Hi all,
I own a few puzzles made from shapeways (including the one I'm holding in my avatar).
Even though they turn great and I don't really mind their surfaces being a bit sandpaper-like, they tend to be a little too light for my taste. This is probably because the puzzle builders try to reduce the price by hollowing out the pieces.
Is there a way to overcome this issue?

You could sticker it with tiles or something else that's heavy.

You could partially fill the pieces with epoxy.

For puzzles you design yourself, if you trap powder in the hollow pieces your puzzles weight will increase a lot. Make a tiny hole in the pieces so that when Shapeways runs calculations on it, it doesn't look like you're enclosing space. A really small hole though can't get printed and all of the powder in the pieces will be trapped.

There are two reasons why you may not want to do this though. First, for most pieces it makes them tumble poorly (very uneven wear). Second, if the outer walls are thin a lot of dye and salt will get trapped in the pieces and they will leach out a ring of dye and salt when they dry (how much depends on the piece).

I tend to agree and I've had some that are so hollow the faces distort. Others though are much thicker and fine. As suggested you could add resin though unless you completely fill pieces the weight may not be very well distributed.

I was going to add 2 more reasons why you may not want to. First, I know some that use this method and have used a microwave to cook the water out after dying and this can result in large flat areas being warped slightly.

The second reason I was going to add was Shapeways has asked us NOT to do this. I recall reading in their site (I'd guess over a year ago) that the price they charge us is based on the volume of the part and that trapping powder costs Shapeways money as that powder isn't paid for. I seem to recall they stated they'd monitor the system for abuse as there really wasn't a system in place to keep someone from printing large thin walled spheres to trap as much powder as possible and thus supply free powder for their own 3D printer for example. However I've seached high and low on Shapeways and I can't find any such statements being made now. I've even found a few posts which state the powder can't be re-used and imply the trapping of powder is perfectly OK with Shapeways. So now I'm wondering if I dreamed the whole thing about them asking us NOT to do this.

I understand that many equate quality with weight and there is a general impression more might be interested in 3D printed puzzles if they were heavier. To me personally this generality isn't true in this case. The SWF material is so strong that making things heavier just raises the cost (assuming one isn't trapping powder) and Shapeways puzzles are already so expensive that I do everything I can to make them cheaper.

So to me this is more of a perception issue and not really a problem that needs to be solved. And I'm still not sure of the ethical issue of trapping the powder. Can anyone else find a place where Shapeways address this exact topic themselves? I felt pretty sure I'd seen it on their site before and if they've taken that down one could assume they are now ok with it. I just don't want to encourage an activity that if too many take advantage of it would result in Shapeways needing to raise their prices to cover their increased costs.

Carl

I'll echo what Tony said. I too have had problems with thin walls with trapped powder distorting really badly.

Also, I have a 15 PSI pressure cooker for dyeing and it can't be used on any pieces that have hollow chambers.

So that's at least 4 good reasons why you shouldn't trap powder.

I'm certain I read or heard (in a video of theirs) that they do reuse the powder a few times. My memory for where this actually was stated is poor.

I seriously doubt the powder is a major cost in the printing process but I could be wrong.

I think their prices are based on the two limiting factors that limit their "supply" (the rate at which they can print orders). Their printers have a finite volume so they can only physically fit a small number of orders. Second, the print time is based on the volume of powder being sintered. Sintering more powder takes more time and slows the whole print down. A print takes 18-24 hours so time really is a limiting factor here.

I think the density discount is meant to reward people who don't take up too much printer volume. Somebody printing a giant hollow rectangle could waste a ton of printer volume. To counteract this Shapeways charges a lot more for low-density models.

I more accurate pricing model would charge you a little bit for your total bounding volume, a lot for the actual part volume (charging for print time here) and a little bit for trapped powder. I think this pricing model is too complicated to explain to customers though so they've decided to just go with part volume and offer a density discount.

Shapeways uses a mix of 50% fresh and 50% reused powder (probably some different ratio, but whatever). This saves on cost while keeping model quality constant and good enough.
Apparently the density of a print job is usually about 10% or less. So each print job will give them more than enough powder to reuse in the next (they're getting 90% back, though they only need 50%) so trapping some powder is not a big concern. They actually have a large container of used powder, looking for an opportunity to be recycled.

What I have done for several of my hollow Shapeways models to make them heavier is to add casting resin. I have used this successfully on the Shapeways SWF (Strong White Flexible) material. I inject this into the hollow interior of the parts.

I have used Crystal Clear 20 Casting Resin. This is a 2 part mixture that has equal parts A and B. The nice thing about this casting resin is that it stays thin for about 20 minutes so you have time to work with it. You can also try 2 part slow cure epoxy. The Casting Resin and Epoxy is available many places online. I have found the slow cure epoxy at hobby stores for RC cars and models.

If your model has an open bottom your can just pour your mixture into the bottom.

If your model does not have an open bottom then you will need TWO holes for injecting mixture inside the model. You can add holes when you create the model, or drill as needed. Make the holes at least 3mm in diameter. One hole is to inject the mixture into. The other hole is for venting air ( otherwise you get a mess ).

I have used Monoject 412 Curved Tip Syringe, 12 cc for injecting the mixture. These are available online, or at many hobby shops. I cut off a half inch or so off the tip to make a bigger hole for the resin to pass through to make it easier to inject. Just make sure that the tip still fits inside one of your holes in the model.

I use small plastic disposable cups for the mixture. Pour some into the syringe. Insert tip of syringe into hole in model. Inject the mixture. Refill the syringe and inject more if needed.

Use a small square of non-porous rubber to cover the holes. Clamp this in place. The rubber makes a good seal, and can be peeled off easily after drying.

Next rotate the model so that the mixture flows evenly over all the interior surfaces of the hollow region of the model. Keep rotating until you reach the cure time. For example until 20 minutes since you mixed your resin. This will keep the mixture from running all to the bottom.

Let fully cure overnight. Remove the clamp and peel off the rubber seal. Your model is now ready for painting if desired.

Hope this helps.

Post your results here if you give this a try.