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 Post subject: Shapeways problem: inconsistent hole sizes
PostPosted: Sun May 19, 2013 6:07 pm 
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I designed my first puzzle and the first print worked nicely. I then just changed some things to make it better and get rid of minor flaws. The new version I ordered is also bigger then the first. About factor 1,25.
Of course I made sure not to scale the entire thing up. The holes for the 3mm screws are still 3.2mm and 2.7mm were the thread goes. The caps have 3.2 mm holes as well. Now I try to assemble the puzzle and it is impossible. The holes in the caps are between 1 and 2 mm and the holes in the core are to small I can't screw the screws in. They get so tight I am breaking the head and screwdriver.
I checked my model and it doesn't have a flaw. It is the exact same execpt that the diameter of the core is larger. Wall thickness, holes, depth of holes, all the same. But it doesn't work anymore.
Also the caps of the center piece don't fit anymore. The old ones had 0.1 mm tolerance on all sides and were a little tight. I made the new ones to have 1.5mm and they are so tight I can't put any cap on. What is going on?
Do larger models make the precision much lower? And why to such degree at such small increase of size?
It really happend to ALL pieces. Everyting has way to much material added by the printer.

Is this a common problem?

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 Post subject: Re: Shapeways problem: inconsistent hole sizes
PostPosted: Mon May 20, 2013 4:14 pm 
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Joined: Sat Apr 21, 2007 11:21 pm
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This sounds very much like the inflation I dealt with on the first Rad13 print. Very frustrating, and hard to prove it to be outside their tolerance.
I think they simply have some bad machines running. Possibly larger format machines, but there is a real difference. I've been lucky since then, but I don't feel it's a problem they've solved.

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 Post subject: Re: Shapeways problem: inconsistent hole sizes
PostPosted: Mon May 20, 2013 4:30 pm 
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I have had a few very similar instances. My holes ended up being more elliptical though, which destroyed the print basically.
Luckily I have gotten refunds as needed


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 Post subject: Re: Shapeways problem: inconsistent hole sizes
PostPosted: Mon May 20, 2013 9:38 pm 
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Joined: Thu Dec 31, 2009 8:54 pm
Location: Bay Area, California
It's hard to know what is meant by "tolerance" because different mechanical designs call for different types of tolerances. You can't just shrink all parts or put tolerances on all surfaces and expect it to work. For twisty puzzles the tolerances need to be on rail + groove system and the concentric spherical faces. You don't put tolerances on faces parallel to the radial lines.

With regard to tolerance amount, never go less than .3mm because the layer thickness of the printer is about .1mm and if you have two parts sandwiching each other, if both round up to one additional layer thickness that's already a deviation of .2mm.

There are a lot of factors influence the accuracy of a print but the most common problem seems to be all of the parts a tiny bit too big so they're really tight or can't be assembled at all. Fortunately it's still a somewhat uncommon problem.

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 Post subject: Re: Shapeways problem: inconsistent hole sizes
PostPosted: Tue May 21, 2013 2:22 am 
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Location: Jarrow, England
Read this article by Shapeways for a rundown of all the issues, including printing parts oversize to allow for shrinkage, how holes work etc.

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 Post subject: Re: Shapeways problem: inconsistent hole sizes
PostPosted: Thu May 23, 2013 6:07 am 
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Hi alaskajoe,

I'm sorry to hear about the issues with your print. I can't really tell from your description if the deviation is within our tolerance or not (see our 3D printing guidelines, for example this one for White Strong & Flexible).

If you feel we've made a mistake, please contact our customer service team at service (at) shapeways (dot) com and they'll help you out.

Cheers,

Bart

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 Post subject: Re: Shapeways problem: inconsistent hole sizes
PostPosted: Sat May 25, 2013 11:01 am 
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Joined: Mon Feb 06, 2006 12:52 am
Thanks everyone for the replies and thoughts.
I managed to assemble it. I only needed a small round file to make bigger holes into the center pieces. The caps, well I am still working on them.
For the core i got smaller screws with really sharp tips first to drive them in a little and then used the file too.

One of the reasons for the really small holes might be the fact that I "exploded" the assembly from one point of origin. Instead of making an assembly file were all the center pieces have the same orientation/direction. They all lie horizontally now in my new file.
Also I rearranged the orientation of the core in a way that all holes for screws have the same orientation in respect to the horizontal plane. So it's not like some holes are vertical and some horizontal anymore. That way they will at least be all printed the same.

Also I made the non threaded part of the holes biger.
I will order the core and one centerpiece soon and check what it looks like.

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