mrbanana101
Posts: 6
Joined: Tue Nov 20, 2018 3:17 am

Print outline/perimeter shells on OUTSIDE of hollow model instead of INSIDE

Tue Jan 28, 2020 5:10 pm

Hey all, looking for some advice for something that may not even be possible. I'm printing a completely hollow (0% infill) model with 2 - 3 outline/perimeter shells. When S3D prints additional outline/perimeter shells, it adds them going inwards to the center of the model, such that the outside surface is dimensionally accurate, but the inside hollow cavity will be smaller. This is expected behavior. But Is there any option I can set so that each additional shell wall that's added prints on the OUTSIDE of the first wall rather than the INSIDE, so that the inside cavity will be unaffected/the correct size? I fear there's absolutely no way to do this directly within S3D, though it seems like it would be some option I can toggle, but I've looked and looked without any success. It sounds confusing, but I've attached a quick drawing to illustrate what I mean.
printshellinside.png
Thanks!

horst.w
Posts: 835
Joined: Fri Oct 17, 2014 5:00 pm

Re: Print outline/perimeter shells on OUTSIDE of hollow model instead of INSIDE

Tue Jan 28, 2020 6:33 pm

That is the question of the surface direction and not changeable. It is always going Outside to Inside. Even turning the print direction will not help (Tab Layer ...)

- adjust your construction or
- use the scaling of the model

horst.w
GER

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dkightley
Posts: 2148
Joined: Tue Mar 10, 2015 4:09 pm

Re: Print outline/perimeter shells on OUTSIDE of hollow model instead of INSIDE

Wed Jan 29, 2020 10:58 am

The only way I can think of to achieve what you're wanting would be to redesign the head so its a big block with a head shaped hole inside it...like this:
Image11.jpg
Image11.jpg (33.54 KiB) Viewed 235 times
Then, when you slice it with zero infill and how ever many perimeters....together with bottom layers for the top half of the model...you will get a big box to throw away...but inside, the model you want!
Doug Kightley
Volunteer at the National Tramway Museum http://www.tramway.co.uk
Railway modeller and webmaster at http://www.talkingtgauge.net

Rocko88
Posts: 7
Joined: Tue Sep 03, 2019 1:26 pm

Re: Print outline/perimeter shells on OUTSIDE of hollow model instead of INSIDE

Thu Jan 30, 2020 9:03 am

Just do a shell function in your CAD program and give the offset surface about .025 inches thick. Then do a 2 shell max on the print.

mrbanana101
Posts: 6
Joined: Tue Nov 20, 2018 3:17 am

Re: Print outline/perimeter shells on OUTSIDE of hollow model instead of INSIDE

Wed Feb 05, 2020 2:44 am

Thanks for the replies all, I apologize for the late response. Just realized I may have posted this question in the wrong subforum (didn't mean to add it to feature requests! So if a mod finds it necessary to move it to a different forum).
horst.w wrote: That is the question of the surface direction and not changeable. It is always going Outside to Inside. Even turning the print direction will not help (Tab Layer ...)
I was hoping I was jut overlooking some option hiding somewhere - thanks for the info!
dkightley wrote: The only way I can think of to achieve what you're wanting would be to redesign the head so its a big block with a head shaped hole inside it...like this:
Coming from a sculpting background with some very limited hands-on experience with moldmaking, that was my initial idea also. Unfortunately, adding a box around it and making the positive a negative via a boolean subtract inflates the print times tremendously (and makes it a bit trickier cutting up the print into appropriately-sized chunks to fit on the bed). Thanks for the suggestion!
Rocko88 wrote: Just do a shell function in your CAD program and give the offset surface about .025 inches thick. Then do a 2 shell max on the print.
Thanks Rocko, do you have any tips on doing this? This is something I've tried before but didn't have much success. IIRC, I had opened my model in Meshmixer and ran an "offset" command to give the wall a bit of thickness. at 0.025 in., it causes a lot of odd artifacts and wouldn't slice correctly. at 0.0314 in., in S3D it sliced fine but in some areas there's a bigger gap between the two walls and I'm guessing attempting to print it would cause poor wall adhesion in a lot of areas. Do you have any suggestions on what software I could use? I'm an autodesk subscriber so I have access to most of their software (Maya, Netfabb, etc.). Not too sure if it's meshmixer messing up, or I'm just doing something wrong.

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