LR3 in Carbon Fibre PETG?

Thoughts? Seems to be available for a great price and I already have the steel nozzle.

Supposed to be 2 to 3 times stiffer than PETG but I can’t find anything comparing it to PLA.

Well, there’s a base comparison for PLA versus PETg, so the CF PETg should be more rigid than regular PLA. Of course a real head-to-head comparison would be better.

I did my LR3 in PLA, but do most of my printing in PETg Foodsafe PETg for that matter, since I end up with a lot of stuff that lives in the refrigerator holding food, or ice… I did not opt for CF reinforced stuff, but went with base PLA.

The largest load, so far as I can see is in the beam for the LR3, with the second largest load being the XZ plates. The XZ plates can be milled from metal, aluminum or steel are available from the V1 store. Much of the actual stability of the beam comes from the strut plates, through the braces. The weakest link there is probably the strut plates, but the braces are certainly important.

If I were concerned about rigidity of a potentially more flexible material, I’d probably just add an extra brace or two to the main beam design, and call it a day.

The XZ plates could be printed with extra infill, but it’s diminishing returns past about 70% or so. Still, I’d probably print them in the CF PETg and if there are any identifiable issues, maybe replace them with milled metal. I can say that I have not identified any problems with the PLA XZ plates that I have, but… I’m replacing them with steel anyway, and now, I know that there wont be a problem.

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Good to know… I had some rigidity and strength issues with the LR2 but wasn’t sure where they would crop up on the LR3. Not sure if I have the printer size to print the plates. I see you can get carbon fibre sheets various thicknesses at reasonable prices these days too.

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CF sheets are very bendy, not very rigid at all. It’s being flexible like that that gives them their tremendous yield strength – they don’t crack and break when flexed.

The YZ plates could be printed on a larger printer, but I think they’re way better off being milled. I expect that 12mm plywood or MDF is going to be very good for stiffness, particularly when you consider that it’s being reinforced with 2 vertical steel bars being bolted to each one. If you already have a LR2, it makes a lot more sense to mill parts, but while I am considering acrylic, I don’t think that I’d go with CF. Too hard on the tools, and no strong advantages IMO.

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Disclaimer: I’m not a an engineer. This is all hearsay!

I used 3DXTech brand CF+PETG in my LR2 refresh and posted about it here. After 2 Years, LR2 Gets a Rebuild in Erie, PA

You’ll even notice a remix of your endstop blocks on it! (at least I think you designed them)

Here’s some data sheets. I couldn’t find a bog standard PLA data sheet. This PLA blend mitigates some brittleness.

The basic low down is that, on paper, CF+PETG is stronger and more rigid than PLA which is represented by the tensile modulus and flexural modulus respectively. Other benefits are a much higher heat tolerance and the superb layer adhesion you get with PETG. It’s also surprisingly easy to print and the CF acts like scaffolding making overhangs look great! And damn that matte finish looks cool…

If heat tolerance doesn’t matter to you, how about CF+PLA? Not as strong as PETG but more rigid than both.

If any of that matters for the LR3 I don’t know. But you wouldn’t be making a mistake by using CF+PETG on your build. Just make sure you get the quality stuff like 3DXTech. Cheap stuff might just have pulverized CF for a matte finish.

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I won’t comment on which parts would benefit from CF filament, but I will add to the general CF discussion. I agree, avoid cheap CF and stick to 3dxtech and the likes. They make actually improved engineering materials, not just marketing gimmicks. Also, carbonX PLA-CF is yeah, stiffer than their PETG-CF, but I’ll add that it is kinda hard to print with an all metal hotend. If you have a teflon lined heatbreak available, I’d use that for the PLA-CF to avoid jams. Also, I didn’t know this until the other day…

CarbonX PA12-CF is actually stiffer than CarbonX PLA-CF?! It ain’t cheap by any means, but it has me thinking… my primo core clamps and z motor clamps… good targets for that stuff. That’s got to be the ultimate filament for CNC parts I’m thinking, other than like metal printers and stuff.

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Mine is printed in cfpetg. Haven’t assembled it yet though. Need to make a table first, and that’s not going to happen until a bit after we get back home from the mrrf trip. gotta save up the monies.

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This is opposite to my reading… a 5mm CF plate should be more rigid than a 6mm aluminum plate. If you start comparing by weight the difference is even bigger. It sounds like pretty awful stuff if you wind up with the fibers getting into your skin/eyes/lungs though which is the main reason I am leaning away from it.

http://www.dexcraft.com/articles/carbon-fiber-composites/aluminium-vs-carbon-fiber-comparison-of-materials/

My only concern with PLA-CF is strength… my problems with PLA have been failures not bending.

You guys are right about the cheap CF-Petg it looks a little sketchy. I can count on the filament costing double PLA if I went with some more mid-grade filament instead of the cheap stuff.

I’m actually printing mine with CF-PLA, 0.12mm layer height. I think if you build it right where it doesn’t need to flex as much to compensate, you might be fine. I’m also printing mine with an infill multiplier so it’s less likely to crack.

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I think you should be in good shape… to be fair I only had issues with one part on my LR2 and I expect there will be no issues on a LR3. I’m looking at overbuilding my LR3 since I wound up spending so much time getting my LR2 dialed in to a crazy degree probably no one else is bothering with.

My primo has a couple parts that like to crack if you’re not very careful. For those CF-PLA may not be the best idea, vs PLA or CF-PETG.

@wachpwnski , 0.12 and it doesn’t clog? That’s not a good sign for the quality/quantity of CF in that filament. Most of the good stuff requires at least 0.2 layers or more, due to the high concentration of long virgin CF fibers in it. The stuff with recycled CF powder is also sold as CF… there’s no laws against that form of advertising, so you just have to know who the legit vendors are.

@truglodite Whoa, we don’t make fun of the CF quantity of another man’s filament. :joy: It’s Atomic Filament’s CF PLA, I’m pretty sure it’s good because I can occasionally see wisps of it, and they are like 10mm long.

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Yea, Atomic uses milled cf. I’ve had stuff in the past that just uses powder. It’s not as strong, but it does print nice. That’s one of the nice things about the fiber infused filaments, they generally don’t string.

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@wachpwnski , lol sorry yeah that was off base for sure on my part… sounds like I need to check out atomic filaments actually. Cheers!

@tailslide I’m thinking about doing the same with mine. The 4ft x 8ft sheet of carbon fiber to use for strut plates is going to be like 800-1500 bucks here in the US, and then I will have to pay someone to waterjet it because I don’t want to eat that carbon dust.

If you’re interested, I started a build log of mine so far: Lowrider V3 - Carbon Fiber by Wachpwnski

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Aliexpress has 5mm 400mmx200mm carbon fibre plates for like $50 so it’s not too bad if you just want to do the side plates. Also ali express has places offering CF machining I’m guessing cheap.

I’m looking to use it for the strut plates, I don’t need to make the XY or XZ lighter.