Maybe its me but I dont understand the big issue with a 1% or 1mm accuracy whichever is greater. Thats a quite large tolerance. If you cant print within that you need to work on your printing skills. I typically get under 0.2mm tolerance on parts I print. Looking at a part I did a while ago its off by .08 to .1mm
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No offense but if you don’t understand it, you haven’t read this thread. There have been numerous points as to why it’s not feasible, and I have even stated that hitting the targets isn’t even my personal concern, it’s people manipulating those rules to get free prints. I suggest you start at the top and read your way down to get a full understanding of the points raised.
Well the same customer that is going to manipulate these rules to get free prints would most likely still complain and get a free print without these rules. This is also why you should price your prints to accommodate for the once in a while customer that causes issues. Same with any business you need to weigh the risks and prepare for them or close up and find something else to do
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This is true, but tolerances as you’ve stated, have never been an issue for me. These rules seem to only be giving the customer more power over the hubs, when it’s unnecessary. If the hub communicates properly with the customer prior to the order being accepted then there should never be an issue in the first place. These guidelines make it easy for someone to improperly set up a pair of calipers, take a few photos and bam, there’s a 200$ order down the drain when the hub did nothing wrong. There have been other issues raised by the community on this forum, but I would be a broken record if I repeated them again. Also please don’t feel I’m attacking you. You’re raising different opinions and challenging what we thing which is good, and encouraging! So long as both sides of this argument are open and understanding to one another.
If you have a dispute you can call 3D hubs in and they can act as moderator… thing is at the end of the day you gotta play the role of a customer… if you get a part in that you specified as needing to be precise and someone send you a WILDLY out of tolerance part… you would not be very happy would you?
I feel like if you have a potential issue with an order its your job to communicate that with the client BEFORE you guys go agree on a print… That said I do understand your concerns but having a guideline you AND client can refer to would be a good thing in the long run.
One of my points though is that until now I’ve just done this personally, why is there suddenly a need for 3D hubs to intervene? And a customer doesn’t need to give ‘wildly’ out of tolerance parts, only 1% off. As some have brought up, unless we as hubs are to now measure every part we make and document it, there is no way to prove otherwise.
Quoting the list above: “FDM parts need to be produced within an accuracy of +/- 1mm or 1% depending on which is greater.” +/- 1MM is BIG… That means that your 20MM calibration cube could be 19 - 21 MM and STILL be a-ok. That is a huge tolerance. Their not asking you to hold .0005" tolerance on a 3" deep hole…
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That’s a tiny tolerance, make a 200mm part and it’s got to be within 2mm?
It’s not about how it comes off your machine, it’s about how it measures when you get it there. Many materials can grow and shrink more than that just from differing moisture levels. Never mind the rest of the stuff I mentioned earlier.
It comes off your machine and measures perfect, gets to the customer and it’s out of tolerance. Now, who is footing the bill and who has to prove it was in spec (and how, since the guidelines are so vague with obviously no proper QA process in place) - guess what, it’s the hub.
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1% for 20mm is 0.2mm (1/5th of 1mm)
1% for 200mm is 2mm (2*1mm)
bye, Tibor
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1% or 1mm maximum. 20mm object= 0.2mm tolerance. 200mm object=1mm tolerance
bye, Tibor
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Georgei
94
Dimensional accuracy: +/- 1mm or 1% depending on which is greater
So
20mm object = +/- 1mm tolerance
200mm object = +/- 2mm tolerance
cobnut
95
@Vienna3DPrint the guidelines say “whichever is greater”, so for a 20mm cube, 1% is 0.2mm, yes, but 1mm is greater so you could print anywhere between a 19.01mm and a 20.99mm cube and still be (just) within the 1mm tolerance for a print that should be 20mm.
The whole sentence says: “FDM parts need to be produced within an accuracy of +/- 1mm or 1% depending on which is greater.”
greater=accuracy
Maybe a native English speaker could formulate a less contradictory sentence.
bye, Tibor
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
Georgei
98
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.
cobnut
99
@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
Until the 19.01mm cools a couple of degrees and then it’s out of spec.
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
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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.
