Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

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Default Geometry question (seal screw)

On Friday, April 17, 2015 at 5:23:40 PM UTC-4, wrote:
On Fri, 17 Apr 2015 12:00:26 -0700 (PDT), rangerssuck
wrote:

On Friday, April 17, 2015 at 12:50:11 PM UTC-4, wrote:
On Fri, 17 Apr 2015 10:40:37 -0400, Joe Gwinn
wrote:

In article ,
wrote:

All-
I need to put an o-ring groove in the underside of 500 1/4-20 flathead
screws. So I need to make a groove tool to do the job. A straight
groove tool won't work because the sides of the groove are curved. I
have made tools like this before but this is a small one and I'm
machining 304 SS so I need carbide and only want to make the tool
once. So I think to find out what radii to grind the sides of the tool
can be determined by drawing the screw head with the groove in it.
Then extend the sides of the head until they meet. Then mirror the
drawing around that point. Then I can directly measure with the cad
program the two different radii of the sides of the groove. Am I
correct?

From the rest of the thread, a picture or sketch would be very helpful.

People already make screws with O-ring seals: http://www.zago.com/.

And, Kaiser Tool Company makes lathe tool bits for cutting circular
grooves at various angles. I think that their ThinBit line is what you
seek. http://www.thinbit.com/

Joe Gwinn
Greetings Joe,
Zago does indeed sell those screws. $2.90 each in quantity. I need to
be able to make these for about 25 cents. And I will. Thinbit does not
make the groove tool I need. They will though, for about &175.00. I
have been through this before.
Eric


Not for nothin', but it seems to me that for $125 total project income (500 pieces at $0.25 each), you're going to have a tough time making a profit on this. You've probably spent more than $125 worth of time just thinking about the tooling.

After 30+ years in business, I've learned that there are some jobs you just ought to walk away from. Tell the customer he can buy the parts for $2.90 from Zago.

Just sayin'

I get paid for tooling and setup and programming and engineering. Then
I get paid per piece. The job will come up several times a year. Each
time it does I get paid for setup and tool attrition.
Eric


Fair enough.

Now, for a possible solution: After checking with the o-ring manufacturer who will almost certainly recommend a rectangular groove, why can't you do this with a rectangular grooving tool set parallel to the screw head and fed at right angles into the head?

I see in your original post that you said the the sides of the groove are curved, but then where does the o-ring squish to when the screw is tightened?

I haven't seen this much discussion about o-ring grooves since Feynman dropped one in a glass of ice water. https://youtu.be/8qAi_9quzUY
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Default Geometry question (seal screw)

On Fri, 17 Apr 2015 14:59:26 -0700 (PDT), rangerssuck
wrote:

On Friday, April 17, 2015 at 5:23:40 PM UTC-4, wrote:
On Fri, 17 Apr 2015 12:00:26 -0700 (PDT), rangerssuck
wrote:

On Friday, April 17, 2015 at 12:50:11 PM UTC-4, wrote:
On Fri, 17 Apr 2015 10:40:37 -0400, Joe Gwinn
wrote:

In article ,
wrote:

All-
I need to put an o-ring groove in the underside of 500 1/4-20 flathead
screws. So I need to make a groove tool to do the job. A straight
groove tool won't work because the sides of the groove are curved. I
have made tools like this before but this is a small one and I'm
machining 304 SS so I need carbide and only want to make the tool
once. So I think to find out what radii to grind the sides of the tool
can be determined by drawing the screw head with the groove in it.
Then extend the sides of the head until they meet. Then mirror the
drawing around that point. Then I can directly measure with the cad
program the two different radii of the sides of the groove. Am I
correct?

From the rest of the thread, a picture or sketch would be very helpful.

People already make screws with O-ring seals: http://www.zago.com/.

And, Kaiser Tool Company makes lathe tool bits for cutting circular
grooves at various angles. I think that their ThinBit line is what you
seek. http://www.thinbit.com/

Joe Gwinn
Greetings Joe,
Zago does indeed sell those screws. $2.90 each in quantity. I need to
be able to make these for about 25 cents. And I will. Thinbit does not
make the groove tool I need. They will though, for about &175.00. I
have been through this before.
Eric

Not for nothin', but it seems to me that for $125 total project income (500 pieces at $0.25 each), you're going to have a tough time making a profit on this. You've probably spent more than $125 worth of time just thinking about the tooling.

After 30+ years in business, I've learned that there are some jobs you just ought to walk away from. Tell the customer he can buy the parts for $2.90 from Zago.

Just sayin'

I get paid for tooling and setup and programming and engineering. Then
I get paid per piece. The job will come up several times a year. Each
time it does I get paid for setup and tool attrition.
Eric


Fair enough.

Now, for a possible solution: After checking with the o-ring manufacturer who will almost certainly recommend a rectangular groove, why can't you do this with a rectangular grooving tool set parallel to the screw head and fed at right angles into the head?

I see in your original post that you said the the sides of the groove are curved, but then where does the o-ring squish to when the screw is tightened?

I haven't seen this much discussion about o-ring grooves since Feynman dropped one in a glass of ice water. https://youtu.be/8qAi_9quzUY

The groove is rectangular in cross section. And is cut with a
rectangular tool. Imagine cutting an o-ring groove in the face of a
part. This groove is rectangular in cross section yet has curved
sides. The grooves I need to cut are exactly the same. Curved sides. I
drew up a screw with the groove sides parallel to the screw head top.
But it has disadvantages. Not as much squeeze on the o-ring unless the
groove is shallow. Which then raises the possibility of the o-ring
extruding over the edge of the groove and getting damaged. The
customer didn't like it. I didn't either except it would have saved
the customer some money. By putting the groove normal, that is to say
perpendicular, to the angled face, then the groove can be cut to the
proper o-ring dimensions. In fact, people keep telling me to look up
in a catalog or online at the o-ring specs to get the groove
dimensions correct. This is the first thing I did. This is one of the
reasons why the groove is normal to the angled face. BTW, thanks for
mentioning me, albiet obliquely, in the same sentence as feynman.
Eric
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Default Geometry question

On Thu, 16 Apr 2015 11:04:10 -0700, wrote:

I need to put an o-ring groove in the underside of 500 1/4-20 flathead
screws.

snip
This just showed up in my inbox. They may have something in
stock.
http://tinyurl.com/pe2y3bm


--
Unka' George

"Gold is the money of kings,
silver is the money of gentlemen,
barter is the money of peasants,
but debt is the money of slaves"

-Norm Franz, "Money and Wealth in the New Millenium"
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Default Geometry question

On Thu, 23 Apr 2015 11:14:09 -0500, F. George McDuffee
wrote:

On Thu, 16 Apr 2015 11:04:10 -0700, wrote:

I need to put an o-ring groove in the underside of 500 1/4-20 flathead
screws.

snip
This just showed up in my inbox. They may have something in
stock.
http://tinyurl.com/pe2y3bm

Greetings George,
Thanks for posting the link but what I need is what I described in the
first place. I appreciate all the advice about different screws but
the customer wants what he wants. I also was surprised that only one
person directly addressed the original question, the one about
geometery.
Eric
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Default Geometry question

wrote in message
...
On Thu, 23 Apr 2015 11:14:09 -0500, F. George McDuffee
wrote:

On Thu, 16 Apr 2015 11:04:10 -0700, wrote:

I need to put an o-ring groove in the underside of 500 1/4-20
flathead
screws.

snip
This just showed up in my inbox. They may have something in
stock.
http://tinyurl.com/pe2y3bm

Greetings George,
Thanks for posting the link but what I need is what I described in
the
first place. I appreciate all the advice about different screws but
the customer wants what he wants. I also was surprised that only one
person directly addressed the original question, the one about
geometery.
Eric


The original question was:
All-
I need to put an o-ring groove in the underside of 500 1/4-20 flathead
screws. So I need to make a groove tool to do the job. A straight
groove tool won't work because the sides of the groove are curved. I
have made tools like this before but this is a small one and I'm
machining 304 SS so I need carbide and only want to make the tool
once. So I think to find out what radii to grind the sides of the tool
can be determined by drawing the screw head with the groove in it.
Then extend the sides of the head until they meet. Then mirror the
drawing around that point. Then I can directly measure with the cad
program the two different radii of the sides of the groove. Am I
correct?
Thanks,
Eric

What's lacking is whether or not you can tilt the bit to the same
conical angle when you rotate it in the grinder and grind with a very
narrow wheel, to duplicate the changing radius of the tapered hole
(not that you may need to). The projected relief radius will be
different if ground with a wide wheel, parallel to the tool shank and
feed direction.

I don't know enough about carbide form tools to guess if the larger
working relief you'd get by just circular grinding to the small end
radius of the groove would support the cutting edge well enough.

This solid geometry problem is difficult to put in words.

-jsw




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Default Geometry question

"Jim Wilkins" wrote in message
...
wrote in message


I think I see how to do this now.

Draw the cross-section, extend the bottom of the groove to the
centerline and use the distance from the centerline intersection to
the OD of the groove bottom as your hole radius, to figure the outer
edge circular relief. The inner edge relief can be flat since the
groove curves away from it.
-jsw


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Default Geometry question


"Jim Wilkins" wrote in message
...
"Jim Wilkins" wrote in message
...
wrote in message


I think I see how to do this now.

Draw the cross-section, extend the bottom of the groove to the
centerline and use the distance from the centerline intersection to
the OD of the groove bottom as your hole radius, to figure the outer
edge circular relief. The inner edge relief can be flat since the
groove curves away from it.
-jsw


That was ambiguous. Extend the line that defines the bottom end of the
groove inward to the centerline. It will be parallel to the angle of
the screw head.


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Default Geometry question

On Thursday, April 23, 2015 at 2:42:08 PM UTC-7, Jim Wilkins wrote:
"Jim Wilkins" wrote in message
...
"Jim Wilkins" wrote in message
...
wrote in message


I think I see how to do this now.

Draw the cross-section, extend the bottom of the groove to the
centerline and use the distance from the centerline intersection to
the OD of the groove bottom as your hole radius, to figure the outer
edge circular relief. The inner edge relief can be flat since the
groove curves away from it.
-jsw


That was ambiguous. Extend the line that defines the bottom end of the
groove inward to the centerline. It will be parallel to the angle of
the screw head.


The operation you describe will not, however, generate the conic section (which
is an ellipse) which is perpendicular to the cutter's travel direction. Ideally,
oughtn't the radius be matched to the osculating circle of that ellipse at
the point of cut? I think what is called for, is the Riemannian curvature
of the cone (of whatever angle, at whatever radius) which is the workpiece.

Gee, I still sound like a math major, and it has been some years...
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Default Geometry question


"whit3rd" wrote in message
...
On Thursday, April 23, 2015 at 2:42:08 PM UTC-7,
Jim Wilkins wrote:
"Jim Wilkins" wrote in
message
...
"Jim Wilkins" wrote in
message
...
wrote in message

I think I see how to do this now.

Draw the cross-section, extend the bottom of
the groove to the
centerline and use the distance from the
centerline intersection to
the OD of the groove bottom as your hole
radius, to figure the outer
edge circular relief. The inner edge relief
can be flat since the
groove curves away from it.
-jsw


That was ambiguous. Extend the line that
defines the bottom end of the
groove inward to the centerline. It will be
parallel to the angle of
the screw head.


The operation you describe will not, however,
generate the conic section (which
is an ellipse) which is perpendicular to the
cutter's travel direction. Ideally,
oughtn't the radius be matched to the osculating
circle of that ellipse at
the point of cut? I think what is called for,
is the Riemannian curvature
of the cone (of whatever angle, at whatever
radius) which is the workpiece.

Gee, I still sound like a math major, and it has
been some years...


Were you involved in the developement of the
turboencabulator? ;)}



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Default Geometry question

"whit3rd" wrote in message
...
On Thursday, April 23, 2015 at 2:42:08 PM UTC-7, Jim Wilkins wrote:
"Jim Wilkins" wrote in message
...
"Jim Wilkins" wrote in message
...
wrote in message

I think I see how to do this now.

Draw the cross-section, extend the bottom of the groove to the
centerline and use the distance from the centerline intersection
to
the OD of the groove bottom as your hole radius, to figure the
outer
edge circular relief. The inner edge relief can be flat since the
groove curves away from it.
-jsw


That was ambiguous. Extend the line that defines the bottom end of
the
groove inward to the centerline. It will be parallel to the angle
of
the screw head.


The operation you describe will not, however, generate the conic
section (which
is an ellipse) which is perpendicular to the cutter's travel
direction. Ideally,
oughtn't the radius be matched to the osculating circle of that
ellipse at
the point of cut? I think what is called for, is the Riemannian
curvature
of the cone (of whatever angle, at whatever radius) which is the
workpiece.

Gee, I still sound like a math major, and it has been some years...


I was stuck on how to fixture and grind the osculating circle, but all
it takes is a slightly tighter radius on an offset center for
clearance, assuming the tool doesn't have to hold exact shape when
reground.
-jsw


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