Problem with prints, knife like gashes

[motl3y]

Hi all. New to the group and new to resin printing.
I just received my Mars printer recently, leveled the bed and printed the Rook test piece. Both pieces printed perfectly.
Now where my trouble starts.
I loaded something (medievil castle)  into ChiTuBox, sliced it, checked the layers via the slide bar. Everything looked okay until it finished printing. There's a knife like slash going down the back of the print, refer to pic. 
I then proceeded to load 6 x skull paracord beads on the build plate, all printed with the same part missing, refer pic. The print preview on the Mars screen showed that part being cured but missing. I loaded 1 skull bead , sliced it, printed it with the same result.


       

[cliffyk]

How were these models oriented (relative to the platen's plane) when printed? Were supports used?

Can you post screenshots of what they looked like in Chitubox just prior to slicing?

[motl3y]

How were these models oriented (relative to the platen's plane) when printed? Were supports used?

Can you post screenshots of what they looked like in Chitubox just prior to slicing?

Thx for reply. They were angled with supports

[Gauntfield]

auto supports or did you manually put them in?

I would suggest manually putting them in

[cliffyk]

Thx for reply. They were angled with supports

I can't see much amiss with the castle (would need to see other angles of view); however the skulls appear to have insufficient support at their backside where the cranium projects, cantilevered off the jaw/frontal skull.

I have marked up your screenshot and present it "upside-down" as I find it useful when adding hangers¹ to envision that their function is to suspend (against the forces of gravity and FEP adhesion) as yet non-existent structural elements of your model, as they are created.

This is the direct opposite of supporting existing elements to prevent structural collapse[/b].

At some point in the build process those 3 or 4 hangers could no longer resist the FEP's adhesion and they broke away, resulting in none of the lower half of the skull being printed. Later in the process however the upper portion of the skull (the portion being an extension of the jaw and frontal skull) was able to build as it was in cantilever support by the frontal portion of the model.

Are you certain there was no debris in the resin vat, remnants of the hangers, their rafts, and any part of the lower skull that did print. I would have expected to find something?




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¹- I find also it helps to think of them as "hangers" not "supports" as that is their true function in resin based SLA printing--they are loaded in tension, not compression.

"Adherence to a project specific and shared nomenclature is essential to effective communication in any team effort."
-me- ca. 2005; in a commissioned review of a failed $4.5M IT project

[motl3y]

Thx for reply. They were angled with supports

I can't see much amiss with the castle (would need to see other angles of view); however the skulls appear to have insufficient support at their backside where the cranium projects, cantilevered off the jaw/frontal skull.

I have marked up your screenshot and present it "upside-down" as I find it useful when adding hangers¹ to envision that their function is to suspend (against the forces of gravity and FEP adhesion) as yet non-existent structural elements of your model, as they are created.

This is the direct opposite of supporting existing elements to prevent structural collapse[/b].

At some point in the build process those 3 or 4 hangers could no longer resist the FEP's adhesion and they broke away, resulting in none of the lower half of the skull being printed. Later in the process however the upper portion of the skull (the portion being an extension of the jaw and frontal skull) was able to build as it was in cantilever support by the frontal portion of the model.

Are you certain there was no debris in the resin vat, remnants of the hangers, their rafts,  and any part of the lower skull that did print. I would have expected to find something?




---------------------------------------
¹- I find also it helps to think of them as "hangers" not "supports" as that is there true function in resin based SLA printing--they are loaded in tension, not compression.

"Adherence to a project specific and shared nomenclature is essential to effective communication in any team effort."
-me- ca. 2005; in a commissioned review of a failed $4.5M IT project

Thanks for the reply.
I see what you mean. I have sliced another test piece ready for when I finish work. I have rotated a skull 90 degrees, and another a complete 180. See what happens. When I drained the remaining resin I did not see any form of support in the filter.....
I sliced and printed another test piece last night. The barbarian. It printed fine.

[cliffyk]

Once I came to realize they were "hangers" and not "supports" my placement of same changed a bunch and my success rate with more complex models shot up a couple notches...

[motl3y]

Once I came to realize they were "hangers" and not "supports" my placement of same changed a bunch and my success rate with more complex models shot up a couple notches...

*update* I tried to print the above with no success, I resliced another with more light hangars around the back of skull. This time I kept the orientation level, no rotation, no success. I have since then sliced another with heavy hangars around the problem area, see what happens tonight.

[cliffyk]

Once I came to realize they were "hangers" and not "supports" my placement of same changed a bunch and my success rate with more complex models shot up a couple notches...

*update* I tried to print the above with no success, I resliced another with more light hangars around the back of skull. This time I kept the orientation level, no rotation, no success. I have since then sliced another with heavy hangars around the problem area, see what happens tonight.

Year
s back I had a girlfriend with "heavy hangers", never found it to be a problem area--it was her attitude--she was gorgeous and knew it making her overall a real PITA...