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Information about O-rings

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Information about O-rings

Unread postAuthor: Velocity » Fri Dec 28, 2007 12:24 am

As I approach the final setup of my lathe (weeks away, given my short Christmas break, loads of homework, and general laziness and disorder), I am trying to find some information on making O-ring grooves, one of the more useful applications of a lathe for spudgunning. I read the Spudwiki article, which was fairly helpful. Regarding the depth of an o-ring groove:

This depth can determined by the formula O*(100%-S%) - 1/2(OD - ID) Where O is O-ring thickness, S% is the percent of squeeze (higher percents make tighter O-ring seals), OD is the outside diameter of the interior part, and ID is the inside diameter of the exterior sleeve.


Logically, this seemed to make sense to me. However, I still was unable to determine how to choose which size of o-ring to use. Could someone perhaps provide some insight regarding this issue?

I have a specific case as well. I have a 1.25" x 12" cylinder of 6061-T6 aluminum stock, and a piece of aluminum tubing with an OD of 1.25" and an ID of 1.12". If I wanted to machine the stock into a piston and a bulkhead, how much should I turn the stock down and what size o-ring should I use?

Also, if anyone has any other information regarding lathe processes, it would be greatly appreciated. I am sure that if I paid the money for the premium content on <a href="mini-lathe.com">mini-lathe.com</a>, but I would rather not.

Thanks.
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Unread postAuthor: cdheller » Fri Dec 28, 2007 3:39 am

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Unread postAuthor: jrrdw » Fri Dec 28, 2007 6:46 am

The paid content wont help you on the o-ring. As for turning your stock down, go for a clearance of .002 if your wanting to use o-rings. Watch your tube thickness in this equation, you don't want weak ends, 6061 gets brittle when thin! Look around http://www.cnczone.com for turning info.

Edit: Link fixed, thanks guys! :D
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Last edited by jrrdw on Fri Dec 28, 2007 7:48 am, edited 1 time in total.
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Unread postAuthor: Hotwired » Fri Dec 28, 2007 6:57 am

jrrdw wrote:Look around http://www.cnc-zone.com for turning info.

Umm... thats some kind of search engine advert site listing stuff related to CNC.
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Unread postAuthor: bluerussetboy » Fri Dec 28, 2007 7:14 am

Hotwired wrote:
jrrdw wrote:Look around http://www.cnc-zone.com for turning info.

Umm... thats some kind of search engine advert site listing stuff related to CNC.

try it without the hyphen

http://www.cnczone.com

amazing, the creativity we can muster in times of trouble
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Unread postAuthor: Novacastrian » Fri Dec 28, 2007 6:29 pm

You need a wonderful little pocket book like this, http://www.pitstop.net.au/view/technica ... plu/16837/

I'm not sure if it has o'ring depths in this particular book, if i was at work i would check- Im busy doing nothing on holidays.
Similar book is called Kenwells i think.
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Unread postAuthor: jrrdw » Fri Dec 28, 2007 6:55 pm

The "The Home Machinist's Handbook" is a good referance also, probly the most popular.
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Unread postAuthor: clide » Fri Dec 28, 2007 11:04 pm

The Little Machine Shop guide was very helpful for me in terms of how to properly maintain my mini-lathe and general info on how to use it.
http://littlemachineshop.com/Info/MiniL ... sGuide.pdf

For a very detailed o-ring groove design http://www.sealseastern.com/OringDesign.asp is pretty good. Choose your seal type and enter a diameter and it will give you detailed information about the o-ring groove. I haven't really actually tested using the dimensions they give so I can't really vouch for them.

I've found that o-ring grooves for low pressure applications like we use are generally pretty forgiving and don't require real exacting tolerances.
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Unread postAuthor: tansit234 » Sat Dec 29, 2007 2:06 am

rmich732 I don't really have anything to add except I'm curious about which lathe you're getting. The 8x12 is much larger than the 7x12 and the bedways are much wider then the 7x12 or the Emco cloned 9x20. I have the Harbor Freight one and its not bad, the runout is only about +/- .001". Little machine shop has the extras for it but HF has them for about half the price. The tooling is all the same for the 3 for the most part. Just something to think about if you haven't already. I'm needing to order the steady and follow rests and a 4 jaw chuck and faceplate here soon.
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Unread postAuthor: cdheller » Sat Dec 29, 2007 1:35 pm

a free for the downloading program inPHorn from Parker Hannifan turned up this.
you probley want to do your own numbers though.
Im guessing clide's o-ring program is similar.
inPhorm has a really ,really long reference section with it
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