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Printing problem with Mars Pro: solid resin filling in undercuts


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I've recently acquired a Mars Pro printer and I'm having some problems with print quality. The prints have acceptable finish on the side facing the LCD and rubbish finish on the other side, facing the build plate and the supports. The machine seems to be filling in the spaces between the supports with cured resin. It's as if the resin sitting on top of the undercuts --- which are, of course,  on top during printing --- is getting cured by the LCD instead of remaining liquid and getting washed off after printing.

 

Does anybody recognise this kind of problem, and does anybody have a cure?

 

It's transparent resin. I wonder whether that leads to light passing through the print and curing the waste resin on top? Perhaps transparent resin is good in laser-based printers and inappropriate for LCD printers?

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Yep. It's something that is common to all liquid resin printers. Basically your models are not well enough supported. 

 

Think of it this way, When a print gets to the top of a support the next layer is going to be just one layer thick, and if the layer is too wide it can bulge as the print goes into the resin. If this happens the next layer will be thicker than it should be as it fills in the empty space under the first layer. This is the real reason that you are advised to print with the model at an angle to the build plate in both the x and y directions. 

 

The best advice I've been given to deal with this is to decide which edge or face you are willing to compromise the quality of and build with that toward the build plate. 

 

 

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This is the model; it's a glazing carrier for a coach. The face towards the LCD, that prints well (rebate represents the visible part of a droplight frame):

1363099590_ScreenShot2020-11-24at21_01_21.png.494f1d2dc0ddd42fa2347136b0a8cf03.png

 

Face towards the build plate, that gets messed up (rebate is supposed to hold the glazing, but gets partly filled in, plus minature mountain ranges form around the rebate ):

128350998_ScreenShot2020-11-24at21_01_42.png.ebb340aec30cd7a43b3a208ccbfbed4c.png 

 

This is what Chitubox thinks are suitable supports for printing it horizontally:

1888940555_ScreenShot2020-11-24at21_07_56.png.bf3f871dcf004994684dc2be75ae143f.png

 

If I tilt it ~20 degrees off horizontal, Chitubox allocates similar supports and I get the same problems with filling in between supports; plus the edge of the part nearest the build plate then seems to warp. I'm trying another run with the long side vertical in the printer.

 

Bill, thanks for the insight. I've already positioned it with the sensitive, cosmetic face towards the LCD and I can do a little clean-up on the other face by filing. But should I really be getting nearly a millimetre depth of unwanted resin for several square millimetres around the support attachments? Seems excessive.

 

BTW, it's not just this model. Every single print so far on this machine has had similar issues, and I've run five different models so far.

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Guy,

 

I agree with what Bill says.   There are times when I have umpteen attempts with orientations and adjustment of supports to get a good underside on some prints.  I'm having that fight right now and have come to a compromise where the excess on the underside can be filed off smooth - rubbing it with my finger on an old smooth file.

 

With your piece I might have tried putting it on edge and rotating it by,  maybe, 45 degrees so that the inner aperture is printed with no need for supports acrfoss the top of it.. The one drawback with this suggestion is that it increases you print time considerably,  but if you are going to make a good few,  you can get a lot on the plate and that might be a fair offset for the print time.

 

Jim

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Print that flat on the bed, or upright - like Bill’s images. 
 

You’re righting gravity if you print anything with a large surface area parallel to the bed - it’ll just sag between the support contact points. 
 

I find the transparent resin just as easy to use as any of the others FWIW, I don’t think that’s the problem. 

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The original piece is recessed both sides so I don't think flat on the bed would work. You will also get a suction effect when pulling off of the FEP. Near vertical would be my choice.

 

As you guess clear resin will transmit UV and could result in uncured trapped resin being cured especially if too high an exposure time is used. Near vertical would improve drainage of the resin considerably.

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Last night's shot, with the model vertical, warped and cracked. Today's, with extra supports, avoided the worst of the warping and ended up like this (without any cleaning up, but primed so it's easier to see):

IMG_1613.JPG.a4fec5be637985cff18acb3288c8250a.JPG

IMG_7341.JPG.41204e922e3e0cd1f2ba76073c12e7f2.JPG

It's slumped on all the undercuts and the visible part of the droplight frame has actually shrunk in its lower third. I can fix the slumping of the base and side cut-outs with extra supports, and these areas are anyway neither cosmetic nor of critical dimensions so can be filed square. What I can't fix with a file is the slumping and shrinkage of the cosmetic droplight frame. I'm not sure how I'm going to improve that. Possibly I have to thicken the thin lip; it's only 0.33 mm thick at present.

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When you placed the part vertical,  it looks as though you left it otherwise square to the plate,  therefore getting the excess resin build up on the horizontal surface.   I suggested earlier that a further rotation of the part so that there was no horizontal ledge could provide better results.

 

Jim

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Just a thought. What ambient temperature are you printing at? Resin needs to print above 20 degrees c (need to check for the resin you are using), anything lower and it becomes more viscous restricting draining. It still looks like insufficiant supports being used as well.

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1 hour ago, MikeTrice said:

Just a thought. What ambient temperature are you printing at? Resin needs to print above 20 degrees c (need to check for the resin you are using), anything lower and it becomes more viscous restricting draining. It still looks like insufficiant supports being used as well.

The machine is in a heated room of the house, so ~19 Celsius in the evening, and warmer in the day when the sun is on. If it needs to be somewhat warmer, I can put a fan heater in there. BTW, the printer is not sitting in sunlight; it's on a shelf in an ex-wardrobe where it never sees the sun.

 

The resin is 3Dream Lodour transparent, which claims to be of low viscosity. I chose it for the lack of pong rather than the other aspects. They don't post on their website any advice for temperature or exposure, but I might email them.

 

Most-recent supports look like this:

37520792_ScreenShot2020-11-26at09_57_26.png.5422576fe6c579ce84928236164fbe43.png

...and it's still failing. One bottom arm of the I shape got truncated underneath, despite the supports; the top of the droplight frame filled in again, despite the supports to stop it slumping; the sides of the droplight frame shrank back again; and it warped into an S shape, then broke when I tried to flatten it (before curing). This is with an adapted model, where the visible lip of the droplight has been thickened from 0.33 mm to 0.5mm. The rebate (0.33m deep) on the non-cosmetic side now runs the full height of the piece so that it's easier to clean out with a file.

 

So I am not happy with this resin and will try again with some Elegoo grey resin when it arrives.

 

I may also add some supports to the the back of the droplight frame, contacting in the rebate, in the hope that this will stop it shrinking away. I may as well do one more run while I have the 3Dream glop in the tank.

 

Plan C is to redo the model with a flat back and a single rebate on the front into which I can glue the etched droplight-frames. But that seems defeatist.

Edited by Guy Rixon
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Those supports look pretty good. From your earlier print it looks as if the bottom supports are failing so for a real belt and braces approach you can add some light supports along the rear edge thus (shown in red) and perhaps some more further up:

supports.jpg.4b84a30cd600d326970215be0d13ceca.jpg

 

As you currently have it the bottom edge is currently only supported by the bottom supports and it is not until it gets to the upper supports that any strength is given to supporting the sides (each time the print is pulled off of the FEP the bottom supports are taking all the strain including the piece trying to straighten upward potentially snapping the lower supports) hence my suggestion of other rear supports part way up. These will leave slight blemishes on the back but it should be easy to sand them flat. Hope that makes sense.

 

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19 minutes ago, MikeTrice said:

Does the warping occur during printing or on curing? If the later try curing with the pieces under water.

During printing. I've been trying to straighten it by bending and pressing after trimming and before curing. Some times it works, other times it breaks.

 

Anyways, here's the latest, with the supports shown in my last post:

IMG_7912.JPG.76d72c858090934bb7edaeb967afa4d4.JPG

The warp is avoided and the drippy areas can be cleaned up ... but the failure to print the visible edge of the droplight ruins the whole part.

 

Try again when I have the other resin, I guess. Or redesign as a two-part assembly with no rebates on the back and print it flat on the bed.

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1 hour ago, ianmaccormac said:

 

 

is one of the more sensible and understandable Youtubers. I find some of his recommendations help. Cheers Ian

 

 

Thanks for linking to that, it was very informative and sensible. Actually applies to FDM printing as well.

 

Simon

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I was thinking of oroientating something like this

 

rmweb02.jpg.41255ec41dba1e77bad0e5c9a667d11a.jpg

 

rmweb01.jpg.0fa9ad931c6c5865f7d7597f3a0e3165.jpg

 

...which gets rid of horizontal ledges.  I've only done a quick support creation and basically it's along the two bottom edges and with only one side supported to stop it waving about in the breeze - it might need supports on both sides .  Just a thought.

 

Jim.

 

[Edit]  Just seen two areas I haven't supported - the very bottom corner,  and the down-pointing corner near the top. :-)

Edited by flubrush
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It was the resin. I changed from 3Dream clear to Elegoo grey and I now have a useable print.

 

IMG_8597.JPG.45dd7e5812c1cfa718cd0e3b26c0aff1.JPG

IMG_3047.JPG.7b1f60006b908caf047739eb9d2a778d.JPG

This is with the supports on the non-cosmetic face only, and the orientation as before; I slightly thinned out the forest of supports. It's not a perfect print, but it can be made useable by sanding and filing with very little work. Notably, the lip of the drop light is fully formed in this resin.

 

The scratches in these photos are from me scraping away uncured resin during the washing process. I should probably use a stiff brush for this so as to scratch less. I haven't filed or sanded anything after curing. 

 

I conclude that the 3Dream resin is not really useful in a Mars Pro printer for the things I want to make. Or, at least, its happy place is off in a corner of parameter space that I'm not likely to find. Possibly that stuff is more at home in SLA printers. 

 

Thanks to all who offered advice and and insight.

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Straight out of the Photon:

IMG_3187.JPG.71e0b1a17815bb178798288065e04005.JPG

 

I have gone OTT with the supports:

IMG_3191.JPG.405d9ca97614d6bef646963e08b7edf2.JPG

 

IMG_3192.JPG.0793c6354748b675c25d3e9cdbd6fc88.JPG

 

After clean up before curing:

IMG_3193.JPG.57e3870d8d101ce3cede1c941c6ce182.JPG

 

IMG_3196.JPG.0243275fca48d96f3e4459b417eb4bfc.JPG

 

Anycubic Grey, 0.04mm layer height anti-aliasing 8, 6 bottom layers at 90 secs and other layers at 8 sec. Lift speed 40

SECR-coach-glazing-brake-3rd_supports1.stl SECR-coach-glazing-brake-3rd_supports2.stl

Edited by MikeTrice
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I ran Mike's supported version of the model with his settings and this came out:

 

IMG_8012.jpg.ff2492258e72e8933e2855895c1e353d.jpgIMG_8013.jpg.0823fdbb135128009ae7b3e7cd9d5ada.jpgIMG_8014.jpg.7cb64041bc0546f684f07dfe85661279.jpg

It's clearly better, and I shall use Mike's settings for exposure, lift rate etc. from here on. It's not as good as Mike's prints and is still filling in around the supports. Possibly my printer is just not as good. Both prints broke while I was removing supports.

 

Now that it's not filling in on the front face, I can minimise the thin, central area again to make it stronger.

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