How to print this small bolt?

[terrypin 3]

As a novice, this is my attempt at an M3 bolt (approx 3mm diameter, 17 mm total length). Printing it vertically gave a just about acceptable result, but I read that it would be significantly stronger if horizontal.

 

Obviously it's impossible to have all of it on the bed, so could I get suggestions on the best approach please?

 

For instance, should it be at an angle, with just two points touching the bed, as in my screenshot?

 

Or exactly horizontal, supported by the 2 mm deep head, plus Cura support of constant height under the thread?

 

Or something else?

 

Whatever the placement, I'd greatly appreciate advice on specifying the Cura Support settings please (for my Ender 3 V2 if that matters).

 

BTW, is it possible to remove the 'shadow' displayed around the model?

 

Terry

[ahoeben 2,010]

The most obvious advice is: don't print M3 bolts. You can buy them for very cheap (cheaper than you can print them for if you factor in the cost of the printer, maintenance and your time), and the ones you buy will be much stronger.

 

No, you cannot remove the shadow.

[geert_2 558]

Most of the time small printed bolts and nuts won't fit anyway: they are way out of spec. As ahoeben said: buy standard screws (nylon, PC, inox,...), and cut them to length (if required). I do that all the time.

 

In Europe there are lots of good online suppliers, like RS-components, Skiffy/Essentra, INDI, Farnell,... Or go to a brico-shop.

 

The only reason to design a custom threaded part, is when there is no standard available. Let's say you invented a nice water gun for your kids in summer, and you want to fit a standard Coca-Cola PET bottle to it as water-supply. Then you could design a custom threaded cap in your gun, so it screws onto standard bottles.

 

Standard nylon M4 thumbscrews and nuts in a custom design:

[terrypin 3]

Thanks both, understood.

 

 I do have some bought packs (Amazon UK). But this (a one-off replacement for a plug), is not included in any of my mixed packs. And my motivation anyway was largely a learning exercise: about screw/bolt threads and also the more general topic of how best to place a part of this sort.

 

But I'm sold. I'll forget the print project and rummage through my junk box tomorrow, although I rather doubt  I'll find one so small in diameter that's at least 17 mm long 😉

 

Terry

Edited June 14, 2021 by terrypin

[ahoeben 2,010]

18 hours ago, terrypin said:

my motivation anyway was largely a learning exercise: about screw/bolt threads and also the more general topic of how best to place a part of this sort.

Start with an M8 or bigger nut and bolt and see how it prints. See what the problem is when printing it upright, and see that you will get other problems in the other directions too. Learn from these experiments.

 

If you want to print the bolt sideways, experiment with sinking it into the buildplate a bit. A bolt does not have to be 100% circular to work.

 

But I would say an m3 thread is too fine to experiment with and learn from.

Edited June 15, 2021 by ahoeben

[geert_2 558]

1 hour ago, ahoeben said:

...

If you want to print the bolt sideways, experiment with sinking it into the buildplate a bit. A bolt does not have to be 100% circular to work.

...

Yes, this is a good point.

 

For designing parts, a lot of the rules for injection moulding apply here too, although not all. You can find online manuals on how to design plastic parts for injection moulding, from big companies like BASF, Bayer, DuPont, etc... How to design plastic threads is also explained in some of them. But this is more suitable for bigger sizes anyway, like plastic bottle lids.

 

The company protolabs also has good manuals on designing for 3D-printing, I think.

 

With a standard nozzle of 0.4mm, you can not print lines and corners narrower than this 0.4mm. So an M3 bolt sideways won't work. I consider 0.5mm my minimum linewidth in design.

 

An M3 (or any similar thread) upwards will also not work: such very steep overhangs of 60° tend to sag and to curl up at he same time, severely distorting the shape. Also, when printing too small items, the hot nozzle stays on top of that area, radiating heat, so the print can not cool and not solidify: it becomes a mess. If you need to print very small items, you need a dummy "cooling tower" next to it, to move the nozzle away for some time.

 

See these effects, with and without dummy cooling tower (the square blocks):

 

 

 

Minimum practical dimensions: text caps height = 3.5mm, text leg width = 0.5mm. Note how much more crude the text is than the standard M4 screw thread:

 

I would recommend that you design several small (and not so small) test items, and experiment on them. While they are printing, stay with the printer and watch closely what happens. Change temperature and speed on the fly, and see how that affects print quality. In this way, you will quickly learn a lot.

 

 

[terrypin 3]

Many thanks for that comprehensive advice. Much to study!