Inserting items during the print - reliable alternative to "pause at height"

[purps 9]

Firstly absolutely no disrespect intended to anybody maintaining/developing Cura, but personally I just haven't got on with the "pause at height" plugin. Everything else is awesome :-)

I wanted to be able to insert COTS items, nuts, bolts, etc into my designs during the print, and then have  my printer continue on its merry way and trap the items inside. Naturally I looked at the "pause at height" plugin. The first layer following the pause never seemed to go right, no matter what I tried. I even tried manually editing the Gcode, but again I struggled to make it work.

So I came up with this alternative method. Essentially it involved modelling a dummy structure some way away from your print. Just a thin-walled square or circle so as to not waste filament, and then at the height where you would like to "pause", add a one-layer-thick roof to the structure. You have to keep an eye on things, but when the roof starts to print, you can quickly (and calmly!) insert your item. See thumb screw example below...

Green arrow is removable support structure to accommodate the length of the screw when it is dropped in.

Red arrow is the top of internal hex-shaped pocket to accommodate the bolt hex head.

Blue arrow (same layer height as red arrow) is the one-layer-thick roof.

Hope this helps!

Cheers,

Matt.

Edited July 19, 2017 by Guest

[kmanstudios 1,120]

Just out of curiosity, what material and how well does it hold when applying torque?

Does it strip out or a soft torque usage?

[purps 9]

PLA and stainless steel bolt.

I cannot physically break it (and I am at least reasonably strong). In fact during a very unscientific test, the bottom of the thumbscrew started to bulge, because the material under the bolt head was beginning to squash - that's how much torque I was putting into it.

Perhaps one day I will do some proper tests.

You need to 1. make it as tight a fit as possible (so do some test prints) and 2. don't model the hole as a straight sided hexagon - instead introduce a slight radius. This means the torque is carried through the flats of the bolt head and into the surrounding material, rather than the point of the bolt head digging away at the relatively weak PLA.

Cheers,

Matt.

[kmanstudios 1,120]

You need to 1. make it as tight a fit as possible (so do some test prints) and 2. don't  model the hole as a straight sided hexagon - instead introduce a slight radius. This means the torque is carried through the flats of the bolt head and into the surrounding material, rather than the point of the bolt head digging away at the relatively weak PLA.

Cheers,

Matt.

 

Good to know. But, WOW!~ What a cool tip for making it work well. Kudos and thanks for the illustration! It really helps me as I am a complete visual thinker.

[purps 9]

You're most welcome.

The other thing I would say is don't go any smaller than an M4 (a good rule generally I find!). M3s (and smaller) are definitely more likely to deform the surrounding plastic to the point where the bolt will spin freely, rendering the thumbscrew useless.

Cheers,

Matt.

[kmanstudios 1,120]

You're most welcome.

The other thing I would say is don't go any smaller than an M4 (a good rule generally I find!). M3s (and smaller) are definitely more likely to deform the surrounding plastic to the point where the bolt will spin freely, rendering the thumbscrew useless.

Cheers,

Matt.

And here my ignorance shines like a beacon......

I am assuming that M4 is the size of the head and the larger the number, the larger the head?

Or, is it like wiring where 12 gauge is larger than 30 gauge?

Just making it thorough for me wee noggin.

Edited July 17, 2017 by Guest

[geert_2 558]

"M4" defines the thread's outer diameter in millimeters, in this case 4mm. Thus a bolt with an M4 thread will just slide in a hole of 4mm diameter. An M6 will slide in a hole of 6mm. The thread will fall through, not lock. Thus the inner thread of a nut is smaller, to get the screwing action, but I don't know the dimensions by head.

The outer dimensions of the hex heads are bigger: about 7mm from flat to flat for an M4.

Google for "metric thread dimensions", for tables with the full specs. These also show the required drill sizes before tapping the thread.

If you want dimensions of plastic screws, see the site "www.skiffy.be". This is the biggest European manufacturer of nylon and other plastic screws. Their site shows all dimensions per product.

@ purps: your somewhat rounded "flats" are an excellent idea. I have seen hex wrenches with such shapes, but it has never occured to me to do use it in 3D-printing too. Next time I need one, I am definitely going to try this.

For "moulding in" nuts and bolts in a 3D-printed model, another option is using openings with small undercuts, or a sort of snap-fit clips. So the nuts can be pushed in with brute force, but they can not fall out. Then the models can be printed unattended.

[kmanstudios 1,120]

Cool, thanks!

[SandervG 1,521]

 

You need to 1. make it as tight a fit as possible (so do some test prints) and 2. don't  model the hole as a straight sided hexagon - instead introduce a slight radius. This means the torque is carried through the flats of the bolt head and into the surrounding material, rather than the point of the bolt head digging away at the relatively weak PLA.

Cheers,

Matt.

 

Good to know. But, WOW!~ What a cool tip for making it work well. Kudos and thanks for the illustration! It really helps me as I am a complete visual thinker.

 

Indeed, great tip! Thanks! Did you discover it by trial and error or is this a well known approach which is apparently missed completely by @kmanstudios and me!

[geert_2 558]

Hoi Sander: the concept of spanners that grip on the flats of bolts, instead of on the corners, exists for years in hardware tools. Especially in car shops, since those bolts and nuts get corroded and dirty, and require huge forces to remove.

But then it still takes someone to have the bright idea to teleport this concept to 3D-printing, where it is equally needed.

There do also exist similar spanners that can handle both metric and imperial bolts and nuts, based on this concept, the so-called "metrinch" spanners. Next time I am in a hardware shop, I will pay more attention to it.

For example, see:

https://sites.google.com/site/harkosworkshop/technical-posts/bihexsocketsvsinglehexsockets

http://www.metrinch-tools.com/website/introductie.php

[purps 9]

@SandervG - I totally blagged the idea from a socket set I have (I like rusty cars).

@geert_2 - you've answered all the other questions brilliantly as usual. May I take this opportunity to say thank you for all the times you have helped me. Your posts always pop up whenever I search the forums! That thread about how to design your own support structure - I keep coming back to that time and time again as it has so much useful information.

I am currently working on a simple prosthesis, for new amputees, which will combine the techniques discussed here to create a lockable hinge, and also the support structure techniques funnily enough. Watch this space!

Cheers,

Matt.

Edited July 20, 2017 by Guest

[purps 9]

Oh the other thing I would say as well is to make sure you add a nice bit of margin on the height of the cavity. For a 3mm thick nut for example, and 0.1 layers, I would make the cavity 3.2 mm tall. Better to be too big than too small. The first layer over the nut (or bolt head) will "fall" onto the metal, much like with support structure, so it won't actually be loose after the print. If the cavity is too small, the nozzle can hit the metal part, which is not good.

Cheers,

Matt.

[SandervG 1,521]

\Watch this space!

I am!

[geert_2 558]

...

@geert_2 - you've answered all the other questions brilliantly as usual. May I take this opportunity to say thank you for all the times you have helped me. Your posts always pop up whenever I search the forums!

...

Cheers,

Matt.

You are welcome!

In my experience, helping others is well spent time: it requires me to think about things, and to see the situation from lots of different viewpoints. Whenever a solution is found (it doesn't matter who finds it, me, one of the other people here, or the original topic starter), we also know that anwer and we can use it four ourself. So this is a very fast way to learn, with a high "return on time investment".

[purps 9]

Hi all, I finished the prosthesis prototype a few months ago, sorry I only just round to posting pictures.

 

The thumbscrew and hinge were printed separately, but the whole of the hinged part is printed in one piece.