Printing Of Hollow Circular Objects

Discussion in 'Suggestions & Feedback' started by CapHerlock, Oct 27, 2019.

  1. CapHerlock
    CapHerlock Well-Known Member
    Hello everybody,

    I have been playing around with this idea for some time, but I just can't get around it. I wanted to printed a replica of a spear in Versatile Plastic, about 2mt high (6ft) and 25mm (1in) wide, with the largest point being 35mm in diameter. Now my problem is the insane price for a cylindrical shell, 25-35mm in diameter, 1mm thick, which has a volume of between 13-25 cm3, that has a cost of between $30-60! That's absolutely insane.
    I have been here on SW long enough to understand that they have certain prices to make a profit for themselves, but having machinery costs like those for a piece which is not worth half of the cost is beyond me.
    I have already tried to cut the pole in various ways and laying it in different positions, but my efforts have been to no avail. Does anyone have any idea or tips on how to get around this? I'm running out of ideas. And I think SW needs to rework the pricing algorithm for hollow parts.

  2. stonysmith
    stonysmith Well-Known Member Moderator
    You need to understand that the biggest cost is not the plastic, but rather the electricity and time to run the machine.
    If you have a large space inside a model that "blocks" that area of the machine from being used, then it costs them more than if they could use the space for printing other items.

    When you say "hollow".. is the inner void open to the outside? If not, then the model becomes a solid, and is no longer "hollow".

    Even with an opening, the rule is that the inner void has to be 40mm or larger (and open to the outside) so that other small objects could be placed inside, such that they can recoup the cost of machine space which is blocking other small items from being printed. Your inner diameter is less than the 40mm - so it's going to cost more in machine space.

    You might be better of setting up the spear in sections, each of them a "pipe" (open ends) rather than a cylinder (closed ends) and then glue the sections together later. Of course, you'd also have to provide an inner diameter of 42mm (40 minimum+1mm gap on all sides) - making your outer dimension more like 45mm.

    I can't imagine that you could get away with 2 meters long for only $60.. i would have expected something more like $500
  3. CapHerlock
    CapHerlock Well-Known Member
    They are. The hole is all the way through, although yes it is less than 40mm wide.

    I never thought of getting away with a 2mt pole with just $60, but when just a tenth of it (195mm, which is the maximum I can fit using Processed Plastic) is $60 just that single piece, it starts to get annoying. I honestly hoped to stay below $250 if at all possible, but considering a price which takes into account very costly and very cheap pieces in the range of $40, and having to make at least 10 pieces, a $400 cost is unacceptable.

    I see, thank you for your explanation. I guess I'll have to figure out some other way to cut the parts so they'll occupy less volume.
  4. 8_Perf
    8_Perf Well-Known Member
    What Stoney said. However, I am curious. Why does this part need to be printed in the first place? Its a relatively standard size and could be done using a one piece aluminum tube from a hardware store. Could always cut it if that had to be a thing. The whole tube would cost less than $10 US and be far more durable.
  5. CapHerlock
    CapHerlock Well-Known Member
    Mainly two things: first, it's easier to put together two pieces of the same material rather than one of plastic and one of metal, and secondly because of anyone who could be interested in that could find the entire product available. It's up to them whether or not they want to purchase the staff along with the rest or use an aluminum tube. Keep in mind this is not a straight staff however, it's larger at the center, so using a tube won't really work all the way through.
  6. 8_Perf
    8_Perf Well-Known Member
    Like I said, just curious. I was mainly concerned with the possibility of having to glue together 10 pieces and how durable it would be as a functional staff. Carry on. I hope there is a way to get the price lower, for your sake and ours. :)
  7. CapHerlock
    CapHerlock Well-Known Member
    I'm sort of figuring something out, although it's not a very efficient solution. I clipped every hollow part in four identical parts along the length, basically having a circular section divided into four quarters of a circle. This way I can use the full length of the part but reducing the space inside to the minimum required to distance the parts so as not to have them printed solid and allowing for a blade to get in between to cut the sprue connecting them. I had to sprue them otherwise they would be read as four separate parts and the price would have skyrocketed.

    Let's just say it was at least half a success: I can have the entire lance printed with about $220 give or take, but it was an extremely laborious and time-consuming process. It works as far as reducing costs efficiently, but it took me two whole days to do the entire thing. So yeah, I guess next time I have to make a hollow piece I know how to deal with it, but it's not a solution without drawbacks. At the moment I can't think of any other way that works as efficiently.
  8. Greaseball
    Greaseball Well-Known Member
    If you can gain access to a wood lathe why not turn a few pieces to your desired profile and then glue them together with internal dowel rods? You could paint the pieces or stain them if you want to retain the character of the wood. You should be able to find a lathe service or hobbyist woodworker that can help you.

    Or build up the profile over a smaller constant diameter rod using paper mache or gauze and plaster? There's not much point in 3D printing something like this unless you need the precision and have deep pockets. Is this a project for a museum quality replica? Cosplay? Just for fun?
  9. CapHerlock
    CapHerlock Well-Known Member
    It's a replica I want to build for myself. That said, I've already explained the other points. It's not just for me, but anyone who may be interested in this could have the choice of either getting the full kit 3D printed or make the pole on their own, it's their choice. But I'd like to at least have that, and let people decide their own way of making it.