Sprues - new 2mm rule

see
https://www.shapeways.com/forum/index.php?t=msg&goto=104 751#msg_104751
for an already ongoing discussion on this topic ...

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Today I got 2 new rejections, caused by the sprues I'm using to connect multiple parts.

There was already a recommendation some time ago to use 1mm sprues.
Recently I got a rejection and I added a 2nd sprue layer so that the items are connected on 2 points.

Now there's a new rule asking for 2mm, which is really rather fat.

Maybe there's somebody ´who can explain that or maybe makes a usable proposal how a proper sprue structure can be designed.

In the last months you have changed the pricing forcing the people to change multiple part items. Now for all who have taken this hurdle you change once more ....

In the design rules there are connection recommendation for wires of 0.9 mm, for unconnected 1mm but suddenly for sprues you ask for 2mm?

Is this design really to weak for polishing?


Woody64
Changes done so far:
- adding sprues for multiple items 5 years ago
- changed to 1mm some months ago
- added a 2nd sprue for 2 points connections
- doing the next change to 2mm?

What about being polishable at all? Or in other words, waste of money for the extra processing. To avoid this going one more step down.

I had a model arrive this month which used a 2mm 'spine' with 1mm sprues connecting the figures. Some of the figures had broken away where the 1mm parts met the 2mm spine so I'm guessing it was too weak to withstand the polishing...

<a href="https://www.shapeways.com/model/2827844/" target="_blank"></a>

Shapeways were kind enough to ship me the parts without rejecting the model but I'll thicken the whole thing up 2mm before it goes on sale.

The issue is not just about breaking in polishing, but with that shape, not getting polished much in some areas, because they are "unreachable".

I also got a rejection for a 1.6mm sprue.

Also, an item had a supported wire of 0.99mm and got rejected for that.
Is there a difference between 0.99mm and 1mm ? Every other item in the order with the same 1mm supported wire printed successfully.

What a joke !

There is nothing new about the rules. They are being enforced more thoroughly to prevent shipping broken parts. Yes, sprues are intended to be broken, but we don't know what parts are sprues, and what are wires that are important. So it slows everything if we have to ask the designer for permission to ship something that is broken, and adds labor that, chances are you sprued to avoid paying for. It can also lead to lost parts that would require a reprint. As you can see in the diagram, a supported wire is a wire that runs from a part to itself. And even then the rules state "To ensure the successful creation of your product, make sure supported wires are thicker than the minimum requirement. If they are not, try making them thicker, or consider a material with a thinner minimum supported wire requirement." The same is said in the unsupported wire section. If the manual checker feels a part will fail, it will be rejected. .99mm or 1.01mm. If it's printed and breaks on a thin wire, chances are it'll be rejected instead of trying to print it again. This isn't to make it more difficult on you. This is to make the product that we are shipping out consistently correct.

These rules haven't exist in that way some months ago and even after the new material sides were introduced the sprues were set to 1mm. That I can remember very clearly since I had to change the code for my addon in blender which generates this bearer.

Would be nice if somebody from SW jumps in and starts a discussion how a proper design for the different cases could be.
See the other thread were already some examples were discussed.

SW has started to change a lot in their rules, setup, behaviour to ensure proper deliveries of their print. That's understandable but we as designer also do need that to protect our invests in these shops here ...

Woody64

Is there an archive somewhere that lists revisions in design rules over time?

Here is a version from around 23-oct-2014 :
https://www.shapeways.com/materials/strong-and-flexible-plast ic?li=nav

Thanks,

So Shapeways DID change the design rules with regard to the sprues.

While SW is happy to change teir ways of working, it makes sense to inform the designers.
It also helps if SW employees would inform the designers properly.

I don't think using archive.org is the optimal way to track rule revisions and revisions dates within a company! I realize that Shapeways is not an "engineering" company as such, but it strikes me that not documenting such fundamental changes in an easily accessible manner can be problematic for everyone. Old and new models can be affected so it's a big deal. Having a linked revision list with dates explaining changes at the bottom of each material page would be a good start. It's the logical place to start hunting for revisions.

For example I just noticed that stainless steel thicknesses are now bracketed based on size and have no idea when that happened. I don't recall a notice although I suppose it could be buried somewhere in the forum. I did a search using "thickness" and another using "rule" in the Official Announcements section of the forum. The only relevant result I found was for a FUD escape hole size requirement change but nothing about steel rule changes.

Hmmmm somehow frustrating.

1) Currently I get the information from SW what's not working or at least what they deny out of their last years printing experience.
2) Changing a model (with 100% success rate) results in a FirstToTry, a new manual check and a deny due to the actual rules

Who wants to discover the sinter cage rules? ^_^

This raises the issue of when is a sprue not a sprue, but in fact a supporting wire. Without a proper mathematical definition it all comes down to interpretation, and therefore open to dispute.
Also, the number and spacing of sprues can be as important as their thickness.

Yes would be really fine if somebody jumps in from SW side discussing that.

Service gave me the tip to ask an experienced designer out of this forum. Maybe that's the common misinterpretation they have.It's not a design issue it's a production issue:
- currently I'm guessing what may work
- to prove that I have to do an order (which I really did already a lot of times)
- so far if the message "Help us resolving ..." I could react within a day usually solving the topic in 30 minutes. but now I have to say: sorry, rules have changed, no idea what will work to change it ...

Woody64

When long time users are the ones asking... @_@

I have some ~1.4mm diameter sprues I used for alumide and that gets rejected in both regular and polished. In this case the sprues are contained inside a hollow cylinder so they are never contacted by polishing pellets although I suppose a part sticking out of the cylinder could break off the sprue due to stresses. Anyway I'm working within a fixed diameter small cylinder and increasing the round sprue diameter to 2mm will be rather impossible.

However I can convert the round sprue into a ribbon, or a "unsupported" wall if the definition applies which allows a 1mm min thickness. I could convert to something rectangularish like 1.2mm x 3.5mm or thereabouts. What is the key physical parameter that's important here? Is it cross sectional area of the "sprue" ? In my interpretation of the rules I should be able to go down to a ribbon sprue wall thickness of 1mm and a wall width of 3.14mm and still have it be equivalent to a 2mm dia round sprue, Has anyone ever tried doing this?

I asked customer service directly about the feasibility of rectangular shaped sprues and they seemed pretty determined to only recommend round sprues. This is somewhat at odds with previous comments by Shapeways staff in older pre 2015 or 2014 threads, but any old comments are now pretty much obsolete. It would appear that the only path forward is to submit designs that I think can bend the rules without failure, hold on tight, and hope things aren't rejected.