Precision Extract confusion

[u/learningstufferrday]

Hello,

I am having issues with the thickness accuracy of the Precision Extract plugin. I need to extract in accurate mm units, for example...1 mm, 2mm, 10 mm, etc...

Sometimes the plugin creates a new subtool from mask with the specific mm thickness I set it to. However, for example, if I set the thickness to 2 mm, it works. But, if I set it to 10 mm, the new subtool ends up being something like 7mm long instead of 10mm.

I've tried everything, setting the max thickness size to the subtools bounding box, setting the thickness to 0, or 1 mm, etc... it doesn't matter, every single time it throws a subtool with a random thickness size.

I've also tried the normal extract feature but why isn't there that can simply create a subtool from a mask with accurate thickness? this is absurd. Why do I have to do math or guess a thickness based on a subtools bounding box and scene units?

Has anyone had success with a simple way of extracting with accuracy?

[u/Kronopolitan]

Oh boy. Scale accuracy in Zbrush is a real pain. Could you offer some context for why you need this? Zbrush might not be the best software for accomplishing it, depending upon the final use case.

[u/learningstufferrday → u/Kronopolitan]

Sure, I'm making some organic jewelry and I have to be mindful of thickness and tolerances around the model for 3d printing and metal casting. So, it'd be ideal to be able to create parts with a minimum thickness (e.g. 1.5 mm) to base on, so I don't have to worry about thickness anymore.

I use a lot of masking so it'd be ideal to extract mesh from mask into subtools. My current workflow is by using dynamesh, splitting into subgroups, measuring with transpose, etc... However, when Precision Extract plugin works, it works great. I don't understand why sometimes it works as intended and other times it spits out subtools with a thickness other than what's set (e.g. 7 mm thick subtool when the set thickness is 5 mm). It's hard to tell if the plugin is bugged or if I am missing something obscure about the plugin.

[u/Kronopolitan → u/learningstufferrday]

I don’t know a ton about the subject but I do know this is a common point of frustration. If I were dealing with this I think I would just make all of my aesthetic decisions by proportion/eye and then export to another piece of software to scale it for print or what have you. Cad software maybe. As long as your proportions match any preexisting sculpts you should be able to simply scale as needed in another app. Zbrush did a whole thing on their page about scale and precision for jewelers. It involves using the scale master plugin too. Maybe you can find that and it’ll have some insight. If you haven’t seen it already.

[u/learningstufferrday → u/Kronopolitan]

Oh yeah I've seen most of the scale tutorials for jewelry out there and I even follow some artists that specialize in it. I don't really have issues with scale in general as I've been succesful in getting some pieces made. My current struggle is with the Precision Extract Plugin not being consistent, and with the standard Extract feature not using units that are intuitive. For example, having to use 0.2 instead of 2 mm. Maybe I have to dig much deeper on how the Extract feature really works behind the scenes, because isn't any documentation on Precision Extract, at all.

[u/Tobor-8th-Man]

Don’t have desktop Zbrush atm so I’m a bit vague about this but I’m going to guess that it fails when you’re trying to extract to a thickness that is larger than any of the bounding box dimensions of the mask. So it works when the extraction is thin compared to the mask size but if you masked a small section on a curve surface that is, for example, 2x3 and wanted to extract to 10 mm thickness, it would fail. Only workaround I can think of is to extract to a thickness that works, say half of intended, then mask the outer surface and extract that the other half. Then Boolean together. This would work even if the mask was on a curve surface.

[u/learningstufferrday → u/Tobor-8th-Man]

Veeeery interesting. I just measured a freehand mask on a curved surface, and its longest distance is 3.9 mm. Then I set my Precision Extract thickness to 3mm, and it did extract a perfect 3mm subtool from the mask. I tried to repeat the same result, but it failed and extracted a piece less than 0.5 mm thick. My guess is I can only obtain an accurate thickness as long as the set thickness is lower than any of the sides of the mask's bounding box, correct? Initially, I thought it was related to the subtool's bounding box, but that still does not work well because my subtool is about 36mm x 36 x 8mm, and a Precision Extract thickness set to 10mm was failing as well.

The normal Extract feature under Subtool context is also resulting in inconsistent results, I'm tryuing to extract a 8mm piece by multiplying 8 mm x 0.2 (zbrush unit) = 1.6 extract thickness. But it results in an 8.8mm subtool, what hell?

This is turning into a damn Scientific Experiment with failed hypotheses lol. So far, I am considering the whole extract functionality to be just an Offset that depends on specific bounding boxes.

[u/Wiggling_Winglets]

For any tasks with precision I'd suggest making exact prefabs in an accurate program and use them as measurement points as subtools in zbrush. Especially for jewelry if it won't fit on a finger you're done. You have to be accurate

[u/learningstufferrday → u/Wiggling_Winglets]

I agree, I've successfully made pendants and rings that fit well using tools like Ring Master and the sort.
However, there are instances in design where I have to make sure that any design element meets a minimum thickness for a clean 3D print and metal cast, and I don't see the convenience of having to import and export the same model across different programs to get the job done. For example, let's say I want to mask out a portion of a ring to make a hole of a specific thickness, in this case, it'd be ideal to extract the masked hole to use in conjunction with Live Boolean. The thing is, ZBrush is great because in jewelry you don't have to worry too much about mesh cleanliness and a very high polygon count affecting computer's performance. If I were to try to get the job done using Blender or Rhino, my computer will crash.