Tolerance for 3D printed parts?

[kevinz]

Hello,

I was able to get my Dipole Feedpoint printed at the library, using PLA on a Lulzbot Mini 2. I was pleased with how it turned out:





However, when I went to insert the BNC connector, it wouldn't fit through the hole. I measured the diameter of the connector as 47/128 inch, and made the hole 48/128 (3/8) in. I realize that this only left 7.8 thou clearance, but I thought it might be enough. I had to ream it out slightly to make it fit.



So, my question is more general that just this specific case. How much tolerance do I need to leave when 3D printing, when making parts that will mate with other, manufactured parts? Does it depend on the printer, or on the material?

I'm guessing that many of us are familiar with Machinery's Handbook, which contains lots of tables of things like this. For instance, my 28th edition, from 2008, has table 11 in the self-threading screws section, that details exactly what size hole to drill for a #6 AB self-tapping screw, in plywood, asbestos, metal or phenol formaldehyde plastic. Is there any similar reference for plastics and 3D printing, that gives standards for designing and printing parts?

Thanks for your thoughts and comments. I've included my FreeCAD file, in case I made a mistake with it.

-Kevin

[Joyas]

So, my question is more general that just this specific case. How much tolerance do I need to leave when 3D printing, when making parts that will mate with other, manufactured parts? Does it depend on the printer, or on the material?

It depends on a lot of details, even if your printing plate is too close to the nozzle (it reduces the diameter of holes in the first layers).

User experience is your best friend here.

I have used a upside-down drill bit to make a hole bigger, I did not want to cut material, so I used the friction to move it down. I believe that the hole would be stronger doing this.

[chrisb]

It depends indeed on material - I even discovered differences with different colors -, printer, and printer configuration/slicer software. I almost never get it right the first time. Thus I think it is ok if you have to rework your part.

The addon Fasteners workbench has parameter settings for compensation of printed threads, and they are different for inner and outer threads, which shows, that a general parameter cannot be given.

[kevinz]

Okay, it's good to know that. I should remember that 3D printers are best for quick prototypes, to test for conditions like this.

However, I'm still thinking about this. Are 3D printer files ever turned over to a commercial manufacturer to reproduce in quantity by a different manufacturing process, such as plastic injection molding? Does someone have to go through the entire file, making adjustments to each dimension to account for the different production techniques? Just curious.

Thanks, again, for your help and advice.

-Kevin

[chrisb]

In case of (injection) molding the manufacturer will probably not get a printer file. A common way is that he rather gets a STEP or IGES file. He then creates a mold respecting his manufacturing process with shrinking percentage and whatsoever.

[sgrogan]

He then creates a mold respecting his manufacturing process with shrinking percentage and whatsoever.

Clones are useful here. I needed to make some gaskets that were thermo-compression molded with different elastomers. I modeled the finished gaskets and then applied scaling on clones of these to make molds for elastomers with different shrinkage.