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Alawadhi

Making of a Cyr Dumbbell replica

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Alawadhi

Hello guys

I have ordered few dumbbells which are coming to me as we speak and one more to be ordered soon for my comp. But I need one more dumbbell. Need some help in making a dumbbell. I found a good company that will do a dumbbell out of a CNC lathe tooling and is a single piece (not a two globes then molded to a handle). So I need the calculation of the parts. I want to do a Cyr Dumbbell replica (almost). 117 KG. I want the dumbbell in steel. The handles should be 51MM thick and 4.5 Inch long (yes 4.5 inches not 4). A globe dumbbell like the inch. So, what is the length of the full dumbbell? What is the length of the globes or spheres? The circumference of handle, spheres? Will the specs be same if I decided I want to go Stainless? Thanks in advance!

Edited by Alawadhi
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Climber028

Can't do this at work right now but can get you the info tonight if nobody else chimes in.

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honk

I used to have a CAD-model for this...

If Chris doesn't want to, I'll calculate it with pen and paper for you. 🙂

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honk

I'd go for a globe diameter of 24,06cm :)

Edit: that's based on 7,9kg/dm^3 for 18-8 stainless steel also known as V2A. 

Edited by honk
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Alawadhi

Thanks a lot guys :rock I think @climber511 can give his input too. Chris?

Edited by Alawadhi

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Alawadhi
15 hours ago, honk said:

I'd go for a globe diameter of 24,06cm :)

Edit: that's based on 7,9kg/dm^3 for 18-8 stainless steel also known as V2A. 

Christopher, if it was Stainless Steel will the calculations be same?

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climber511
3 hours ago, Alawadhi said:

Thanks a lot guys :rock I think @climber511 can give his input too. Chris?

Sorry but this is beyond my abilities - sounds like  great project!

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Climber028
8 minutes ago, climber511 said:

Sorry but this is beyond my abilities - sounds like  great project!

Just username confusion again.  I really should change mine at this point haha

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Climber028

Okay so you want that specific handle size and a target weight of 117kg. What you're trying to confirm is the diameter of the globes and the total length. Is there anything else you need or do I have everything?

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Alawadhi
On 1/24/2019 at 7:35 PM, Climber028 said:

Okay so you want that specific handle size and a target weight of 117kg. What you're trying to confirm is the diameter of the globes and the total length. Is there anything else you need or do I have everything?

That's it. I think I have everything already. But today I was told they need the dumbbell length too. Total length.

Others are helpful. Told me Diameter times 2 plus handle length. Which is only logical. Just to reconfirm.

Edited by Alawadhi

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Stanislav
34 minutes ago, Alawadhi said:

That's it. I think I have everything already. But today I was told they need the dumbbell length too. Total length.

Others are helpful. Told me Diameter times 2 plus handle length. Which is only logical. Just to reconfirm.

Just to remind total length = 596.48 mm or 59.648 cm or 23.4835 inches

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Alawadhi
8 minutes ago, Stanislav said:

Just to remind total length = 596.48 mm or 59.648 cm or 23.4835 inches

Thanks!

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Climber028
5 hours ago, Alawadhi said:

That's it. I think I have everything already. But today I was told they need the dumbbell length too. Total length.

Others are helpful. Told me Diameter times 2 plus handle length. Which is only logical. Just to reconfirm.

It's not exactly twice the diameter plus handle because the globe goes into the handle a little bit, so you need to subtract that distance from each side. Using the diameter given above of 24.06cm that would give final dimensions of:

  In cm
Handle Thickness 2.007874016 5.1
Handle Length 4.5 11.43
Globe Diameter 9.472440945 24.06
Total Length 23.22963163 59.00326434

 

This would weigh 116.45kg,  using 0.284lb/in^3 for the density of steel. 

My numbers for a 117kg bell would be:

  In cm
Handle Thickness 2.007874016 5.1
Handle Length 4.5 11.43
Globe Diameter 9.4876 24.098504
Total Length 23.26030164 59.08116616

 

It's as exact as I can get without knowing the specific type of steel, there's thousands all with slightly different densities but I don't think the variance would end up being more than about 3/4 of a kilo at this size. 

Edited by Climber028
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Alawadhi
38 minutes ago, Climber028 said:

It's not exactly twice the diameter plus handle because the globe goes into the handle a little bit, so you need to subtract that distance from each side. Using the diameter given above of 24.06cm that would give final dimensions of:

 

  In cm
Handle Thickness 2.007874016 5.1
Handle Length 4.5 11.43
Globe Diameter 9.472440945 24.06
Total Length 23.22963163 59.00326434

 

This would weigh 116.45kg,  using 0.284g/cm^s for the density of steel. 

My numbers for a 117kg bell would be:

  In cm
Handle Thickness 2.007874016 5.1
Handle Length 4.5 11.43
Globe Diameter 9.4876 24.098504
Total Length 23.26030164 59.08116616

 

It's as exact as I can get without knowing the specific type of steel, there's thousands all with slightly different densities but I don't think the variance would end up being more than about 3/4 of a kilo at this size. 

Thanks a lot. But this will be made of a single steel. Nothing cut and molded into another. I mean was it taken into consideration as the handles won't be going in the globes?

Edited by Alawadhi

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Climber028


Best picture I could find on google, but imagine if you had two spheres and just stuck them to a handle, it would be all wobbly and wouldn't work at all. The globe of a dumbbell is not actually a sphere, it's a sphere with a small section missing. In the photo, you would subtract length M from the diameter of each sphere, then you also need to calculate the volume of that section, called a spherical cap. Now this is a small difference, it only comes out to be about 10mm in total length, and maybe 200 grams of weight. These things don't matter when you're lifting but they make a different if you're trying to build one. 

Sphere.svg

Edited by Climber028
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Alawadhi
1 minute ago, Climber028 said:

71_2.svg
Best picture I could find on google, but imagine if you had two spheres and just stuck them to a handle, it would be all wobbly and wouldn't work at all. The globe of a dumbbell is not actually a sphere, it's a sphere with a small section missing. In the photo, you would subtract length M from the diameter of each sphere, then you also need to calculate the volume of that section, called a spherical cap. Now this is a small difference, it only comes out to be about 10mm in total length, and maybe 200 grams of weight. These things don't matter when you're lifting but they make a different if you're trying to build one. 

Understood. Thanks. The company said they'll do it in MATERIAL GRADE ALLOY STEEL 6850. How good/bad is that?

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Stanislav
1 minute ago, Climber028 said:

71_2.svg71_2.svg
Best picture I could find on google, but imagine if you had two spheres and just stuck them to a handle, it would be all wobbly and wouldn't work at all. The globe of a dumbbell is not actually a sphere, it's a sphere with a small section missing. In the photo, you would subtract length M from the diameter of each sphere, then you also need to calculate the volume of that section, called a spherical cap. Now this is a small difference, it only comes out to be about 10mm in total length, and maybe 200 grams of weight. These things don't matter when you're lifting but they make a different if you're trying to build one. 

this deviation is not so critical, by the way, could you specify steel density you took into account while was calculating in kg per m^3.
In general steel density = 7850 kg/m^3

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Climber028
8 minutes ago, Alawadhi said:

Understood. Thanks. The company said they'll do it in MATERIAL GRADE ALLOY STEEL 6850. How good/bad is that?

Just about any steel used in manufacturing is far stronger than the needs of a dumbbell, the only different it changes is calculating the precise weight, but even if you use the average steel densities you would be off by less than a pound in either direction. 

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Climber028
7 minutes ago, Stanislav said:

this deviation is not so critical, by the way, could you specify steel density you took into account while was calculating in kg per m^3.
In general steel density = 7850 kg/m^3

I used 7861kg/m^3. I made a mistake earlier the 0.284 was actually lb/in^3. Getting confused going back and forth between standard and metric. That difference would only amount to like 20 grams of the final dumbbell, I agree these are very minor but if you're a machinist the measurements probably need to be precise.

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Raymond

Did you ever get one of these made?

I'm thinking of having a circus dumbbell made myself, not a beast like the Cyr dumbbell though  that would be an ornament for me. I was thinking of making one with a handle threaded on both ends and screwing the globes on so I could upgrade to heavier globes if I ever got to the stage where I could lift the first one. I was a machinist in what now seems like a past life.

I modeled one with your dimensions (as 1 solid piece) using Onshape and I calculated the mass for a few different materials.

18-8 ss - 1188951.041g  @ 8.030 g/mm^3   - 118.9kg (rounded)
Steel -  116284.542g  @ 7.850 g/mm^3  - 116.3kg  (rounded)
Brass  - 125765.173g  @ 8.490 g/mm^3  -125.75kg (rounded) This can vary quite a bit because brass can have a lot of different compositions and the mass can changes depending on the composition.

Most steels (except for some specialty steels) are very similar to the density myself and the others have given so the final weight will be very similar with almost any steel. I'd just go for ordinary mild steel. I'm not suggesting anything @climber said was inaccurate, mass calculations are largely based on the standards charts you use to calculate mass and different sources quote slightly different values.

 

 

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Climber028

I've always wanted to have a thick handle with interchangeable globes, even additional handle sizes too would be a crazy good training tool and a space saver, tho not much of a wallet saver. I don't even think about a brass bell that's huge bucks but would love to see someone else do it. 

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Raymond

Yeah I imagine it wouldn't be cheap, screwing the second globe on could get a bit tricky too. I could turn the handle myself and then get the globes made by a machine shop, At least that way my Mrs wouldn't see the full amount on the credit card statement all in one hit.I wouldn't be able to lift for a while either, so I might start by making pipe cast with lead in the center that I can load with plates or something similar to progress my way up to it.

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