Changing Infill for just One Area
I am making a frame out of 1" square aluminum tubing. I'll be printing out the connectors to plug into the ends of the tubes. While friction seems to do a good job of holding the connectors in the tubes, I'd like to make sure and use a self-tapping metal screw. Once I get the connector in the end of the aluminum tube, I want to pre-drill a hole through the aluminum and into the printed connector so I can hold them together with the screw.
Normally I use a gyroid infill pattern, but around where I want to use a screw, I'm thinking I should use something more solid.
First, does anyone have thoughts on this? Should I make the infill solid all the way through? Or is there even a need to change the infill? Instead, should I specify a thicker wall?
And if I want a thicker area where the screw will go in, how can I set that up? Should I do the thicker area as a separate object that's inside the connector and change the settings for just that object? (I have an MMU3 on my printer, and am using the updated PrusaSlicer that can use different filaments and settings for different objects.)
I'm interested in any experiences people have had with this kind of situation.
(Note: I don't want to make a hole all the way through and just put a nut on the other side. I'll be using adhesive magnetic strips on the aluminum, putting plastic over those strips, then magnets on the plastic to hold it in place, so I want a smooth surface on 2 sides of the framing tubes to make that work better.)
RE: Changing Infill for just One Area
Add Part>cylinder, imbed it into the model where you want it. Add smaller negative volume cylinder in its center for the screw
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RE: Changing Infill for just One Area
@tango
Started with modifier with more infill.
After reading what @jp-guitars wrote regarding perimeters I added more perimeter.
Aaaand, after reading what @reddawg wrote I added negative volume
Prusa i3 MK3S+ FW 3.11.0 (kit dec -20), PrusaSlicer 2.6.1+win64, Fusion 360, Windows 10
The simplest resolution is to model a pilot hole for the screw and then use a modifier in that area to increase the perimeter count.
- and for an engineering part of this type I would suggest cubic infill.
Cheerio,
RE: Changing Infill for just One Area
A few things I've worked out since I posted this:
- It turns out I need some adjustment room. I planned for exactly 48" x 48" for the frame size, but I've had to change from lifting it with hinges to putting 2 sides on drawer sliders so I can slide it out of the way. I've never found the kind of drawer sliders I'm using to fit perfectly in the width they provide - always seems to need a bit of fudge room. So I won't know exactly where the screws would go through the side of the tube or into my connectors. I'll need wiggle room
- I did a test print and was hoping to find a size that fit snugly into the tube, but I couldn't. Due to filament with and so on, 22mm square is too small to be smug, and 22.5mm is too wide.
I'm wondering about the width and filament size. I haven't experimented with this, but I've read a few comments about that width differences of less than .5mm can be tricky and not always reliable. Comments on that, anyone? Is it worth trying 22.25mm, or would there be issues with that when compared to 22 or 22.5mm?
So I'm going to have to make a larger area than I thought solid. I'm wondering about just making the whole thing solid - again, any thoughts? Other than taking longer to print and using up filament and making it heavier (and it's not going to be too heavy anyway), are there other issues with that?
I would user a modifier to put a lot of extra perimeters where you are going to put the screw through so the screw is effectively biting into solid plastic
That's what I was thinking. I like it when I can do whatever I need in my STL file, and often I just load the STL (sometimes several) into PrusaSlicer and send it right to the printer. But it's clear this is one I'll have to keep the slicer files as well.
for an engineering part of this type I would suggest cubic infill.
I've read that gyroid fill may use more filament and take more time, but that it's one of the strongest infill patterns there. But I also find that many times I read a webpage and later find out that person is speaking from only a small amount of experience, so I'm always glad to learn more or to find out if something is not correct. Why would you suggest cubic?
RE: Changing Infill for just One Area
"I'm wondering about the width and filament size. I haven't experimented with this, but I've read a few comments about that width differences of less than .5mm can be tricky and not always reliable. Comments on that, anyone? Is it worth trying 22.25mm, or would there be issues with that when compared to 22 or 22.5mm?"
For a project I did recently, I was looking for pieces to grip tightly to 1" aluminum square tubing, and also for some that would slide more easily (it is a folding display rack for quilts).
To test exactly this, I printed square tubes with inside measurements of 25.6 mm, 25.7 mm, and 25.8 mm. I found that the 25.7 mm was snug and had no wobble, while the 25.8 mm allowed sliding easily. You should definitely do some experiments in between your 22.0 and 22.5 sizes!
(More photos of my project here although not directly related to your question: https://forum.prusa3d.com/forum/postid/713008
Prusa MK4 since Jan 2024, Printables: @MikeB_1505898
RE: Changing Infill for just One Area
To test exactly this, I printed square tubes with inside measurements of 25.6 mm, 25.7 mm, and 25.8 mm. I found that the 25.7 mm was snug and had no wobble, while the 25.8 mm allowed sliding easily. You should definitely do some experiments in between your 22.0 and 22.5 sizes!
Now that you mention it, I think you were talking about this project in another thread I started.
I'll go on and try for a tighter fit, thank you! Now that I'm thinking about it, it's quite possible, with all the other junk I'm dealing with now, that I got things mixed up. Am I right that I should at least get accurate sizing in a print down to .1mm? It's just the kind of thing I'd get twisted in my head to be off by a decimal place!
RE: Changing Infill for just One Area
I've read that gyroid fill may use more filament and take more time, but that it's one of the strongest infill patterns there.
Why would you suggest cubic?
Gyroid has very little directional bias and it's resilient, excellent for decorative objects and functional parts that may flex. Cubic is stiffer and good for rigid structural parts but *might* have a bias - in which case you use 3D Honeycomb and put up with the shaking.
Am I right that I should at least get accurate sizing in a print down to .1mm?
The best advice is to regard 3D prints as unfinished engineering parts - print fractionally oversize and machine to fit. In this case, print 0.1mm oversize and remove the high points with abrasive paper used wet.
Cheerio,
RE: Changing Infill for just One Area
I'll go on and try for a tighter fit, thank you! Now that I'm thinking about it, it's quite possible, with all the other junk I'm dealing with now, that I got things mixed up. Am I right that I should at least get accurate sizing in a print down to .1mm? It's just the kind of thing I'd get twisted in my head to be off by a decimal place!
I wouldn't go so far as to call it "accurate", but at least it's usually consistent. To be snug, you would expect 25.4 mm to fit. But the 25.6 mm design size fit snugly, which means it was off by 0.2 mm. But since it was off the same every time I was able to use it for all my parts!
I think the slicer and printer are capable of positioning the print head with very good accuracy, I would say < 0.01 mm, but then you're squishing out plastic while moving the print head and all that great accuracy gets lost in the variables of squish, flow rates, etc. So, prototyping is the best way to go...
Prusa MK4 since Jan 2024, Printables: @MikeB_1505898
RE: Changing Infill for just One Area
Since you're using self-tapping screws, having a more solid infill around the screw area is advisable. While gyroid infill is great for general strength and weight savings, for areas where screws will be used. This can provide maximum strength and support for the screw threads. If you want to maintain some flexibility, you can opt for a higher density (like 50-100%) in that specific area instead of solid https://forum.prusa3d.com/forum/postid/713008 wordle unlimited
RE: Changing Infill for just One Area
Update on this issue.
Here's the shape I'm working with:
That's 2 test pieces, done in different thicknesses to test the fit. To help make sense of the shape, this is for a vent hood. One piece will be at each of the 4 corners. The diagonal connector that sticks up a bit is for the tubes that will meet near the center, where the vent outlet will go. When printing, I'm using PETG and I slice it like this:
The diagonal is at a 12° angle when it's sitting flat, (like in the first photo), so I need to orient it like this to get a good print instead of wasting support material. For ease of reference, I'm using this screenshot from PrusaSlicer and referring to the two squared struts/connectors as "vertical" and "horizontal."
First, I printed it using a 50% infill for the full object. Due to an accident (I'll get to that later), I found pre-drilling a hole in the end and using a #10 screw in it and found that, with the 50% infill, the screw gripped it quite well, so I'm thinking that'll be sufficient.
I ran into a problem, though (and might start a 2nd thread addressing just this issue - we'll see if people can help me here). I found the diagonal and vertical struts fit in my 1" square aluminum rods just fine. The horizontal strut was too tight and I had to use a rubber mallet to pound it in. On the one hand, that's not an issue, since I seriously doubt I'll ever want to disassemble this hood once it's done. But it would be nice if all 3 struts fit in snugly, but not so tight they done come out.
Why is the horizontal strut a slightly different size square than the vertical and diagonal ones?
As to the screw - once I got it in, to verify I could do it, I used the rubber mallet to try to knock it out of the tube. That broke the piece and left a good part of the strut in the rod. Here's the connector when that happened - and the remains of the strut that was inside the tube:
I was going to just use larger drill bits to try to break down the part stuck inside, but I realized that was a great chance to see if 50% infill would work. So I pre-drilled into the end and screwed a 3" #10 screw into it - it held as tight as I can imagine, so I think the 50% infill is enough. Then I went to a bigger bit and drilled a hole down it, then an even bigger one, then used a screwdriver to chip away and break down parts of the stuck part until the end, at least, was loose enough for me to grip it with a vice grip and pull it out.
Overall, I'm going to just use 50% infill for the entire part. I was going to use higher infill for just parts of it, but I think it'll handle stress better if the interior is all consistent. Also, the hood will be attached to drawer sliders and some connectors may have 2 screws in a strut instead of one, and it'll be a pain to work out just where to put the reinforcements since I might have to adapt to how things fit, so I can't be sure, until it's together, just where screws will go into the connectors.