OK, help me out here; the core gantry piece needs to be printed at 70% infill? That is going to be seriously stiff; but weigh a lot. Is this necessary? What is everyone else doing?
Thanks (as always)
–BA
In the enormous primo thread (I think), Ryan said you can do the middle at lower infill, but the ends need to be 70%.
Actually, what about printing with more perimeters? I am using more than 3 for the top and bottom and 4 for the perimeter. What if I was to do something like 45% infill with 5 top and bottom? At 70% the part is over a 1lb. That just seems a lot. I will experiment with S3D and multi-function printing. That thread is impossible to find anything. Sorry to be redundant.
–BA
Right now there is also discussion of printing a test object that goes up that high.
Some people are discovering issues around 80% of the way up, and the current theory is that people don’t usually print that high so there could be problems with binding rods or lead screws.
Definitely an important take away from the 1.8k post thread. 
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I have been concerned with the amount of material and the weight of the part. 45% infill just in general does not increase the rigidity as much as wall perimeter. By increasing the external solid perimeter layers and decreasing the infill, you can gain a significant amount of strength and cut the weight of the part.
I stopped going to the thread that you all are talking about. There is just to much going on. My recommendation would be to close the thread and have everyone start up thread specific to a topic. It is just to noisy and hard to follow.
–BA
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I’d agree, that thread is losing its value and even draining the value from comments that then get lost.
After looking at this in S3D a lot, I think I am going to leave the infill at rectilinear (45x45), infill at 25%, exterior layers at 6, and a solid layer every 150 layers. with a .2 layer height there is 700 layers. I am printing at 210, which is hot enough for PLA. This reduced the weight of the output by .25 lbs.
Thoughts?
I agree it is a rolling conversation. This is the kind of thing that I hate in chat apps. It will find its own way out though. There are a few primo build questions and build show and tells. Those will keep going. Once the primo is completely released, it will stop right away.
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I will look at this setup as well. As always Jeff you are the best.
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There are certain areas that need a stronger, denser infill because certain forces will be applied to those areas.
Filament is cheap, and cheaping out here on the core might cause you serious issues in the long run; but if you must, Ryan mentioned the exact height where you can reduce the infill and then increase it towards the top.
Gyroid infill also uses less filament (at the same %) and there is discussion about possibly dropping the % when using gyroid (because its much stronger); but there there isn’t conclusive data here to suggest the exact % you should do.
I suggest just doing it at 70%. A roll of PLA is $15-$20, so at most you will save a couple dollars which is a drop in the bucket in the long run.
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Correct, I am not asking about this because of the cost. I am thinking of the mass involved with moving .25lbs around. I am going to look at the items that Jeff put on this thread. I have some other parts to print that are ahead of it.
This is all good stuff.
–BA
This keeps coming up. The exterior walls do have a benefit. But I am fairly certain the tests everyone is referring too are not relevant to the way I design these parts. I am pretty sure they are referring to a video where ultimate strength was tested, not rigidity. Even the tests I have seen on gyroid infill are testing layer adhesion and compression strength. I design these parts in tension and we add tension along the layer lines. At least on any part that matters, clamps and core.
When you put these things in tension, that means one side is getting stretched, the other is getting squished and the infill in the middle is also playing a very large part.
I promise I did not just make assumptions I tested many many previous versions of the core and the lower end of the tension scale improved as infill went up until about the 70% mark, I know any higher and we start to get print issue from all the people that over extrude. The higher forces did not benefit from higher infill but were not hindered. We are for more concerned with the first 0.1mm of endmill deflection than anything else. The less it moves initially the better. and it takes infill here.
You are worried about weight, I see and understand that. ~2mm wall thickness and stuff the interior of the tops and bottom of the core as much as possible. With the heights I said previously that Jeff Linked you can lose an easy 100G But that is nothing compared to the giant routers everyone is strapping on. Mass has it’s place and if anything this is the exact place to have it. That mass can add to vibration damping and reducing chatter (maybe), that part is an assumption.
I can tell you 25% is not advised at all. 6 walls will leave very little infill in some places. I would love for you to do a comparison side by side but I would rather you print with my recommendations if you only want to do it once.
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Another way to think of it is if you printed all walls and no infill you will just be creating a large spring when put under a bending load. Hard to break but flexible as all heck. Now what if you printed all infill and no walls? Rigid, probably takes a lot less to break it ultimately but it would snap, not flex to failure.
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OK, 70% it is. On my printer it is going to take 2 days and will weigh about 1.2lbs.
I appreciate the direct feedback, all of this helps with the information.
–BA
You can do the variable infill 70-30-70.
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I printed all of my parts as listed in the docks but with a .30 layer hight with a .4 mm nozzles a lot of people are using .2mm and that seems like it would be weaker correct at the least a lot longer by 1/3
Thicker layers are stronger. No more than 70% or so ratio layer height to nozzle diameter.
I thought it was 80% so I may have gone overboard at 75%
I may do that. I have never done this on S3D; so it will be a learning experience.
–BA
Update, I have it sliced and it is off to the printer.
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Hi All,
New guy on the Block i have printed all the parts for the 25.4 Primo and am now in the process of printing the CORE and WOW is it killing me. I have burnt through 1KG of filament with all the failures i have had.
I have a layer height of 0.1 and 70% Infill. Not fussed on time taken to print. I had a few mishaps printing the other parts but nothing like this. Im trying various methods fix this issue. Not sure if the variable printing is the way i am using Cura anyone able to direct me to the settings in there. Kinda new to 3d Printing as i have Borrowed one to get the prints done.
I’m using RAFT as well for the print. Beds is level no lifting i’m wondering if the 70%/30%/70 will help with the constant failures. Probs not but Worth asking.
Cheers