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  1. #1

    Question Replacement part for model railway wagon

    HelloI am new to 3d printing (first filament arrived today, first printer - Creality Ender 3 Pro - due next week).The part I am trying to design is a railway wagon coupling mounting arm for a Hornby KFA container wagon. Four images are attached, the main one shows dimensions in mm. The measurements along the bottom are various features measured form the datum on the left. The 2 measurements on the upper edge are the centres of the red and blue rings measured from the datum. The 4 on the right are the inner and outer diameters of the rings.The red and blue rings were my attempt to start designing the shield-shaped part from two native rings, this was a failure. My first attempt was in Tinkercad, the second in Sketchup. I am mow using Mattercontrol which is more to my liking but I am still struggling to get past the first step on the very steep learning curve.My next thought was to prepare a 3rd angle projection and convert it to STL for slicing. Is this possible? and if so which app should I use? Failing that any hints on designing the shield shaped part of the item would be very welcome.After that it will be a case of designing and adding the remaining parts, plus figuring out how to add support structures, etcBest regards Brian (bkk-bkk)
    Attached Images Attached Images

  2. #2
    You'll want to avoid SketchUp, as it's well known that it generates unprintable STL files. I'm a big fan of OpenSCAD, but for your project, you may have better luck with Fusion 360 or a similar sketch based program. Matter control and Tinkercad are founded on manipulating primitives (as is OpenSCAD) and can make things challenging. OnShape is another sketch based program that should work.

    You've done a great job of presenting the necessary measurements, a key factor in building a model and half the work for something like Fusion 360 or OnShape.

    Even though Fusion 360 has changed some of the aspects of the license, it's still free for hobbyists and worth a look.

  3. #3
    Super Moderator curious aardvark's Avatar
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    Jul 2014
    The other thing to remember about 3d printing is that you DO NOT HAVE TO copy the existing part exactly.

    I can see a couple of ways you could change the end couplier so that you do not need to use supports.
    Any part printed without needing supports will be better than a part where you have to cut and sand/file them away.

    As long as the part does the same job - it does not need to be identical.

    To do that you do need to see the part in use, but can't envisage why you could not get away with a part that did not need supports.

    Also you can make the part in 2 non-support necessary sections and simply glue or clip them together.

    I don't think in the last 7 years I have ever designed a part from the ground up that has ever needed supports.
    Very occasionally if I am copying an existing and broken thing - there is no way round it. But for the vast majority of things - you should never need supports.

    Don't get hung up on feeling you have to replicate an injection moulded part exactly.
    You have the luxury of being able to make something new and often, better, to fit your production method. :-)

    Also until you have worked out the particular quirks of your printer - you really have no idea what it will do and not do.
    I did start designing stuff before i got my first printer.
    None of it was practical.
    3d printers are amazing machines, but you need to learn the capabilities and limitations before actually designing complex things.

    So don't start from : 'I have this thing I need to duplicate exactly.'

    Start from: 'I need a part to do this job, what can I actually make and how will my printer cope with my design.'

    You coudl well end up with a better designed coupler that you can mass produce and sell to the model railway community :-)
    Last edited by curious aardvark; 10-01-2020 at 06:44 AM.

  4. #4
    Hello Fred
    Thanks for your reply. I have spent a couple of days checking out Fusion 360 and some of the videos on YouTube. It seems to be the one for me! especially the sketch and extrude features as well as the general organisation of the available features and work flow. Still haven't found the best way to construct the battle shield shape but I'm sure it will come to me eventually.
    Incidentally, Fusion 360 is free for non-commercial users for one year and then Autodesk require an annual subscription. Also, the free version was modified today 1 Oct 20 to exclude some of its features but nothing too drastic I understand.
    Thanks again Brian (bkk-bkk)
    Last edited by bkk-bkk; 10-01-2020 at 10:50 AM.

  5. #5
    For the casual hobbyist, the features that will be lost in the free version should not impact the 3D printing aspect too severely. I have used Fusion 360 in the past to convert other formats and that may result in an inconvenience, but only time will tell.
    I'm glad to hear that I've been of some help.

  6. #6
    Hello Curious AardvarkThanks for your reply. Good point about the need for a flat base. This was at the back of my mind and I was wondering whether to bring the subject up on the forum. I will take your advice and print the part with a flat base and see how that works. The rectangular tube at the left-hand end can be printed separately in the upright position and then glued in place. I have about 70 wagons to repair and this is the only one with that type of coupling mounting arrangement. Your comments about getting to grips with the printer and getting it to produce acceptable objects was also at the back of my mind. I'm sure it's going to be a case of not getting anything right on day one, week one, or even month one. I'm looking forward to the challenge and I'm thankful that there will be plenty of help from YouTube and especially our community.Best regardsBrian (bkk-bkk)PS:A theory: To make a flat base, I suppose it would be possible to split the design into two parts and then glue them together back-to-back after printing. But in this case that would leave very thin portions of about 0.05 mm in each printed half. Would this be a viable option for such a thin component?For a wider/thicker object such as a model viaduct I suppose it would be achievable and could easily incorporate holes for alignment dowels.Am I thinking along the right lines here?RegardsBrian (bkk-bkk)
    Last edited by bkk-bkk; 10-01-2020 at 11:43 PM. Reason: Additional topic

  7. #7
    Super Moderator curious aardvark's Avatar
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    Jul 2014
    okay the key - I find - to mgetting good prints that don't need supports, is to build up at an angle.

    so instead oif the end coupling part being a vertical lift from the base, you would have an angle to the edge of the square part.
    Obviously this is dependant on whether or not the wagon blocks the chance of an angled support.

    And it also depends how well the cad program you use makes this kind of thing.
    I just use openscad. and in that the 'hull' command is king.
    It automatically wraps a 'skin' around two parts, creating a seamless transition between the two parts - no matter what shapes they are.

    Without seeing how they connect to the carriage I don't really know how I'd do that particular model.

    The other thing to bear in mind is that you can also print the model at an angle.

    Here's an example for an insect catcher I made.

    basically it's a pyramid on a stick with a sliding door. You swivel so the door is open, put it over the insect and swuivel so the door slides closed and remove insect to the outside.

    The tricky part was the channel the door slid in.
    In the end I split the body into 2 parts. That way I could print the main part on an angle so that the channel printed clean and wthout needing any suport.
    I then had a cylinder with square foot that pushed through the hole and formed the top cyolinder that the flexible tube pushed onto to link the catcher with it's stick. (literally sticks I curt from a piece of pine shelf).

    By printing at an angle you can make shapes that would otherwise not be possible without supports. And removing supports from a 2mm channel is not something I relished.

  8. #8
    Super Moderator curious aardvark's Avatar
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    Jul 2014
    I made them from transparent pla with 1mm thick walls. You can see the insects walking around inside them:

    It's an example of how you can make fairly complex shapes without supports.

    The beauty of 3d printing is that you can think of a thing that nobody else in the world has ever though of and inside a couple of hours actually hold it in your hand :-)

    I'm currently printing a tool to smooth down masking tape.
    Got a bunch of window frames to mask off - and something better than my gloved finger (they are outside) to get a really good flat application of tape was needed.
    I've actually made three all slightly different in design to see which is best :-)

  9. #9
    Hello curious aardvark
    Thanks for your excellent description of the insect catcher and your ideas about printing at an angle.
    I have put the wagon coupler to one side for now until I get more hands on experience about 3d design and printing. I have continued with Autodesk Fusion 360. It is a complicated programme but I will not be using many of the functions. I will concentrate on the functions that I will need which are mostly in the sketch and design sections.
    The original Creality Ender 3 Pro printer that I order from Amazon US is stuck in Bangkok airport customs and I have been asked to register as a dangerous goods importer and apply for an import permit. While I was thinking about this strange turn of events I received an email from Amazon apologising for the delay and offering a full refund if I wished to cancel the order. So I quickly hit the cancel button, waited for the refund to arrive in my credit card account and ordered a new printer from a local website. It was a lot cheaper and is a more advanced model (Creality Ender 3 V2). It should arrive tomorrow and I will concentrate on building and testing until I am confident. After that I will choose a simpler model part to design and print and eventually move on to the more complex parts that I need.
    Thanks again for your valuable help.
    Best regards bkk-bkk (Brian)

  10. #10
    Super Moderator curious aardvark's Avatar
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    Jul 2014
    first thing you need to do for the ender 3 v2 is to add a second z-axis screw.
    Either through a kit that joins the screws at the top or by adding another stepper motor.
    That will not only eliminate a lot of the standard ender 3 issues, but also allow you to move the extruder to the top of the hotend, which will give you a direct drive extruder and make life better all round.
    The second z-axis screw will also speed the machine up by considerable amount.

    They're not awful machines - just deliberately badly designed to save a few bucks.
    But the second z-axis screw fixes much of that and a direct drive extruder fixes mnost of the rest. The frame and bed you're kind of stuck with - but that's the least of the issues and the 'bed leveller' on it will help compensate for that a lot. (bed levellers do not level the bed)
    They map any uneven areas - you still need to level it with the levelling nuts :-)

    But there are more videos and user groups for fixing the inherent issues with the ender series than for any other model or make of machine on the planet :-)

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