As I mentioned before: greater is misleading, as I don´t think the dimension is meant, but the accuracy.
Robin must reformulate the sentence, as it leaves room for interpretation.
bye, Tibor
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The greater refers to the dimension (i.e. +/- 1mm or 1%) and not the accuracy. It is common statement in engineering at least.
The below text is from the original quidelines draft text from 3DHUBS
FDM parts need to be produced within an accuracy of +/- 1mm or 1% depending on which is greater.
For example, in the case of a 40mm cube, a 1% accuracy requirement would result in a max of 0.4mm deviation. As this is below 1mm, the 1mm is leading and determines the maximum. A printed part of 40.6 x 39.4 x 39.3mm would be acceptable as the deviations are within this 1mm. Printing a cube that is 38.8 x 39.4 x 39.4mm would not pass the dimensional accuracy requirements as the width deviates more than 1 mm.
@Vienna3DPrint hmm, good point, I’m now wondering if I’ve read it the right way (as a native English speaker!). A better (but not necessarily ideal) sentence would be either of:
“FDM parts need to be produced within an accuracy of +/- 1mm or +/- 1%, whichever is the lesser inaccuracy.”
(so the 20mm cube should be produced to within 0.2mm, because 1% is less inaccurate)
or
“FDM parts need to be produced within an accuracy of +/- 1mm or +/- 1%, whichever is the greater inaccuracy.”
(so the 20mm cube should be produced to within 1mm, because that is the greater inaccuracy)
depending upon which meaning 3DHubs are actually looking for, and the 1% should be +/- as well. @Robin3D ?
edit (just noticed the doc does include examples)
Also with example it makes no sense.
40mm=2,5% (1mm), 400mm=1% (4mm) Why should the tolerance be bigger at smaller objects ?
40mm=1% (0.4mm), 400mm=0,25% (1mm) would be more accurate.
Maybe more understandable would be: Accuracy can be expected within 1mm deviation in any direction for objects below 100mm expansion and 1% deviation in any direction for objects above 100mm expansion.
But ok. Shall it be. I´ll pass on any questions to 3DHubs. It´s their guidelines, it´s their explanation.
bye, Tibor
Ok since it is easier than typing out my opinions on the new “rules” I thought i’d throw them into a quick little video… 3D Hubs FDM Rules? - YouTube
Anybody can get a part off the machine in that tolerance, even the inept, the issue is keeping it in tolerance. I could take nylon parts off my machine accurate to 0.01mm and I still wouldn’t guarantee a general 1% accuracy in nylon to a client unless it was to very specific measurement/temperature/moisture levels.
I’ve just taken a part off my cheap home machine which is supposed to be 130 x 50 x 25mm - it measures 130.05 x 50.02 x 24.95mm. You couldn’t really want any better, it’s full of 13mm holes which are 12.94-13.00mm in diameter, there’s 6 x 3mm holes in there which are all 3.00mm. The ovality and coning are all way within 1% of true too.
The issue? They won’t be tommorow when it’s absorbed some moisture and the temperature changes. Or next week when the stresses have relieved after spending some time at working temperature.
Hi all,
Allow me to check-in on this thread as well with an attempt to summarize and hopefully shed some light on the most asked questions (forgive me if it’s a bit lengthy).
Why these guidelines?
As mentioned in the original thread, the goal of the FDM quality guidelines is to improve FDM printing standards globally.
One of the top customer complaints is about print quality being below expectations. Phrased differently, there’s a huge opportunity for both Hubs and 3D Hubs to grow their business if a cross platform standard is set. This can be used to set the right expectations up front, as well as setting a minimum requirement for FDM printing, which enables us to cater to more professional audiences.
To be clear, the main message is to manage the customer’s expectation. These guidelines serve as a standard reference (e.g. backup) whenever there’s a dispute between customer and Hub. If a Hub and customer agree to deviate from the guidelines, that’s completely fine.
I hope this also explains that this is not about “policing” Hubs, but rather a tool to help set clear expectations.
Implementation of Guidelines
As many of you highlighted, after we’ve asked for feedback over the holidays (and you delivered) we failed to respond. This was a mistake on our side and I understand the negative impression it has left. I do want to stress that we’ve discussed all feedback elaborately and made changes accordingly. Below, more information on the main topics.
On dimensional accuracy
After checking with a significant sample of top Hubs as well as 3D printing experts from the industry, the current suggestion is considered to be reasonable.
To illustrate the variety of opinions, while the feedback here has been that the requirement might be too harsh, the opinion on Reddit has been that the requirements are too loose. My personal opinion is that with a well calibrated printer these requirements should be met without difficulty in most cases.
Clearly, there are scenarios in which an accuracy of 1mm might be tough to achieve - say, a FDM printed sphere. In those cases, be sure to set expectations with your customer before accepting the order. Again, the guidelines will be the point of reference whenever there’s a dispute between customer and Hub. If you both agree, then all is good.
On support removal
The majority of the customers expect to receive a finished product when ordering a print and we think that’s reasonable. Delivering a print with the support still on is considered below the minimum required level of service. Another indicator is that a large part of Hubs already delivers support removal in their service.
That being said, if a Hub and customer both agree that support can stay on the part - for faster delivery for example - then that’s their decision and 3D Hubs will not get involved.
We are aware that at this point there’s no automated system in place for calculating (and thus pricing) support. These tools are planned for Q2 / Q3 2017. Currently, we communicate to customers that possibly cost will be added for models that need a lot of support. For example, in the checkout; “Models with overhangs steeper than 45 degrees, needs support material possibly resulting in additional costs”.
Ok, hope that explains a bit. Please let me know if any questions remain.
Best,
Filemon
What about policing the dimensional accuracy? I really do not feel comfortable with only pictures, and what happens if I measure the parts before I send them, and so does the customer, but we have different measurements? This is really my main point of concern, so if this could be clarified, that would help quite a bit.
Agreed. No offense @filemon but you’re just saying the same argument that has been countered time and time again on here. Our concerns weren’t hitting the targets, as a few of us have stashed several times, it’s enforcing them. It’s starting to feel a bit like beating a dead horse here, plenty of people have come onto this forum saying that these tolerances are easy to hit, which in my opinion they are, excluding post processing expansion or manipulation. Our concern was people manipulating the system to their advantage, or at least a fair few of us had this concern and I do feel it must be addressed.
For 2. I fear the comments below touch on some good points.
I like the idea in 1. If the guidelines work (test) we can expand with this kind of finetuning (or if necessary to work). Will put the on the list with the experts (@Robin3D)