Printing overhangs - are these items a problem? What is the general rule about this?
 
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Printing overhangs - are these items a problem? What is the general rule about this?  

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Tango
(@tango)
Trusted Member
Printing overhangs - are these items a problem? What is the general rule about this?

I have a few items I'm designing for my own use and I want to get an idea of what is and isn't safe to print. I have printed this filament guide and that shows me that I an have a short unsupported span. Before I start printing (or finish designing) a few things, I want to know if I'm trying to do too much.

This is a lampshade extender, but not yet to scale. The big part is part of a sphere about 2" high and, at the top, about 4" across. If you look on the right, above the larger object, there is, basically, a hook with a line above it. The radius of the semi-circle part of the hook is about 1/4" and the line sticking up is at an angle and will probably be about 1/2" high. It's to help slide the hook over the rim. I'll put one of these at 3 spots around the top, each curved with the large object and about 1 1/2" wide.

Here's a different view so you can see the curve of the band of the sphere.

I would think the main part is okay and that the part that's a concern would be the semi-circle on the hook. That will snap over the inner rim of the current lampshade to hold this lamp shade extender on the current lamp shade.

The other is a sign holder. I'm putting a laser on my CNC system, so I want to easily be able to stick this sign on the shop door. The only issue is that the shop door is a sliding door. If I tape the sign on, or try to use a tack, it could easily catch whenever the door slides open. This will hold the sign on the door and has bevels so if, as the door is being slid, it's too close to the frame, with the simple bevels, they won't catch on the frame, but the door will be pushed back from the frame enough so it can keep sliding open or closed. For dimensions, the total width of this piece is 1/4" high, 1 1/2" wide, and the sloped part that is not supported is 3/4" from where it leaves the bed until it reaches the side of the object. Front to back, it's 3"

If I'm printing with PLA, are these objects okay as they are or do I need to plan on making changes to them?

Respondido : 06/07/2022 8:27 pm
Diem
 Diem
(@diem)
Famed Member
RE:

Your semicircles approach the horizontal at top and bottom and will not print without support - but if you could cut the top and bottom from a larger semicircle so the top and bottom of the section never got steeper than 45 degrees (you might get away with 30) it would become an easy, supportless print.

I can't judge the design of your second part but be aware that PLA, although strong, is brittle and does not do well with impacts.  I would print this sort of thing in PETG.

Cheerio,

Respondido : 07/07/2022 12:52 am
Tango
(@tango)
Trusted Member
Topic starter answered:
RE: Printing overhangs - are these items a problem? What is the general rule about this?

Your semicircles approach the horizontal at top and bottom and will not print without support - but if you could cut the top and bottom from a larger semicircle so the top and bottom of the section never got steeper than 45 degrees (you might get away with 30) it would become an easy, supportless print.

I was pretty sure that wouldn't work that well, but I wasn't sure. I'm also thinking of other ways to do it, such as making it as multiple parts. I need these shade extenders because the bulb goes about 1" below the shade on the lamp. It's a stupid design and I'm fixing it. But I plan on using translucent filament, so I'm concerned about shadows or ugly looking shapes or blotches showing through if I have to do something funky in fitting it all together. My other concern is that I want to make sure the shade extension fits right over the current lamp shade so there isn't a line of light shining through and getting in my eyes when I'm working. I'll keep tinkering with different ideas.

I can't judge the design of your second part but be aware that PLA, although strong, is brittle and does not do well with impacts.  I would print this sort of thing in PETG.

Still so new to this I wasn't aware of that issue. I figure PLA would be find if I'm opening and closing the door or if my wife is, but that might be a problem with grandkids, so I'll take that into consideration. I haven't printed yet with PETG or started looking into what issues to be aware of when switching from one material to another.

Respondido : 07/07/2022 2:25 am
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