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  #11  
Old 10-31-2018, 10:05 PM
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paranday paranday is offline
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Quote:
Originally Posted by rdshackleford View Post
Oh, I forgot to mention tribology in response to your review.



Even though I am an engineer, this word was new to me when I learned it recently at the ripe age of 51.

I was pretty excited to learn not only the world, but about the field of study that really cuts to the heart of speed bag swivel design. I think understanding the basics of tribology can help you make that "next level" swivel.
That's a great word. I'm not an engineer but appreciate tribology.

The swivel I currently use was inspired by a late 1800s design. It consists of a lube free stainless ball bearing and a paracord. loop to attach the bag loop to an eyebolt where the paracord glides in an arc freely to permit bag movement. With zero lube frictional losses are low and bags rebound like crazy. However, it could likely be improved. Could punch a hole in the top center of the bag loop, run a single cord and attach it through the bore of a lube free bearing. That arrangement may be more ideally omnidirectional and eliminate the eyebolt.. The swivel in the photo is omnidirectional in practice; it relies on the low inertia of the bearing / eyebolt to keep things sorted.
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  #12  
Old 11-01-2018, 03:03 PM
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I'm not sure I understand your design with just that one view. Was the pic taken while it was attached to the platform? why are the 4 countersunk holes empty? What is that washer with the socket head cap screw? Is the bearing friction fit into the wood block?
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  #13  
Old 11-01-2018, 06:11 PM
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Quote:
Originally Posted by rdshackleford View Post
I'm not sure I understand your design with just that one view. Was the pic taken while it was attached to the platform? why are the 4 countersunk holes empty? What is that washer with the socket head cap screw? Is the bearing friction fit into the wood block?
That photo was of it off platform. The photo below shows it attached to a Balazs 24" drum with the Title big blue bag. I had the bearing friction fit but it would pop out which is why the washer was added to restrain the edge of the bearing. The swivel looks crude, it was built in an afternoon years ago, never got around to making a finished version. It works. I mentioned it for the idea of using paracord as a swinging rotating element. I don't know how to do that without either altering the bag loop or attaching a paracord loop to each bag (as illustrated) to get the quick bag change feature. Maybe the ball hook is the ideal form for a swivel. But paracord is quiet and long lasting and super lightweight and the friction in this usage is very low.
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Last edited by paranday; 11-01-2018 at 06:13 PM.
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  #14  
Old 11-01-2018, 06:18 PM
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I think I understand now. That is a nice setup.
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  #15  
Old 11-01-2018, 10:44 PM
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Paranday,

Do you have a link to buy the bearing & bolt combo to make this "swivel" ?
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  #16  
Old 11-01-2018, 11:27 PM
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Originally Posted by JoMan View Post
Paranday,

Do you have a link to buy the bearing & bolt combo to make this "swivel" ?
This is the bearing I used.

https://www.amazon.com/SR4AZZ-Stainl.../dp/B002BBFEVG

The dust covers on the bearing are thin and easily dented. If you make a friction fit into a base careful not to push against the covers or they'll be mashed into the bearing and cause it to rub and not spin freely.

The bolt I got at the local hardware store. Stainless steel, with a nut placed below and above the bearing. The eye was opened up just enough with a drift pin so the loop will pass through with much effort. Open it too far and the bag will fly off sometimes.

The knot in the paracord loop is special. The one I use is called the zeppelin bend. Other knots I tried quickly slip, the zeppelin bend never slips and it is easy to untie if you need to make the loop shorter. Tying that knot is not so simple but there are videos on YouTube like this one,



I tie it with a long enough piece of cord, then cut the ends to a short length and use a flame to melt and keep the ends from fraying.

Below are shown the parts of the swivel.
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  #17  
Old 11-02-2018, 10:57 AM
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Ah, I understand the design now, thanks. I'm interested in knots, even have a book on knots. But I really suck at learning them.
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