Question for anyone who has built a home gym in the UK

[Nockian]

Never buy any cyclically-loaded part made out of aluminum.

Doesn’t that depend on the MTBF ? Do aluminium pistons last as long as steel pistons ? Possibly not, but they last for thousands of cycles if they are designed correctly. Not wanting to start a huge discussion on it, I’m just drawn to query absolute statements in order to understand if they are true, or just perceived wisdom.

[Nockian]

We are using the LockJaw Hex 50mm collars, on Amazon. They work very well, but we just got them so I have no idea about lifespan.

Amazon.com

Did you happen across “the machine” lockjaw collar ? Aluminium, but not a split design, so it’s more like a competition collar but using a clip instead of a locking screw.

[Mark Rippetoe]

Doesn’t that depend on the MTBF ? Do aluminium pistons last as long as steel pistons ? Possibly not, but they last for thousands of cycles if they are designed correctly.

"Cyclic loading" refers to elastic deformation, where the shape of the part changes and then returns to its original configuration. Pistons are not cyclically loaded in this sense.

[Sib]

Did you happen across “the machine” lockjaw collar ? Aluminium, but not a split design, so it’s more like a competition collar but using a clip instead of a locking screw.

After reading the book several times couple, I found it on audible. Now I can listen to that soothing voice as I squat.

[Nockian]

"Cyclic loading" refers to elastic deformation, where the shape of the part changes and then returns to its original configuration. Pistons are not cyclically loaded in this sense.

Got it.

[AndrewLewis]

Cyclic-loading refers to a load that is applied, then removed, then applied, then removed, etc for many cycles. Elastic deformation is a necessary part of that.

The reason you should never buy cyclically-loaded parts made out of aluminum is that aluminum has a face-centered cubic unit cell structure. Materials with FCC unit cell structures cannot be designed for infinite life like body-centered cubic materials (like steel) can be. A steel spring clip can theoretically be designed for infinite cycles without fracture (or at least upwards 10^9 cycles which might as well be infinite).

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"S-N curve" and "Endurance Limit" are helpful Google-able terms

[Nockian]

Cyclic-loading refers to a load that is applied, then removed, then applied, then removed, etc for many cycles. Elastic deformation is a necessary part of that.

The reason you should never buy cyclically-loaded parts made out of aluminum is that aluminum has a face-centered cubic unit cell structure. Materials with FCC unit cell structures cannot be designed for infinite life like body-centered cubic materials (like steel) can be. A steel spring clip can theoretically be designed for infinite cycles without fracture (or at least upwards 10^9 cycles which might as well be infinite).

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"S-N curve" and "Endurance Limit" are helpful Google-able terms

It made intuitive sense that opening and closing a piece of aluminium would be problematic, but intuition is never very good in that regard.

[Sib]

Cyclic-loading refers to a load that is applied, then removed, then applied, then removed, etc for many cycles. Elastic deformation is a necessary part of that.

The reason you should never buy cyclically-loaded parts made out of aluminum is that aluminum has a face-centered cubic unit cell structure. Materials with FCC unit cell structures cannot be designed for infinite life like body-centered cubic materials (like steel) can be. A steel spring clip can theoretically be designed for infinite cycles without fracture (or at least upwards 10^9 cycles which might as well be infinite).

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"S-N curve" and "Endurance Limit" are helpful Google-able terms

Thank you

[Sib]

Doesn’t that depend on the MTBF ? Do aluminium pistons last as long as steel pistons ? Possibly not, but they last for thousands of cycles if they are designed correctly. Not wanting to start a huge discussion on it, I’m just drawn to query absolute statements in order to understand if they are true, or just perceived wisdom.

Nockian, you are becoming increasingly cantankerous. Are you OK?

[Nockian]

Nockian, you are becoming increasingly cantankerous. Are you OK?

I’m just asking questions. Andrew came up with a technical reason for not choosing specific materials in certain situations. I’d have been OK with “don’t buy it, because it breaks”. The technical answer was more intriguing. I would now disregard a product with that material and a cyclic element.