How to machine a small positive feature?

Tim.

Presuming you want this 'feature' standing up from a surface of the same part, I would make a rod the right diameter (probably from wire as has already been suggested) and a hole in the surface. In other words a two-piece solution. Trying to chew away everything that isn't the little cylinder would be a job for grinding, I think. Harold or another guru-level person would know better.

I'm doing some work on this scale right now and it is ... interesting.

... or a piece of spring steel or drill rod. Metric! ;-)

Nick

=============================== Sounds like this is on the borderline of what is possible with mechanical machining. If you are a wizard and have unlimited time/funds it *MAY* be possible.

(1) How are you going to measure the diameter, length, cylindricality?

(2) Is your milling machine capable of making these kinds of moves? Depending on the resolution [granularity] the best you may be able to do is some sort of square or hexagon approximation to a cylinder.

My first thoughts would be some kind of chemical [etching] or electro-chemical [reverse plating] process. Another thought would be some kind of miniature EDM process. If your milling machine has the required accuracy/resolution you may be able to adapt these processes to it.

Sounds like a fascinating project. What's it going into? I know cell phones are getting smaller every day, but this seems a little extreme.

This month's issue (March 2006) of "Today's Medical Developments" on page 65 advertises a machining center. The object machined is a 5 by 5 grid of vertical pins machined from NAK80 (mold steel). The pins range from .02mm diameter x 2mm tall (.00078" x .078") to .10mm diameter x 10mm tall (.0039" x .390").

The ad can be found at

The machine is the new NTC Zu3500.

So, the part you want is machinable. You just may lack the proper equipment to do it efficiently. Good luck.

Possible? Yes, but it requires one hell of a lot of patience. You made no mention of the tolerance required, however, so that could be the limiting factor. A boring head with the properly configured tool will easily make the cut. I'm assuming the "post" will be at a right angle to the surface. If material isn't a serious concern, you may enjoy making it from 12L14, which will machine without tearing and leave a decent finish. 7075-T6 aluminum might also be a good choice, as well as 2024-T351. It likely goes without saying that light cuts are in order, and a fine feel.

A permanent stop should be set, along with an indicator so you have an idea where the tool is relative to the part in question. I'd suggest a finely honed HSS toolbit for such a challenge, not carbide. You'll need reasonable positive rake and virtually no radius on the tool. Measuring the diameter will be challenging, but it's possible a comparator could be used.

How are your eyes? Seeing the part and the cut will be a big part of the challenge.

Harold

a couple of summers ago my daughter was working on a device that had an array of pins that I believe were on 1 um spacing and about .01 um in diameter (if I remember the dimensions) - created by etching techniques - one big problem was making electrical connections to the carrier - these pins were pretty fragile - so moral here is that you can get pretty small, but at some point you stop using conventional cutting tools.

Bill

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What about chemical milling? I don't know much about it at all other than knowing it may be worth looking into.

Chemical milling suffers from undercutting, so making something deeper than the feature size becomes very hard. The pin would end up tapered with almost any liquid etching technique. Ion etching can do stuff like this in Silicon materials. But, these techniques may be way too slow for such a large part. Those systems are used for making parts with dimensions in the nanometer range.

Jon

sounds awfully like a facing cut on the lathe with the tool just below centre. ...the pip left in the centre.

btw you want a small rod feature above the surface. you only think you need a mill to do it :-)

Stealth Pilot