[PBryson]

I need to have an electrical probe machined; but I am unsure how to specify my requirements. I am an electrical engineer with only moderate mechanical knowledge.
The probe will be machined from 0.125" diameter stainless steel round stock. The last 0.25 inch before the point necks down to a smaller diameter - maybe 0.031" - 0.062".
My question is in how to specify the pointed end of the probe. I want it to be sharp enough to dig in a little to the circuit under test but not so sharp that the point is fragile. Also, I don't want to specify overly-tight tolerances and push up the cost.

What is "sharpness"? Is it the angle leading to the point or is it the diameter at the very end?

My initial stab at it would be something like: "a cone with 60 degree angle sides". But this seems to imply an infinitely small point.
Should I specify a flat end of a certain diameter? (i.e. a conical frustum instead of a cone?)

And generally, "Is this design practical to produce at low cost?"

[RCaffin]

The taper angle will control how deep the point penetrates. Your choice.
Don't worry about defining 'sharpness' - just give them a drawing and specify that you want the tip 'sharp' as a probe.

Cheers
Roger

[PBryson]

Thanks. Yours is the only practical information I have found.
In your opinion, is a "sharp enough" point so trivial to achieve that I do not need any rejection criteria?

[john-100]

I guess another way is to see what ready made sprung test probes are like


http://www.farnell.com/datasheets/1662675.pdf

Attachment 308830


P25-5223 - HARWIN - PCB Test Point, Star Series, Beryllium Copper, Rhodium Plated Contacts | Farnell element14

http://www.farnell.com/datasheets/24045.pdf


John

[RCaffin]

> I do not need any rejection criteria?
Sounds fine to me. You are probing for an electrical contact, not trying to manipulate bacteria one by one.

The Harwin test probes are a good example as well. None of those are especially sharp.

Cheers
Roger

[beege]

I'd try to specify the size of the spherical radius on the tip of your probe. .0005" may be too sharp. .010" may be too blunt. .002" could be just right, and all are measureable.