How best to construct a 3D printed coach/multiple unit?

[njee20]

I've dabbled in 3D printing various wagons for the last few years, both in N and latterly in O. I've been messing about with the CAD for an Electrostar (again, to start in N, with a view to doing in O and potentially OO if anyone was interested). With wagons I adopt the approach of single bodies, for ease, but obviously that doesn't work for a coach/unit, where there's an interior/glazing to sort.

 

How do people do this? I've got the makings of the CAD for a DMSO body, and done a test print, which worked well. CAD looks like this FWIW:

 

 

But I don't know how best to do the floor/underframe - interference fit? Screwed, if so into what? I worry that having clips, like on RTR models, won't work too well - the test print I did bowed outward along its length (which was fine, I didn't try to combat it), but wondered if I needed some sort of strengthening to keep it together, perhaps with a clip in underframe, a bit like a Dapol mk3 if anyone's disassembled one! Then I wasn't sure how easily the glazing would go in.

I wondered about cutting the end off, so printing it as a 'tube', into which the glazing and seating could be fitted, and the end pushed on. Like an Electrostar shaped Pringle tube.

 

Advice welcomed!

[Jeff Smith]

This thread might interest you, I'm thinking of the 'print flat and wrap around bulkheads' approach!

 

https://www.rmweb.co.uk/community/index.php?/topic/168451-3d-kit-of-parts-for-ltsr-4-4-2t-no80-thundersley/#comment-4703134

[njee20]

Interesting approach! Can’t see that working with a resin print without a sort of skeleton to wrap it around, which would seem to defeat the purpose, but good way of doing it!

[KeithHC]

My thoughts would be do it as a kit of parts. So sides ends etc. you could then also produce bulkheads that would then resolve the bending issue. Also you would end up with sides that could be also used for the turobostars as well. This would need new ends etc.

 

Keith

[njee20]

With RTR Turbostars out there I've no real interest in replicating those; plus I'm focusing on the later build Electrostars which have the distinct windows, rather than the 'ribbon' glazing. The problem (particularly in N) with doing a kit of parts is that there are so many joins to fill; for me the advantage of 3D printing is that I can produce a perfectly profiled one piece body (or more significantly I can produce 50 identically profiled bodies!). 

 

I'm not too worried about the distortion, that's easy to mitigate, what I'm not convinced I can easily do is having a natural 'spring' in the bodyshell to make an interference/clip fit work like an injection moulded body would.

[spsmiler]

I have some Shapeways 3D bodies (in OO) and some of them have flat bars joing the two sides across the bottom which prevent the sides from bowing, maybe if you did this (for instance where the sliding passenger doors are, as that way they won't be in the way of seating units)  then you could screw the chassis in to that.

 

You could possibly also add a 5mm ridge at the same height just inside the body at each end, these too could be used for screwing the chassis / underframe to the body. Just need to ensure that does not foul the bogies, wheels, etc as they swivel when negotiating curved track.

 

I think that OO Electrostars will very much interest modern image modellers, as would the more recent Aventra trains. 

[Mike Harvey]

For my printed SNCF Corail coaches in 1/160 everything is a potentially interference fit. Proprietary close couplers and bogies clip into the chassis. Interior locates on chassis with a small square of double sided tape at a couple of points for extra security if desired.  Donor coach windows clip in, but a drop of PVA provides extra security. Chassis plus interior clips into body, but couple of short strips of double sided tape can provide extra security. Interference in this case is 0.1mm play between the main assemblies.

[LMSfan72]

I’ve taken the Pringle tube approach on a lot of my OO gauge ones. I also sometimes have cut outs in the underside to help and have fill in chassis sections. It’s been an experimental journey - some of which is on my blog on here!

[njee20]

3 hours ago, Mike Harvey said:

For my printed SNCF Corail coaches in 1/160 everything is a potentially interference fit. Proprietary close couplers and bogies clip into the chassis. Interior locates on chassis with a small square of double sided tape at a couple of points for extra security if desired.  Donor coach windows clip in, but a drop of PVA provides extra security. Chassis plus interior clips into body, but couple of short strips of double sided tape can provide extra security. Interference in this case is 0.1mm play between the main assemblies.

Thanks Mike. I looked at the print I have of your excellent Corail coaches and did assume they were just an interference fit. Double sided tape does work miracles!

 

1 hour ago, LMSfan72 said:

I’ve taken the Pringle tube approach on a lot of my OO gauge ones. I also sometimes have cut outs in the underside to help and have fill in chassis sections. It’s been an experimental journey - some of which is on my blog on here!

That’s good to know it could work! My nervousness was around things like cab glazing, lighting etc, unless I made the cab front the ‘lid’, but then you’d have a visible join right at the front, and there’s a lot going on in the shape. Good to know it conceptually works though. 
 

3 hours ago, spsmiler said:

I have some Shapeways 3D bodies (in OO) and some of them have flat bars joing the two sides across the bottom which prevent the sides from bowing, maybe if you did this (for instance where the sliding passenger doors are, as that way they won't be in the way of seating units)  then you could screw the chassis in to that.

 

You could possibly also add a 5mm ridge at the same height just inside the body at each end, these too could be used for screwing the chassis / underframe to the body. Just need to ensure that does not foul the bogies, wheels, etc as they swivel when negotiating curved track.

 

I think that OO Electrostars will very much interest modern image modellers, as would the more recent Aventra trains. 

Yes, I’m not worried about the bowing, it’s easy to fix with something like you say - simply having joining bars. I know CMAC do Electrostars, and his designs always look great, I don’t model OO, but I’d make them available if there was interest given I’ll have the files!

 

Mike Trice of this parish very kindly sent me some details of his approach too, which involves screwing the underframe in using M2 screws and threaded inserts in the body, similar to how you describe. That looks very elegant, and I would hope is the toughest.

[MikeTrice]

9 hours ago, njee20 said:

Mike Trice of this parish very kindly sent me some details of his approach too, which involves screwing the underframe in using M2 screws and threaded inserts in the body.

I split the carriage down into 3 parts, body, interior and underframe. Two mechanisms are employed depending on accessability, screwing the parts together with a M2 steel countersunk screws and tab and slot locators. The interior is trapped between the body and underframe (my initial approach was to print interior and underframe as one unit but now prefer them be separate). Pictures paint a thousand words so:

 

 

 

The holes that take the screws are printed undersized and enlarged with the correct drill prior to running a M2 tap through them. When assembled the whole thing is very solid and warping minimised. I use Anycubic standard grey resin.

 

I put together a small prototype to test the principal (the central holes were not used):

 

Edited January 12, 2022 by MikeTrice

[JimFin]

My approach - in N - has been a single print for the shell with 2 horizonal cross members, about where the doors are on your cad,  to prevent bowing, with the lower face being at the height to match the top of a plate carrying the underframe detail and bogie mounts. Plate is drilled and screw fixed to the cross members. Interior detail can be split to accommodate the cross members.