pillars, columns and printing supports

I want to use my 3D printer to create science projects which for example might require coil formers to be created etc.
I have made up a simple 3D printed shake-a-gen torch that consists of a magnet that you shake through a coil of wire
... the change of flux through the coil creates enough voltage to light an LED etc.:

[www.creative-science.org.uk]

Now so far I have printed out the device as four seperate bits: main tube, coil former (2 parts) and top section.
The two coil former parts slip over the main tube (see photos on the link above).
I print these two coil former parts on the bed, so the circular discs come out nice and sharp and at right angles to the tube.

I would like to be able to print the whole thing in one (or perhaps two) piece(s) but as the coil former has the thin circular disc jutting out
it tends to print out fragmented into 'fibres' because the printer is trying to print -out into 'space' rather than onto something.
I need supports for these overhang prints.

So my question (or call for help / advice) is how should I go about deciding how many supports I need for an over hang print?
do these supports need to be thin vertical 'wires' or pillers / cylinders?

maybe these exact questions are a bit like asking 'how long is a piece of string'
but I hope this general problem will bring up some useful comments from people on the forum for relative beginners like myself.

Thank you :-)
Jonathan

I would personally just use a slicing program that calculated the support required for me I am currently experimenting with Simplify3D that seems do this kind of thing very well - if you produce the .stl files you want for me, I'll happily slice them for you and give you back a g.code file with the support in place if this would help - if you want to do this, please PM me your email address as I anticipate the .stl files will be too large for the forum attachment limit

ok, thank you.
That's what i will have to look into next.

I don't think I will send you any files at the mo as I will be testing all sorts of things out.

But thank you very much :-)

btw you can always e-mail me via my web site if you ever need to.
Thank you
Jonathan

You can use the slicer's support option, but in this case I would tend to add support myself. A thin column to support the outside of the coil cheeks should work - it will support the cheek perimeters and hopefully they will then infill OK. A column with the same wall thickness as the slicer's perimeter (usually about 0.5mm) will result in a single perimeter support that can be easily broken away and the cheeks touched up with a needle file. Maybe make the support column 0.5mm smaller in diameter (0.25mm smaller radius) so that two perimeters will fall halfway on the support.

However - be aware that many CAD programs (including OpenScad) will not correctly generate STLs for designs that have a completely enclosed void - the void will end up being filled. My suggestion creates an enclosed void between the cheeks. As a workaround make a small (0.1mm) hole through the wall so that the void is no longer fully enclosed. The slicing application will usually ignore holes that are smaller than the nozzle diameter.

I have attached a quick mock-up of what I mean. The part on the left is what you want, the part on the right is a cutaway of the same part with the thin cylindrical support.

Dave
(#106)

ok thanks very much for the suggestions / help :-)

I want to print out say 15 to 20 'kits' for school workshops
so practically I would like the least amount of 'cutting things off and filing' for the prep on each kit

I will have to play around and see what works.

Jonathan

Any support needs some degree of touching-up after removal. One technique that you could use (together with my suggestion regarding the structure) is to leave a one-layer gap between the support and the part it is holding up. The support will still holds up the plastic, but the layer is not squashed firmly onto the support and so does not bond very well and is more easily broken away.

The other way to solve the issue would be to split the part vertically - with the part you show it should be possible to print in just two halves. Gluing the halves together should be pretty quick & easy - or get the students to glue them. The glue need not be strong because the winding will bind the halves together. That would also have the advantage that the core would not be printed in the Z direction which is the weakest, and so it would be far harder to snap the part. Example attached to show what I mean.

[edit] - I decided to create the exact part in OpenScad, with all dimensions expressed parametrically so you can easily change them to what you want. If you have not used OpenScad give it a try with this:
1) Download & install the free OpenScad from [www.openscad.org]
2) Download and save my Scad file attached.
3) Open (double-click) on that Scad file to open in in OpenScad
4) Hit F6 to render the part
5) Change values as desired - setting the variable "Split" to "true" will create the part in two halves as suggested
6) When you have something you want to print, click the "Design" tab in OpenScad and then "Export as STL"

Dave
(#106)

Edited 1 time(s). Last edit at 09/09/2014 09:08AM by dmould.