3D Printing: Self cutting M3 thread inserts - anybody tried this?

[RC-Dude]

I have a Carbon Z Piper (2,1 meter wingspan) and the magnets of the brushless motor came loose. Then I broke some magnets trying to see if I could fix it. Anyway I ordered a new motor and I have to print some spacer block for the propeller to fit nicely before the engine cowl. Now the positioning of the original holes to attach the motor is 36mm. The new motor has a 40mm hole spacing. So I need a set of 4 screws to attach the spacer to the aeroplane and a set of 4 screws to attach the new motor to the spacer. So first I have to attach the spacer to the motor with nuts and screws. I'd like to do that with a self cutting M3 insert so I can skip the nuts. Otherwise I have to remove the spacer first from the aeroplane (plastic attachment with a limited life of screwing screws in and out) when I have to reach the ESC.

Has anyone got some experience with this? Do I have to design the thread into the holes for the M3 inserts (other diameter M5) or just print it with 4,2mm and let the self cutting screw do the job. (M4 would also do and M6,5 external thread). I think TPU with lots of infill should be good. Or greentec PLA as it's more heat resistant in summer but it might split or create tension with the self cutting inserts.

Here rough pre-print but I would have to attach the motor to the spacer and have the nuts on the front side. So thread inserts seem appealling so I never have to detach the spacer from the aeroplane again. Used modifiers to strengthen the area around the holes with more infill and separate perimeters.

Forgot the center hole so I had to drill it.

This is how inserts look like. Here another example.

 

[Dan B.]

I have a Carbon Z Piper (2,1 meter wingspan) and the magnets of the brushless motor came loose. Then I broke some magnets trying to see if I could fix it. Anyway I ordered a new motor and I have to print some spacer block for the propeller to fit nicely before the engine cowl. Now the positioning of the original holes to attach the motor is 36mm. The new motor has a 40mm hole spacing. So I need a set of 4 screws to attach the spacer to the aeroplane and a set of 4 screws to attach the new motor to the spacer. So first I have to attach the spacer to the motor with nuts and screws. I'd like to do that with a self cutting M3 insert so I can skip the nuts. Otherwise I have to remove the spacer first from the aeroplane (plastic attachment with a limited life of screwing screws in and out) when I have to reach the ESC.

Has anyone got some experience with this? Do I have to design the thread into the holes for the M3 inserts (other diameter M5) or just print it with 4,2mm and let the self cutting screw do the job. (M4 would also do and M6,5 external thread). I think TPU with lots of infill should be good. Or greentec PLA as it's more heat resistant in summer but it might split or create tension with the self cutting inserts.

Here rough pre-print but I would have to attach the motor to the spacer and have the nuts on the front side. So thread inserts seem appealling so I never have to detach the spacer from the aeroplane again. Used modifiers to strengthen the area around the holes with more infill and separate perimeters.

Forgot the center hole so I had to drill it.

View attachment 312711


This is how inserts look like. Here another example.

I can’t speak to the reliability without running nuts, but small screws cutting their own threads is very common. I‘m going to look for a chart I had that stated exactly what size hole to drill for what size screws when they’ll be cutting their own threads. I’ll see if I can find it, or you can Google one I’m sure. I know that for me, the instinct was to drill the holes a little larger than they could have been, resulting in weaker threads.

 

[Tex Koder]

I have a Carbon Z Piper (2,1 meter wingspan) and the magnets of the brushless motor came loose. Then I broke some magnets trying to see if I could fix it. Anyway I ordered a new motor and I have to print some spacer block for the propeller to fit nicely before the engine cowl. Now the positioning of the original holes to attach the motor is 36mm. The new motor has a 40mm hole spacing. So I need a set of 4 screws to attach the spacer to the aeroplane and a set of 4 screws to attach the new motor to the spacer. So first I have to attach the spacer to the motor with nuts and screws. I'd like to do that with a self cutting M3 insert so I can skip the nuts. Otherwise I have to remove the spacer first from the aeroplane (plastic attachment with a limited life of screwing screws in and out) when I have to reach the ESC.

Has anyone got some experience with this? Do I have to design the thread into the holes for the M3 inserts (other diameter M5) or just print it with 4,2mm and let the self cutting screw do the job. (M4 would also do and M6,5 external thread). I think TPU with lots of infill should be good. Or greentec PLA as it's more heat resistant in summer but it might split or create tension with the self cutting inserts.

Here rough pre-print but I would have to attach the motor to the spacer and have the nuts on the front side. So thread inserts seem appealling so I never have to detach the spacer from the aeroplane again. Used modifiers to strengthen the area around the holes with more infill and separate perimeters.

Forgot the center hole so I had to drill it.

View attachment 312711


This is how inserts look like. Here another example.

Instead of using those ,you should consider these inserts..

https://www.amazon.com/ruthex-Threaded-Insert-Pieces-Ultrasound/dp/B07YSVXWS8/ref=asc_df_B07YSVXWS8

Just place these in the hole you made in the spacer and use a soldering iron to heat the inserts up as you push them into place. It will 'bond' them into your spacer ,nice and secure.


I would suggest you design your spacer with a bit more material around those holes also. Not just adding more perimeters from the slicer.

 

[Steve B in Vegas]

Yes, yes, and yes; Tex is spot on. This is the correct approach.

s

 

[RC-Dude]

Thanks for the input. I will have to see about the diameter to print for an M6. In the first link above it is a picture of different diameters according to material. Only saw that just now. I already ordered M4 with external M6 thread. Will see if that was a good choice. Also heating the metal to get a good fit - good idea did not think of that. Did not think of melting the material. More material around the holes I did with modifiers (see picture) and like 90% infill. Ideamaker has that cool option.

 

[Tex Koder]

Thanks for the input. I will have to see about the diameter to print for an M6. In the first link above it is a picture of different diameters according to material. Only saw that just now. I already ordered M4 with external M6 thread. Will see if that was a good choice. Also heating the metal to get a good fit - good idea did not think of that. Did not think of melting the material. More material around the holes I did with modifiers (see picture) and like 90% infill. Ideamaker has that cool option.

View attachment 312736

View attachment 312737

I meant the outer portion of those holes (AND the holes beside those) needs to have more material.. It will need it to allow you to "melt" those brass inserts in properly, otherwise it'll burn right through those thin wall sections.

Unless you are severely restricted in space to have to make your spacer perfectly round & of that size.

 

[RC-Dude]

That's what modifiers (local modificaton of printing characteristics) allow. In the picture above the modifier has 3 shells. Could bring that up to 10 or so.

 

[Tex Koder]

That's what modifiers allow. In the picture above the modifier has 3 shells. Could bring that up to 10 or so.

I understand what you're saying about the additional shell walls, but you will not get 10 walls at those thin sections on the outer perimeter ,no matter how many you add in the modifier.

Your nozzle size will prevent it.

Unless you are printing with a 0.1 nozzle, then maybe you'll be able to squeeze in another two shell walls.
Just a heads up.


******************

Or, unless the photo is deceptive and your spacer is much Bigger part.. than what I'm imagining.

 

[RC-Dude]

The purple part above was printed at 160 or 200 mm/s. Just a rough first PLA print. No real time to bond. And infill was set at a lower flow. The Kobra 2 allows those speeds.

OK, I get what you mean. Was missing the perimeter and position of hole you meant. Wrong thinking on my side. More infill around the holes instead of perimeters. Would have to check if more perimeters are only printed at the outer side of the perimeter or also around the inner holes.

 

[Tex Koder]

...
OK, I get what you mean. Was missing the perimeter and position of hole you meant. Wrong thinking on my side. More infill around the holes instead of perimeters.

Correct.

 

[RC-Dude]

Oops - already working on post above...

 

[RC-Dude]

Turns out it's just about impossible to turn the inserts (External M6 thread) into PLA. M6 with holes 5,3mm to 5,8mm. Inserts jam scew all the time using the flat screwdriver. A bit what I suspected. An Insert with a hex drive would be the only option but did not find this option for small threads. TPU works fine with the inserts. Easy to drive them in with hole diameters like above. TPU here not my first choice but will be OK. Not sure how well the threads actually cut into the TPU. But I had to pull quite a bit to get the insert out with screw and pliers using the 5,3mm hole. Soldering iron should do to melt the TPU. Superglue actually also works with TPU.

 

[LibertyMKiii]

When I was printing and selling GPS protector covers I could print the holes at 2.5 or 2.8 mm (I cannot remember exactly what it was) then print it out just as a straight circle hole. You would drive the screw in and it would basically cut its own thread into the plastic. It gets very hot so you let it sit for an hour to cool down and you have left in there a perfect melted plastic thread to match the screw.

Just as always its not as strong as an insert like Tex shared.

 

[Denvermatt]

I use heat inserts all the time on my projects. When I built my voron 0.2 I went threw about 150 of them.

Put your design in tinkercad and open up the holes larger for the heat inserts. The hole size you need for the heat insert will be somewhere on line with a quick google search. They are really easy to use once you get a hang of it. I would also print those mounts in ASA but that's just me. You need an enclosure for ASA or abs. You can probably get away with pla. Check out COPA by Polymaker, it's a nylon / nylon 6 blend that's tough as heck and has heat resistance temp of 180C (356F) and you don't need an enclosure to print it. I definitely wouldn't use tpu for a motor mount .

 

[RC-Dude]

Update:

I opted for TPU. Layer adhesion is what I need. The propeller pulls with about 5 kilo. Turning a rotation wheel or propeller takes extra force. Add on to that G-Forces in aerobatics. And the danger of already damaging layer adhesion when screwing in the M4/M6 insert into TPU / PETG and turning the screws tight. The above mentioned inserts would have been better I think but I had ordered M4/M6 inserts already. Printed with 98% infill. TPU plate is solid. Tried melting the thread into the TPU but did not work nicely when applying torque inserting the screws. Just turned the insert. Used superglue which works with TPU.

Can't speak about nylon or ABS as I have no enclosure to retain heat.

If that's not working nicely I'll use wood. Will see if there is any kind of vibration. This kind of application is where 3D printing is at it's absolute limits. Layer adhesion and tractive power due to using screws with the applied force 90 degrees to the layers. TPU has incredible layer adhesion but needs near 100% infill to reduce flexibility. So now the plate is attached to the fuselage with 4 screws and the motor to the plate with 4 screws. Not much to flex there.

I found with rc car prints that TPU beats everything when it comes to mechanical rc car forces. Unfortunately it's too flexible for some applications and needs a lot of infill. I wish there was a filament like TPU but a lot harder and less flexible.

 

[Tex Koder]

...

I found with rc car prints that TPU beats everything when it comes to mechanical rc car forces. Unfortunately it's too flexible for some applications and needs a lot of infill. I wish there was a filament like TPU but a lot harder and less flexible.

Very easy solution.
Make yourself some hybrid composite...

Just purchase some Nylon M4 or M6 nuts and redesign Your TPU adapter mount to accept those. Now you'll have the benefit of the two materials you're looking for.

And if you need you can melt the brass inserts into those Nylon nuts.. you can achieve even more mechanical strength for your screws to bolt into.


*****************

Also if you need to bond those nylon nuts to your adapter, you can lightly scuff up those nuts with sandpaper and print your TPU part with Fuzzy Skin activated in your Cura slicer to give the part extra surface area...
For better adhesion when you epoxy those nuts in.

 

[RC-Dude]

Thanks! The nuts are a cool idea. Did not think of that.