Clutching Power vs. Part Color

[DrJB]

I was building a contraption (Platonic Solids) using a combination of the parts below

 

I had gotten a large number of the last one in 'pearl gold'. Such color however is made of a different/softer plastic than other typical colors, and this results in the mating parts having very little clutching power.

Of course TLG is very well aware of this, and they simply cannot design different molds for different materials. The point here is, when you're planning your next project, choose your colors 'wisely'.

In any event, what I found is:

1. Highest clutching power - trans colors

2. Typical clutching power - typical solid colors

3. Lowest clutching power - pearl gold and most parts used in the Bionicle sets

Any member on here with expertise in plastics cares to comment?

Edited December 15, 2022 by DrJB

[Saberwing40k]

I'm not an expert, but I do know that transparent parts are made out of a different kind of plastic than the opaque ones. I think it's actually a kind of polycarbonate, versus ABS for the standard parts. Indeed, Lego actually has rules against using certain kinds of connections with transparent parts due to the amount of clutch power and friction the PC parts can have, especially against each other. As detailed in this presentation:http://bramlambrecht.com/tmp/jamieberard-brickstress-bf06.pdf

So, your results fit with this. However, translucent plastic is more brittle than ABS, so that's something to consider.

I know that some metallic Bionicle parts look and feel different than ABS parts, but I don't fully know what kind of plastic it is. It also seems to be a lot softer and bendier than ABS, but not rubber, or overtly flexible, like some spear elements. Pearl gold must also be a similar kind of plastic, but I can't name what it is.

[DrJB]

Thank you for the info and the link. You're absolutely correct, If I recall, the trans colors are based on acetate (bio-degradable plastic from wood sources), most parts are made from ABS, and the soft Bionicle only God knows ... It seems they used soft plastics for Bionicle for durability considerations and the relatively 'younger' audience.

Edited December 15, 2022 by DrJB

[Jurss]

I have noticed that in black beams this part turns more freely than in gray beam f.i.

Then some combinations of these rims and tires

and

are not firm. In some combinations rims slips in tire.

[Kostq]

9398 had it's rims and tires slipping too. The bigger ones than the above.

[2GodBDGlory]

5 hours ago, GTS said:

9398 had it's rims and tires slipping too. The bigger ones than the above.

An easy solution to that is to find some small rubber bands and put them in the bead of the rim. I did that a lot on my Racing Small rims, though ones large enough for those other rims, yet small enough to fit in the bead, might be hard to find.

[Alex Ilea]

Noticed that all of the pins and axels since 2020 got much softer. I keep them separate from my good old pins.

[lmdesigner42]

Same here. I noticed most of the pins in my 42125 seemed substantially weaker when I built it, and after disassembly have kept them all in a separate box. I'm not sure if I'll use them for anything, but it doesn't seem right to toss them either.

[N-4K0]

I too feel the difference in grip towards the weaker side in the pins as well as pins with pinhole, especially for the pin/pinhole parts it annoys me, but I've had these and the 3L blue pins crack over time and if this softer plastic can prevent cracking, I guess it's an aceptable trade-off even though I prefer stronger grip.

I also feel the difference in grip depending on the liftarm color, the same pin can have noticeable difference in grip between e.g. LBG/DBG and black liftarms.
The most annoying thing to me however is the significantly weaker grip in the axle holes of parts like the 2L axle/pinhole beams and the #1 connectors. The 2L beams feel like they'll almost slide off the axle...

Edited December 16, 2022 by N-4K0

[DrJB]

On 12/16/2022 at 5:51 AM, N-4K0 said:

... The 2L beams feel like they'll almost slide off the axle...

Interesting that you mention that. From my experience, the thin 2L lift arms have very strong clutching power, and after sitting for some time, they become very difficult to move. Also, I have not bought a new lego set for the past 6-7 years, so could be that your experience and mine are due to different mold generations. Also, those 2L thin liftarms tend to be amongst the most durable. In contrast, the 4L thin arms tend to crack rmore often.

Taking a slightly 'scientific' approach, the clutching power should be a combination of at least 2 parameters:

1. The fit between the two mating parts (e.g., H7g6 for the mechanical engineers) - depends on shrinking properties when plastic comes out of mold.

2. The friction coefficient between the two parts - depends on the actual plastic materials and the surface finish

This brings out the realization that Lego is way more than just a toy company, they must have chemists in there who know a lot about plastics. We tend to give a lot of credits to the designers, but there must be a large number of engineers (manufacturing, process, mechanical, chemical, ...) who do not get any visibility at all.

Edited December 17, 2022 by DrJB

[N-4K0]

17 hours ago, DrJB said:

Interesting that you mention that. From my experience, the thin 2L lift arms have very strong clutching power, and after sitting for some time, they become very difficult to move.

I just have to clarify that I was talking about the regular thick 2L axle/pinhole beams, not the thin ones, in case it wasn't clear 

I have the same experience as you with the half beams although I generally feel like the axleholes in those, of all variants, tend to crack too easily.
I appreciate the stronger clutching power, but I'd rather have weaker clutch if it means the parts won't crack, though the axlehole clutch in the thick 2L beams are way too weak IMO.

Edited December 17, 2022 by N-4K0