Scott_M
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Undersized holes

Sun Apr 09, 2017 10:51 am

I am fairly new to 3D printing but I am well versed in CNC and G Code. My printer is a Qidi Tech X-One and so far I am very pleased with it. I have it calibrated pretty well and my prints are coming out great except for internal dimensions. I have read many forum posts and understand the reason why this happens. I have tried the flavor of Cura that ships with the Qidi printer, regular Cura, Slic3r, and Repetier as well as CraftWare. So far my favorite is CraftWare and I use it almost exclusively.
I have been considering buying Simplify 3D to gain a little more control over my prints.
My big question is Does Simplify have a way to cure the small hole problem ? Something like skipping an interior loop ? My outside dimensions are spot on and I do not want to "shift" the whole print to the outside just the interior features. If I print say a bushing with an outside diameter of 1" I can hit it within a couple of thou. .001"-.003" I am very happy with that. But lets say that bushing has a .750" hole in it. No matter what I try I end up way undersized like .735". I do not want to design around it and end up with 2 models for everything ( 1 for the printer and 1 for the mill or lathe ) So I am currently machining the interior dimensions to size. Almost defeats the purpose of Rapid Prototyping.

So, Has Simplify come up with a way to offset the inside without affecting the outside ?

Many thanks for your thoughts.

Scott

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thingismith
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Re: Undersized holes

Mon Apr 10, 2017 10:35 am

I've never had the problem you're describing, my prints are always offset equally everywhere. The only solution I can think of is to scale your model so that your outside diameter and hole diameter print with the same offset (so the hole is .742 and the outer dia is 1.008), then use the "Horizontal Size Compensation" in the Other tab to shave off the edges, so to speak, in the slicing process. Just convert the inches into mm, which is around -2.0mm.

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Leeway
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Re: Undersized holes

Mon Apr 10, 2017 11:25 am

Does the busing print with that size all the way up?
Different layer heights can make a difference as well as getting that first layer down the same height as the rest of the print. At least then you will have it consistent from top to bottom.
Honestly though, if the printed is calibrated well and you are happy with the exterior results, why not fudge the model. A whole lot faster and likely to succeed better than messing with any slicer settings.
Lee

Mogal
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Re: Undersized holes

Mon Apr 10, 2017 11:55 am

I'm with the OP here.
I've been printing for a few years now, and have constantly had this issue.
(Inside dimensions, especially holes) are small then they should be)

Thanks for the 'work around' but I would rather have a solution.

In the meantime, I will continue to modify the model.

Scott_M
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Location: Ohio

Re: Undersized holes

Mon Apr 10, 2017 12:34 pm

Thanks for the replies guys.
Lee
I recognize your name and avatar from CNCZone :) I have not been very active there lately.
I tend to print my bottom layer heavy and hot for good adhesion and do get a bit of "Elephant foot" but after that my dimensions are good all the way to the top.

If I know the designed part will only be printed I will design accordingly. But come on people, this is a known problem and has been here since the first printers, I would have thought some clever programmer would have figured a way around it.
It is more of an issue when printing files from elsewhere like thingverse. Most people model "to size" and let you worry about sanding and drilling to size after printing. Fortunately I have a well equipped machine shop and can make the parts work but it does seem that it should not be necessary.

So I am guessing that S3D does not have the ability to compensate for this issue. I would happily buy it if it did.

Oh, and Lee I cannot remember if you got the turret on your SBL15, if you did I have modeled some right angle coolant nozzles for the turret that get the coolant down to the shank of the tool so it blows in the hole not on the face of the part. Let me know if you need the stl.

Many thanks to all, it is appreciated !

Scott

upsm
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Re: Undersized holes

Mon Apr 10, 2017 6:49 pm

it's a problem most slicers have and it's well documented. I personally prefer to drill my holes after printing but that's not the point of this topic I'd say.

The basic compensation table (not ideal but great starting point) is made by Adrian and is available on reprap's wiki:
http://reprap.org/wiki/ArcCompensation

More in-depth analysis is done by Chris and I suggest you read his post if you are interested in the problem:
http://hydraraptor.blogspot.com/2011/02/polyholes.html

Something not directly related but related from Chris:
http://hydraraptor.blogspot.com/2014/06 ... wrong.html

I assume that the problem is "solvable" since Chris made a patch for skeinforge that prints holes at perfect size, how he solved it is still unclear as one can find mention of the solution on number of places but few have seen his code.

Fighting with printers for a while I'd like to emphasis the Chris's "corner cutting" description. This makes for most of issues on my prints with regards to round holes. Square holes I get perfectly precise but round ones are always small.
When filament is dragged round a corner it likes to take a short-cut. This depends on how elastic the filament is and how much it is being stretched. I think when the nozzle moves in a circle the filament is continually trying to cut the corner and ends up forming a smaller diameter circle. I think this is the dominant effect on my machines.
As for the "why fixing it in design is bad idea" I also agree with Chris:
Ideally all these effects should be compensated for in the slicing software but what has happened instead recently is that people are using parametric values in OpenScad to tweak the holes to come out right on their machines. That is the wrong approach because when the holes comes out smaller than they should be, without the slicing software compensating for it, then the infill doesn't meet it as tightly as it should do.
Also - seriously important thing to understand is:
When I started printing Prusa Mendel parts I found the values in the configuration file far too big. I have also noticed this when downloading some designs from Thingiverse. That implies that my holes shrink less than a lot of other peoples, which is odd because all the effects above don't depend on the machine, apart from segment pausing.
From this one should easily conclude that there's no "all round solution" and that slicer should have a whole "plugin" that handles this issue with a whole set of configurable parameters so one can properly configure and calibrate this for specific machine. Unfortunately none of the slicers I ever had a chance to work with (apart from stretch plugin in skeinforge that was just a very basic attempt to fix this) had this done properly. Expecting Simplify3D to raise to the challenge, well, I'd certainly be impressed if they do, but I don't "hold my horses" :(
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Leeway
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Re: Undersized holes

Mon Apr 10, 2017 7:11 pm

Yeah. Changing anything usually effects something else. Resizing the hole in CAD is certainly a work around, but does work pretty well in lew of a correct approach. I do expect some big boys in the CAM World to step up over the next few years. Autodesk is already underway with Fusion 360 and the basically adorned Print Studio. It's a start. There are many things lacking in slicers that are available in even the most basic cnc CAM packages. I do think some major steps will be taken in the next 5 years.
That doesn't help us out now though.

The reason the CAD adjustment works most of the time is because there is rarely anything else needed from the hole than to just be a hole. Self tapping screws can handle undersized holes. The infill better still be getting to the hole perimeters. Infill is done after the fact, so there should not be any gaps as mentioned above.

I can see where it would be an issue for downloaded models printed on multiple machines, but for personal use, it is currently the best work around. For me that is.
Lee

upsm
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Re: Undersized holes

Mon Apr 10, 2017 7:23 pm

Leeway wrote:I can see where it would be an issue for downloaded models printed on multiple machines, but for personal use, it is currently the best work around. For me that is.
Designing stuff yourself, using parametric design tools, having your holes defined by the startup parameters so you can easily regenerate the STL from the source after you change hole sizes by changing a single number works like a charm for all of us!

It gets bit more ugly when you want to use part designed by someone else but you don't have a source. STL's are not interchangeable files, most of us know this, but still, it's often all you have, and redesigning from scratch takes time. Editing STL is PITA. Dunno what you guy's use but I'm using Art of Illusion to edit them and I can't say I'm happy how that works.

With regards to "cad tools will step in", well, there's meshmixer, it works as a slicer too, anyone tried it? I didn't read anything good about it as a slicer, ppl still use it only to edit stl's, add support and then slice the output in Slic3r or Cura or Simplify3D or CraftWare or Kisslicer or ... SolidWorks works as a slicer too, I didn't try it out as it requires Windows10 (that spyware will not come near my computers) and support only handful of printers but again, I didn't notice anyone was writing on the Internet that it comes with some killer features?
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Leeway
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Re: Undersized holes

Mon Apr 10, 2017 7:35 pm

I have basically given up trying to edit STL files. It never turns out very good for me. Better just to spend my time a draw it up to start with. Depends on the need and how complicated the model is of course, but for most objects, this is the case.

Off topic a bit here, but why must we use meshes and STL files? Isn't there another model output that yields smoother geometry? That can be sliced? STL format may actually be a stumbling block, though it is the universal file type.
Just curious here.
Lee

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Leeway
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Re: Undersized holes

Tue Apr 11, 2017 4:28 am

Lee

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