When asking for help, please provide as much information as possible about your inquiry.
This will help everyone to better understand your problem, and provide you with the best solution.
Detailed description of the problem
Printer model used
Slicer settings used
Type of filament used
Photos that clearly show the problem
.3mf file (if the file can be shared)
Any potentially useful information that is related to the problem
Brand new p2s
M20 x 2mm pitch bolt printed and a m20x2 mm nut printed .
Thread looks good but they will not go together , sizes measure good too .
Any suggestions, new to printing but I’m an engineer so have a reasonable understanding.
If they measure up perfectly, that’s probably the problem. A 20mm bolt will not go in to a 20mm nut. The nut has to be bigger than bolt. For 3D printing I use a 0.25mm offset where the nut is effectively 20.25mm in diameter.
I have to say, if the modeling is correct to actual M20x2 thread specifications, and both the printed nut and the bolt are within manufacturing specifications for M20x2 hardware, there will be no issue with them fitting together.
So either the modeling is wrong, or the printed product is out of tolerance.
Rotate the bolt and look at the thread start, it will look like mine it wont work, the thread is flat on the bottom of the chamfer, it would work if you were cutting threads on lathe or mill but it doesnt ,model correctly for 3d printing.
That is not the only way to do that chamfer, just using it as an example. after fixing your chamfer problem the threads will still be tight but you should be able to at least get it started and force it a ways. There are a few youtubes on how to create thread clearance in fusion for 3d printing.
The problem with threads is that the standards were designed to work with steel and brass, back during the industrial revolution, and do not print so well on 3D printers. Being as you are using Fusion, there is an easy work around that produces threads that print better, are stronger, and operate more smoothly.
Create a treaded bolt in the usual way, orientated up and down.
Scale the threaded bolt 2 times in the z direction while keeping the x and y directions at 1. This allows for a better angle on the overhang, resulting in a smoother surface.
Create the inner nut profile by subtracting the threaded bolt from a sold object.
Scale up the nut, keeping the z direction at 1 while setting the x and y directions to some small number like 1.1 or a little more. This is where you dial in the clearance you need. A little extra clearance is okay as they will still bite tightly when screwed tightly.
You will then have the go back and trim the nut to size.
Yeah, I agree. A part designed to be fabricated from metal, with the tolerances that material allows, will not work well on a 3D printer. The feature sizes of the 3D printer are “quantized” because, well, the nozzle’s opening is fixed and the layer step is not infinitely variable. You have to design for a bigger tolerance stackup with FDM or parts won’t go together, or if they do, friction will make them gall up. The threads have to be kind of loose.
You also have to design for the plastic’s coefficient of thermal expansion. Assuming the printer’s positioning system is working correctly, the model prints in the size as-designed. But, for example, ABS has a large CTE. It can shrink dimensionally by as much as a percent. And the shrinkage isn’t uniform, it depends on how stress is relieved within the body of the print. Which is another reason you need to open up your tolerance range.
