Feedback request for upcoming FDM Quality Guidelines

cobnut · 2016-12-16T14:48:34.000Z

Sorry, @Perry_1 I really, really, hate to do this, but the pedant in me simply can’t let it lie… If printing results in a 0.5% shrink, i.e. a 100mm wide part becomes 99.5mm when printed, then the model will need to be 0.5025% larger, not 0.5% larger. Sorry, I’ll go away now…

chrislloyd · 2016-12-16T14:59:09.000Z

Hi,

Yeah I appreciate ‘perfect’ is not a completely helpful term in this sense. Although the reason I used it is because it is used in the FAQ of 3D hubs quite freely and used in terms of what would happen in the event of a dispute between printer and customer. 3D hubs have an expectation that a print will be perfect, otherwise a refund is available. As such, it needs to be dealt with in the guidelines or removed from the FAQ.

Understand on seams (these were layers in my mind) I’m slowly getting up to speed with the terminology. My concern was for steps in the seams, where the print is misaligned.

I would love to move to other techniques, but realistically, at my price point i’m only interested in FDM.

Perry_1 · 2016-12-16T15:17:35.000Z

It would be nice if 3dhubs did not have to do this. This should really be handled by the hub. I know this is not happening, and this is why 3dhubs is trying to fix the customer expectation every time, because the number of complaints is too high, which costs them and the hub revenues when resolved. I know I am a prolific communicator on every order, and have even had customers exasperatedly declare to “just print it!” This is worth it, every time. I have had good luck with my reviews, and almost always it is about typing a lot up front!

-----------------------

Support marring is a complicated issue, and needs a lot of explanation. For a small thin overhang that requires a little support, the print should show little marring. For a larger, wider, longer, flatter section that requires support, I tell the customer they should expect a very rough, marred surface.

This is because on a such a supported area, the surface is mostly bridged across the support material, and will sag minutely as it is printed across that area. The more of this that occurs, the less perfect that surface will be.

Additionally, support material across long surfaces also means that section of the print is being printed on less stable terra firma, and is thus going to be subject to a little more “wiggle” as the print is occurring, resulting is much messier surfaces on long, wide, flat surfaces held up by support materials.
---------------------------------------

As for warping, shrinking, and corner curling with high shrinkage materials such as ABS, the customer should always be told this is a possibility or expectation. I always communicate this to a customer who has a print with large, long, flat models. I don’t have the issue usually, but I tell the customer it can happen, because I do not want to do a 10 hour print that the customer is expecting the next day, without them understanding that it COULD happen.

----------------------------------------

Infill expectations I usually do not have to communicate. But it should be stated by 3dhubs, as it is unclear to many hubs what the minimum infill is supposed to be. I see many hubs that say they print 15%, but 20% is the minimum for 3dhubs, I believe.

-----------------------------------------

It would be easy for a large ABS print to shrink outside this tolerance of 1%, and I mention it as a possibility when ordering a print in ABS. ABS is a material used for injection molding, because it shrinks away from the mold so well!

----------------------------------------

Additional expectations should be communicated to the customer when they order, by the 3d hub. Sometimes I can see the use of the model right away, and can see there will be no problem. A bust of Ceaser is all good with a little shrinkage. A phone case could easily shrink to the point of not being usable with ABS. Small holes in the objects are going to be the wrong size, almost always! So I always discuss these tolerances when I see them in a model.
A 10mm hole in one model, and a 10mm post that goes in that hole on the other model; I can almost always be sure there is going to be an issue. We are printing in a smashed hot thread with FDM, and it is going to smash outwards a little. If this is the case, I need to discuss it with the customer.

---------------------------------

I always type a lot before I accept an order. It takes time, but it is always worth it. It is all about looking at the model, material, etc., and discerning the use of the final print, or asking questions when that is not discernable. I ALWAYS want the customer to get what they want, not necessarily what they think they want.

I just did a quick review of some of my comments with customers, these are real:

-the posts on the thingiverse raspberry pi case will be very weak, and will likely break off if they are not careful

-some ABS orders should be printed in PLA

-gold PLA will not look like gold, it will look like plastic.

-get the drill bits out, because it will not work without it

-support material is going to leave your model unrecognizable, lol

-white will look better than black

-using it for cosplay, and going to paint it grey, it should be printed in grey, so that when it chips, it will be less noticable

-I cannot accept the laptop stand you designed, because it is so weak it will simply collapse

I am never shy about adding costs to the order for things the customer needs, like stronger infill, more shells, or better resolution. I offer .4mm layer height, because some customers just want a quick, cheap prototype. But I get orders from customers at that layer height, and I have to tell them not to do it! And I have had 3 orders where I told the customer to get it done with SLA, even though it will cost more and possibly take longer.

This is all key to a good experience for both parties. I have even told customers to get the order in PLA, and if it did not work out, I would reprint it again in ABS for free, to get them to switch away from a shrink prone disaster. I have never had a customer get it reprinted.

Perry_1 · 2016-12-16T18:34:19.000Z

@cobnut

Thanks for that, that is pretty good! I would have printed that part, and it would have been off by 25% of the width of the hole in my nozzle, on each side!

cobnut · 2016-12-16T18:44:37.000Z

Sorry, I had an attack of Friday afternoon mischief As it happens I’m doing an order now where the customer needs very accurate dimensions. One print had an X of 117mm and it came out (in ABS) as 116.68mm. Pretty happy with that but an going to reprint at 100.4% to see if I can get closer.

Perry_1 · 2016-12-16T18:49:07.000Z

I did not know remember that in the FAQ, and sure enough, you therefore have every right to expect it. It really is a bad term to use for complaint resolution. Wow, that needs to be a different phrase.

As for your price point, that is exactly the key. Realistic expectations for the technology, and thus realistic expectations for the price.

There are more perfect ways to 3d print, and less perfect ways to 3d print, but there are probably no perfect ways to 3d print.

But sometimes the customer is looking for that perfect price point, in which it is likely FDM will be more perfect!

Jackson_Moody · 2016-12-16T22:59:06.000Z

Great! That makes perfect sense! Thanks!

Odense3DPrint · 2016-12-18T11:08:29.000Z

@Robin3D

also that is on an ultimaker… but maybe 3dhubs does not care what printer is in use?

Enza3D · 2016-12-19T19:33:43.000Z

I do want to add that guaranteeing dimensional accuracy is a bit of a point of concern for me. I am not concerned by my ability to meet it, I am concerned by customers potentially misinterpreting what that means. Guaranteeing dimensional accuracy does not make any difference if the part is poorly designed; i.e. the design of the part does not take into account tolerancing for mating parts and such. This is the classic example of making a 2 mm hole for a 2 mm rod; even if the hole is perfect, the rod will never fit into that hole, because the hole does not take into account dimensional variations that will occur in the rod. It will need to be made explicitly clear to customers that this guaranteed dimensional accuracy is based off of the model they provide, not what they intend it for. If a part is provided that is 2"x2"x2", then it is only the Hubs responsibility to make sure that the print is within your set dimensional variation.

My other concern with this is that it’s a royal pain in the butt to get dimensions from STL files as that is not really their intention; STL files just contain information about the geometry of the surface but contain no data about dimensions. If 3D Hubs is going to implement dimensional accuracy requirements, either the customer needs to provide the dimensions (such as via a drawing or by filling out a form), or Hubs needs to require uploads of parametric models instead of/along with STLs. I do not want to be held responsible for a dimension being wrong because I more or less need to guess as to what the dimension should be. Just my 2 cents on it.

PepCo_Parker · 2016-12-19T19:48:42.000Z

This raises a good point, a customer may ask for money back on a part that is according to them dimensionally inaccurate as it doesn’t fit into other parts, when in reality the issue may be the part design itself. This would be very hard for 3D hubs to gauge when siding with disputes. Almost impossible I would think in fact.

Enza3D · 2016-12-19T19:57:38.000Z

If the issue is with the part design, then it is the fault of the customer if the final print does not work as expected. Tolerancing is a core tenet of mechanical design; if you brought a poorly designed part to any prototyping shop, it’s on you if things don’t work once manufacturing is done. If a print is within the allowable accuracy range (1 mm or 1%) then it’s not the Hubs fault.

Shapeways and any other larger print shop is very much what you see is what you get; as long as they deem a part printable, they will print it but that’s it. If it was printed how it was supposed to, they do not care if the design itself was incorrect.

PepCo_Parker · 2016-12-19T20:11:35.000Z

Yes but let’s say two parts were designed to fit each other, but we’re designed improper via a hole or gap being a mm too small or too large. Diagnosing these issues before printing is nearly impossible, and the customer could argue they don’t fit due to tolerances of the hub being poor. Both of these sides of argument are hard to prove unless you are there in person. With the way 3D hubs handles refunds I could forsee it being an issue

Enza3D · 2016-12-19T20:54:15.000Z

That improper design will show up in the model, and that is why I suggested also requiring either a form/drawings or parametric models. If the feature in question is in the model, there is no argument about who’s at fault and parametric models display all this information with a couple clicks. It is not the job of a Hub to comb through a model and find problems, that is the job of the designer to prevent in the first place. If a feature is designed to be 10.5 mm wide, and the Hub produces it with a 10.1 mm width it’s correct by 3D Hubs definition. I know each Hub handles this differently, but this is the reason my Hub does not guarantee pieces will fit together unless we designed them. It is on the customer to make sure the design is correct, we just make what they give us. If we design it, it is designed with appropriate tolerancing for any mating features and I have no issue guaranteeing it will work because I made it and know what I am doing and the tendencies of my printers.

This is also why I think implementing a guideline like this will cause problems, and I agree with you there.

Odense3DPrint · 2016-12-19T21:54:10.000Z

@Robin3D has an “official” test piece been made?

i want to be on this “wagon” since it will indeed ensure somewhat a minimum level of print quality

Also how will you verify this? i could imagine that the hub print the test bit an use a caliper and photo document that it can be printed right.

Just like that you have to print a marvin when you create a hub

And while at it i think that there should be an option to reverify this… ie when hub rebuilds printer etc

Joerg_4 · 2016-12-20T07:28:17.000Z

Good points, you are absolutely right!

Hopefully one of the 3D Hubs officials will reply to your post, may be @Robin3D

Cheers,

Joerg

Robin3D · 2016-12-20T10:15:47.000Z

Hi @Boelle,

That’s correct, the FDM Quality Guidelines will be the same for all FDM printers. We can’t expect every customer to know what kind of quality they can expect from a specific printer model/brand so that’s why these guidelines will set a standard for all FDM printers.

Best,
Robin - 3D Hubs

Perry_1 · 2016-12-20T14:26:15.000Z

@Enza3D you are so smart.

Yes, there is no way, outside of the dimensions of the final X,Y,Z part, that a tolerance can be checked, in any realistic way, without donating hours to each model.

I would assume we are not being asked to load some software, put the model in, check the size of all the various features, check the tolerances on each, etc., and make sure they are all within spec.

SO, this dimensional accuracy should always be on the final XYZ measurement, as the tolerance “guarantee” if you will. The size that is displayed on the 3dhub page, or in the slicer software as bounding box size, if you will.

Robin3D · 2016-12-21T15:21:38.000Z

@Enza3D, @Joerg_4, @PepCo_Parker, @Perry_1

Hey guys!

Thank you all for expressing your concerns and giving me your feedback. I really appreciate it. The reason that we have to set guidelines on dimensional accuracy is because we have to draw the line somewhere and we thought setting a 1 mm tolerance would be a reasonable first step.

I completely agree with the fact that you, as Hubs, cannot know the application of your customer if they do not communicate it. Ofcourse in some cases you will have an idea by looking at the design that it’s part of an assembly and in this case you can double check with your customer if a 1 mm tolerance is sufficient.

But in most cases this is not the case and also, not your responsibility. If you receive a model from a customer and you print it within the guidelines that we as 3D Hubs set, you will be paid out for the job no matter what.

When a customer is not happy because the print does not exactly fit, we will ask them to take a photograph of the print next to a measuring device such as a digital caliper to show the exact size of the print. Of course we do want to keep our customers happy but this is not always the responsibility of the Hubs.

Feel free to reach out to the 3D Hubs admins (such as myself) at any point if you have a situation where the customer is not happy with the result but you printed the part according to the guidelines, we’ll definitely be able to help you resolve such a situation.

Best,
Robin - 3D Hubs

PepCo_Parker · 2016-12-21T16:48:02.000Z

Hello again Robin, So to me this means hubs will have to start watching our backs by taking photos our selves of parts with calipers next to them, it wouldn’t be hard to fake photos to make it seem like parts aren’t the right sizes when they really are. This would be the only way to insure people aren’t cheating us out of good parts, but even then now we have to charge for our time photographing and setting all that up

Enza3D · 2016-12-21T16:56:11.000Z

My costs are definitely going to go up because of this; even if the verification is for my own insurance, it’s now another step I have to do for every print and that will be reflected in my prices. Because you’re right, there’s no way to prove it is correct unless I have already verified it myself and have pictures of it.

The problem is, how do I know if a dimension is right or not? Unless I have a parametric model file, or the customer explicitly specifies the dimension of a feature, I have no way of knowing (other than guessing from the STL) if it is correct.