Print layers drifting towards rear

[DDLLC]

I wonder if altering the strength of the pre-load spring in the head would change anything, or lubricating the ball within the sleeve? The latter is counter-intuitive, however practical solutions often are...

I appreciate the suggestions. The preload spring does have a rather low spring constant, but the way I envision it working is that its force is in the direction of the ball diameter essentially parallel to the spring vertical axis. To replace it with something much stronger (i.e., more force than I can apply on the edges by hand leveraged by the offset distance) would likely risk cracking the LCD. I already worry about the force I'm applying that I may crack the LCD. It doesn't seem that a spring will do much to resist the ball rotating as the sleeve compresses it. Of course at the same time I can't envision why squeezing the slip cylinder should cause a rotation in the first place. The basic design seems as it should squeeze around the ball somewhat uniformly.

I'm not sure if the system shipped with any lube on the ball but when I first disassembled the clamp to better understand it, I didn't notice any hint of lubrication on the sleeve or ball. When I reassembled the clamp I did wipe on a light coat of 3-1 oil. Mostly be I thought the ball might not be stainless steel.

Today I cleaned it with acetone to remove any lubrication film. Unfortunately the result from today's still shows the same slant and thickness differences. From rear left to front right, the thickness (mm) are: 6.48. 6.53, 7.39, 7.30. The angle is still in the 3-6 degree range. Like a previous print there is a set of curved layers on the thick side during the last few layers printed as you can see in the picture.

I could put some grease on the ball, which is a simple test, but I'm starting to think that maybe I should shift to looking at what is causing the print to be so much thicker than in the cad file. My thought is that if the Z axis is trying to move to a location that is prohibit by solid material stopping it prematurely, a lot of force could be generated. It's a heck of a stretch, but I'm running out of ideas as to what mechanically occurring.

Greg

[cliffyk]

Another thought I had while driving today. In your diligence you are running close to exhausting the pool of potential mechanical alignment issues. So let's consider the overall process.

It occurred to me that any consistently uneven intensity, phase, or wavelength of the curing light across the field would cause deviations in the cured thickness of each layer. a deviation that would logically be cumulative as the number of printed layers increased.

Not quite certain how to gauge this though.

At 405 nm the sensitivity of our eyes is pretty damned poor and Intensity/phase/wavelength variations that might be sufficient to cause such cumulative variances over 50 to 110 layers may well be below our unaided ability to visualize. I know from recent observations with Elegoo's water washable resin that a 12.5% increase in exposure (8 s to 9s) made the difference between hangers breaking from the main body of a print and not. +12.5% change in exposure is not a whole lot.

Perhaps some sort of pattern analysis of a digital image of the LCDs transmission could spot such variations.

I know this has to be intensely frustrating for you, nonetheless I enjoy our ability to discuss the issue--too bad we cannot be tossing back pints while doing so...

[DDLLC]

Pints are good; problems are bad... so does that mean they cancel each other out?

There does appear to be some variation in intensity and one would expect that since the light system is an array of LEDs + lenses. A given LED has a very narrow spectral distribution but there can be a good bit of difference of the spectra from LED's even on the same wafer (I used to be involved with metrology systems to measure this for binning the led chips.) Certainly intensity and wavelength center point will have a strong influence on the crosslinking. I'm not so sure about the phase unless you mean the possibility of destructive nodes from nearby led's interacting. Certainly the polarizers on the LCD will be sensitive to the phase so it's possible.

The nested rectangles were an attempt to sample across the build plate. I started with a large solid rectangle and went with "hollow" rectangles to reduce the resin used. The larger rectangle is designed to be 95 x 65 x 5 mm and the inner one is 25 x 25 x 5 mm. Both are centered on the build plate and the wall width is 5 mm. Most of the time the center rectangle has released from the build plate, but when it did adhere, it showed the same kind of angle and thickness difference as the larger rectangle. The thickness range was not as extreme but it did match up to the corresponding central portion of the larger rectangle as one would expect.

I could probably design something to measure the relative intensities over the screen but it might be cheaper and faster to just replace the light source. Do you know if such a replacement is readily available from Elegoo?

I have not torn apart the light box, but if you or somebody has, is it possible to rotate it 180 degrees (move the light now towards the front to the back edge)? If so I could do that and see if the thick part moves to the back which would then indicate it's a light source problem.

I had another thought last night and that is whether the FEP film is parallel to and/ or in contact with screen. If not then that could be a source of the problem. I will look at that tomorrow.

[cliffyk]

This is the 30 W LED i used in my converted microwave curing oven. (see my post here). It's constant current p/s requires a 120 VAC input.

Same vendor sells a 405 nm 100 W LED. They also offer a 50 W device.

The OEM curing LED(s) on the plain ol' Mars consume 40 W (my direct measurement), I have been "eying" the 50 W (or maybe the 100 W) device as a possible upgrade. I could feed 120 VAC separately into the printer base and drive a relay from the LED supply to control the 100 W LED.

I have not stuck my head "right into it", however casual observation seems to tell me the LED cluster could be "spun" 180° with little difficulty.

[DDLLC]

I'll look into the light source after I've opened my box.

I did take a picture of the exposure test this morning and it seems ok. I've posted pictures with and without the paper. It seems to me I've seen other pictures of the exposure test and it seems to be the entire field of view and not just an open rectangle. I'm not sure if that is a software version difference or something else.

Also I checked the vat and the FEP seems to be in direct contact with the glass. I've put a straight edge on the rear and really don't seen any gaps. I can slide a 0.0015 in gage under the straight edge but that is likely an artifact of the FEP flexibility.

Putting the resin vat on my granite flat did show that the corner at the spout and the opposite corners were about 0.004 inches raised off the flat. I could slide a 0.0015 inch gage under any other areas.

Running a test now with vat rotated 180 degrees from my normal. After tightening the build plate did have a 0.005-0.006 lift on the left side.

[DDLLC]

The attached picture shows the result after rotating the vat 180 degrees. It didn't fix the problem but the rectangles all stuck and looked better than previous trials. One difference is that I did lightly sand the build plate with 320 grit and cleaned, so that probably enhanced the adhesion.

Also the differences in average thickness is closer to the design parameters. From left rear to front left the thicknesses are : 5.96, 6.17, 6.73, and 6.47 mm. Rough average length and width are: 95.4 by 65.25 mm (design 95 x 65 ).

Running another trial with the exposure times back at 60 and 8s to see how that looks.

[DDLLC]

Results with lower exposures show the same problem but the "foot" might be a hair smaller. The side edge to right is at the front of the printer.

Small rectangle separated from build plate.

Overall average thickness was about 7.3 mm with individual values from rear left clockwise to front left are: 6.74, 6.9, 7.9, 7.67.

One thing I can mention that occurred on both runs today is that I changed how I loosen the set screws after printing and loosened the front screw first. As I did that the plate was pushed forward meaning the left screw was no longer pushing hard enough to hold the ball in place which I find odd.

[cliffyk]

I once, in error, ran the built-in exposure test with a vat of resin on place. It produced a thin cured layer, stuck to the FEP of course. I saw no value in it at the time and just scraped it off and tossed it. It had been exposed for 20 to 25 s. Would have been interesting to measure it's thickness to determine how much depth (thickness) of resin was cured by 20 to 25 s exposure.

I was pondering your situation and it occurred to me that this repeating my faux pas (with perhaps a longer exposure), and making multiple measurements of the resulting printed film, might reveal something of the equality of exposure across the field...

[DDLLC]

Did it print a hollow rectangle?

I suspect it might produce interesting information especially in base lining different resins, but I'm not clear how that info might give me a direction of something to fix. Can you explain in a bit more detail what you were envisioning?

I have sent an email to Elegoo and am awaiting a response. Maybe they know of something to try.

I did use the Photo Validator SW to image the printing and it shows cbddlp file working as designed. I'm taking that as a sign it is not likely a defect in the slicer data.

[cliffyk]

Yes, a flat rectangle just as "projected" by the LCD.

The "printout" should be flat (parallel top and bottom surfaces)--if not, and assuming the resin is homogeneous, any variations in the cured thickness have to be the result of unequal exposure to the curing light--thicker in longer exposed areas and thinner in less exposed areas. As the cross-field duration of exposure will be as near to identical as can be (the LCD is only ON or OFF), variations in cured thickness will have to have been caused by the intensity of the light.