For short, I am going to buy my first prototype on shapeways very soon. Before ordering it, I checked my model again to be sure that all is ok, and I noticed a few things that I am not sure.

First, for the screws holes, I used Solidworks hole wizard for the centerpieces and choose the size M3 (3.4 mm). If I am right, this is a clearance hole. And I wonder what must be the size of the hole of the core, for the screw to "screw-in".

Secondly, for now, my centerpieces are too small to contain a spring. Is it really necessary to have springs ?

Edit: Also, I know that if the part are too close they will fuse while printing. Is 0.5mm too close?

I use 2.75mm for the core hole. I use 3.5mm for the clearance hole, and 6mm for the place where the screw head would go. (Those are all diameters, not radii!)

No, springs are not absolutely necessary and some puzzle designers even think they're bad. I absolutely love them though and use them wherever I can since they do seem to help with the general feel of the puzzle, in some cases, at least.

0.5mm is right on the edge. I've got no clue why you'd want to have parts that close anyway, you've got a lot of freedom when spacing out the parts and it's easy to get them all 1mm apart or so. Much safer.

Thanks a lot! Very helpful and you gave me all the info I needed.

I have now another question: I exported my model in .stl, and it has over 2 million polygons. What is the best thing to do? Try to reduce the number with meshlab or splitting the pieces over two file ( and maybe more) or using shapeways backdoor?

I haven't tried this but I tend to think for the best turning you don't want to give up resolution.This is what I do and it works for me.This is what Tom does and if Shapeways ever makes this their front door I'll do it too. However as is, the reason I don't like it is it requires you to intervene with each and every order. If you are ordering for yourself that isn't a big deal. However if orders are open to the public and someone orders without you being aware I'm not sure what happens.

Oskar sort of does both. For his Over The Top Cube you should order 1 of these:
http://www.shapeways.com/model/182113/80b41945cfcb2485e7ede445be20e9b6/over_the_top_v14b___set_1___1x.html
and 26 of these:
http://www.shapeways.com/model/182112/8e3845c0f0d6659c03e6c0a04e9a30e6/over_the_top_v14b___set_2___24x.html

However I believe someone could also order this:
http://www.shapeways.com/model/64058/

And Oskar use the back door method. I don't have a clue what would happen is someone were to order that last one and not notify Oskar though. I think it could be very very bad.

Carl

I agree with you completely, hense why I have been put off of the idea of selling puzzles like that (for a while I was wanting to make my own website and sell them through there, just so my OCD would be satisfied by the fact that there wouldn't have to be multiple files ordered).

I would like if it Shapeways allowed you to group files and in turn produce a 'master kit', which you can set a price for and includes all of the files to make the puzzle. Then you could just hide the other files and show the 'master kit' file.

Oh I think something like that has been in the works (or at least talked about) for a while now. Here is where Shapeways details their "backdoor" method.
http://www.shapeways.com/blog/archives/564-How-To-3D-Print-High-Polygon-Models-with-Shapeways.html
Note they say "if there is enough uptake we can automate and speed up the process" and this was back in August 2010.

If you go back even farther you will see this thread started by Oskar.
http://twistypuzzles.com/forum/viewtopic.php?f=9&t=15967

And this thread on Shapeways.
http://www.shapeways.com/forum/index.php?t=msg&th=1358&start=0&S=1dc7056cae26b475bce88ba9815267ca#msg_num_18

Where on 24 January 2010, Peter Weijmarshausen an enployee of Shapeways stated they were working on this and we needed to be just a little more patient.

I just made a post in that thread today myself asking anyone that wants this to be supported to please vote for it here.
http://feedback.shapeways.com/forums/111989-shapeways-feedback/suggestions/2435883-composite-model-support

I didn't know about this voting until today. Oskar helped me find this link in his thread here.
http://twistypuzzles.com/forum/viewtopic.php?f=9&t=22772

Carl

I’m pretty sure if you didn’t email them about your order, you would just receive the large cube that was uploaded in place of the file.

Maybe. Their directions tell you the dummy file which contains your large cube should be named 'POLYGONENFILE'. I would HOPE that if they saw that name coupled with the fact the file was just a solid cube that they'd not print it till they had received some instruction. I don't trust that far enough to test it though for I fear you may be right.

Carl

Minimum resolution on the STL's is not a problem. I use SW2010 and I put minimum resolution which is pretty much the same as the shapeways precision limit so it's the same as if you put high resolution (except on a spherical core where there's a small difference which doesn't affect turning)

So there's the answer to your last problem good luck on your first print !