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Boucher
01-08-2010, 12:27 PM
I would like to learn to machine both external and internal o-ring grooves. Nominally I am interested in about 1/2 in to 1 1/2" diameter. The blade type micrometers looks like they would work for measuring depth of external grooves. What is the best way to measure internal grooves? What tools are best used to machine internal grooves? Any instruction or suggestions to get me started would be appreciated.

Black_Moons
01-08-2010, 12:37 PM
How about a simple caliper?
http://www.ptreeusa.com/Peach%20Graphics/caliper_divider_set_200_08.jpg

The spring loaded action lets you contract the ID caliper to remove it and let it expand bad to about the same size to be messured by other calipers or micrometers.

http://ep.yimg.com/ca/I/yhst-46161119373328_2082_32475618
I believe these let you 'extract' an ID to the other side of the caliper and messure it on that side.

You can also just do it by looking at your dials, theres verious ways to 'set' the tool to a known distance from the part. then you just plunge in by however many mils you want the grove to be deep (may require multiple passes) and trust your dials.

http://www.rlhudson.com/O-Ring%20Book/designing-tables.htm is a good book for all the sizes of diffrent types of o-ring groves. Seems to be down at the moment but maybe it will be up later on.

Some of these tools are cheap (<$20) so you can feel free to sharpen/bend/modify them as needed to reach into tight areas.

jimsehr
01-08-2010, 01:44 PM
Blade mirometers for od, special groove mic's for width of grooves and internal dial caliper gages for id checking and depth mic's with a flange on them to check location in a bore. And hand calipers all work. Some can get expensive.

Jim

Doozer
01-08-2010, 02:19 PM
If you don't have to inspect your work (as in its for you), just run your numbers and the groves should be close to good.
The Parker O-ring handbook is really your friend for dimensions and tolerances.

--Doozer

ckelloug
01-08-2010, 02:31 PM
Having done a couple o-ring grooves in a part for my research, o-rings do not like square corners.

If you're just considering round o-rings, there are of course no square corners. but if you are doing a seal on a square object, you will have to radius the corners of the groove.

--Cameron

Doozer
01-08-2010, 02:37 PM
Cameron-
"o-rings do not like square corners"

Please explain this. The square corners of an 0-ring grove give the
rubber some place to go when squished. If the o-ring grove was a
round profile, the o-ring would have no choice but to extrude into
the flange area when it is tightened. Square groves are a necessity.
Unless you are thinking of some special application.
As mentioned before, the Parker O-ring handbook is full of some
good info on this.

--Doozer

masondixonmetalworks
01-08-2010, 04:14 PM
I do not have alot of expierence cutting grooves like these @ home, as my lathe in a new addition to my home shop, however, at work these kind of grooves are a standard on 90% of our lathe work, CNC's.

For measuring, we use something called Indi-cals. They are a kit, that consists of a main body, a set of incrimental legs, and tips. The kit may or may not come with an indicator, as that is attatched to the top of the indicals via a dovetail slot.

Found a link with some pictures of a pair set up, and accessories. Note the left hand picture is a pair set-up, but do not have any brass legs attached, just the measuring tips, carbide or tool steel. They are a bit tricky to set-up, but once you get the hang of it, making sure you have enough travel on your dial, etc, they really are a great tool to use. I've set them up, where I can get them through a .247-.253 hole and measure an ID groove in the .350 range.

Seen here:

http://www.penntoolco.com/catalog/products/products.cfm?categoryID=661


As for the radius in the bottom of the grooves- all of ours we cut, ID and OD have a radi bottom and top of groove. These are mainly compressor and hydraulic components, but I always assumed this was the norm? We assemble some cylinder heads there, and the O rings that go in the grooves have a slight radius edge as well, the pressure, I'd say is a good bit, as they are for hydraulic cylinders, which, I'm sure is common knowledge, is pushing alot of pressure. Leaks tend to only happen if someone was trying to hide scrap and sent an + o/s ID groove through.

Hope this helps you out.

black powder
01-08-2010, 04:19 PM
If you look at the cross section of a "o" ring groove in the Parker book you will find that the bottom corners are raised and the walls are sloped , also the finish is critical because the "o"ring is not stationary in the gland .It will flow with the fluid or gas to form a seal .Hence round corners create less wear on the "O"ring when it moves.

Carld
01-08-2010, 04:47 PM
The seal and Oring manual I have shows the Oring grooves to be square sided and square corners in the bottom. I have always cut a square groove as has everyone I know that does Oring grooves.

The width and depth is important for the right expansion of the Oring when assembled.

smalltime
01-08-2010, 04:56 PM
I would like to learn to machine both external and internal o-ring grooves. Nominally I am interested in about 1/2 in to 1 1/2" diameter. The blade type micrometers looks like they would work for measuring depth of external grooves. What is the best way to measure internal grooves? What tools are best used to machine internal grooves? Any instruction or suggestions to get me started would be appreciated.

As far as machining goes:
OD rings are easy, just pay attention to the tool. Don't go too fast and keep it sharp. Break the the corners of the tool with a stone. To get rid of sharp edges on the od, simple break them with a file.
For checking, I would avoid buying any big buck tool that you will only use once, simply get a sacrificial o ring that is the proper size, install and mike over it.

For id rings it's a little more complicated:

Same general idea if you're on a lathe, but for a mill. it's a different story. You need to buy or make the boring bar out of high speed steel, and you NEED a boring head.
Set up accordingly, and get the tool tip just rubbing the hole. then stop the machine and dial out .005", then quickly turn the spindle on and off. allowing the tool to make about a dozen revs. then repeat untill you have the desired depth.
Install the o ring as above and check with drill shanks or gauge pins.

You're on your own when it comes to deburing though.:D

beanbag
01-08-2010, 04:56 PM
I would like to learn to machine both external and internal o-ring grooves. Nominally I am interested in about 1/2 in to 1 1/2" diameter. The blade type micrometers looks like they would work for measuring depth of external grooves. What is the best way to measure internal grooves? What tools are best used to machine internal grooves? Any instruction or suggestions to get me started would be appreciated.

If you have extra stock of the material that you're trying to cut an internal groove in:

Turn down a very short segment of the tube until it's OD is the same as the ID of the internal groove you're trying to cut. Then part off this section and cut it into a few arcs. Now you have a few reference pieces for how deep the groove should be.

ckelloug
01-08-2010, 06:06 PM
Doozer,

I explained in a bad way. It sounded like I meant the cross section of the groove when in fact I meant the shape of the groove in the xy plane. I was working on a static face seal o-ring using a long piece of glued o-ring cord. What I found from both the vendor books and the experience is that you want to round the corners of the groove in the way the attached diagram describes. It seems like there was a minimum radius vs. the cord diameter but I don't remember right now. As for the groove cross section, it seems like the books I checked wanted it slightly rounded on the edges but that just milling the groove to the right depth with an ordinary 1/8" endmill was acceptable and sufficient for my 3/32" diameter o-ring cord.

E.G. my lesson was that if you are milling grooves, mill the groove like the diagram on the right, not the left where you are looking at the end of the part and the line represents the path of the groove on the part, not the cross section of the groove.

http://i161.photobucket.com/albums/t202/ckelloug/groove.png

--Cameron

Doozer
01-08-2010, 06:27 PM
I'll buy that. A pic is worth a thousand words.
Looks good. I really like o-rings. I was told
that they came about due to aircraft technology.
Makes sense to me.

--Doozer

Carld
01-08-2010, 11:01 PM
I believe he is talking about Orings on a round shaft and Orings inside a round bore not an Oring in a square or rectangular pocket.