Pre-threaded screw holes(!) in a 3D model

[bbussey]

I discovered something very cool last night. I use SolidWorks and it has the provision to create screws and threaded rods with accurate dimensions (diameter, thread count, thread pitch, etcetera).  I’m sure other cad programs have a similar provision as well.  I have designed various coupler conversion mounts on occasion to adapt non-MTL rolling stock for body-mounted MTL couplers.  Sometimes I integrate the coupler box in the mount so a model can stand at a better ride height. This coupler mount is for the Atlas 11k gallon tankcar. It both body-mounts MTL 1015 knuckles and allows a swap-in of Atlas Barber S-2A (or Atlas/BLMA ASF A-3) trucks to lower the model. The adapter requires an MTL 1015 box lid and for the hole in the pivot post to be tapped. I’ve had these on Shapeways for years, but I decided to see if i could print them on the DLP printer pre-tapped. First, i filled in the existing hole. I then created a threaded #00-90 rod, positioned it through the center post and performed a subtraction-combine. That left a threaded hole in the post.

After printing, I tested it with a J.I. Morris brass #00-90 screw. It worked without issue. This opens up additional possibilities in fastening 3D-printed parts together. No more worry of splitting posts while tapping and/or drilling out holes.





NOTE — I mis-reported originally, stating the test was #0-80. It was #00-90 and I’ve made the corrections above.

[samusi01]

I’ll have to give that a shot. My present 100 ton flatcars could use this for both 2-56 for the trucks and couplers… I wonder if it’d work for the 00-90 that MTL include with their couplers…

[timwatson]

Great find @bbussey! I'll have to try that. Thanks for letting us know.

[C855B]

Amazing that the replicator technology is already to this level of refinement. I need to get off my butt and finish unpacking the DLP printer received last week and get’r’done.

[bbussey]

I’ll have to give that a shot. My present 100 ton flatcars could use this for both 2-56 for the trucks and couplers… I wonder if it’d work for the 00-90 that MTL include with their couplers…

It definitely would. The above is #00-90, I don’t know why I wrote #0-80. It will work with #000-120 and #0000-160 if necessary.

[bigdawgks]

I assume this worked because of limited precision in the printer, but aren't threaded holes supposed to have tolerances between the threads in the hole and in the screw or else it would be very tight to screw in?

[samusi01]

It definitely would. The above is #00-90

Good to hear. I figured you had some good reason for sourcing 0-80, whilst I am cheap and just use what MTL includes... I don't think I'll get this done today but I am reconsidering my end sill design already.

Edit to add:

Have you tried printing them vertically, as would happen if you are printing a car vertically? I don't think the slicer would necessarily add any supports in there, nor should there be need to.

[bbussey]

I assume this worked because of limited precision in the printer, but aren't threaded holes supposed to have tolerances between the threads in the hole and in the screw or else it would be very tight to screw in?

As long as the virtual screw specs are correct (or rather, the virtual tap or die specs), there is no issue.

[JeffB]

Very interesting Bryan!

Also a Solidworks user...  Will have to look into this.  I've done coil springs in SW, but haven't attempted threads yet (other than worms)

Most of the time, I just design a part that will have a threaded hole using the tap drill diameter.  It almost always fills in a bit during printing, so in preparation for threading, I drill it out with the tap drill, or one that's a thou or two oversize.  To thread, I form thread using an oiled up screw of the size I want to use on the model.

Works great and is remarkably strong so long as you follow the rule where you use at least 3X the screw diameter as thread depth.  I use 1mm screws a lot, and try to shoot for a minimum of 3mm of thread depth, but often end up around 4mm or so.

Works well in home printed 3D resins, works well in Shapeways "Frosted detail" resins too.

Jeff
 

[dem34]

Fusion360 also has the feature. I used it for my first set of TTraK curve modules. (The module level bolts went into a 3D printed angle piece. The part had printed threads for 1/4" bolts. They worked ok until somebody decided to get ahead of themselves and stripped them out with a full torque drill. A learning lesson for all).

[Chris333]

Surprised you didn't need to enlarge the screw to get it to print the correct size as holes usually end up smaller than drawn. But hey I love the idea! 

[bbussey]

Surprised you didn't need to enlarge the screw to get it to print the correct size as holes usually end up smaller than drawn. But hey I love the idea! 

Technically I used the die thread (as opposed to a screw thread) so it worked without being forced.

This is a BFD as it allows for models to be designed for screws fastening, such as rolling stock or caboose floors to bodies.

[Chris333]

Yes it would be nice. I usually thread holes after cleaning and before curing.

[samusi01]

@dem34

Regarding Fusion, did you simply use the out of the box library for creating your threads, or did you end up doing something like mentioned below with the die threads? Did you have to do any cleanup or did it work fairly well? Last, was it a through hole or a blind hole? I plan on experimenting with the much smaller 2-56 and 00-90 but the ideal would be blind holes.

[brill27mcb]

It's an amazing possibility. I have to wonder how long the printed threads will hold up, especially if the screws are taken in and out. I have the same type of concern about wear resistance for gears that are 3D-printed.

Rich K.