3D printing a school for a model railway

[Harry50]

I want to 3D print something very specific, but I'm not sure exactly how to go about it.

I've been referred to this forum from the Hornby community forum. Basically I'm wanting to 3D print a school for a model railway. It would be printed in sections, with one wall which opens out like a cupboard, to create a dolls house effect. Can anyone help me out with the design? A lot of the design would depend on the hinge and screws, I'm not sure which is the best plastic to use that won't split when I drill it? 

[Mike Harvey]

How big/what scale is the school building? You could make the hinge integral with the printed walls so no need to drill anything.

[RobjUK]

I use PLA for everything - I got a reel of ABS originally, thinking it may be needed, but I've never had reason to try it.

With PLA I've drilled it, files it, reamed it etc. with no problems, it is very tough.

 

However most parts are made hollow, with a honeycomb internal reinforcement - if you try and put holes in at random, you will not have structural locations where you drill.

You must build-in the holes in your design, so the 3D-to-print conversion program (a "slicer") can allow for them and include the appropriate structures where needed.

 

Just design the parts to be a direct fit together, with mortise joints / holes / recesses / counterbores for fixings etc. at the required sizes.

A decent printer used with a properly set up slicer program will make the parts to exact size.

 

I made a height gauge for something a few days ago and over several versions, the main block was coming out consistently to no more than 0.001" off the design size.

 

I also made a replacement battery box cover for a young relative's toy, complete with locking pegs at one edge and a spring latch at the other, and the first was an exact fit.

 

I use "Designspark mechanical" to create the 3D models, as that's one of the few programs that allows you to set absolute sizes for dimensions as you work.

That is free, here, and I'd highly recommend it for precision designs:

https://www.rs-online.com/designspark/mechanical-software

 

 

Some examples of parts with fastening positions and & joints built in - this is a 3D scanner from a Kickstarter project, so someone else's design, but printed on my machine.

 

The nuts are and exact push fit in hex recesses and all the holes and countersinks for the screw heads are printed in.

The swivel joints for the laser line modules just push together then clamp with screws and the "cable chain" elements are all identical and just snap together.

 

You can also see the internal grid inside the shell in the thin crossmember in the first photo - that's all done by the slicer, you just design the parts you want and the slicer software adapts them so the printer turns them out correctly.

 

 

I did not really bother cleaning anything up much before assembly & the slight gaps with a couple of covers are due to them only resting in place.

 

[RobjUK]

Also have a look on "Thingiverse" for printable items you can adapt:

https://www.thingiverse.com/

 

eg. Search for buildings or architecture.

 

One I found quickly - a "building kit" 

https://www.thingiverse.com/thing:645328

 

Note that you can re-scale objects in the slicer program if they are not the correct size for your requirements.

Just use the same scale figure on all the parts and they should all fit together at any reasonable scale.

 

[Marbelup]

If designing a multi-part model in PLA or similar, you can “weld” parts together using a fine tipped soldering iron.  I mostly use Colorfabb PLA/PHA blend for larger models as it is less prone to warping.  

[Harry50]

On 09/11/2019 at 08:29, RobjUK said:

However most parts are made hollow, with a honeycomb internal reinforcement - if you try and put holes in at random, you will not have structural locations where you drill.

You must build-in the holes in your design, so the 3D-to-print conversion program (a "slicer") can allow for them and include the appropriate structures where needed.

 

Just design the parts to be a direct fit together, with mortise joints / holes / recesses / counterbores for fixings etc. at the required sizes.

A decent printer used with a properly set up slicer program will make the parts to exact size.

 

 

Thank you for your answer. If I use plastite screws, do I design a pilot hole into that is one size smaller than the screw? The screws are self tapping, so they seem like they should go in easily, but I've never used them before and I don't want them to split the PLA.

 

 

[RobjUK]

8 hours ago, Harry50 said:

If I use plastite screws, do I design a pilot hole into that is one size smaller than the screw?

 

I'd size it a few thou larger than the "core" diameter of the thread, or half way between core and outer diameters if you want to play safe.

 

I've used metric taptites without any problems. They leave a true metric standard thread, rather than the random groove a self tapper cuts.

This is what they look like:

https://www.stanleyengineeredfastening.com/-/media/web/sef/resources/docs/other/taptite_2000_brochure_1.ashx

 

eg. these are they, but RS don't use the name:

https://uk.rs-online.com/web/p/self-tapping-screws/4831230/

 

 

[Harry50]

Thanks for that! Do you know where I can get a countersunk black version of these ?

I'm going to use concealed black hinges. Although the hinges will be on the inside, you'll still see the screws when the door opens like a cupboard.