<p>One possibility, if the wall thickness is sufficient, might be to put <em>screw threads</em> in the actual tube wall.</p>
<p>The wonderful thing with CAD and 3D printing is you can absolutely control the thread start points and shoulder position, so the clock orientation of the parts when they're screwed together is perfectly repeatable from one part to the next.</p>
<p>The potential down side is that threads require some minimum wall thickness to avoid introducing a line of weakness where the root diameter is too close to the inside or outside diameter of the main part.  One way to help this is to use finer threads, or square or Acme thread profile, which can grip strongly without a great deal of engagement depth.</p>

CC BY-SA 4.0
2022-10-05T07:29:10.483Z
Actually, this is a great idea. I have to play a bit with the CAD to understand if I have enough knowledge to design the threads in that way.
Mark
CC BY-SA 4.0
2022-10-05T07:33:05.063Z
The only downside I can see (but it can be acceptable) is I have some slots that run across all the rings to put in cables. With your method it's impossible to inspect a ring after assembly.
Mark
CC BY-SA 4.0
2022-10-04T15:27:10.537Z
2022-10-04T15:27:10.537Z
Zeiss Ikon
<p>You could use velcro. I find it very easy to work with because you can cut it precisely with scissors or craft knife, and it's great for just holding things together but won't come undone by accident.</p>
<p>It's cheap and there are lots of different thicknesses at sewing shops. The ones I use come in sheets and have an adhesive backing. Takes a day for the adhesive to cure but once it's stuck on it won't come off.</p>

CC BY-SA 4.0
2022-10-06T12:13:23.373Z
2022-10-06T12:13:23.373Z
Kilisi
<p>I have a PLA 3D-printed object made of several rings with a diameter of 150 mm and a thickness of 6 mm. The height of each ring is about 30-35 mm but it does not matter so much.</p>
<p>I'm looking for a way to keep the rings together (one on top of another). I cannot place anything inside the ring (like a thicker area to host a nut). Most of the rings may have a closed top or bottom, so I cannot access the inner part.</p>
<p>I'm using three tabs (at different angles to force the correct alignment) that fit inside matching slots on the counterpart:</p>
<p><a href="https://i.sstatic.net/VSajN.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/VSajN.png" alt="enter image description here" /></a></p>
<p><a href="https://i.sstatic.net/IiPn8.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/IiPn8.png" alt="enter image description here" /></a></p>
<p>They are a bit stronger than pins and holes due to the greater surface of the base layer, but of course are useful only for alignment.</p>
<p>Due to the very small thickness of the ring I cannot place a screw inside them to keep in position, the inner wall cannot hold a screw!</p>
<p>I was thinking about L-shaped tabs and slots to fix the rings rotating them a bit, but:</p>
<ol>
<li>it would not easy to clean the horizontal leg of the slots</li>
<li>nothing would prevent to rotate the rings in the opposite way (even accidentally) so the disconnect</li>
</ol>
<p>For my use-case scenario, I don't need anything too strong. Just avoid to disconnect the rings when taking the object in hands. I tried with magnets but:</p>
<ol>
<li>to make an acceptable resistance I needed 7-8 per ring (due to their small size)</li>
<li>the electronics inside uses Hall sensors so I cannot use magnets!</li>
</ol>
<p>Any idea?</p>

CC BY-SA 4.0
2022-10-04T13:06:07.913Z
Do you need to be able to disassemble this at random times?
Zeiss Ikon
CC BY-SA 4.0
2022-10-04T13:33:09.287Z
@ZeissIkon yes, it may happen. Otherwise I could just glue them
Mark
CC BY-SA 4.0
2022-10-04T14:57:22.897Z
Double sided tape? Not the foam tape type, but the tape that is used to glue kite fabric together before stitching, is this something that you can use?
0scar
CC BY-SA 4.0
2022-10-05T07:27:29.407Z
@0scar, not sure which type are you talking about. Do you have any link? I would avoid tapes and glues, but I may definitely give it a try
Mark
CC BY-SA 4.0
2022-10-06T13:04:55.640Z
@Mark E.g. 3M GPT-020F is only 0.2 mm thick, but I think I used Nitto double sided tape for my kite ages ago...
0scar
<pla><cad>
Make a joint to keep together rings of PLA
Mark
# Make a joint to keep together rings of PLA

(Asked by: username_0 on 2022-10-04)

I have a PLA 3D-printed object made of several rings with a diameter of 150 mm and a thickness of 6 mm. The height of each ring is about 30-35 mm but it does not matter so much.

I'm looking for a way to keep the rings together (one on top of another). I cannot place anything inside the ring (like a thicker area to host a nut). Most of the rings may have a closed top or bottom, so I cannot access the inner part.

I'm using three tabs (at different angles to force the correct alignment) that fit inside matching slots on the counterpart:

[![enter image description here](https://i.sstatic.net/VSajN.png)](https://i.sstatic.net/VSajN.png)

[![enter image description here](https://i.sstatic.net/IiPn8.png)](https://i.sstatic.net/IiPn8.png)

They are a bit stronger than pins and holes due to the greater surface of the base layer, but of course are useful only for alignment.

Due to the very small thickness of the ring I cannot place a screw inside them to keep in position, the inner wall cannot hold a screw!

I was thinking about L-shaped tabs and slots to fix the rings rotating them a bit, but:

1. it would not easy to clean the horizontal leg of the slots
2. nothing would prevent to rotate the rings in the opposite way (even accidentally) so the disconnect

For my use-case scenario, I don't need anything too strong. Just avoid to disconnect the rings when taking the object in hands. I tried with magnets but:

1. to make an acceptable resistance I needed 7-8 per ring (due to their small size)
2. the electronics inside uses Hall sensors so I cannot use magnets!

Any idea?

**Tags:** pla, cad

> **Comments:**
> **username_1**: Do you need to be able to disassemble this at random times?  
> **username_0**: @username_1 yes, it may happen. Otherwise I could just glue them  
> **username_2**: Double sided tape? Not the foam tape type, but the tape that is used to glue kite fabric together before stitching, is this something that you can use?  
> **username_0**: @username_2, not sure which type are you talking about. Do you have any link? I would avoid tapes and glues, but I may definitely give it a try  
> **username_2**: @username_0 E.g. 3M GPT-020F is only 0.2 mm thick, but I think I used Nitto double sided tape for my kite ages ago...  

---

## 2 answers

### Answer by username_1 on 2022-10-04. Score: 1 | Accepted answer

One possibility, if the wall thickness is sufficient, might be to put *screw threads* in the actual tube wall.

The wonderful thing with CAD and 3D printing is you can absolutely control the thread start points and shoulder position, so the clock orientation of the parts when they're screwed together is perfectly repeatable from one part to the next.

The potential down side is that threads require some minimum wall thickness to avoid introducing a line of weakness where the root diameter is too close to the inside or outside diameter of the main part. One way to help this is to use finer threads, or square or Acme thread profile, which can grip strongly without a great deal of engagement depth.

> **Comments:**
> **username_0**: Actually, this is a great idea. I have to play a bit with the CAD to understand if I have enough knowledge to design the threads in that way.  
> **username_0**: The only downside I can see (but it can be acceptable) is I have some slots that run across all the rings to put in cables. With your method it's impossible to inspect a ring after assembly.  

---

### Answer by username_3 on 2022-10-06. Score: 1

You could use velcro. I find it very easy to work with because you can cut it precisely with scissors or craft knife, and it's great for just holding things together but won't come undone by accident.

It's cheap and there are lots of different thicknesses at sewing shops. The ones I use come in sheets and have an adhesive backing. Takes a day for the adhesive to cure but once it's stuck on it won't come off.


---

