God awful bed heatmap
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@wyvern Just follow the documentation, it's super simple. Now I'm ripping my hair out figuring out how to fix this because a linear rail won't work.
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I have a Hypercube Evolution. Started with 10mm hollow carbon rods for X but quickly replaced them with 10 mm hollow steel rods (ie 10 x 6 tubes) - much better. I also have 12 mm Y rods and 16 mm Z rods so the only measurably deflection is in the X rods. Over a 250 mm bed there is slight deflection but it is acceptably small with no need for bed compensation (Yet ?). Your demands for precision may vary. I also increased the X rod spacing to 90 mm to help with X carriage rotational stability.
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@garis I have 8mm rods on everything, including Z, but there are 4 rods on Z so it should be fine. Why did you move from carbon to steel? Seems like carbon is better from what I have read. I think I'm going to go with 12mm carbon tubes on the X and 10mm steel rods on the y.
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@surgikill
Carbon fiber has a good deal of flex and low frequency natural resonance, and the surface is not made to have bearings/bushings glide on it- it's just epoxy.I have worked with a lot of CF with R/c and race drone frames, even designed a couple frames myself, it's the best if you need light and ridged, but high-grade aluminum and steel are stiffer and stronger.
A large sized steel tube would be a great compromise of stiffness and weight.
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@surgikill I encourage you to go steel tubes. I did the stiffness comparison of carbon vs steel but the data I found or the type of carbon fibre I got from AliExpress didn't line up. End result is steel is much better. Perhaps thinking on the go hear one X rod of large diameter to reduce sag and a smaller one as the helper. Also the X carriage has a tendency to rotate around the X directions so having the nozzle as close as possible to the lower X rod is preferred.
In respect of Y and Z axes I guess you are committed. For future reference (!!) I see no reason to try and finesse those diameters. The only dynamic mass penalty is a slight extra on the Y bearings. For Z the 4 rod solution makes no sense to me. The best solution whether it be for single or double Z screws is 2 Z rods as big as you can fit. For double Z screws the Z rods should be in line with, and outboard of, the screws with a redesigned bed bracket. This allows easy precision assembly, less "over-constrained" z bearings, and hence lower chance of bearings binding, and improved bed alignment and stiffness in the Y direction. The Hypercube Evolution I think is a useful design concept, having improved on the original. However further design enhancements from Scott's version is necessary before it matures. As people simply extend the XY dimensions without understanding the mechanics (mass, acceleration, flexibility etc) leads to unhappiness. I speak as a mechanical person and try and avoid all the electronic corrections where possible.
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So I put a mirror on my bed (mirror side down, used the matte back piece.) and this is what I got. Definitely sag.
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@garis The 4 rods are for the 4 lead screws. There is a rod near each lead screw. Only reason I am leaning towards carbon is due to the weight flexing the Y rods. That's my largest area of deflection right now, and the 10mm rods won't stiffen it up tremendously. What's the weight on 12mm steel tubes?
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I hope I am understanding you - You are concerned about the mass of the X assembly including X rods causing deflection of the Y rods? If that is the case just go big on the Y rods and make them solid - easy to get and cheaper than tubes but normally cost is not an issue here. There is no performance penalty for big Y rods as they are stationary, just the added mass of bigger Y bearings which isn't normally a concern. ie there is no complex engineering trade off here. Going from 10 to 12 is a big step up in stiffness and there is negligible deflection from their own mass. Or go to 14 or 16mm and then you won'y be able to measure any deflection. Only the X rods need to be optimised.
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@garis In a CoreXY printer, the mass of the X assembly not only affects deflection, but it also affects things such as acceleration and resonance. You can watch this video here. I can't just go throwing 16mm steel rods on everything unfortunately. I also can't go too large on the Y rods due to the fact that I would have to once again redesign large portions of the printer. Also, what steel/aluminum tubes do you recommend? https://www.youtube.com/watch?v=AKTvykTPjQw
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have a look at this: https://www.thingiverse.com/thing:2839395
it uses mgn15h for the x axis and its very strong. however it does add quite a bit of weight.
