Heyo I have been reading the forum for a bit and now also started printing my parts and while experimenting a bit with speeds and height and what not, my printer have been randing still for almost 2 years and I don’t really remember what settings I used to run blabla. Anyway, here at the forum the general mode seems to say that higher layers are stronger than lower, but then I found this video at the tube , can’t seem to post links though??
That shows the opposite, so now I wonder what’s the dealio… is it another kind of strength? Is this video out dated and there is a new one? Basically where does this “higher layers for the win”-mentality come from? Is it just printing times motivating this?
I’m no expert but from my experience prints are more likely to fail off the printer due to delamination. The lower the layer height the more layers needed and the more chances for delamination. So a higher layer height is technically stronger all things being equal.
That being said, I don’t believe any of the printed parts are going to fail in use due to delamination if printed in the orientation intended by the designer. With these parts you are more likely to have a failure due to crushing forces by printing with a weak infill pattern and density percentage.
With a year of operation and a 35% infill pattern (forgot the pattern type, bicubic maybe?) I only had one part failure which was the bridge-like structure that joins the X and Z rails together. That seems to be the area that experiences the most clamping force on my build. Reprinted them at 65% and a .28 layer height and haven’t had a problem since.
Just watched the video. CNC Kitchen is a very good source and has pretty reliable information in my opinion. His findings ARE relevant to the one failed part I mentioned where there are two screws pulling two parts together with a gap in between. Very interesting. Still, the rest of the parts shouldn’t be an issue with a decent infill and density.
I print lots of parts for mechanical strength,. not just MPCNC ones.
I tend to print at 0.33333mm layer heights for mechanical parts. (3 layers/mm) and 0.1666666 (6 layers/mm) for aesthetic parts.
I did a fair amount of destructive testing for parts at 0.33333mm, 0.25mm and 0.20mm parts, and tended to find different failure modes for each.
Ultimately, I find best strength overall at the 0.33333mm layer height and a hotter extrusion temperature.
My hypothesis is this: The thicker layer makes each individual stgrand stronger, as it has a larger cross-section. the hotter extrusion combined with the thicker layer means more heat energy in the plastic as it’s extruded, which helps re-melt the lower layer and provides increased layer bond strength.
The thinner layers (0.2mm) are more prone to crushing with lateral stress and higher extrusion temperatures start to show deformation before showing results in better inter-layer bonding. (This is opposite what I initially expected. I had thought that the thicker layers would deform sooner.)
Of course, tensile strength is dependent on several factors, and there are many variables in yourprint settings. With just the right temperature, speed, and layer times, a range of possibilities for print strength are possible. It might also vary based on which plastic you print with, too.
Just to be contrary (I print at 0.2mm for everything, so I don’t have a dog in the fight). One theory as to why smaller layers might be stronger is that only the weakest layer bond matters. So the important thing is which makes a least worst layer bond.
I might argue that the smaller layers (but same sized nozzle) would cause the geometry of a line to be flatter. So there may be more surface contact (as a percentage) than with thicker lines that are more rounded in profile. There may even be more pressure in a smaller layer height, which could increase bonding between layers.
But honestly, it is just me wanting to see both sides get fair guesses. I believe the experiments. One experiment is that many many mpcncs have worked well with chunky layers. And another data point is that I don’t want to triple the amount of time or cost by making smaller layer lines.
This is a good point too. When printing I always try to print at the highest recommended nozzle temp or slightly higher for mechanical parts. This is another really important factor for layer adhesion and strength.
Me too. I am a firm believer in the old adage from my boat racing days ; “If it breaks it’s not strong enough , if it doesn’t break it’s too heavy.”
Yes I’ve seen the tests. Yes under identical circumstances a bigger layer will be stronger, but by how much? IMHO if you are building a piece of equipment that is so close to it’s engineered limits that the difference between a well printed 0.2mm layer and a 0.3 layer is going to make a difference, then perhaps 3D printing is the wrong solution.
That extra layer height combined with bigger nozzle will mean a massively reduced print time and for many that is important. For me, it’s not. If I want a print sooner I’ll start earlier!
For many it’s an aesthetic thing to have those lovely print lines highly visible, and that’s cool. I might get to that one day, but it’s not where I am at the moment.
For now, if I want stronger, I increase the number of perimeters, crank the infill 25% or so, and go and have a long nap.
Always remember if it doesn’t have to be the STRONGEST, just STRONG ENOUGH and there are enough examples in the wild printed at lower layer heights to assure you that as long as your printer is well tuned it’ll all work out in the end.
Interesting discussion, and certainly good to see some form of data to go with it. It seems most here agree, and I was taught the same in college, that inter layer adhesion is the usual weakness with fdm prints. So looking microscopically at what variables affect this is most important… and we can see that the process which lays down a single line has control over the strength of the bond of that line to whatever is below. Thick and thin lines will have variant geometry… Jeff hit closely on this one. Taller layers will have a more rounded layer interface, thinner will look more square… likely more surface area.
The other part that I think is even more important, is the level of molecular entanglement happening between layers. We know plastics can be melted and cooled so molecules can rectangle when mixed, which gives plastic it’s insane strength and superior recyclability. So, how would thick vs thin affect this inter layer mixing and entanglement? It could go both ways. Thin layers mean the brass nozzle is closer to the previous layer, which would conduct more heat into the previous layer and improve mixing. OTOH thin layers have less heat per x section area… a thicker layer will stay hotter longer, transferring more heat into the previous layer.
Which effect will dominate? That is the million dollar question that I think only research can prove one way or the other. I suspect that at lower print speeds, thinner layers will be stronger (brass has time to really iron the layer down), but above a certain speed the latent heat of thicker layers may lead to more strength (not much time for brass action, so latent line heat dominates). So there may not be an always true conclusion anyways.
The geometry of the part wrt overhang angles will also play a big role in what layer height is strongest. Thinner layers handle steeper overhangs better in general. Draw up some constant width layers of varying thickness, and see how they stack with say a 45degree overhang. You will see far less surface area contact between layers for taller layer heights always. Taller layers have more of the line dangling in the wind vs thinner layers.
This is mainly why for my mpcnc, I chose to take forever and print 0.1mm layers, slowly.
As noted above, because of all the variables in the outcome between individual setups, I think that if the engineering margins are so fine that ultimate strength matters, we should probably be looking for a different method of construction.
This argument for thicker layers falls down a bit if no mention is made of filament. Shouldn’t we also be talking about higher strength (polycarbonate or carbon reinforced PLA) filaments vs el-cheapo water logged left-over anything?
Absolutely, if the op was open to more then there is certainly a ton more that can be done to improve part strength and durability. That is why I enjoy printing and Cnc so much… both are rabbit holes that keep on giving.
Just to add a little to this. We are not really concerned with layer bonding strength. The parts are designed to not stress along the print direction. We don’t ever rip parts apart, the only breaks we ever have is over torquing the screws and bolts. A #6 screw is easily capable of 380lb of clamping force and a 5/16" bolt is 2,160lb. Most people do not realize this and just crush or rip apart with the force they apply…not the milling forces.
Ultimately, we are far more worried about the actual material rigidity.
CNCkitchen is saying 50% nozzle diameter layer height, higher print temps, more walls is stronger for the way we use them…but we are making large parts that are not stressed much at all under normal use. So instead of printing the core for 72 hours to gain 10% strength on top that will never get used we typically tend to print giant layers that are more than strong enough and get it done in 12 hours.
Yeah of course a bolt can easily crush a print and I’m glad to hear that you thought about layer directions in the design! Smart.
Still haven’t really looked at that, one step at the time.
But then basically it’s all about printing speed with the higher layers, assuming the printer is setup good and don’t get insanely bad layer bonding of course…
And now when writing I’m thinking there should be a fair amount of torsional forces in the layer bonding of the core when routing??
Really looking forward to trying your design, going to be very interesting I have worked quite a bit on different industrial standard cncs for furniture and sign making, and of course don’t expect for the mpcnc that I’m printing (accidentally posted in the lowrider section somehow) will be getting close to those speeds and feeds. But I’m very excited to see what can be made on a low budget like this
Yes and no. The router transfers the load to the bearings, that load moves up to the nearest perpendicular rail, a couple inches at worst. Remember, this is at the top and bottom. I think it equally tries to spread the center open as much as twist it.
When you build it you will get to twist and tug on it and watch what happens. This is the 5th or 6th center section design for me and it took that many to get it right, each step along the way I would say the rigidity nearly doubled.