Collars on the Bar: The Details

[Mark Rippetoe]

Pulling the article down until I can make the correction to the friction problem.

[AndrewLewis]

The problem of not selling ductile plates.

That's the only thing I can think of for why they'd do this.

I've been to Crossfits where they abuse their gray iron kettlebells for years, and I've never seen a fractured kettlebell.

[jfsully]

This is so weird. What problem does this solve?

However, my experience has been that ridged barbell sleeves slide less easily than smooth ones - which makes sense to me because interactions with smoother surfaces generally have lower coefficients of friction.

I have a cheap CAP barbell that came with some cheap plates. The bar has pronounced ridges on the sleeves (compared to the SS bar which has very fine low ridges) to the point where loading and unloading the bar makes a loud ZIP sound. I think that in this case the ridges do help plates stay on the bar, not because of the change in surface area or friction, but because there is significant slop in the ID of the plates, and they don't slide off the sleeves so much as wobble and "walk" down the sleeve during the course of a lift. The ridges grab the edges of the ID of the plates, and keep them in place a little bit. So there is more to the ridged/smooth issue than just friction and surface area, at least in some cases.

[Shiva Kaul]

I am not a tribologist, but I can confirm that the chromed+ridged sleeves on my Ohio Power Bar are both slippery and pretty.

[mitchless]

Is there a brand you recommend? I've seen various versions of the quick release plastic ones, but the ones they had at the local Y tend to wear out and get sloppy.

I really like the Rouge USA Aluminum collars. They hold great, and they're easy to operate.

Garage Gym Reviews has a fun video wherein Coop tests every collar in his possession, if you want to see how various options hold up to abuse.

[Soule]

Rust works pretty well.

[m s]

This is so weird. What problem does this solve?But idk JUST A GUESS LOL



This is true of translation, but when rotation caused by moment comes into play, it matters because location of friction changes the moment.

In the squat, for example, a plate that slides directly along the axis of the bar is only affected by the coefficient of friction and force imposed. Plates that "slide off" because they are moving back and forth orthogonal to the cross-section of the bar will move less if the plate is tighter to the bar because it's not just sitting on the top. Most of the bar on the sides are in contact with the plate.
I
However, my experience ha

You may choose an icon for your message from this lists been that ridged barbell sleeves slide less easily than smooth ones - which makes sense to me because interactions with smoother surfaces generally have lower coefficients of friction.

Plates that slide off are not necessarily "moving back and forth orthogonal to the cross-section of the bar". A plate with a very large inner diameter that will easily slide off, can do so without moving orthogonal to the cross-section. The same little area stays in contract with the bar whole sliding. I'm sure you can picture this in your head. However, now introduce some imperfections in the machining of the bar. This does cause the plate to move back and forth orthogonal to the cross-section as it moves along the axis of the bar. For the plate with the very large inner diameter, it doesn't matter. The plate moves up and down a bit as it slides, but the side opposite the point of contact never hits the bar. Now take a snug fitting plate with a smaller inner diameter. What happens as the plate moves up and down? It comes in contact with the bar even if it just moves a little, due to the snug fit. So now it is bouncing back and forth. And each bounce is another normal force between the plate and bar that adds to the force of friction opposing the bar.

So the area still doesn't matter. It's that the plate and bar are constantly colliding, adding to the normal force which resists sliding.

I think that might only be half of it though. Placing a plate onto a bar that that fit very snug, may deform the plate and the bar, which would apply a pressure to the other surface at all points of contact, and that pressure would add to the normal force as well.

that's my guess.

[AndrewLewis]

Plates that slide off are not necessarily "moving back and forth orthogonal to the cross-section of the bar". A plate with a very large inner diameter that will easily slide off, can do so without moving orthogonal to the cross-section. The same little area stays in contract with the bar whole sliding. I'm sure you can picture this in your head. However, now introduce some imperfections in the machining of the bar. This does cause the plate to move back and forth orthogonal to the cross-section as it moves along the axis of the bar. For the plate with the very large inner diameter, it doesn't matter. The plate moves up and down a bit as it slides, but the side opposite the point of contact never hits the bar. Now take a snug fitting plate with a smaller inner diameter. What happens as the plate moves up and down? It comes in contact with the bar even if it just moves a little, due to the snug fit. So now it is bouncing back and forth. And each bounce is another normal force between the plate and bar that adds to the force of friction opposing the bar.

Yes. "Not necessarily" is the key here. I didn't mean to imply this was the only mechanism of a plate sliding off a bar.

I think that might only be half of it though. Placing a plate onto a bar that that fit very snug, may deform the plate and the bar, which would apply a pressure to the other surface at all points of contact, and that pressure would add to the normal force as well.

An interference fit between the plates and bar would be obscene - any small change in room temperature would change the level of interference. On warm days, it would be impossible to load the plates. On cold days, it would be a close fit. The plates wouldn't shrink much but the bar would a lot.

If you're interested, check out "freeze fit" or "shrink fit". It's a pretty creative way to not have to hammer pieces into place.

[m s]

An interference fit between the plates and bar would be obscene - any small change in room temperature would change the level of interference. On warm days, it would be impossible to load the plates. On cold days, it would be a close fit. The plates wouldn't shrink much but the bar would a lot.

True. I forgot about thermodynamics.

[Fulcrum]

That's the only thing I can think of for why they'd do this.

I've been to Crossfits where they abuse their gray iron kettlebells for years, and I've never seen a fractured kettlebell.

you've never seen a fractured or cracked cast iron plate ?

Rogue came out with those new Made in USA plates, and just used ductile...
They made them a vintage deep dish design for 'reasons' ... maybe the ductile will make the lip hold up better.
They are cheaper than the grey-machined-iron (non-usa) plates they sell.

The cost is really no difference at a certain point when volume is really high.
Especially if its a made is USA plate, the because the bulk of your cost problems are 'merican labor, overhead, profit, admin, quality control costs, etc.