Screw thread in connection

I have a vessel connection here. I printed the vessel with the 3D printer. The hose connections are put into the holes. But the system is not waterproof, so I would like to redesign a screw thread. The hose from the hardware store has a 33.3 mm (G 1) external thread. How can I construct the thread inside. I tried it with the plugin boltgen but I can’t orientate the thread and connect it to the hose connector. Can anyone help?


16102020_screwthread.gh (16.8 KB)

You’re not going to 3D print threads that size, you would cut them with a tap, or use some kind of an insert or 3D print a connection you can use with flexible pipe and a hose clamp, or something like that…

Can’t I get the thread right with a dual extruder and an insoluble and soluble filament. If you print the thread with one single filament, you will have problems with the thread turns and the support structure, right?.or is the thread pitch in my case (1mm)
too fine?

Here’s a GH file I found a couple of years ago in the old forum. It generates ISO metric threads both male and female. You only need to make changes to the dark blue group; the various other groups feed back their geometry to there.

I’ve only used this a couple of times, but when I did I gave up on using both the male and female parts. I did this because it seemed like the tolerances between the 2 were just too tight for 3D printing. So I used the male threads and then scaled them up in XY just a few % and used the result to SDiff from a solid cylinder shape.

ISOmetricscrewthread.ghx (741.2 KB)

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thanks very much. I will try it. do you have experience with 3D printing and threading? Is it only possible to print threads with a coarse pitch like in a PET bottle in 3D (https://www.thingiverse.com/thing:4383931)? The hose from the DIY store has a rather coarse thread, doesn’t it? I am not an engineer.

Why don’t you forget about the thread and just print your three hole part with tubes that fit into the hose.

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Hi @pa-weinmann,

I have some experience, especially with PLA, hybrid PLAs, PETG, ABS and PVA (water-soluble support filament much like glue sticks).

When 3D-printing with FDM, you should consider both the orientation of the part to print and overhangs (if you want to print without a support structure, which has many benefits).

The orientation on the build plate later defines the structural strength of the part. Since you print in horizontal layers (parallel to the build plate), parts usually have good compression strength, but are prone to de-lamination or breaking, when tension forces are applied in the normal direction of the print layers (or build plate).
Threaded cylinders or holes would thus be best to print in “horizontal” direction, meaning when the center line of cylinder is parallel or in the plane of the build plate, which in your case seems feasible.

If you want to print without supports all overhangs should be 45° (max. 60° if your printer is super well calibrated and precise) or less. If you print with supports the overhangs don’t really matter that much.
Soluble supports like PVA are nice, but time consuming and prone to produce failed prints. Printing with dual extrusion usually at least doubles the printing time and things like PVA need to soak for a long time, if you have no “professional” setup that circulates the water and heats it before it gets too cold. Otherwise you need to change the water and agitate the part every few hours for at least a day. Hydrated PVA is also a nightmare to print with. Unless you have a fresh spool or optimal storage (moisture deprived), you should consider drying the filament before printing. It absorbs moisture from the air, when not optimally stored, that evaporates inside the hotend of your printer and thus disturbs the regular flow of molten plastic.

PET bottles are not really 3D printed, but rather injection molded and then inflated to take their final shape I believe.

If you have a soldering iron, I would consider threaded metal inserts (brass or stainless steel).
They are pretty straightforward to install. You just have to plan out cylindrical holes in the 3D model about 1 mm smaller in diameter than the insert. Also don’t go crazy with the heat of the soldering iron! This is probably the best way to handle reusable connections for 3D printed parts.
When you only want to install the part and never take it apart, you could as well use screws with predefined, cylindrical holes in your model. The diameter should roughly be smaller than the screw itself (i.e. 3mm ø for M3). The screw threads into the plastic and usually is held in really well, but when you screw it in and out a couple of times the plastic gets destroyed.

Printing really small threads is not a good idea, except when you need them like in your case. I’d rather go with one of the two methods above if at all possible.

As diff-arch said, printing threads is tricky business and, in my experience, always requires some trial & error. The answer to your 2nd question is “sometimes” - meaning sometimes you can print fairly fine threads that work OK. The inside/outside diameter, thread pitch, and thread depth are what matter and it’s hard to predict the results of any particular set of parameters.

There are several ways to make threads. This was my first attempt: https://www.thingiverse.com/thing:1349360. To make the bolt I made a hexagon with filleted corners, stacked 30 of them up vertically, rotated each one by 1 degree more than the one below, and Lofted the results. For the nut I offset the bolt threads 0.5 mm and use this to Sint with a solid hexagonal extrusion.

Another way is to use a helix as the rail curve for a Sweep1 with a triangle as the sweeper. You can allow for the tolerance between male/female parts by changing the size of the triangle or simply moving it horizontally a small amount.

The last way is to use that ISO metric thread generator I posted before.

Of course the precision of the printer used to make the threads is a critical component. I print only PLA and never use supports, and none of my threaded prints ever had to withstand much tension - for example I made a few round containers with threaded lids. If there is any real tension on the threads I agree with diff-arch that de-lamination would be an issue. Its probably true that some material other than PLA would be better for cases like this.

Finally, don’t allow your expectations to exceed reality. A 3D printer is really only a 2 1/2 axis machine (because it prints only horizontal layers), so it is simply not possible to print truly smooth threads. This means that finding the proper tolerance between male/female threads is always a trial/error process.

If it’s an internal thread I would print the tapping size and then cut the thread by hand with a tap. Or use a threaded insert. I’ve found both methods are easy and work well.
For an external thread you might be able to cut it with a die if you are careful.

Have you ever used a soluble filament? It’s not anything close to the hype. For one you’re not supposed to dump the after water down the drain. For two it takes forever to disolve. For 3 the prints are slimy after.

I bought into it and overpaid for a printer capable of it only to learn the truth later.

That said, I’ve found that I can successfully print 60° machine screw threads without supports as long as the screw axis is printed vertical. May need to chase the threads, especially internal ones, with a tap/die.

They likely will leak somewhere from a little to a lot.

EDIT: All that said, keep in mind that printed threads in this orientation will be quite weak in tension, so need to be much larger than if in metal, to have strength.

I have no experience in 3D printing with soluble materials.
I will try this tip and print the connection point a little bit smaller than the metal thread. Then heat it with the soldering iron and press it in carefully.


Here is a photo of the component. Actually it should be 50% stretched in xzy direction. The smaller prototype uses about 1/3 of a 1kg filament at 20% infill, PLA for the overall 3D print (part + support material) at normal orientation. If you print horizontally, the amount of supporting material will probably be even higher, won’t it?

In the hardware store I found another part with a quick coupling, that should work? But how do you construct the counterpart with Grasshopper?
16102020_screwthread.gh (16.8 KB)

I kind of like that object and decided to model a similar part with SubD tools

20_10_23_hose_connector.3dm (5.9 MB)

You could first do an online search to see if the manufacture, or anybody else really has published any details about this part. If you find plans or exact dimensions, remodeling the part should be pretty straightforward.
If there is no information out there, you pretty much have to measure the part yourself, make test prints, readjust parts if necessary, and reprint, until you have a counterpart that fits well. At least that’s what I mostly do. It helps to only print smaller, relevant details and not the entire model every time. This way you can at least save some filament. For precise measuring, digital calipers are an invaluable tool to have in your arsenal!
I wouldn’t use Grasshopper for this though, or at least not for the initial model, especially since you want to do a custom part that fits another one. I’d stick with Rhino.