Design Parts with through pieces for Strength

[Aaron Wintersmith]

I designed and printed this bead spinner for my wife's jewlrey projects.

The center shaft failed and ripped off the print.

I knew a 90 deg turn here would concentrate forces, so I designed a fillet.

But the real issue turns out to be how the object is sliced. In the slicer there is the top surface of the bowl, then the center rod outline (a circle) is printed on top of that in the subsequent layers.

This leads to an adhesion/layer issue.

I know turning the object will result in the layer lines running another way and increasing strength, but that introduces other printing issues.

Can I draw/design the part in such a way that the slicer extends the vertical rod thru the top layer into the object and is better supported?

I was hoping if the parts were not actually combined/booleaned in the drafting software this might result in the rod being a thru part, but that didn't seem to work.

[vrfx]

Aaron - Two suggestions for you!

1) The modeling SW I use - 3DS Max - which is NOT a true CAD Package (Solid modeler) - allows you to create an object via Lathing! And, your object is super simple for a lathing process. I do NOT have enough knowledge of CAD SW - in regards to Lathing - PLUS - you didn't state what SW you use. Do let us know. If you CAN Lathe in your SW - give that a shot!

2) You also didn't tell us what type of plastic you used. Myself, if I did this in ABS - I would Acetone Smooth it - and that may ALSO give you the strength you need in the part!

Either way - give us some more feedback - and potentially try my suggestions. Hell - if you gave me some dimensions - I would Bang out your Part in 3DS Max & hit you back with an STL.

-K

[vrfx]

I just realized - if you sent me the STL - I can probably pull that into Max and Easily replicate it THAT way via the Lathe operation!

-K

[Ray Price]

With a tall thin post like this, this just seems to scream to make the model 2 pieces and print the post on its side.  That will give you maximum strength for the post since the layers will run parallel to the length of the post as opposed to perpendicular.  Printing the post on its side with supports will initially be a rougher surface, but that should be able to be smoothed out with sanding / post processing.  Given that the post rises from within the bowl, you'll probably have to design your own hole (in the bowl) and peg (on the bottom of the post) to fit the post in the bowl, as opposed to using the slicing and joining function of something like prusaslicer. 

The other alternative is to get a dowel or an acrylic rod that you can design the bowl around.

It took me a while before I recognized that:

1. Not every print has to be, or should be, a single part print

2. 3D printing doesn't have to carry all the weight of a design.

Just my .02

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[Aaron Wintersmith]

Interesting comment about post and a hole. That's basically what my questions was getting at, except printing it all in one go.

if I could have a hole (and associated #walls) plus a post (again with # of walls) that ran all the way thru the part, then I would likely get plenty of strength. 

So my question is basically can I convince the slicer or CAD software to model it this way. Without actually printing two parts.

[Aaron Wintersmith]

@ K - here is the STL if you like. Note there's a bearing recess in the bottom. I've been printing that with close PETG suporst.

Regarding the plastic, yes this defin. makes a difference. One of my early porotypes used PLA plus and didn't have this issue. The one pictured here used Silk PLA, 'cuz that's what was loaded, and had a failure.

If you have a success with the Lathing feature that would be cool to know.

[vrfx]

Thanks for the STL. Did you design in Inches or mm? I have not yet opened the STL - but, if designing in inches - would be good to know ahead of time so I can properly scale the STL.

Will keep you posted. 

-Kurt

[3D Printing Tips and Tricks]

You never mention what SW you used to design this. Regardless, it looks as though the center rod and the bowl were two separate objects. You don't want that. They need to be joined.

[Scott Bussinger]

Try designing a tiny hole down through the middle of that post. All the way through from top to bottom. You’ll have to experiment a bit on the diameter, until you get the right effect in the slicer. Maybe start with a 0.25mm hole.

 

The idea is to make the slicer think the center of the post is really an exterior wall (and thus print perimeters), but the hole is so small that it's filled with plastic when you print it. Too small and the slicer might ignore it, too large and you could actually have a hole there. Thus the need to experiment a bit. Make sure you set enough perimeters to get the strength you want.

 

Another approach would be to use a cylinder modifier shape over the post and down to through the base, then set the infill there to 100% so there's solid plastic under the post.

 

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From: 3d-printing-...@googlegroups.com <3d-printing-...@googlegroups.com> on behalf of Aaron Wintersmith <onecol...@gmail.com>
Sent: Tuesday, February 20, 2024 5:50:57 PM
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Subject: Design Parts with through pieces for Strength

 

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[vrfx]

Hey there Aaron,

So - yeah - we still want to know what SW you used to create your 3D Design.

And, Scott's suggestion sounds like a good idea - putting in a minimal hole. And, if a slight hole in the middle is not problematic for your use case - I can do it EASILY! Attached is the New STL I created using a 3D Lathing process. 

Keep us posted!

-K

[Anthony Rothert]

Off the top of my head, you should also be able to add a part modifier in slicers like Orca Slicer or Prusa Slicer.  They can allow you to modify particular areas with different printing features.  For example, you could use a cylinder shape modifier for your post.  Make it several millimeters larger in diameter than you post and place it in the center of the part.  Then change the settings for the cylinder to be... something like 20 walls/perimeters, then re-slice.  That should create the area where that cylinder exists to be perimeters in that entire area.  

Also, silk PLA filament has a tendency to be noticeably more brittle in functional situations like threads and axles, spinning features, etc. 

[vrfx]

Anthony - good point! 

I suspect, for the purposes of Aaron's part - he may need to print in something like PETG - although, HONESTLY - PCTG is an even BETTER Material!

Of course, if done in ABS - and Vapor Smoothed - that MAY Help make a better more functional part. But, ABS Printing can be a BITCH!

-K

[Aaron Wintersmith]

Sorry about missing the software issue, I designed in TinkerCAD.

Design is in mm.

Thanks for the ideas about the modifier and mini-hole, both are definitely worth some testing.

And yeah, admittedly, making better material choices is an obvious first move! My post here is more about exploring other design strategies for, you know, knowledge!

[Anthony Rothert]

From my experience with printing in only a couple of years as well as career experience, material choice is also a big part of designing!  If you want to print that in silk PLA, maybe you need to add more perimeters in the area with a modifier.  That means for repeated prints, saving that as a project in the slicer so the modifier is always there on the slicer when you open the file.  Or adding a much larger fillet at the base to take the extra stress.  There are all kinds of things to be learned just by trial and error.  That’s as much fun to me as it is a pain.  I’m right there with you about gaining knowledge.