from the cost, with producing these as 3D prints. The first is the minimum wall thickness allowed. From the photo it appears that the pylon is mainly 3" x 3" angle. By making the model from 1mm square section rod both the Shapeways FUD and WSF could be used. Chamfering off one corner of the section will give the illusion of an angle section.

The other restraint is the maximum size the machine will accommodate. For FUD this is 175mm and for WSF 660mm. The pylon appears to be about 90' high, or 360 mm in 4 mm scale, which would rule out using FUD. There are problems with large thin WSF models warping and so there is a recommended minimum wall of 2.2 mm for models of this length. Since the structure is open you may be able to get away with using a nearer scale wall thickness, but this may take some trial and error to get right.

Because of the relatively shallow angles of the sides of the pylon you are likely to get pronounced stepping on one or more faces.

I suggest you study the material design rules carefully before committing your self to this project.

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I would be tempted to draw one side so that it can be printed flat four times and then stick it together. I can't help but think they would be better as etched parts though, depending on thickness and material section required?

 

Print once, make a mold and take a resin castings from it.

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No harm at all. I guess the only other suggestion I'd make (apologies if this is an egg sucking moment) would be to see what parts are similar in the various designs of tower that you want to do, and split the model in those areas, cutting down on the design time.

 

Best of luck, I look forward to seeing how you get on.

 

Hi Martin, I don't think there will be many if any common parts across the range of towers S2, S10, S30, S60 and ST as the tower shape will increase in width at the tower base the greater the angle of deviation to as to counteract the greater forces imposed on the tower due to the change of angle. So maybe only the crossarms on the S10 and S30 may be similar (I will need to check to be sure on that one - fieldtrip to Cheshire may be required!). So I may have to rethink my approach on this one.

 

Cheers Paul

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Thanks for the comments guys I will have a look and see what the best way to proceed is. If 3D is not suitable then it will be back to a revised brass etch that ideally would be a four-sided tower with half etched fold lines to allow the tower to be folded and built around to close up and form the tower. Then by adding the top of the tower plus the crossarms this would complete the tower with just some insulators. So then the question is would it be possible to do the insulator strings in FUD or WSF to make them slightly more durable than home made efforts.

 

Cheers Paul

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Thanks for the comments guys I will have a look and see what the best way to proceed is. If 3D is not suitable then it will be back to a revised brass etch that ideally would be a four-sided tower with half etched fold lines to allow the tower to be folded and built around to close up and form the tower.

 

I don't think that will work. the corner angles don't provide enough metal to enable the fold to be made at the corners an not, for instance, at the join between the bracings and the corner angles. I would suggest the sides are made in pairs with two side tabbed together at say 30-50 mm. Each pair could then be folded relatively easily with the fold line on the outside and the fold reinforced by soldering a thin wire into the fold line. The two halves could then be simply butt jointed together.

 

So then the question is would it be possible to do the insulator strings in FUD or WSF to make them slightly more durable than home made efforts.

Insulators could be made in FUD, but they should have a hole through the middle so that they can be threaded on wires and hung from the crossarms with a free joint.

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