Are ALL Kirigami bed supports this weak and flimsy?

[ChrisA]

I'm building a V0.2 and just got to the point where you install the Kirigami bed support. The tabs that attach to the two Z-rails were badly out of alignment. I'd say "a few millimeters". There was just no way the holes could line up. I thought I'd have a hard time bending it straight. But no. I could bend those tabs by holding them with thumb and forefinger. I thought I'd need tools to bend the metal but it is so soft the danger is in over bending.

This means the entire pooint of the Kirigami is gone. It's purpose was to be stronger and more rigid than the printed ABS parts. But this is not the case.

If you look at the rear corners where the mount tabs turn there is very metal, a total cross scetion of 11mm x 2mm. The entitre fram, heat and bad is hanging by these tiny strips of metal. The reast of the frame is quite strong bu the critical part is so flimsy it can be bent with two fingers.

Perhaps itis flexible by design? Maybe so it will run without jambinmgof nbadly misalighn z-rails?

It also deflects under a light load, light finger pressure is enough to end the end of the bed a couple millimeters.

Did I just happen to get a bad/cheap one? Are other brands better?

I think I'll get one of these: https://www.aliexpress.us/item/3256805040703674.html

 

[Sandman50]

I have a LDO sourced kirigami. It's as solid as it needs to be.

IMHO, the real benefit is it removes the ABS parts between the slides and the bed support. So less plastic and it should be stiffer and more consistent over time. The bed is on springs anyway.

 

[ChrisA]

So, how thick is the metal in the LDO part, and is there any way you would know the kind of aluminum? Mine is 2 mm thick and the aluminum is very soft, not at all the same kind of alloy as the extrusions.

The problem is the design of the Voron plastic parts was not stiff enough so someone came up with an all-metal solution. The "real fix" would be a better printable design so there is no need for the all-metal part.

The problem to be solved is that the cantilever bed length is something like 6 or 8 times the vertical distance between the M2 screws that hold the bed to the carriage. So 1 unit of force at the end of the bed places 6 or 8 units of force under the heads of four M2 screws. There is VERY little surface area under the head of an M2 sockethead screw.

Maybe someone looked up the allowed tension on an M2 screw? It is not much. But the screw is not the limiting part. It is the plastic directly under the screw head. Tension forces on the screw could be reduced by using either the longer "type H" carriage or two type c garages on the rail. Steel washers under the screw heads would also multiply the load-carrying ability of the joint by quite a lot.

What I'm getting at is that there are ways to make a better plastic joint.

But I think for now the solution is to buy a better-quality all-metal part.

 

[Sandman50]

Unit is at home. Pretty sure it's steel, not AL. Have not put a magnet on it, it's also powder coated black.

 

[majic79]

I've just finished a Formbot v0.2r1 kit, and the kirigami bed it came with it's definitely Aluminium. I also had alignment problems, but because it's not that rigid, it could (and should) be corrected by aligning the surfaces and carefully moving the tabs into position. I think it's a good compromise on stiffness/weight (ally) without the potential softening issues of ABS at higher temps. Steel would work, but it would be a heavier piece (even if you make the flat stick thinner at the start) and no guarantee it'll align better

A stiffer/more robust solution would be to mill it from a suitable piece of bar-stock, but that's a expensive/wasteful operation.

 

[Yaaj]

LDO 0.2 here.
Alumin(i)um, 2mm. First month, had to readjust the thumbscrews every day or so ! Very disapointed... Could see the bed moving down under the extruded plastic pressure.
But after a little while, everything settled. Didn't adjust anything anymore. 3 months later and 300+ hours, I don't even watch the first layer nor play with babystepping.

IMHO, the weak point is there ; have no problems with printed parts, despite the fact they are made of eSun ABS+ :

 

[claudermilk]

LOD V0.2 kit here as well. It's plenty solid for me. When I initially built it I mistakenly used the wrong screws to attach it to the carriages. I used the next length up and they bottomed out before securing the bed. That drove me nuts until I figured it out and used the right screws, now it's rock solid.

 

[ineligible]

If I recall correctly, Siboor's kirigami bed is made out of steel, which would be a bit stiffer than the aluminium ones. And then there's also that option of the Fysetc bed that you've linked to.

Personally I'm using an LDO one and find it rigid enough. I guess there's also the option of doing a tri-zero or crucible mod...