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