Reply With QuoteI see that the image isn't clear. I had to downsize it to bring it under the allowed limit of 19.5 kB.
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Attempt to design a barbell during lockdown
After placing orders for a power rack and bench on a local workshop, I am now planning to make a 'proper' barbell with spinning sleeves because I am not able to find one in any of the local shops. All good barbell manufacturers of my country are in states that are locked down and it looks like I won't be able to order one anytime soon.
Here are my questions:
1) Is the basic scheme shown in the attached figure alright? The scheme is based on what I saw in this Rogue Video:YouTube . (Shim is not shown but I will add it if there is any loose play after the assembly). I will take care of engineering tolerances, fits and finish while preparing the engineering drawings for the workshop. What I would like to know at this stage is that I am not missing anything serious.
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2) What is the recommended grade of the steel?
I checked with a few steel suppliers in my city. Only available high strength steel options in this size are EN-18 (yield strength 35 ksi, tensile strength 80 ksi), EN-24 (yield strength 90 ksi, tensile strength 120 ksi) and super duplex steel (terribly expensive and out of question). In comparison, the tensile strength of Ohio bar is 190 ksi. Since I am unlikely to pull anything beyond 180 kgf (ever), is it okay to go for EN24? Any other material might have to come from another state.
3) What is the engineering specification for the knurl on a typical bar? I prefer to have some medium to aggressive knurl - I just don't know how to specify that to a workshop.
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I see that the image isn't clear
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How are you going to heat treat the steel? You will have to find out the proper hardness for the type of steel that you use to get the desired balance of strength and flex. Making a bar is more complex then just doing the machining.
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I ditched the idea when the machine shop gave a quote that wasn't very far from the price of a new medium quality barbell. And they couldn't even assure the quality of the materials they could source because of the restrictions in the interstate cargo movement.Originally Posted by Ken_L
Also, the barbell manufacturer is now hopeful of shipping my order in the first week of June.
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You made the right call man, I was going to say as an engineer your request to a machine shop was going to be extremely expensive and if you don't know about GD&T and steel grades you're going to get an inferior product at a high cost. Companies like Rouge pump out barbells by the dozen with a refined production process which is why an OPB is about $300 (which is actually really low for what you get quality-wise). If I got an OPB quoted to the exact specs of how Rouge makes them, I'd be willing to bet a local machine shop would run you about $3,000 if they made 1. If you had your bar made from EN-24 (never actually heard of this grade because it's only made in metric [metric round bar is super expensive in the US unless you source from Canada] but looked up the properties) your bar would've been so hard that you would have virtually 0 flex and I mean way less than your standard power bar. You'd probably crack that if you dropped it on a concrete floor or with a heavy deadlift whereas most bars would bend instead.
Sounds like you made out alright though. I admire the drive to get a barbell. Sounds like you'll be back in business soon!
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Thank you snake.
Update:
I would have loved to buy a barbell from Challenge because I have used them in the gym. But the company is not able to confirm when they can resume sales and shipping. So I ordered a Silver Rhino bar from Bullrock on Amazon the moment they returned after the lockdown. The manufacturer claims 210 ksi strength and 1800 lbs load rating for this bar. I paid INR 22000/- (US $ 290) and hope it is worth the investment.
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Never heard of the company before, but I looked them up and they look nice. A little token of knowledge too, tensile strength is kind of a buzzword in the barbell world. Tensile strength represents the pressure at which a material will fail. 210ksi shows the bar is a good, strong material, but doesn't necessarily say anything about its whip. That's why the charts on their website say "max load" for tensile strength. Don't worry about it though, 28mm bars are usually made to have a good amount of whip for Oly lifts, but still be stiff enough for general strength training (heavy squats/DLs).
And the name's Plissken
TMPHBITEU
Whip is a function of diameter, not tensile. And being a 4th order function, a 28mm bar is much whippier than a 29mm bar.
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Sorry Plissken for calling you the wrong name.
BTW, something else happened yesterday. I learned that Amazon had jacked up the price of Bullrock bars by more than 20% when I happened to see their original price list during a chat with one of their executives.
Then Challenge Barbells informed me that they
had started taking orders and offered me a huge discount on the bar and the weights. I was pleasantly surprised to realise that the guy with whom I had been interacting during the past month was actually the owner of the company and not some random sales guy!
I was really pissed off at the raw deal I got from Amazon when I got the news from Challenge. So I cancelled the order on Amazon and bought Challenge's bar and their calibrated metal plates.
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Did you take a material science class back in your college days Rip? You never struck me as someone that would just know this off the top of your head (not as an insult, just you're known for getting people under a bar and not in a crossfit box).
But if I wanted to nit pick, it's technically a function of radius. Second area moment of inertia of a cylinder is (pi/4)r^4 about the horizontal.
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