Geometry question

On Thu, 16 Apr 2015 20:50:32 -0400, "Jim Wilkins"


I haven't tried very hard to follow all of this, but is he talking about grinding a circular or conical side relief on the tool? Because face-grooving tools typically are ground with a straight relief all around.
Unless he really can exploit some extremely small advantage by making the reliefs as compliant to the grooved shape as possible, there doesn't seem to be much of an advantage to making it so complicated.
Or maybe I'm missing the point -- no pun intended.
--
Ed Huntress

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On Thu, 16 Apr 2015 20:54:59 -0400, Ed Huntress

Greetings Ed, The tool is only .06 wide and the groove radius is small so I need circular contours for strength. Remember, I have made tools like this before just because of the needed strength. Eric
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Jim Wilkins wrote:

That's what I thought too . Like clearancing the trailing edge of trepanning cutter , but for a cone . IMO the easiest way to do this cut is with the compound angled to let you feed the cutter perpendicular to the underside of the screw head . If you're careful grinding that tool , the cutter can deburr the cut just as it comes to depth .
--
Snag



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On Thu, 16 Apr 2015 20:35:10 -0400, Bob Engelhardt

The groove is square cross section.
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wrote in message wrote:

The groove is square cross section. ============================================================I hope you meant rectangular, not square. The oring is deformable but not compressible, so the cross-sectional area of the groove needs to be bigger than the cross-sectional area of the oring else you extrude and cut it on tightening. As for the geometry you could do it with a sketch and trig but I would prefer to just draw it in a cad program. Being a lover of run-on sentences here's how I would do it in autocad. Draw an angled line to represent the angled side of the flat head, draw a line perpendicular to that for the end of the oring groove closest to the threads, make an offset copy of the first line offsetting by 80% (or 75% or whatever you choose from the Parker oring handbook for your oring and pressure and oring life but it almost always works out to be between 75 and 80%) to be the bottom of the groove, draw a circle for the oring tangent to the side and bottom of the groove, and finally an offset copy of the first side line offset by 125-150% of the oring diameter to be the second side of the groove (this creates the extra cross-sectional area for the oring to deform into, and isn't critical so long as it is large enough). Draw a line parallel to the screw axis offset from the center of the oring by the radius of the ring (which also be the centerline axis of the screw), trim all the original groove lines to just leave the rectangular groove, then reflect everything around the centerline axis. Now add the top of the flat head and the threaded section, trim the excess from the angled lines, and you can pick off the dimensions you need. That's the stuff I'm sure off, the actual machining I'm less help with. On a manual lathe the way to do this would be to use a tool with a squared-off end like a parting tool and rotate the compound to the right angle and just plunge the compound. On a cnc couldn't you grind the end of a boring bar to the parting tool shape at the angle you need, and then make the angled plunge cut to simulate the straight plunge of a compound link you were turning a taper? Either way I don't see where you need any kind of a radius on the cutting tool, except a tiny break on the two front corners to leave a rounded chamfer at the bottom corners of the groove for stress relief. Hope this helps some :-).
Regards, Carl Ijames carl.ijames aat deletethis verizon dott net
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On Fri, 17 Apr 2015 13:55:38 -0400, "Carl Ijames"

Greetings Carl, I think you described in more word what I said in my first post. Eric
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So my post should have just been "yes"? :-) :-) :-)
Regards, Carl Ijames carl.ijames aat deletethis verizon dott net
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On Thu, 16 Apr 2015 11:04:10 -0700, snipped-for-privacy@whidbey.com wrote:

Firstly, you don't need to use carbide to machine 304, you can do it with hi-speed tooling. Just slow the cutting speed down.
--
Cheers,

John B.
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On Fri, 17 Apr 2015 07:57:21 +0700, John B. Slocomb

Greetings John, I know I can use HSS. I need to do 500 of these at a time and need to do them fast. Eric
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snipped-for-privacy@whidbey.com wrote:

ACME thread cutting insert?
--
Steve W.

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On Thu, 16 Apr 2015 11:04:10 -0700, snipped-for-privacy@whidbey.com wrote:

<snip> Might be overkill. What sort of pressures are involved? What are you sealing? Was a flat rubber/elastomer (urethane?) washer evaluated? How about a combination seal and retaining compound like RTV or Loctite?
If the O-ring groove is mandatory, how about a hollow mill? with the correct geometry? Given the problems in holding/ handling you might be better off making the complete screw from bar stock, although slotting the head may be a challenge. Do you have a CNC with a bar puller? How long is the thread? Style of head/drive?
--
Unka' George

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On Fri, 17 Apr 2015 09:30:48 -0500, F. George McDuffee

Greetings George, I already know how to hold and locate the screw. It will take approximately 4 seconds to remove one screw and put another in the collet. What I really want to know is if my way of finding the radii of the walls of the groove is one correct way. Eric
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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
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wrote:

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
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On Friday, April 17, 2015 at 12:50:11 PM UTC-4, snipped-for-privacy@whidbey.com wrote:

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'
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On Friday, April 17, 2015 at 3:00:29 PM UTC-4, rangerssuck wrote:

And yes, I would definitely consult with the o-ring manufacturer on this. Then you have so real, informed backup for your decision, other than Gunner's "Ayup."
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On Fri, 17 Apr 2015 12:00:26 -0700 (PDT), rangerssuck

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
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On Friday, April 17, 2015 at 5:23:40 PM UTC-4, snipped-for-privacy@whidbey.com wrote:

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

https://youtu.be/8qAi_9quzUY

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

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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I assume that Zago has competitors by now. Given competition and low the production volume, this may be a good price.
One can mine thinbit's catalog for ideas. I've made face grooving tools by grinding HSS. The hard part may be holding the screw to be machined.
And, maybe the better approach is to have special screws made, complete
screw machine would make short work of this. The minimum order may be 10,000 screws.
Joe Gwinn
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