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Printing undersized holes?

Sun Mar 04, 2018 3:22 pm

I design a lot of prototyping and use 3D printer to get the job done before sending to a fab house.

Printing undersized holes is a problem. All outer dimension is spot on, but every slot or hole are too small! It is not filament shrinking.

There are lot of article describing it, and solution too but not for S3D. In FREE slicers there are a function to put in a value to compensate inner hole (not affection outer dimension), how to handle this in S3D?

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Re: Printing undersized holes?

Sun Mar 04, 2018 4:14 pm

This thread discusses my methodology for scaling prints for accurate internal and external dimensions.

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Re: Printing undersized holes?

Mon Mar 05, 2018 1:33 am

This is not a overall scaling problem, only a slot/hole problem.

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Re: Printing undersized holes?

Mon Mar 05, 2018 2:58 am

s3d does not offer a solution attm but you can use some tricks or some external g-code processors or ... you have to start with properly calibrated printer, design for material expansion/shrinkage etc.. then you should have decent precision with holes (for e.g. I get near perfect holes with s3d when I use petg, on the other hand abs parts need to have holes bigger in design..) ... one of the major issues is that if you stretch plastic it tends to pull back and if you do a loop (hole) it will pull closer creating wider trace and smaller hole leaving you both with smaller hole and poor contact with infill... so printing "wider" line and slowing down print helps ... both are not very good for the whole part (wide line == bad small features, slow speed .. well .. it's slow) .. so some modification to print thicker line slower for holes with some compensation like for e.g. would be a winner.. with s3d it's not easy to implement all this externally but there's a good discussion (with an external tool that will drop the speed only for loops) here: viewtopic.php?f=23&t=654
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Re: Printing undersized holes?

Mon Mar 05, 2018 6:58 am

myprinter wrote:
Mon Mar 05, 2018 1:33 am
This is not a overall scaling problem, only a slot/hole problem.
The Horizontal offset on the OTHER tab will work to offset the hole diameters. that will also impact overall dimensions equally. With the tools i provide you can evaluate both scaling and horizontal offset to achieve dimensional accuracy on both large and small features. You can't make a change to small, internal features without impacting other aspects of the scaling.

Accurate extruder calibration and a scaling study will give you the dimensional accuracy you are looking for. I get better than +/- .1mm on large and small features. You can't take a piecemeal approach.

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Re: Printing undersized holes?

Sun Sep 23, 2018 2:17 pm

I've had this issue forever.
My printer is well calibrated. I've had to make holes .42mm larger to compensate. Very annoying.

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Re: Printing undersized holes?

Sun Sep 23, 2018 3:53 pm

3D printing, while very different from injection molded parts, still requires knowing what to do based on experience from having done it (whatever ‘it’ is).

Not all features are in contact with the bed, there is asymmetric environment heating, cooling fan, what you use to hold parts to the bed… not to mention different filaments... Internal stress/strain, asymmetric annealing from sitting on bed...

If your holes are the only issue, then change the diam accordingly to produce the desired result.

0.42mm is the thickness of 4 human hairs - how accurate do you need the holes in a prototype?

Are the holes on the bottom layer (on the bed) where the material gets smooshed out into a Brim?… Are you measuring the brim?

This week I designed a thing with small holes; the goal diam = 2.0mm, the printed result is 1.95mm (the difference of 0.05mm is one-half the thickness of one hair). To get that result, the model uses 2.2mm diam.

Note, I measured with calipers, thus some inaccuracies due to the flats as opposed to using a measuring dowel. If I used a dowel, the actual would probably be ~2.05mm and I did not punch-out the minuscule brim.

And, that’s on machines built from low-cost kits!
Screen Shot 2018-09-23 at 12.33.46 PM.png
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Re: Printing undersized holes?

Wed Jun 12, 2019 7:15 am

As described in the article below, polygons with low vertex count seem to not shrink and can replace "round" holes.

A feature that replaces holes automatically would be interesting.

Posts: 99
Joined: Sat Mar 08, 2014 11:01 pm

Re: Printing undersized holes?

Wed Sep 25, 2019 2:27 am

You may find the following to be of use:

These plates provide holes in increasing diameter between 3mm and 25mm. When designing parts which need to accomodate bolts/screws and other physical objects you can easily find what size hole you need in the new design which will allow that object to pass through - without guesswork!
Posting as a private individual - 3D printing is a hobby activity.
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Re: Printing undersized holes?

Wed Sep 25, 2019 8:32 am

I have several parts I sell that slide on a machined rod that contain round and rectangular holes. To get accurate fit, round holes must be .45 mm larger than the rode within the model. At least with the way I calibrate my machine. With a smaller nozzle and extrusion width, the less the difference. Each new part I start at .4 larger and print multiples at once as printing one by itself (small items) will alter the hole size (smaller). For an accurate read on what you have, you need to print at lest 3 parts at once and not sequentially. Larger parts where layers have a lot of time to cool I doubt would be different like small parts. It would be nice if the hole was the same size when printed as the model dictates so the model could accurately reflect the part size needs. Please note these parts and this sizing is for ABS, I have not documented the size difference for other part, that is just part of the proto type process for whatever filament you are using and how much it shrinks. This one caveat is almost worth trying some other slicers if I could model and print without the testing.. ..

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