How to turn a dimple?

[dp]

A conical dimple, to be specific. I'd like to use an MT2 dead center (60 degree point) in a slightly wider dimple so that the dead center can remain centered at the vertex but float around a bit, a couple degrees or so, at the loose end. That requires a cutter I don't have nor I can imagine what it might look like. I imagine this is quite like a jeweled movement in a watch which is where the inspiration came from.

My other option is to use a wedge shaped cut and a knife edge but that seems less clean. I require only one degree of motion so this is technically a good solution.

Any ideas or experiences?

[lane]

A drill point are a spot drill Just bump the part to depth.

[JCHannum]

Look for a bell center drill like this one at the bottom of the page;

http://www.carbidedepot.com/formulas-centerdrills.htm

[TGTool]

It seems like I remember seeing or hearing about a centerdrill that has a slightly radiussed or bell shape that would be what you're looking for. I hope I'm not imagining that, but in my mind I correlated it with tapers using an offset tailstock in which the line of contact makes a slight diagonal so the bell shape is a better center than a straight 60 degree.

Ah, I'm not imagining that. MSC lists a "60 degree bell-type drill and countersink" at:
http://www1.mscdirect.com/CGI/NNPDFF...4836&PMCTLG=54

edit: Shucks, Jim beat me to it.

[oldtiffie]

Dennis,

can you post a pic or a sketch please?

[Joel]

I prefer the radius type:




https://www.keocutters.com/catalog/p...65cfrq1udn6nd0

[dp]

Dennis,

can you post a pic or a sketch please?

Sure - not to scale, etc.

The usual center drills won't work because they don't allow the vertex of the center to be the point of contact. The objective is to have a restrained frictionless contact point while allowing a limited degree of movement of the free end. The dimple needs to be deep enough only to prevent any vibration from allowing the center to pop out of the dimple when moving the assembly or when in operation.

I've decided a good punch will create a suitable dimple for this purpose but if it were necessary to machine it, EDM would likely be the solution.

[JCHannum]

If that is all you need, why not just use an 82* or 90* countersink?

[dp]

None of my drills or countersinks produce a true point at the bottom of the hole when viewed under magnification. I think a "D" form drill ground to a point may work a bit better and may even be good enough. The problem with spinning tools like drills is they have no swept area at a point so can't cut away the metal. Rather like facing on a lathe - at the exact center of the face the tool is no longer cutting and a raised dimple often results. To be honest I probably now have an adequate solution for my specific requirement but it's become more of a mental exercise now to find a solution for generating a true cone in the general case without EDM.

[RPM]

Can you actually use a jewelled movement. These are commerically available at low prices (try small parts.com) -you can inset the male and female parts into your workpiece, and you're in business. Have done this very successfully, easy to do, relatively cheap , the sapphire female can be up to $8, the SS point $4 .
Richard in Los Angeles