X1C: Torsional rigidity concerns

I'm a little surprised in the X1C's lack of torsional rigidity. Try this little experiment: place the X1C on a solid surface and open it up as if you're about to use it. Then lift the front edge of the laptop, with the rear still resting on the table/ground/whatever. Then grasp the front corners with index finger and thumb and push down at one corner while pulling down at the other. TWIST!

If yours is as bad as mine was then tightening the chassis screws may help. The problem here, which is very surprising to me, is that the top keyboard surface is not tightly attached to the bottom of the chassis so the top can just slide over the bottom and there's little resistance to twist. You can actually feel the top sliding over the bottom if you put a finger on the edge. Mine was *really* bad at first because the chassis screws weren't fully tightened. Now it's a little better but not fully alleviated and I don't want to over-tighten the screws and crack the case.

This is sort of a nitpicky thing but for a thinkpad you sort of expect a certain level of rigidity. Mil-Spec? Really? I don't think so.

 

Imagine what it will be like in three years.

 

Considering loose screws, I'm betting someone at the factory made a mistake instead of a flaw in design.

Notebookcheck said the chassis

i.e. no problems with torsional rigidity.

I would bring up this issue with Lenovo and see what they say. I would say you have a faulty unit.

 

Yes I remember reading that in reviews which makes it even more puzzling. Could someone else try this with their X1C and report back?

I'm also confused about this internal "roll cage" that has been talked about. I've opened up another X1C and saw no sort of "roll cage" or any gusseting that could resist twisting forces. Of course with a machine this thin there just isn't room for much bracing in there.

My screws are as tight as they can be. Any tighter and I feel like I might risk cracking something.

 

I just tried this and didn't notice anything that seemed at all unusual to me. But maybe I'm not doing exactly the same thing (or maybe we just have different expectations).

If you could take a photo (or better yet a video) I could tell you whether mine is different from yours.

 

On the topic of roll cages, I believe the X1C has a "rollcage" in the style of the X2xx series roll cage, i.e. combined with the bottom skin as one big piece of magnesium.

 

I don't think that's normal. From what I see on mine, its only the carbon fibre that can't resist torsion (i.e. the screen/lid). Otherwise, the magnesium base plate seems pretty solid

 

Carbon Fiber doesn't resist torsional forces that well, since the carbon fiber is much like the string which is strong in tension, and weak in compression or torsion. So in carbon fiber composite the forces of torsion is resisted by the resin binding material (i.e. epoxy) and some of the carbon fiber if the weave is complex enough (i.e. multilayer diamond shape). But much of the torsional resistance would depend on the quality of binding material and time/method given to cure it, if they are used in simple flat sheet form.

However, you can introduce various complex shapes (i.e. honeycomb, corrugation) into the carbon fiber chassis to increase their torsional rigidity. But these shapes would add to the cost of producing these components, it would also add thickness.

If Lenovo want to spend a hell lot of money, they could use cobonded structure for the lid, with several layers of carbon fiber weave in multidirection, then in strategic areas bond layers of aircraft grade aluminium sheets. But these are very expensive to make, like 50,000 USD per meter square.

Toray to Boost Borrowing on Demand for Fiber Used in Boeing 787 - Businessweek <-- this is what Toray (they also make carbon fiber or shredded carbon fiber for ThinkPad chassis since at least T22) is doing for Boeing 787 wing, see the corrugation? this adds torsional rigidity!

 

Bi-layer, multi-strand carbon fiber does not add that much expense other that design R&D. Carbon fiber strength is unidirectional. Designers have known that for 20 years. Bi-directional carbon fiber is the standard in applications that require multi-axis strength. I would be surprised if it is not incorporated into the X1's design. Carbon reinforced epoxy can flex signicantly and not fail. My guess is that the designers have properly tested their designs and they are stronger than the seem. I've heard this same debate in multihull racing. Carbon\epoxy catamarans feel flimsy but take an incredible stress load without failing.

 

I was under the impression that OP was complaining about the torsional rigidity of the lower chassis, not the display assembly. That is made of magnesium alloy as usual I believe.

 

I don't have an X1C but I thought that the complaint was about the internal chassis and rollbar, which are supposto be built from carbon fiber. That is where I would worry least about the strength of carbon fiber. The real weakness of carbon fiber is that it does not handle impact very well. I would not be surprised to see a lot of impact fractures on this unit, compared to a more maleable metal alloy like magnesium.