Dimensional error - solved

Software issues and solutions
sun@cpi
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Dimensional error - solved

Post#1 » Fri Sep 26, 2014 11:11 am

Hello everyone!

I recently got my hands on this printer and started to print yesterday. I have a multiple FDM 3D printers so I'm not new to the experience of trial-and-error, just new to the SLA scheme.

The issue I'm facing right now is that when I print calibration parts with easy to read dimensions I get some dimension coming out accurately but most of them are off by multiples of 0.125mm.

I'm using the latest version of the software (1.7.3) and have not changed any values from default.
I'm attaching my layout file and STL file so if anyone can chime in and shine some light on the issue I would be the most greatful.

Thank you!
Image

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mikej
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Dimensional error - solved

Post#2 » Fri Sep 26, 2014 12:39 pm

Off in the vertical (z) axis or x-y plane? Possible you have the wrong configuration or hardware selected in the printer manager for the version hardware and/or resolution?
Measure Twice, Cut Once.

sun@cpi
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Dimensional error - solved

Post#3 » Sun Sep 28, 2014 3:01 pm

Off in the XY plane. Windows reports native resolution to be 1080P and I've used 50 micron calibration grid, double checking to make sure grid is accurate with micrometer.

All the holes are coming out 0.25mm or 0.125mm smaller then designed dimension, however all the exterior dimensions are superbly accurate.

Is there an way to display a slice of a part so that I can measure and make sure what is laid down is dimensionally correct? I hate to keep wasting resin on printing a test piece only to find out the holes are too small.

Thank you.
-Sun

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Robert Howle
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Dimensional error - solved

Post#4 » Sun Sep 28, 2014 3:21 pm

Have u tried a different orientation in the layout. Are your "holes" being printed in the verticle or horizontal plane. Like to see screen capture of your layout prior to slicing. As with micro prongs in jewelry u can tweek the thickness of very small (.3 mm and the like) elements by small changes in the "over" cure times. When perimeter pixels get extra cure time, the "over cure" can cause slight thickning in those areas. What diameters are involved in the model? I think thickening would be more noticable in small openings. I could be wrong here, just speculating, since I haven't seen the model.

I have to state that I don't use default settings due to the fact that I use a 1:1 mix, and there are no default settings for this.

Robert
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sun@cpi
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Dimensional error - solved

Post#5 » Mon Sep 29, 2014 1:34 am

Hello Robert,

Vertical axis appears to be accurate sans the unevenness of the build platform and the PDMS coating. The void, or holes are printed in the horizontal plane.

I just went into the advanced mode and opened up a Slice Manager which shows what's exactly shined onto the VAT as far as I know. On the picture shown I measured the number of pixels which represented 50mm and it turns out to be 1000 pixel even! Hence I can calculate that 20 pixels represent each millimeters.

So using above calculation the square void in the calibration part should be 5 mm * 20 px = 100 px, I measured 101 px, which is close enough. And for the longer rectangular void it is 600 px long which is 30mm, which is accurate.

I think I ruled out any software quirkyness so now I think I can mess around with 'over cure' time as you suggested. Thank you.

ps. I attached all of relevant files on the first post, but it seems like two out of three are missing somehow, I'll re attach them.

Thank you
-Sun

sun@cpi
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Dimensional error - solved

Post#6 » Mon Sep 29, 2014 1:35 am

Here are relevant files.

There should be

50mm Test piece_flat.b9l
50mm Test piece_flat.b9j
calibration_angle.stl
Image

sun@cpi
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Dimensional error - solved

Post#7 » Mon Sep 29, 2014 1:37 am

Forum doesn't seem to like me posting three files or unknown format here or maybe b9l and b9j are blocked.

I've zipped them up so anyone with interest can take a look at it.

Many thanks
-Sun

Edit: attaching a zip file is not working :(
Here's a link to my dropbox https://www.dropbox.com/s/ctrux6wzw818n6c/50mmTESTPIECE.zip?dl=0

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brumbaer
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Dimensional error - solved

Post#8 » Mon Sep 29, 2014 2:45 am

It is possible that some resin gets trapped in the holes.
Please try something like this not as a solution, but to find the cause of the problem:

Image

sun@cpi
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Dimensional error - solved

Post#9 » Mon Sep 29, 2014 4:11 am

Hello brumbaer,

Following your suggestion I designed a shape that won't have fluid retention problem.
https://www.dropbox.com/s/qsaozn5oaxl3nb8/30mm_Calibration_Part.zip?dl=0
However, results are still same. Outside measurements are accurate (30mm) but the thickness of the wall is off by 0.13mm. It should have been 2.5mm but it is ~2.63mm give or take hundredth of an mm.

If I lower exposure time any more the print won't stick to the printbed so I am out of ideas at the moment.

Can anyone chime in and tell me what I'm doing wrong?

Thank you
-Sun

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Robert Howle
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Dimensional error - solved

Post#10 » Mon Sep 29, 2014 4:28 am

@ Sun, To attach files go to the black box bottom right. Click on the "Reply" section only (there are three separate buttons there). Then u can post comments and up to three files.

Start your post there. Don't use the "quick reply"

Robert
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akgold
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Dimensional error - solved

Post#11 » Mon Sep 29, 2014 7:12 am

is this a measurement before curing or after curing ?
I'm so far behind I think I'm First !!

sun@cpi
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Dimensional error - solved

Post#12 » Mon Sep 29, 2014 8:12 am

Hello Robert,

As far as I can tell, it does let me pick three files but only STL files gets attached to the post. I've tried this twice in the above replies.

akgold,

This is a measurement before curing.

On the other hand I've printed a power calibration file, the one with a bunch of vertical cylinders, and I think I see a pattern of problem here. Few cylinders in the center are accurate, but as I go further from the center it tends to grow 'thicker'.

I printed it using scale 0.9 and in the original STL file diameter of those small cylinders were 1.5mm, therefore printed ones should have been 1.35mm. But ones in the center are around 1.41mm and for the ones around left edges are about 1.58mm and for the right side ~1.45mm.

Could it be that the light bleed is causing the whole issue?

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mikej
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Dimensional error - solved

Post#13 » Mon Sep 29, 2014 8:33 am

Probably light bleed, if your outer areas are too thick then you can decrease the Slope in Printer Settings. We're working up a procedure to use the calibration files which will allow you to fine tune the MSM, Slope, Balance & Fade for your particular projector.
Measure Twice, Cut Once.

sun@cpi
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Dimensional error - solved

Post#14 » Mon Sep 29, 2014 8:58 am

Hello Mike,

That's the part where it gets me all the time, the outmost dimensions are always correct, except that anything that resides inside of the outmost dimensions are all over the places.

Right now I've printed few of these
http://www.thingiverse.com/thing:165389/#files
to test if I can correct it by changing exposure value, but all it seems to do is create missing features and meanwhile oversized fingers (as shown on top right corner of the picture on Thingiverse) are still fat.

From the look of the picture he seems to be using RED when he printed that so I believe it must be possible but I just need to find a way to do it.

Still kinda lost so any help is appreciated.

Thank you
-Sun

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Metalcaster
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Dimensional error - solved

Post#15 » Mon Sep 29, 2014 10:19 am

I am having a very similar problem with 1.2 printer using standard settings . All my rings made with cherry are coming out with thicker shanks and thicker prongs.
I grew a band ring (flat on the table) that is supposed to be 1mm thick and it came out 1.7mm thick.

However, when I grow with Made solid Black, they come out near perfect size... except Black is not castable.

I quoted a Platinum ring at 17 grams and the final piece was 26 grams !
Please help !

sun@cpi
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Dimensional error - solved

Post#16 » Mon Sep 29, 2014 11:01 am

Hello Metalcaster,

Could you provide little more information? Did you use exact same setting for Black resin and Cherry resin?
Reason being is that I'm leaning heavily toward the light bleed is the root cause of this issue.

Would it help prevent light bleed if I mix a food coloring into the resin?

Thanks
-Sun

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mikej
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Dimensional error - solved

Post#17 » Mon Sep 29, 2014 12:15 pm

It is best to slice as thick as your pigment will allow for. Slicing thinner will result in bleed, simple as that. Yes, it might give a smoother finish, but that's really because of the bleed. How do you know if you are slicing too thick... the object will fail to build and you will have lot's of floaters (unattached layers as debris in the resin). Adding pigment and/or dye is a way of reducing the light penetration/diffusion. It needs to absorb the active frequencies (blue to UV) or it's not helping.
Measure Twice, Cut Once.

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Metalcaster
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Dimensional error - solved

Post#18 » Mon Sep 29, 2014 12:20 pm

Hi Sun,
No,You have to use different settings for different materials.The black material has it's own set of settings that are very different from the B9 red or cherry.
I do not suggest adding anything to the material.
The B9 material does work well.
These are just settings or calibration issues.I am not sure why my parts are coming out bigger. I guess that I have to run tests to find out what affects the size and thickness of the items.

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behold3d
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Dimensional error - solved

Post#19 » Mon Sep 29, 2014 2:53 pm

I would print a shallow item like coin and see if it is indeed light bleed. i am not convinced

What gets me is that he says "Windows reports native resolution to be 1080P and I've used 50 micron calibration grid". which of the version machines is 1080p? Sounds like that is his monitor or am i confused?

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mikej
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Dimensional error - solved

Post#20 » Mon Sep 29, 2014 4:35 pm

The v1.2 hardware has a HD (1920x1080 or "1080P") projector that can be calibrated to 30, 50 or 70 microns. The v1.1 (and earlier) hardware has a XGA (1024 x 768) projector that can be calibrated to 50, 75 or 100 microns.
Measure Twice, Cut Once.

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