Thread Tolerance Issues When 3D Printing

[lukasdobis]

Hello,

I'm having an issue with thread creation—more specifically, with tolerances.

I need to attach a filter to a compressor, but the filter is interfering with the current mounting location. So I need to design and 3D print a plastic pipe to reposition it.

Here’s my problem: I measured the thread on the filter using a caliper and found it to be 15.4 mm in diameter. Based on the pitch (1.5 mm) and number of threads over a certain length, I concluded that it’s an M16 ISO metric thread.

I expected some challenges since I’m modeling and 3D printing it, but I didn’t think it would be this tricky.

First, I started with the screw (male thread). I managed to model it, but after printing, the thread diameter came out as 15.9 mm—which was way off, likely due to different tolerances used by the original (probably Chinese-made) compressor head.

I followed the steps in this video: https://www.youtube.com/watch?v=aGWrFeu8Hv0&t=367s
By following his method, I managed to get the screw diameter down to 14.9–15.0 mm. It has a bit of play in the compressor, but after tightening, it holds firmly.

Now the problem is with the nut (female thread). After printing, its internal diameter measures only 14 mm, even though I modeled it for 15.4 mm.

How can I enlarge the opening to fit the thread properly?
Any advice would be greatly appreciated.

I haven't moved past just modeling a 16 mm diameter cylinder and a nut, because until I solve the issue of getting the printed parts to fit properly, there's no point in designing the full pipe.

[g-andresen]

Hi,

1. take a look at the dimensions in threaded tables
2. when 3D printing threads, the printer settings and material properties must be taken into account.

günther

[lukasdobis]

2. But how can i do that. My problem is i dont know  how to make more space 

[g-andresen]

Hi,

1. please share the File for reply

File > export > save as f3d on local drive attach> attach to post

2. Create both, cylinder and hole with desired diameters > print > check objects diameter

günther

[lukasdobis]

I'm attaching the model. Step 2 is exactly what I’ve already done—probably around 10 times.

As I mentioned in my first post, I already measured the printed dimensions. My main issue now is that I don’t know how to make the nut looser (with more clearance). I can't get it to print with the correct inner diameter so that it fits properly.

[etfrench]

When you use the thread tool, it changes the minor and major diameters to their specified sizes.  If you need a different non-standard size, you can create it by editing the thread xml. (Search for 'Custom Threads in Fusion' for details).  @MRWakefield has a custom thread file that may help.

[MRWakefield]

Ok, for the purposes of removing any doubt or misunderstanding: the 15.4mm that you measured, is that the major diameter of the external thread or the minor diameter of the internal?

Very often, commercially made threads can be way out of tolerance so this could well be true in your case and it is indeed an M16x1.5 (just undersize).

If you can take a photograph and share it here that could also help. Oh... and make and model of compressor and/or any other pertinent information could also help in determining what thread this is.

[lukasdobis]

"Could you please provide a video or manual explaining how and where to locate the XML file? Thanks

[MRWakefield]

You'll find instructions for locating the thread folder here.

EDIT: Alternatively you could use my Custom Thread Utilities app (associated forum thread linked in my signature below). This makes it much easier to find the correct folder and work with custom thread files.

EDIT#2: I've now had a look at the video you linked to and at your f3d file. I remember seeing this video before (or at least some of it) and the instructions for offsetting the threads to provide greater clearance are incorrect. If you take a look at a post I made regarding this subject here you'll find an explanation of how and why you should apply the offsets in a certain way to avoid problems.

Hope this helps.

[lukasdobis]

I'm attaching pictures of the filter that the nut will be screwed into, and I need to create exactly the same type of thread on the compressor side.

  

I'm measuring the external part of the thread, but I'm not sure about the tolerances.

First of all, I figured out that it's a 1.5 mm pitch just by measuring the total threaded length, entering it into Fusion, and then counting the number of threads — it matches a 1.5 mm pitch.

Based on your recommendation, I downloaded and installed this add-in:
https://apps.autodesk.com/FUSION/en/Detail/Index?id=79972190430973837&appLang=en&os=Win64

However, the problem is that there's no M16 screw listed, which seems strange to me.

Next

I read through the guide you sent (and the instructions in your add-in), and to be honest — it gave me a bit of a headache 😅 Mostly because English isn’t my first language, and also because I’m not a mechanical engineer. 😄

Based on the pictures I shared earlier, I adjusted the thread settings accordingly.

Normally, my 3D printer prints threads just fine without any tuning. But in this case, the outer thread comes out at 15.9 mm, while I need it to be 15.5 mm — so I have to shrink it by 0.4 mm.

The inner thread is also a problem — it's being printed at around 14.0 mm, and I need to increase it by about 1.5 mm.

 

[lukasdobis]

Just to clarify — the internal thread needs to be increased by +1.5 mm, not reduced. Based on those adjustments, I created a new model and this is what I got.

Now I'm not sure if I should go ahead and print it or not — it takes about 3 hours to print because I'm using a 0.05 mm layer height.

Also, I have one more question:
How can I measure the thread diameter in Fusion 360? The Inspect tool doesn’t seem to work properly for me, and I’m not sure how to get an accurate measurement of the thread size directly in the model.

[MRWakefield]

---

@lukasdobis wrote:

..

Based on your recommendation, I downloaded and installed this add-in:
https://apps.autodesk.com/FUSION/en/Detail/Index?id=79972190430973837&appLang=en&os=Win64

However, the problem is that there's no M16 screw listed, which seems strange to me. 

...

---

Sorry, we must have got our wires crossed! I wasn't recommending that add-in, it was the instructions for finding the thread folder on that page that was the important thing.

---

@lukasdobis wrote:
...

I read through the guide you sent (and the instructions in your add-in), and to be honest — it gave me a bit of a headache 😅 Mostly because English isn’t my first language, and also because I’m not a mechanical engineer. 😄

...

---

I'm not sure whether you're referring to the instructions for my standalone Thread Utility app or that screw/bolt add-in. However, I understand it must be difficult for non-native English speakers with so much stuff being in English only, so you have my sympathies.

Thanks for the photos. It's difficult to get a detailed view of the thread you're measuring, I was hoping to see whether I could get some more of a clue. i.e. whether it looks like Metric/UN (60°), Whit form (55° rounded crests and roots) or PG (80°), or maybe something else.

Ok, so let's assume for the moment that it's an M16x1.5. With Metric (and UN) threads, a good rule of thumb is that the minor diameter of the internal thread is equal to the Major diameter (say 16mm) minus the pitch (1.5 in this case). This gives a minor diameter of 14.5mm.

If we look at the actual figures for an M16x1.5 6g (external) we have the following:

Mean Major = Ø15.85

Mean Minor = Ø14.137

...and for the internal 6H:

Mean Major = Ø16.203

Mean Minor = Ø14.526

Looking at your photo above that's measuring Ø15.6mm, this appears to be about 0.25mm down on nominal. You've also measured your printed internal minor at Ø14.0mm so this appears to need an increase of 0.5mm on diameter to get that up to that of a standard M16x1.5 thread.

To answer your last point: to measure a thread from within Fusion you can create a sketch on a plane that is coincident with the screw's axis, then projecting an intersection with the body. You can then dimension the resulting sketch.

Hope this helps.

[MRWakefield]

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@lukasdobis wrote:

Just to clarify — the internal thread needs to be increased by +1.5 mm, not reduced. Based on those adjustments, I created a new model and this is what I got.

Now I'm not sure if I should go ahead and print it or not — it takes about 3 hours to print because I'm using a 0.05 mm layer height.

Also, I have one more question:
How can I measure the thread diameter in Fusion 360? The Inspect tool doesn’t seem to work properly for me, and I’m not sure how to get an accurate measurement of the thread size directly in the model.

---

No, that's not correct. See my previous post for clarification. Don't hesitate to ask if you need further help and don't forget to let us know how you get on.

[lukasdobis]

So I tried to take more detailed photos of the thread on the filter.

 Next 

I didn’t wait for a reply and started the print with +1.5 mm for the internal and -0.5 mm for the external.

The result looks like this:
The screw has a diameter of 15.7 mm and it can be screwed into the compressor — it’s not super smooth, but it works.

So I’ll change the parameter to -0.7 mm next.

The nut isn’t fully tightened — I didn’t feel like waiting. So the filter can be screwed into it, but only partially and with some force. I can only get it in as far as shown in the photo.

The measurement shows about 14.1 mm max, and even that takes effort — I’m not sure if I’m measuring it correctly. The funny thing is that the filter doesn’t screw in all the way. Two things come to mind:

1. It might not be a metric thread, but something else.

2. Or something got messed up during printing — because what you see at the top of the photo is actually the bottom part (the side that was touching the printer bed), so I don’t get it.

Now I’ll try changing the setting to +1.7 and print it again to see if it fits better.

By the way, I still can’t get the printed nut and thread to fit together — the nut is still too big.

   

 Really appreciate your help with this, MRWakefield!

[MRWakefield · Accepted solution]

Ok, so in those top two photos the thread looks much more 'rounded' that the original photo and nothing like Metric, UN, or any common standard 'engineering' thread. I think you're just going to have to experiment until you get a good fit. By the way: if a thread starts off screwing in but tightens the more you screw it in it is usually due to one or both items being tapered or there's a difference in pitch between the two parts.

No problem, you're welcome.