Regular Band Pattern on Surfaces

Let's see some prints you've made with some of your hardware.
BMMal
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Regular Band Pattern on Surfaces

Postby BMMal » Thu Jul 24, 2014 10:08 am

Hello everyone,

I am having a problem with banding on the surface of my prints. I am printing with MakerJuice red G+ at 0.05 mm 2.8S exposure time.

https://www.dropbox.com/s/f6l23zjub26st ... .55.37.jpg
https://www.dropbox.com/s/uyj8twoqvdtkl ... .54.18.jpg

I recently finished building a machine recycling some parts from a mUVe laser system into a 25mm T slot frame. My set up is using a NEC LT265 projector (it's what was laying around our office) at 1400x1050. It is spaced so that I have a 0.1mm X/Y resolution and a nice focus at the center of the platform. (I probably need to get a lens in order to improve the focus across the entire platform). I am using a glass vat with the nice McMaster FEP film. The tilt system is a passive hinge on the vat (it's a little heavy though). My lead screw is an M8 threaded rod with spring loaded brass nuts and an aluminum flex coupler.

Any help is greatly appreciated!

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Re: Regular Band Pattern on Surfaces

Postby Finhead » Thu Jul 24, 2014 10:37 am

I would try upping your exposure a bit at a time, I think what your seeing is the layer is not quit cured enough so it shifts a little when you peel off the FEP. I saw some of this when I first started using Sub G+. It was approx. .5 sec under cured when the prints looked very close to yours, silicone is more forgiving than the FEP as it releases easier.

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Re: Regular Band Pattern on Surfaces

Postby PacManFan » Thu Jul 24, 2014 12:13 pm

RepRapMagazine has an excellent article on common Z-artifacts here : . This article was geared towards FDM based printers, but the same rules apply for many DLP/SLA printers.

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Re: Regular Band Pattern on Surfaces

Postby BMMal » Fri Jul 25, 2014 9:58 am

Thank you for your responses guys. I have attached a picture of all my 50 micron exposure testing so far. I started at 7 Sec (bottom right) and worked down to 3.8 (BL), 2.8(TR), and finally the 1.8(TL) I uploaded before. They all look pretty similar with the exception that I left the top of the 7 second in the resin with projector on over night and a part of it broke as it was building (probably related to overexposure).

https://www.dropbox.com/sc/clvlovt5oqbd ... T84vyKy9ea

The 1.8 is notably less cured than the 2.8 which is notably less cured than the 3.8 and 7 when I pulled them off the machine.

From this it seems that the issue is mechanical. I am going to do some testing with a dial indicator to see if I'm having movement of the build platform. I forgot to mention that my z-axis is a nice linear guide from Misumi.

Thanks!

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Re: Regular Band Pattern on Surfaces

Postby Finhead » Fri Jul 25, 2014 10:31 am

The linear part of your Z is nice, square rail linear bearing. But your using a threaded rod with what nut?
The problem I can see is your side loading the bearing in your configuration so if you have any play in the lead screw (which you will if it's a threaded rod) your pulling bearing forward and back as it wobbles up the axis. The square bearings would work better with a front/back mounted lead screw. Mine is pretty close to your build, I have a 40mm linear rail with a back mounted lead screw (10mm threaded rod) with a Delrin nut. I had very faint Z banding until I dialed in my exposure times correct, and actually got CW to build the layers as it should. It was under exposing certain layers by almost half the time, sat and watched it had to roll back a few versions to correct it.

BMMal
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Re: Regular Band Pattern on Surfaces

Postby BMMal » Fri Jul 25, 2014 11:39 am

The "nut" is two brass nuts with a spring perched on a flange between them. I should be able to try back mounting my screw fairly easily. Running a test with dial indicator right now to see if I can narrow down what's going on.

Edit: My measuring rig is not rigid enough to withstand the shock of peeling so I can't get any good measurement info yet.

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Re: Regular Band Pattern on Surfaces

Postby Finhead » Fri Jul 25, 2014 12:02 pm


BMMal
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Re: Regular Band Pattern on Surfaces

Postby BMMal » Fri Jul 25, 2014 2:10 pm

Thanks for the input Finhead.

I'm going to build a flex bottom. I thought a passive tilt would be good, but it still takes a surprising amount of load to release the parts from it.

Which version of CW did you find works properly? I'm using the newest one and I wonder if I am getting different cure times every so many layers. I also need to get a dedicated PC to run it. The PC I'm using is also used for our Objet printer which occasionally bogs down the CPU when preparing builds for that. But that wouldn't cause the regular spacing I'm seeing.

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Re: Regular Band Pattern on Surfaces

Postby Finhead » Fri Jul 25, 2014 2:17 pm


BMMal
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Re: Regular Band Pattern on Surfaces

Postby BMMal » Fri Jul 25, 2014 2:29 pm



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