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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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#41
Posted to rec.crafts.metalworking
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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 |
#42
Posted to rec.crafts.metalworking
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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 |
#43
Posted to rec.crafts.metalworking
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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" |
#44
Posted to rec.crafts.metalworking
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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 |
#45
Posted to rec.crafts.metalworking
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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 |
#46
Posted to rec.crafts.metalworking
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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 |
#47
Posted to rec.crafts.metalworking
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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. |
#48
Posted to rec.crafts.metalworking
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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... |
#49
Posted to rec.crafts.metalworking
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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? ;)} |
#50
Posted to rec.crafts.metalworking
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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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