Yea, PLA is the stiffest of the home gamer 3d printing filaments. HIPS is stiffer, but you have to deal with the molten styrofoam smell when printing. This isn’t accounting for additives like glass fiber or carbon fiber.
Bill are you by chance a cyclist? I ask because I was under the impression that aluminum is more rigid than steel as well, since bike frames are that way. However, I learned that is not the case.
Steel is more than 3 times as rigid as aluminum. But why are aluminum bike frames so much stiffer than steel ones? It is because aluminum does not fail by bending (like steel), it fails catestrophically by breaking. Because of that, aluminum frames are made way thicker to maintain the same safety factors.
So under the same cross section, steel would be 3 times more rigid than aluminum.
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is there any MK8 mount for primo ?
Ryan has not release one nor is there one on Thingiverse I could find. You can use the Burly nut traps and the Burly universal mount on the Primo and then mount one of the Burly MK8 mounts from Thingiverse. The hole size and position in the Z tubing is the same between both machines.
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There is a difference between yield strength and stiffness. (and different ways to reckon what material is stronger/stiffer).
Steel’s yield strength is indeed ~3x that of Aluminum so for a given rod/bar/tube of the same dimensions you can load the steel one about three times as much before it fails. However Steel is 3x as dense as aluminum so strength-per-unit-weight would be a closer a contest than strength-per-unit-cross-section.
Since we aren’t interested in breaking our machines (or bikes) in half the relevant value for our purposes is the stiffness of the material rather than its ultimate strength. This is expressed as the Modulus of Elasticity (or Young’s Modulus) and there is also a 3:1 (give or take) ratio in stiffness between the two materials. But remember the density. A steel tube that is 1" in diameter w/ .039" wall thickness weights as much per unit length as an aluminum tube that is 1.73" in diameter and .068" thick.
This beam calculator (https://www.engineering.com/calculators/beams.htm) says that for a 24" tube loaded w/ 10lbs in the center the steel beam would deflect .092" and an aluminum one would only deflect .038" under the same load. So if you need to hit some ‘stiffness’ target (and you aren’t constrained by tube diameter (or surface toughness) you can save weight by using an aluminum part.
There is a further complication as Bender mentioned that Aluminum can fail a bit more suddenly (the metal generates fatigue cracks after lots of loading/unloading cycles) which might require larger safety margins. For use in an MPCNC the biggest issue is the point loads of the bearings require a very hard material to not be deformed under this pressure.
There is also material hardness, and the aluminum will be removed by the wear from the hard bearings. N/m the tube, the surface will be destroyed.
Welcome to engineering. Pick a few constraints and work your way forward.
In the case of a bike, you are looking for strength to weight ratio’s…next is probably rigidity. So you pick a giant aluminum tube, then squish it into an oval, or make a special shape. Light and strong. Tangent, Steel motorcycle frames are more sought after because aluminum frames flex too much (in older dirt bikes).
MPCNC, we need a rigidity to size ratio…next probably material hardness so the bearings do not deform the tubes.
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Thanks Frosty. I mainly wanted to dispell a commonly held misconception, that aluminum as a material is stiffer than steel.
Our conversation is centered around EMT (steel conduit) vs. ARC (aluminum conduit), so I plugged numbers into the beam calculator you linked, using the same 24" span and a 10 lb point load in the center of the beam:
3/4 ARC
OD = 1.05"
Wall = 0.107"
Deflection = 0.123"
3/4 EMT
OD = 0.922"
Wall = 0.049"
Deflection = 0.120"
So they both have about the same deflection in that loading condition. As Ryan has said though, the reality is a 3lb distributed load across the beam length.
I think it’s also interesting that machine frames are hardly ever aluminum, and that is because of a really interesting property called endurance strength. It basically says that for a steel frame, if it is designed for the stress to stay below a certain threshold, it can theoretically last forever. For anyone interested in material science, check out endurance strength. Steel is the only material that has it.
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Flex-free frames used to be the Holy Grail for GP bikes but these days it seems longitudinal stiffness with designed in and controlled lateral flex is the current thought, as likely affected by tire technology as anything else. And as in most forms of racing, just when folks get to thinking they’ve got it all figured out, a new fly will be tossed into the ointment and the hunt for those fractions of seconds in lap times will start all over again.
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The Wikipedia article on “fatigue limit” has a good explanation of this. It also identifies titanium as having an endurance limit like steel. Fatigue failures of aluminum is a real thing. I’m a cyclist and have personally had an aluminum frame fail. The particular frame was of the first generation of aluminum frames made in the 1980s. They are better engineered now and likely to last longer than mine did, but still an aluminum bike will never be something that can be used forever, and the same would be true for any use of aluminum in machines.
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Somewhere in the distant past of this thread, I seem to recall Ryan stating he was looking into making some minor tweaks of the 1" trucks &/or their clamps, as someone had a problem with them. Was that resolved? I don’t see any updated parts on the Prusa site, and TVerse isn’t working for me at the moment.
They are on the printer now, should be done in a few hours. 1mm standoffs on the stepper mount, nothing major.
The pen/drag knife mount is done as well, I will be taking pictures and releasing it later this evening.
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Cool - glad to know I wasn’t dreaming! Thanks!
Are the links on this page broken?
https://www.v1engineering.com/assembly/
Yeah, a lot of the obvious links are now out of date. Everything is being migrated to https://docs.v1engineering.com/
They seem to be working for me. Are you having problems with a particular one or all?
CORRECTION: I see now some are in-op after going down a layer or two.
What link are you using?
I’m eagerly awaiting a 1” EMT version.
Change of plans, I am printing 3/4" EMT parts now. When I make sure everything works as it should I will get them out to everybody.
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