Kraton About part tolerances in RC

[Barmaleus]

Hey all!

While double checking measurements of hinge pin mounts (https://www.arrmaforum.com/threads/ok-if-something-happens-to-these-i-am-done.70093/), I was astonished. Really.
The pins that go into the mounts (both front and rear) are 4mm (https://www.horizonhobby.de/en_DE/product/hinge-pin-lower-4x63.5mm-2/ARA330731.html).

One would expect the mount holes to be sliiiighly bigger for a tight fit. After all, this is a critical part of the car that holds together a lot of important stuff.

The front mount: 4.02mm and 4.01mm. Looks absolutely reasonable.
The rear mount? 4.36mm and 4.40mm. The holes are 9-10% larger than they should be.

So I am wondering, am I too picky? Do you think such part tolerances should be acceptable?

 

[332_RC]

I've noticed that. Is it because the rears are at a angle for the toe in?? Since the holes are machined in straight? I'm guessing?

 

[Barmaleus]

I've noticed that. Is it because the rears are at a angle for the toe in?? Since the holes are machined in straight? I'm guessing?

I am not a mechanic, but two thoughts:
1. Doubt the hinge mount dictates the angle.
2. Theoretically, if it did, the holes would still be 4.0xmm, just at a slight angle.

I might be wrong of course.

 

[neighborhater383ci]

I am not a mechanic, but two thoughts:
1. Doubt the hinge mount dictates the angle.
2. Theoretically, if it did, the holes would still be 4.0xmm, just at a slight angle.

I might be wrong of course.

You are wrong, of course! If the holes were 4. Whatever tighter tolerance, you would get one pin in and never get the other in because it’s angled the exact opposite way

/\
———

The opposing angles mean that the face of the retainer facing where the pins would meet in space would have to have the pin holes x amount closer together compared to the front face which would have the ends of the pins sticking out, which being angled apart would be a farther distance apart

 

[Dales396lt4]

Think how much stronger it would be if the holes were drilled on the right angle rather than being drilled oversized, so they can sit in the whole crooked. I think this would be a strong selling point for someone who made these parts. My question is do the aftermarket adjustable tow blocks from the limitless, infraction and Felony fit on a K6s

 

[neighborhater383ci]

Think how much stronger it would be if the holes were drilled on the right angle rather than being drilled oversized, so they can sit in the whole crooked. I think this would be a strong selling point for someone who made these parts.

It would be physically impossible, make a v shape with your hands fingers angled away from each other and put a zip tie half way down on both of your index fingers so it’s taunt, now try to get that zip tie to fit over the tips of your fingers holding the same angle. Although a lot smaller of a difference, the very tip of the pins sticking out of the chassis are farther apart than the point where they enter the chassis. Pic over exaggerating the effect

not saying arrma couldn’t have made it a tighter fit by some but they definitely couldn’t make it as precise as the front that has no built in toe angle

 

[lee82gx]

Hard to really see but usually metal stamped parts have pretty tight tolerances. Much tighter than your caliper manual measurement variations. I’m speaking as a mechanical engineer who has designed more stamped parts than I can remember.

The picture shows you are probably measure one on the inner side and one on the outer side of stamping, so there is likely a drafted shape of the hole being designed, so that it is tapered. For what exact purpose is not sure as I don’t have the whole assembly (I no longer have any 4x4 Arrma). But at the very least drafts appear naturally due to metal stamping mass production process

 

[Hector_Fisher]

The reason is 1) cost and 2) because tight tolerances aren't needed. Tighter tolerances cost more and more money at an exponential rate, and that's value that you just wouldn't get back out of an RC for regular bashers.

Most of the race kits will have tighter tolerances and less slop, and it shows in overall quality. But they also cost $$$. And most people looking to bash don't really find any value in buying a race kit to bash for the extra handling and performance and would rather spend half the cost. Just my two cents.

 

[Barmaleus]

You are wrong, of course! If the holes were 4. Whatever tighter tolerance, you would get one pin in and never get the other in because it’s angled the exact opposite way

/\
———

The opposing angles mean that the face of the retainer facing where the pins would meet in space would have to have the pin holes x amount closer together compared to the front face which would have the ends of the pins sticking out, which being angled apart would be a farther distance apart

Ahhhh. Right.
Welp, this is why I am not a mechanic