Geometry question

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

Reply to
etpm
Loading thread data ...

This just showed up in my inbox. They may have something in stock.

formatting link

Reply to
F. George McDuffee

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

Reply to
etpm

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

Reply to
Jim Wilkins

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

Reply to
Jim Wilkins

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.

Reply to
Jim Wilkins

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...

Reply to
whit3rd

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

Reply to
Phil Kangas

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

Reply to
Jim Wilkins

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.