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  1. #1
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    Default 3D printed Flexy/PVC duct connector

    Unless one uses (more expensive) oversize flexy, connecting flexy to PVC has been problematic.

    Given the significant restrictions to airflow produced by flexy, an added factor in this type of connection is to ensure the flexy goes inside any PVC ducting coupler rather than the other way around , which otherwise ends up choking the air flow even further.

    Elsewhere I have shown a connection using a DWV threaded coupler and a hole cut in a threaded cap which utilises "flexy inside the coupler" and works well but I thought I would have a go at 3D printing a threaded coupler with in this case the thread fitting the spiral wound nature of the flex.

    This is what it looks like on the outside - ie nothing special.
    Junction.JPG

    The flexy end has an ~ 2TPI internal thread like this that screws directly over the flex outer spiral.
    Thread.JPG

    Inside the threaded connection it looks as you would expect
    This is with the very flexible PU flexy
    Internal1.JPG
    Half way down the inside of the connector there is a small ridge that prevents the flexy and the PVC from teh other side going in any further.

    And it also fits the stiffer PVC flex
    PVCflex.JPG

    3D printing notes;
    ********************
    I will shortly be putting this design up on Thingiverse and as well as providing STL files, I'll also be providing the SCAD file.
    When I do that I will provide a link back in this thread.
    This Adapter is for a 100mm PVD ducting/flex connector but it should be easy to scale to 150mm or any size flex/duct using the SCAD
    Due to the variability of PVC ducting and flexy, and the accuracy of your 3D printer you may need to adjust the size of the connector if you want a tight fit.

    The STL file can be scaled within most slicer apps but bear in mind if you scale to suit the threaded section for the flex it will change the other side and hence the size of the PVC duct connector.
    The threaded side is slightly oversized in the plan and much more forgiving than the other end so in the first instance I suggest you size for the PVC side and take whatever you get for the threaded side

    The SCAD file is fully customisable so you can size the threaded and non-threaded side independently to your hearts content, plus you can vary the wall thickness, thread pitch, lengths, and even the taper fit of the PVC side. You do not need to know how to program in SCAD to do this, but you do need to download a copy of (free) SCAD and learn to drive the basic functions (eg compile/preview, render, export to STL etc). Once you load the file all the variables are all neatly laid out in a panel on the RHS of the open APP, adjust the variables, hit Preview, when that is finished press render, and when that is finished export the file as an STL) The rendering time depends on how smooth you want the threads. For very smooth threads it can take many minutes especially on a slow computer.

    I printed this adapter in PLA, with 20% fill and 0.16mm resolution using a 0.4mm extruder nozzle.
    Total print time was ~21 hours, so its not fast, but then again not much DIY 3D printing is.
    The cost of the plastic for this adapter is about $2.50 worth of cheap (ebay) PLA, or about $4 for better quality PLA.

    The ~5mm internal ridge between the threaded and non-threaded sections was printed without support. This leaves a few plastic strings and dags that need tidying up but they won't affect the seal. The ridge is just there to limit the internal travel of the PVC duct and the flex from each end. The ridge could be reduced down to 3mm without any problems which would produce fewer strings and dags

    Oh yeah, to program the adapter in SCAD I had to learn about how to make threads in this App which is quite tricky. Fortunately there are many useful libraries/routines available and I used one from Thingiverse by Dario Pellegrini. I printed off my first prototype and simply could not get it to thread onto the flex. Eventually I realised the thread on the two flexy samples I had were LH threads. So I then had to work out how to fudge the threading routine to make a LH internal thread. I tried a few things but eventually I gave up and contacted Dario. He responded in about 15 minutes and it turns out all I needed to do was add a minus sign to the "nthreads" variable. Thanks Dario - what a champ!

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  3. #2
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    Default

    Nice! 3D printers can solve a lot of problems.

    I used Fusion 360 to design my fittings. I really need to work with SCAD some more. Here's one of my threaded hose fittings, it's 150 mm:

    3D printed Flexy/PVC duct connector-threaded-coupler-jpg

    I used much coarser resolution, .6mm line and .3 mm layer because I'm not patient enough to wait for the quality you're getting. I've since switched to a .8 mm nozzle and 1.2/.5 mm lines/layers.
    Attached Images Attached Images
    Dave

  4. #3
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    "$2.50 worth of cheap (ebay) PLA, or about $4 for better quality PLA."

    Better than the $40.00 I pay for the coupler and cap.

  5. #4
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    Default

    Wow - I'd say there is a market for these things Bob. Plenty of us use that type of flexi (and smaller) from ebay.... nice one indeed

  6. #5
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    Quote Originally Posted by draconus View Post
    Wow - I'd say there is a market for these things Bob. Plenty of us use that type of flexi (and smaller) from ebay.... nice one indeed
    I'm not into bulk production etc so I'm volunteering to make any as I'd much rather be working on the next 3D prototype.
    The other thing that would irk me is that as I'm using some of someone else's code I'd be legally obliged to get myself a licence to use it.
    However, I'll be putting the design up for free on thingiverse so people can print their own

  7. #6
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    Default

    Played around a bit more in SCAD and managed to generate a flexible program that allows users to generate a number of different threaded sections.

    Heres some examples of possible cross sections of the thread in graphic form.
    Screen Shot 2021-11-15 at 2.57.33 pm.png
    1) Manual (green profile on graph)
    The example shown is a square thread but the manual profile allows you to enter as many pairs of numbers in the Z/X space too generate a profile to suit unusual flex. I have seen some with flex with square beading so this is where you might use it. Other possibilities would be, trapezoidal, triangular or combinations of several profiles

    2) Sinusoidal (red profile on graph)
    This is a calculated profile as per the OP. Its the most forgiving as you don't need to be too specific about getting the radius of the flex side of the coupler just right, but it will also be the most restrictive, although no more so than a shallow bend in the flex.

    3) Semi-circular (blue profile on Graph)
    This is a calculated profile based on the input of the pitch (mm per thread) and the radius of the outer flex bead (in mm). Its not that forgiving in terms of fit (print mast be close to requirement) hence it may take several attempts to get this right for your flex, so to save you repeatedly printing out the whole coupler you can just print out a short section of the threaded section of the adapter. I printed this bit 5 times to get it fitting snugly.

    This is not the best one but its close.
    demicirclegroove.jpg

    Will shortly upload to Thingiverse for those that are interested.

    And here it is
    Threaded flexy/PVC ducting coupler by BobL - Thingiverse

  8. #7
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    Thank you Bob for sharing your work on this. There is a real need for this in most sheds with ducting.

    I'm in the process of extending/re-configuring the ducting in my local Men's Shed and some of these would make the task so much easier and cheaper.

    My immediate thought was to take your Thingiverse file with required parameters for our flexi to our community library for printing, but their 3D printer isn't big enough to render a 150mm fitting (viz, maximum build size of 227L x 148W x 150H mm).

    The other snag is the 8hr time limit the library has placed on print times. I read that your 100mm fitting took about 21hrs to print on your current 3D printer. I expect a 150mm fitting would take a lot longer on your level of printer. I don't know where the library's 3D printer fits into the hierarchy of printer speeds, but given its size limitation I expect not that fast.

    Anyone know how economical it would be to take (say a 150mm fitting) like this to a 3D bureau printing service?
    Stay sharp and stay safe!

    Neil



  9. #8
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    Thanks Neil, and you make some good points

    Quote Originally Posted by NeilS View Post
    My immediate thought was to take your Thingiverse file with required parameters for our flexi to our community library for printing, but their 3D printer isn't big enough to render a 150mm fitting (viz, maximum build size of 227L x 148W x 150H mm).
    My first printer was given to me by my son in 2016? and was slightly smaller than your library's printer. Even back then I was thinking of printing custom dust extraction stuff but with the printer being too small was one reason why I did not pursue 3D printing at the time.

    The other snag is the 8hr time limit the library has placed on print times. I read that your 100mm fitting took about 21hrs to print on your current 3D printer. I expect a 150mm fitting would take a lot longer on your level of printer. I don't know where the library's 3D printer fits into the hierarchy of printer speeds, but given its size limitation I expect not that fast.
    the 21 hr time was for a high resolution print[/QUOTE]

    The 21 hours is for a "medium high" resolution print at standard speed but I don't think that is necessary and even lowest quality at faster speed would suffice.

    Here are some calculated printing times (all at standard speed) for various adapter sizes and print qualities

    100 mm
    Lowest quality 11 hours
    Medium High quality 21 hours
    Highest quality 29 hours

    150 mm
    Lowest quality 22 hours
    Highest quality is 62 hours

    Faster print times could probably get you a 30% reduction in time but as you can see it's all slow to very slow stuff.

    Anyone know how economical it would be to take (say a 150mm fitting) like this to a 3D bureau printing service?
    I might send one a file and ask for a quote.

  10. #9
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    A larger nozzle can help a lot with print time when you don't need so much resolution. I switch to a 0.8 mm nozzle for dust fittings and print with 1.3 mm line widths and 0.6 mm layer heights. That lets me use the maximum filament flow rate from the extrusion system.

    I've also found that the fittings don't need to be as long as regular PVC fittings. Instead of a 50% hub depth I've been using 33 or 35% of diameter. That alone is about a 30% time savings.

    This 100 mm hose fitting took two hours and 7 minutes actual print time with a Cura prediction of 2h 33m:
    Mag Hose End_2.jpg
    That's with a Volcano hotend; your printer would likely take about twice as long without a higher flow hotend.
    Dave

  11. #10
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    Thanks for the info Dave.

    Quote Originally Posted by BobL View Post
    Here are some calculated printing times (all at standard speed) for various adapter sizes and print qualities

    100 mm
    Lowest quality 11 hours
    Medium High quality 21 hours
    Highest quality 29 hours

    150 mm
    Lowest quality 22 hours
    Highest quality is 62 hours
    I forgot about changing the nozzle size and using a 0.8mm nozzle. When this is used in the printing app, forecast print times are reduced by ~32%
    Reducing the coupler ength by 40% (62mm long) reduces the print time by a further (as you'd expect) 40% which brings it from (for say the 22 hours for the 150mm lowest quality) to about 6 hours compared to the original 22 hours.

    I've used 0.8mm nozzles on my printer at 150mm sec print speed, and apart from very slightly puffing on sharp X-Y corners it prints fine. I have also just installed a Micro Swiss all metal hot end. So far I can really tell the difference with PLA. although I haven't pushed it speed wise and I don't have any larger nozzles for it - yet!

  12. #11
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    Knees are playing up so can't stand for long, so less shed time and more 3D printer time.

    Been experimenting with a few flexy hose threaded connectors like this one,
    A is the connector that is permanently on my 3D printed hand sander
    B has a 38mm flexy hose internal thread at B1 and taper fit at B2 that slides onto A.
    A's ID fits my 32 mm vac hose fitting.
    3mnnHose.jpg

    A couple of mag style fitting prototypes .
    There's no flexy threads on these as I was just testing the alignment and mag setup/system
    Magflanges1.jpg

    To reduce the need for printing support the flanges with the proud pins are composed of and printed as two pieces separate that are joined like this
    Magflanges3.jpg

    This all works fine but I'm not sure I will continue with any sort of pin alignment method as no one else seems to bother with it.
    Next will be a pinless version.

    I've just finished working on a CAD design that makes an "any size to any size" adapter, with any length taper adaptation, and with screw or mag connections on each end

    This means it should be able to make long tapered adapters like this. These should be much better than the usual "level invert" adapters in widespread use (simply because there is nothing else out there.
    Screen Shot 2022-07-20 at 8.38.16 pm.png

  13. #12
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    Quote Originally Posted by BobL View Post
    Knees are playing up so can't stand for long, so less shed time and more 3D printer time.

    I've just finished working on a CAD design that makes an "any size to any size" adapter, with any length taper adaptation, and with screw or mag connections on each end

    This means it should be able to make long tapered adapters like this. These should be much better than the usual "level invert" adapters in widespread use (simply because there is nothing else out there.
    Screen Shot 2022-07-20 at 8.38.16 pm.png
    That looks like time well spent Bob. I’ve seen the tapered adapters on thingiverse but as you noted not threaded. Will you be putting the scad file with adjustable variables on one of the 3D print libraries.

  14. #13
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    Quote Originally Posted by apple8 View Post
    That looks like time well spent Bob. I’ve seen the tapered adapters on thingiverse but as you noted not threaded. Will you be putting the scad file with adjustable variables on one of the 3D print libraries.
    Thanks,
    Yes I will upload the program eventually.

    I need to spent some time tidying up the program, test print out some variations, and the add some documentation.
    The program current exists of a combo of 3 other programs and contains some redundancies and irrelevancies.

    Because of the flexibility and large number of options the program and numbers of variables are becoming quite unwieldy so I need to tidy this up a bit.

    This is the current parameter list - some parameters are redundant
    Screen Shot 2022-07-21 at 6.15.39 am.jpg

    Here are some sample variations of what should possible
    100mm flexy threaded, to 100mm duct magnetic connect
    Screen Shot 2022-07-21 at 6.08.13 am.png

    100mm flexy threaded, to 150mm duct magnetic connect
    Screen Shot 2022-07-21 at 6.23.06 am.png

    100mm flexy threaded, to 150mm plain connect
    Screen Shot 2022-07-21 at 6.31.34 am.png

  15. #14
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    Quote Originally Posted by BobL View Post
    Thanks,
    Yes I will upload the program eventually.

    I need to spent some time tidying up the program, test print out some variations, and the add some documentation.
    The program current exists of a combo of 3 other programs and contains some redundancies and irrelevancies.

    Because of the flexibility and large number of options the program and numbers of variables are becoming quite unwieldy so I need to tidy this up a bit.
    Thanks Bob, I couldn’t get the SCAD file to display properly on my iMac, so that set me another challenge in Fusion360. Turned out better than I expected, after finding the coil tool in Fusion I was able to come up with this adapter for 55mm flexy to 50mm SWV pipe. The variation in colour is me using up some short ends of filament, another thing I wanted to test.

    F3ABC180-D92E-4933-AB09-569813DE07CC.jpg EFB0C701-670B-4424-92BA-C7A0D435716F.jpgD018CE53-0677-4030-8F88-9ACA4A683595.jpg

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