embedded nut next layer not sticking

[css 0]

I want to print a small cylinder with an embedded nut (see attached file). This will ultimately be part of a bigger project.

My problem is that no matter what setting I try in Cura it will always place a line on the nut when resuming, and this will of course not stick to the metal.

I was hoping to find a setting to make it print concentrically from the outside in, so that the first lines will stick to the PLA of the outer rim and then to the previous line as it works its way inside over the nut.

Is there a setting for this or how do you solve this problem when embedding a nut?

Because of the hole you always have an inner wall placed on the nut. Is there some trick to make the PLA stick to the metal? Maybe heat up the nut before inserting it?

 

Thanks for any help you can give me.

 

Christian

17_Halterung.stl

[Torgeir 245]

Hi CSS,

 

Welcome in here.

Hmm, -this was kind of special, so too say.

I'm thinking that there might be a glue to be used for such a problem, or maybe a piece of blue tape.

Sure "prepared" before use. 🙂

I'll think using heat might lead to other "problem", well never tried that.

 

Anyway, just a thought.

 

Good luck

Torgeir

 

[gr5 2,184]

At first I didn't understand - PLA bridges just fine.  But I realize you have a hole in the middle of your layer above the nut.  When it goes to print that layer it prints a circle just above the hole in the nut.  That circle turns into an ugly mess.

 

So the solution is simple.  In CAD model 2 layers above the nut to be a slot that reaches end to end over the nut.  That way it won't print a circle of the nut.  Then the next 2 layers make it a square hole.  Then the remainder can be a round hole above that (if you don't like square holes).

 

Here - pictures are better than words - this is your issue almost exactly:

 

 https://shop3d.ca/blogs/blog/3d-printing-tip-1-designing-better-3d-printed-holes

 

 

 

 

[geert_2 558]

This is a good

19 hours ago, gr5 said:

At first I didn't understand - PLA bridges just fine.  But I realize you have a hole in the middle of your layer above the nut.  When it goes to print that layer it prints a circle just above the hole in the nut.  That circle turns into an ugly mess.

 

So the solution is simple.  In CAD model 2 layers above the nut to be a slot that reaches end to end over the nut.  That way it won't print a circle of the nut.  Then the next 2 layers make it a square hole.  Then the remainder can be a round hole above that (if you don't like square holes).

 

Here - pictures are better than words - this is your issue almost exactly:

 

 https://shop3d.ca/blogs/blog/3d-printing-tip-1-designing-better-3d-printed-holes

 

 

 

 

 

This is a good idea, worth remembering. This concept could be usefull for lots of other models too.

 

[Oliveros 11]

I've embedded parts before and through the troubles of figuring out sequences and timing and all that, I've found it to be much easier to just sink the nut into the plastic once it's done.

 

Heat the nut with a torch or whatever you got (I do this as part of my job as an engineer, so I have tools and toys) and just sink it in. 

 

I've made remote flash units that were crap with the original plastic thread, redesigned the part so I could sink a nut into it and it works great, done it on many different parts and it's just easier than trying to do what you are.

 

The only time I go through the trouble to do what you are doing, is if It's a magnet I'm trying to put inside.

[geert_2 558]

Yes, if you have the tools, I can imagine that heatsinking-in real knurled inserts is the best. Probably the strongest also, less likely to go rotating.

 

For completeness, if the design allows it, and if forces are low, inserting the nut via side-openings might also be an option. See the pic below. I use this for light clamps. Advantage is that this is very easy.

 

 

[css 0]

Thanks to all. I tried the solution suggested by geert_2. Unfortunately my cylinder seems to be just a bit too small to make this work well. Because of the size I can't do the side insert. The opening would reduce the mechanical strength too much.

In the end I decided to dump the machine screw and nut in favor of a wood screw biting into a simple cylindrical hole in the middle. Seems to work ok for this. But I'll go back to this problem when I have a bit more time. If I find a working solution I'll post it here in case someone else has the same problem.

[Oliveros 11]

Just heat it up and sink it in, it works every time, make the hole slightly too small to fit the nut and sink it in.

 

For smaller brass inserts we use a soldering iron to heat it and just push down on it.

 

Anyways, good on you for trying, wood thread and these types of thread are normally good until you have to take it out once or twice, then they start to loose a lot of strength.

[geert_2 558]

My experience: try to avoid self-tapping screws, or thread-tapping, in PLA. Tapping is likely to melt the plastic and destroy the thread, even when tapping/screwing very slowly and carefully. At least in the sizes M3 and M4 that I use most. The heat generated by the friction and deformation from tapping immediately goes above 50°C. Also, PLA is sensitive to creep-deformation under load, so it comes lose soon. It might work with other materials like PET, but I haven't tried that yet. This is much less of a problem with inserted real nuts/inserts.

 

Although I haven't tried it myself yet, this is why I believe that heating the nut/insert as Oliveros said, and then sinking it in, is a better solution indeed. After cooling and solidifying there will be less rest-load, and less tendency to crack and deform.

 

By the way, I prefer nylon nuts and screws for plastics, when possible, as in the pic above. These don't fall out easily, and are a bit flexible. This makes fastening PLA parts more reliable and softer, not so On/Off as with metal screws, and it withstands creep-deformation better for low force applications like the clamps above.

[Torgeir 245]

I'm using the tread function i Fusion 360. So if you're able to "tune in" the model, those tread just need a little cleaning by using a tap. Here, only using my fingers to rotate the tap. And yes, PLA and 3 mm, -but do not use to much torque here.

 

BTW. interesting topics.

 

Torgeir

[gr5 2,184]

I do a LOT of printing of parts that use M3 screws (3mm diameter metric steel machine screws).  The same button head screws that are used in the Ultimaker printers themselves.

 

I typically make the holes too small, drill them out and then let the screws self tap.  If the screw is longer than 1.5cm I usually go half way and do another screw and then come back to it.  With the electric drill.  This gives the heat time to enter the steel screw and prevents it from melting the PLA too much.

 

I also have a "real" tap but don't often use that.  It makes it much easier to screw in and out later if you have to tighten and loosen a screw often.

 

I have sold about 30 laser interferometers.  Each with 4 self tapped screws in PLA.  And stages - those also have an additional 2 self tapped screws.

 

I have one interferometer for myself and I've loosened and tightened some of these screws 100 of times over the last 2 years and I haven't had a problem.

 

 

[Carla_Birch 116]

I personally use 3mm also at times and i make the hole small at like 2.5mm and then screw in the bolt a little and back it out and then go again to clean the tread of the bolt to stop it becoming thread bond, what if happens risks stripping the thread thats been cut into the plastic.

 

I also have tap set but i found the taps like to just spin around more than just cut the thread in plastic.

 

Edited July 18, 2020 by Carla_Birch

[Oliveros 11]

GR5

 

What is these devices you speak of?

[gr5 2,184]

Interferometers?  Here's my interferometry video channel.  Some of these videos are better produced than others but I put dozens of hours into all of them.  Except the shortest one.

 

These interferometers measure telescope mirrors to test them - it's for people grinding their own mirrors (small market worldwide).

 

https://www.youtube.com/channel/UCvz4goKtjouHwmS-qAjp8Tw/videos

[geert_2 558]

Another reasonably easy method: design a nut, add a cone-shape on top, and a rounding at the bottom for easier inserting of the nut. And then subtract that coned nut from your design. Due to the cone on top of the nut, it prints well without causing overhang-problems.

 

See the pics below. This is a metrinch-style design, which gives a tighter fit. This is an M4-nut, and the distance between the "flats" is the standard 7mm. Nylon M4-nuts can be pushed in with a little bit of force, and don't fall out. Although they can be pulled out by inserting a screw and then pulling. I tried printing this with 0.12mm and 0.3mm layers, 50mm/s, and both worked well. Try this on a small test piece first until you get the dimensions and tolerances optimal (might depend on material, layer thickness, temperature and speed).

 

My procedure was: design the nut (red) outside of the model (cyan). Make as much copies as required if there are multiple holes. Move the nut into the model, and align its axis with the hole, and its bottom with the model-bottom. Then subtract the nut from the model.

 

 

 

 

Edited August 16, 2020 by geert_2