What is causing these stripes and tears?

[garethashenden]

I have a new Photon Mono 4K. I've been trying it out with some 2mmFS wagons and I've got some weird problems. The beginning of the print has some ripples and tears in it, then it sorts itself out and prints beautifully. I have the whole body angled upwards. Once it gets above the end of the wagon it looks great. I tried it at 20° and 30° with the same results. All the other settings are the same, 0.035mm layer height, 2 second exposure, and Anycubic Craftsman DLP resin. While I have been printing for a while I still don't really know how to fix things like this. My two ideas are either a 0.050mm layer height or increasing the exposure a bit, but I'm not sure how much a bit should be. 

 

 

In the most recent batch I also printed a cattle wagon. It needs more supports in places, but doesn't have the ripples per say, but there are some gaps. There should be gaps, but they should be straight.

 

Edited April 8, 2023 by garethashenden

[MikeTrice]

On the open wagon I suspect the issue is caused by suction as the body prints. Try turning it through 180 degrees so the supports feed into the top edge. Another option is to include some holes in the floor of the vehicle or leave the floor out altogether.

[BG John]

I don't know if it's the answer, but my understanding is that the optimum angle is related to layer height and pixel size. I've got an original Photon (that I haven't used for ages), and someone produced a graph showing the angle for each layer height specifically for it. So if you have a new printer, the angles may need to be different to your old one. But this may not be the answer to your problem, as I'm still learning!

 

I've got the Chitu upgrade kit for my Photon, and am assuming as it will effectively make it a new printer, when I get round to installing it, I'll have to start again working out the best settings.

[drduncan]

Chitu upgrade kit?

[stevel]

6 hours ago, garethashenden said:

I have a new Photon Mono 4K. I've been trying it out with some 2mmFS wagons and I've got some weird problems. The beginning of the print has some ripples and tears in it, then it sorts itself out and prints beautifully. I have the whole body angled upwards. Once it gets above the end of the wagon it looks great. I tried it at 20° and 30° with the same results. All the other settings are the same, 0.035mm layer height, 2 second exposure, and Anycubic Craftsman DLP resin. While I have been printing for a while I still don't really know how to fix things like this. My two ideas are either a 0.050mm layer height or increasing the exposure a bit, but I'm not sure how much a bit should be. 

 

 

In the most recent batch I also printed a cattle wagon. It needs more supports in places, but doesn't have the ripples per say, but there are some gaps. There should be gaps, but they should be straight.

 

The first recommendation I have, is to raise the print by 10mm off the print platform, as your supports are to close to the model. This also helps to warm up the resin, which aids in getting a cleaner print.

The second Is to raise the temperature of the printer and resin, to 25C or higher.

The third is to add sacrificial supports to the model, this takes out the initial mishappen edges, leaving very little to clean up.

The angle to print at is dependent on the model, I would suggest the cattle wagon may need to be as steep as 60 degrees, to get the gaps to print straight.

here is an example of my system, of supports and snap off supports.

 

[MikeTrice]

To help illustrate the problem of vacuum I have taken the liberty of annotating your image:

 

Note also how @stevel image shows the wagon is orientated open side towards the build plate. This avoids the vacuum issue.

 

Edit: Regarding the vacuum issue consider a cup placed on the surface of water rim side down. When you try and lift it you can feel the suction effect. Placing the open side of the wagon towards the build plate there is no longer an unvented void to cause this.

 

I generally try and print at 45 degrees. This would help ypur cattle wagon a lot but you could probably do with some support to the horizontal planks that are open. It should be possible to add some feeds to the inside of the wagon to help support them.

Edited May 10, 2023 by MikeTrice
Clarification/Typo

[BG John]

13 hours ago, drduncan said:

Chitu upgrade kit?

https://chitusystems.com/product/6-08-inch-mono-lcd-upgrade-kit-for-anycubic-photon/

[drduncan]

Ah, I see. Many thanks!

D

[BG John]

42 minutes ago, drduncan said:

Ah, I see. Many thanks!

D

If you're interested in it, the apparently otherwise helpful installation video shows the screen being put in upside down! I'm glad I discovered that before fitting mine, which I haven't done yet.

[garethashenden]

What do you think of this setup? I added sacrificial skirts to the open. I can't add them to the cattle wagon as I didn't design it, I only have the stl. Its at 60 degrees and the open is upside down at 30°. The supports are the ones generated automatically by Chitubox. 

[BG John]

3 minutes ago, garethashenden said:

I can't add them to the cattle wagon as I didn't design it, I only have the stl.

You could add them in TinkerCAD (online), Blender, or (maybe surprisingly) PrusaSlicer.

[MikeTrice]

On the open the sacrificial skirts are only needed for the parts facing the build plate. The rest are just wasting resin. Otherwise looking good.

[garethashenden]

17 minutes ago, BG John said:

You could add them in TinkerCAD (online), Blender, or (maybe surprisingly) PrusaSlicer.

And I just saw a video on how to do it in Fusion360 as well. Thanks!

[stevel]

43 minutes ago, garethashenden said:

What do you think of this setup? I added sacrificial skirts to the open. I can't add them to the cattle wagon as I didn't design it, I only have the stl. Its at 60 degrees and the open is upside down at 30°. The supports are the ones generated automatically by Chitubox. 

This looks okay, the only reason I add strips on the buffer beams is  to stop a slight curvature, I can't seem to stop otherwise. if there is a floor to the cattle wagon you my need to add supports  to the floor.

If there is no floor I would support it upside down, as the roof is easier to clean up afterwards.

If you add a 10 degree tilt sideways, this would help alleviate suction as well, and would not require side supports.

[njee20]

That open wagon will just hold resin and will cause problems, it needs a hole for the resin to escape if you're going to do it that way up. I'd stick with the other way around.

 

In your original post you may be able to mitigate it with a light off delay. The basic problem is that the resin is still moving around when the light comes back on, hence is doesn't adequately cure. This is because the shape is like an inverted cup - and the retracting plate is squashing the resin. That's why it starts once the wagon becomes a 'box', and stops once the top is reached - the resin can be adequately displaced outside the model by the retracting plate. By adding a light off delay once the plate retracts it'll wait until the resin stops moving before the light comes on. This may not be the answer, as you may need a very long LOD to mitigate it fully. There are a few factors at play - resin viscosity, retract speed, wall thickness etc.

I would personally mitigate this by rotating in both the X and Y, rather than just choosing a steeper Y angle.

Edited April 14, 2023 by njee20

[Durley]

I have found angling wagons at 45 degrees gives the most consistent results. 45 degrees is commonly considered the maximum overhang for each layer that is self supporting, and both the sides and the ends print with the same amount of overhang, minimising drooping or tearing between support attachment points. On my Creality Halot One, the screen pixel width is 0.05mm and by matching the layer thickness to this, you end up with the horizontal and vertical surfaces having the minimum step size which minimise visible layers in the print. This video is a good explanation of angle and print quality https://youtu.be/Qs2Rb0ExnIM

 

I have had problems with getting slicer generated supports in the optimum place so have drawn up my own angled support ‘wedge’ that I combine with the wagon in CAD. I then use breakaway supports to attach the wagon to the wedge, similar to the supports Stevel has shown, either along the top edge of an open wagon or bottom of the solebar on a van. I then add some light slicer generated supports to any details on the overhanging end of the wagon to avoid any protruding details from failing to print due to islanding.

The attached photo shows a print of  3 plank wagon that I have scaled down to 2mm/ft scale. The lattice structure is the wedge that I printed with the wagon and have since detached. Note this model is drawn to exact scale so has very thin sides in 2mm/ft scale, circa 0.35mm. O gauge version is in the background for reference which was printed exactly the same way.

Edited April 17, 2023 by Durley
Typo

[Durley]

Wagon as supported.

[drduncan]

I have been following this thread with interest because I too am experiencing distortions at the earliest part of the print.

 

You can see the buffer beam is twisting away from its correct alignment.

 

Folluwing suggestions from @MikeTrice @njee20 @stevel and @Durley…

 

I have tried printing with the floor towards the build plate with a twist as well.

You can see that this merely changed where on the model it occurred - although still at the point closest to the build plate. It also produced heavy striations which can be clearly seen.

 

I tried breaking any vacuum by putting 0.25mm slits between the planks at the low end. 

This removed the horizontal marking seen on the body of the first image but did not eradicate all distortion of the solebars and headstock at the point closest to the build plate.

 

I then wondered if it was due to the thickness of the buffer beam or weakness at the join between the solebars and headstock that might be the cause so printed a wagon with reinforced corners and one with a thicker headstock

Niether solved the problem but the one with an extra 1mm thickness on the headstock appears to be slightly better. 

The distortion of the solebars abs headstock rather than above the wagon floor makes me wonder if it is entirely a vacuum issue and whether angle supports might be contributing. I intend seeing if changing the angle of supports alters things. 
 

Thoughts and observations very welcome.

 

Duncan

[MikeTrice]

Can I suggest you check the tension of the FEP and lubricate any lead screws?

[drduncan]

Hi Mike,

 

Thanks  for the reply. The FEP seems ok - the photon mono comes pre-fitted in a replacement frame.

 

When you say lead screws what do you mean and any suggestions as to the best lubricant? (I use PTFE to reduce print’s adhering to the FEP too)

 

Regards,

 

Duncan

 

 

[MikeTrice]

The screw that raises and lowers the build plate. I use a white Lithium grease. The lines you are experiencing could be jerking of the lead screw which the grease will help avoid.

 

It is also worth grabbing the build plate arm and seeing if there is any play when moving it up and down. If there is it could suggest fitting an anti backlash nut, or if one is already fitted, a better one.

 

Edited April 23, 2023 by MikeTrice

[drduncan]

Thanks

D

[stevel]

I have some new ideas on ways to solve this issue, and when I get home next weekend will test them out. I have changed the way I do my sacrificial supports to make it easier to clean up, and they have helped improve the warping issues, but not eliminated the problem, 

Do you do your own supports, or do you use the automatic supports in the slicing program, I stopped using auto supports because of the crazy way Lychee was grouping them and leaving large areas bare, the auto system seems more suited to the common figure printing than the straight edge things we are trying to produce.

 

Stephen

[garethashenden]

What I eventually did to eliminate my problem was this. Find the pixel size, on the Mono4K I have its .035mm. Set the layer height to that and then print everything at a 45 degree angle. Everything has been coming out smooth since then.

 

For the Photon Mono the magic number is 0.051mm.

 

The reason this works is that the printer either needs to print a pixel or it doesn't. With other angle and heights it needs to fudge things a bit and we see artifacts as a result of that.

[BG John]

I didn't post this when I commented on it before because it's specific the the OG Photon, but this what I understand to be the relationship between layer height, pixel size and print angle. I think I had a write up on this that explained it, and possibly had a formula, but I can't find it. Basically I think this shows that to calculate the angle, you draw vertical lines that correspond to the pixel size, and horizontal lines for the layer height, then draw a diagonal line where the lines intersect, and measure the angle.

 

I haven't done any resin printing for some time, and being a cheapskate I reduced resin use, as well as print time, by printing wagons flat on the build plate, compensating for the elephants foot where I could, and it seemed to work fairly well!