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Help with using Nylon

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Luke
 Luke
(@lmf5000)
Expert Moderator

Hi Kev,

It can't be done in fusion, as fusion already outputs a solid body (i.e. to fusion, the design is a solid billet of steel, it's the slicer that is turning it into a solid shell with hollow infill). You can't make a solid body more solid, but at best in Fusion you could thicken the wall around the hole - however that would change the appearance and fit of the design, so not really an option for you if you need an exact copy of the original.

To do what you're asking, you can use a modifier. This is actually something only PrusaSlicer and Slic3r can do (out of the 3 main slicers). It's not possible to replicate in cura or simplify3D.

So, what you do is you right click the part and add modifier. I'm going to use a sphere but you can use a cylinder on its side, or a box:

image

Then move, resize etc the shape to cover the areas you need extra reinforcement:

image

Then right click the gear on the right and click infill:

image

And make your settings:

image

NB: you can't use adaptive cubic for the override (since it it constructed considering the shape as a whole, you can't just override a specific area).

If you're going to go for 100% infill (i.e. a totally solid block around the hole), use rectilinear. That would look like this:

image

For any other high-density that's below 100% infill, use gyroid, triangles or grid as they are stronger than rectilinear (but they don't support 100% infill because they involve overlapping lines). You'll get something like this:

image

---

You might be tempted to add extra perimeters, but the way it's implemented in PrusaSlicer actually makes the hole weaker since the outer perimeters become discontinuous. That looks something like this (here's 7 perimeters) -

image

The hole itself becomes very strong this way, but it's basically an island that's only very weakly attached to the rest of the print so it'll pop out easily because the perimeters are broken, like so:

image

So I don't recommend upping the perimeters for local reinforcement - increase the infill density instead.

Hope this helps! 🙂

Regards,
Luke

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Posted : 30/03/2021 11:46 am
SubseaUK
(@subseauk)
Member

Hi Luke thank you for your detailed explanation above.

The modifier was something I was looking at Luke but I could not see how best to implement it but I get the drift of what you're saying. The only thing I need to confirm would be do I create the hole first or do I just add the area of reinforcement and drill the hole after? If I  print the hole I would need to create a hole with a slight chamfer around it in 360 first I'd guess??

Thanks

Luke

ReplyQuote
Topic starter Posted : 30/03/2021 1:15 pm
Luke
 Luke
(@lmf5000)
Expert Moderator

Hi Kev,

You still design the hole in fusion - that way you get perimeters in the walls of the hole, which are the strongest way to 3d-print this.

 

If you export your design as a solid in fusion360, you will end up drilling into infill in the physical print (or, at best, a solid block inside you cylinder that's made of infill, if you use the modifier in that area). Neither of these are as strong as an actual hole printed with its outline made of walls, because of the orientation of the lines. 100% rectilinear infill is merely a zig-zag pattern that is full of weak joints; a wall is an uninterrupted circumferential band that is very strong and will resist radial forces extremely well - almost as well as a solid block of molded plastic of the same wall thickness would.

 

I suggest uploading the stl or 3mf in your other thread so I can review the orientation of the holes and advise the best solution.

Regards,
Luke

ReplyQuote
Posted : 30/03/2021 3:46 pm
SubseaUK
(@subseauk)
Member

Hi Luke,

The holes have not been incorporated into the print as yet. The guy machined them into the PETG print just to get the feel of the fit but I dont think doing it that way would be ideal with this more flexible filament. ( Before I saw your note LoL ).

Once I get the actual positioning and size required of the holes I will incorporate them into the STL from Fusion360 and send you the 3mf file in here. I dont think there is a major panic at the moment, the current print is taking 36hours using the quality setting in PS plus your suggestions made previously.

Rgds

Kev

ReplyQuote
Topic starter Posted : 30/03/2021 8:22 pm
Luke
 Luke
(@lmf5000)
Expert Moderator

If you drill into a 3D printed part, the hole will be very very weak because all you have is a bit of top and bottom skin and some infill that's 80% air by definition 😆 . Drilling a prototype to get a feel for the position will work, but for actual load bearing you'll want to have a printed hole so it'll have enough underlying perimeters to give it the strength needed 🙂

Regards,
Luke

ReplyQuote
Posted : 30/03/2021 8:51 pm
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