So what's the proscribed method? I expect I need a pretty consistent radius
bottom. What's the best way. Make a rough semi V lathe bit, and then make
a decent round one to finish?

"Bob La Londe" wrote in message
...
So what's the

spproscribedsp


prescribed method? I expect I need a pretty consistent radius
bottom. What's the best way. Make a rough semi V lathe bit, and then
make a decent round one to finish?

LOL.

Silicone o-ring for modest heat. Upto about 325 degrees.

Bob La Londe wrote:

"Bob La Londe" wrote in message
...
So what's the

spproscribedsp

prescribed method? I expect I need a pretty consistent radius
bottom. What's the best way. Make a rough semi V lathe bit, and then
make a decent round one to finish?

LOL.

Silicone o-ring for modest heat. Upto about 325 degrees.



Most O-rings I look at are seated in square grooves. I believe you need
the extra space afforded by the square groove to allow the O-ring to
deform and seal properly. For a piston though, you should probably be
looking at cup seals and the like on McMaster.com.

In article ,
"Bob La Londe" wrote:

So what's the proscribed method? I expect I need a pretty consistent radius
bottom. What's the best way. Make a rough semi V lathe bit, and then make
a decent round one to finish?

Most o-ring grooves are square - there's little or no need to match the
profile of the ring, just get the size right so the ring compresses
adequately to work...

If you want a round bottom, and you are HSMing rather than production,
just use a round-nosed tool and take it easy, unless you've gone and
decided to work in stainless where you can't take an easy cut, in which
case you'll need a machine that will stand a real cut. Roughing out with
a V does not reduce the power needed to make the final cut at full
radius, and making the cut in any normal material is not likely to dull
the tool much.

--
Cats, coffee, chocolate...vices to live by

On May 7, 9:29*am, "Bob La Londe" wrote:
So what's the proscribed method? *I expect I need a pretty consistent radius
bottom. *What's the best way. *Make a rough semi V lathe bit, and then make
a decent round one to finish?

The Parker O-Ring Handbook (9 Mb) discusses some of the design
criteria for o-ring grooves. See Section 4:
http://www.parker.com/literature/ORD...g_Handbook.pdf

"Pete C." wrote in message
ster.com...

Bob La Londe wrote:

"Bob La Londe" wrote in message
...
So what's the

spproscribedsp

prescribed method? I expect I need a pretty consistent radius
bottom. What's the best way. Make a rough semi V lathe bit, and then
make a decent round one to finish?

LOL.

Silicone o-ring for modest heat. Upto about 325 degrees.



Most O-rings I look at are seated in square grooves. I believe you need
the extra space afforded by the square groove to allow the O-ring to
deform and seal properly. For a piston though, you should probably be
looking at cup seals and the like on McMaster.com.

Not an engine piston. A modest temp single stroke hand injection pump
piston. After I posted I was thinking a square groove might work better.
Thanks. I have not grooved the piston itself yet.

On Fri, 7 May 2010 07:29:29 -0700, "Bob La Londe"
wrote:

So what's the proscribed method? I expect I need a pretty consistent radius
bottom. What's the best way. Make a rough semi V lathe bit, and then make
a decent round one to finish?

Check this out:-

http://www.parker.com/literature/ORD...g_Handbook.pdf

Pretty much all you need to know about static and dynamic O-ring
seals.

"The shape of the seal groove is unimportant as long as it
results in proper compression of the seal between the
bottom of the groove and the cylinder wall, and provides
room for the compressed material to flow so that the seal is
not solidly confined between metal surfaces"

Bob La Londe wrote:

"Pete C." wrote in message
ster.com...

Bob La Londe wrote:

"Bob La Londe" wrote in message
...
So what's the

spproscribedsp

prescribed method? I expect I need a pretty consistent radius
bottom. What's the best way. Make a rough semi V lathe bit, and then
make a decent round one to finish?

LOL.

Silicone o-ring for modest heat. Upto about 325 degrees.



Most O-rings I look at are seated in square grooves. I believe you need
the extra space afforded by the square groove to allow the O-ring to
deform and seal properly. For a piston though, you should probably be
looking at cup seals and the like on McMaster.com.

Not an engine piston. A modest temp single stroke hand injection pump
piston. After I posted I was thinking a square groove might work better.
Thanks. I have not grooved the piston itself yet.



Not engine piston, they use very different seals, think hydraulic piston
as most of those use some variety of cup seal.

On May 7, 11:04*am, "Denis G." wrote:
On May 7, 9:29*am, "Bob La Londe" wrote:

So what's the proscribed method? *I expect I need a pretty consistent radius
bottom. *What's the best way. *Make a rough semi V lathe bit, and then make
a decent round one to finish?

The Parker O-Ring Handbook (9 Mb) discusses some of the design
criteria for o-ring grooves. *See Section 4:http://www.parker.com/literature/ORD...g_Handbook.pdf

The other big name in o-rings is Apple. I am sure they also have
information on the web about grooves for O-rings.


Dan

Pete C. wrote:

Bob La Londe wrote:

"Bob La Londe" wrote in message
...

So what's the

spproscribedsp

prescribed method? I expect I need a pretty consistent radius

bottom. What's the best way. Make a rough semi V lathe bit, and then
make a decent round one to finish?

LOL.

Silicone o-ring for modest heat. Upto about 325 degrees.




Most O-rings I look at are seated in square grooves. I believe you need
the extra space afforded by the square groove to allow the O-ring to
deform and seal properly. For a piston though, you should probably be
looking at cup seals and the like on McMaster.com.

Correct. Most O-rings are intended to be seated in nearly square
(rectangular) grooves. Rubber is essentially like a fluid ... it is
nearly incompressable. When pressure is applied it DEFORMS, but does not
compress significantly. That's why it's used for some kinds of
one-sided-mold stamping operations. It applies a uniform pressure just
like a hydraulic fluid.

Assuming a square groove with a round O-ring, the groove should be about
the same width as the O-ring's diameter, and bit less in depth than the
ring's diameter. Then, when the cover-plate (or whatever) moves to put
pressure on the O-ring, it deforms, swelling sidewise to press against
the sides of the groove as well as the bottom. It effectively makes a
three-point seal in the groove, with one seal against the closing element.

A round-bottom groove doesn't allow the ring to deform properly, and it
will "mushroom" out of the groove, deforming oddly, since there's no
other place for it to deform into.

Now, it's true that a round bottom groove CAN work, for low-pressure or
unusal applications, where the O-ring is not overly deformed, but it's
not what's usually recommended. Check most any o-ring manufacturer for
specs.

Dan Mitchell
============

"Spehro Pefhany" wrote in message
...
On Fri, 7 May 2010 07:29:29 -0700, "Bob La Londe"
wrote:

So what's the proscribed method? I expect I need a pretty consistent
radius
bottom. What's the best way. Make a rough semi V lathe bit, and then
make
a decent round one to finish?

Check this out:-

http://www.parker.com/literature/ORD...g_Handbook.pdf

Pretty much all you need to know about static and dynamic O-ring
seals.

"The shape of the seal groove is unimportant as long as it
results in proper compression of the seal between the
bottom of the groove and the cylinder wall, and provides
room for the compressed material to flow so that the seal is
not solidly confined between metal surfaces"

That paragraph pretty much sums it up and describes one of my problems on my
first tests.

I guess I need to go make some square lathe tips in the right sizes. I was
going for an exact fit round groove.

"Pete C." wrote in message
ster.com...

Bob La Londe wrote:

"Pete C." wrote in message
ster.com...

Bob La Londe wrote:

"Bob La Londe" wrote in message
...
So what's the

spproscribedsp

prescribed method? I expect I need a pretty consistent radius
bottom. What's the best way. Make a rough semi V lathe bit, and
then
make a decent round one to finish?

LOL.

Silicone o-ring for modest heat. Upto about 325 degrees.



Most O-rings I look at are seated in square grooves. I believe you need
the extra space afforded by the square groove to allow the O-ring to
deform and seal properly. For a piston though, you should probably be
looking at cup seals and the like on McMaster.com.

Not an engine piston. A modest temp single stroke hand injection pump
piston. After I posted I was thinking a square groove might work better.
Thanks. I have not grooved the piston itself yet.



Not engine piston, they use very different seals, think hydraulic piston
as most of those use some variety of cup seal.

Ok... if I ever go to high production (if I do remind me I'm a hack) I'll
look at that. Most of the "commercial" models of this are using an o-ring.

On Fri, 7 May 2010 07:29:29 -0700, "Bob La Londe"
wrote:

So what's the proscribed method? I expect I need a pretty consistent radius
bottom. What's the best way. Make a rough semi V lathe bit, and then make
a decent round one to finish?

Use a rectangular groove.

Lots of information (11 meg download) in
"The Sealman's O-Ring Design Handbook"
http://www.physics.harvard.edu/servi...g_handbook.pdf

On May 7, 10:39*am, " wrote:
On May 7, 11:04*am, "Denis G." wrote:

On May 7, 9:29*am, "Bob La Londe" wrote:

So what's the proscribed method? *I expect I need a pretty consistent radius
bottom. *What's the best way. *Make a rough semi V lathe bit, and then make
a decent round one to finish?

The Parker O-Ring Handbook (9 Mb) discusses some of the design
criteria for o-ring grooves. *See Section 4:http://www.parker.com/literature/ORD...g_Handbook.pdf

The other big name in o-rings is Apple. *I am sure they also have
information on the web about grooves for O-rings.

Dan

Thanks, I found them and bookmarked them for future reference (though
you have to register to read their technical library).

Don Foreman wrote:
On Fri, 7 May 2010 07:29:29 -0700, "Bob La
wrote:

So what's the proscribed method? I expect I need a pretty consistent radius
bottom. What's the best way. Make a rough semi V lathe bit, and then make
a decent round one to finish?

Use a rectangular groove.

Lots of information (11 meg download) in
"The Sealman's O-Ring Design Handbook"
http://www.physics.harvard.edu/servi...g_handbook.pdf

What everybody said. I've had good luck with
a cutoff tool ground to the proper width and
the corners lightly stoned.

If you want the seal to hold a high vacuum,
the bottom of the groove will probably have
to be polished.

In general I prefer to design with metric O-rings
as there's a much wider range of sizes.

On Fri, 7 May 2010 07:29:29 -0700, "Bob La Londe"
wrote:

So what's the proscribed method? I expect I need a pretty consistent radius
bottom. What's the best way. Make a rough semi V lathe bit, and then make
a decent round one to finish?

No..use the round one to start and finish with.

If you have a tool and cutter grinder and can make some fixtures..you
can turn out a decent half round tool

On the other hand...unless you are handling really high pressures...you
CAN often times get away with a simple V groove.

Gunner

--


"First Law of Leftist Debate
The more you present a leftist with factual evidence
that is counter to his preconceived world view and the
more difficult it becomes for him to refute it without
losing face the chance of him calling you a racist, bigot,
homophobe approaches infinity.

This is despite the thread you are in having not mentioned
race or sexual preference in any way that is relevant to
the subject." Grey Ghost

"Bob La Londe" wrote in message
...


"Bob La Londe" wrote in message
...
So what's the

spproscribedsp

Ah, you caught yourself !
Proscribe means to ban, veto, bar, forbid, exclude, make illegal, disallow,
rule out etc.
Prescribe would be a better choice.

In any case, thanks to your question, I'm about to learn something.

Ivan Vegvary

"Bob La Londe" wrote in message
...
So what's the proscribed method? I expect I need a pretty consistent
radius bottom. What's the best way. Make a rough semi V lathe bit, and
then make a decent round one to finish?

It has been a few years, but like others have said, just go with a square
groove. Seems to me we would make the groove same width as the o-ring, and
the depth 90% of the thickness, .250 thick ring, cut the groove .225 deep.
Now that depends on your clearance from the piston and cylinder wall too, so
I suppose you should go with the cylinder diameter, minus 2x of 90% of the
o-ring thickness. so .250x90%x2 subtracted from the cylinder diameter.

On 5/7/2010 11:04 AM, Denis G. wrote:
On May 7, 9:29 am, "Bob La wrote:
So what's the proscribed method? I expect I need a pretty consistent radius
bottom. What's the best way. Make a rough semi V lathe bit, and then make
a decent round one to finish?

The Parker O-Ring Handbook (9 Mb) discusses some of the design
criteria for o-ring grooves. See Section 4:
http://www.parker.com/literature/ORD...g_Handbook.pdf

http://www.allorings.com/
I like this site. Click on "O-Ring Gland Design"
Randy

What's that Lassie? You say that Greg O fell down the old
rec.crafts.metalworking mine and will die if we don't mount a rescue
by Fri, 7 May 2010 18:03:41 -0500:

It has been a few years, but like others have said, just go with a square
groove. Seems to me we would make the groove same width as the o-ring, and ...

No. The width of the groove should be equal or greater than the width
of the O-ring.
--

Dan H.
northshore MA.