Micro drilling

[Sceadwian]

Can anyone recommend any methods for micro drilling? I'm looking to put a .25mm to .5mm through hole in 1mm bar stock (wire) the material will be file hard steel. Only thing that comes to mind that might be possible for a hobbyist is small scale EDM or electrochemical removal, anyone got some better suggestions that might be practical? Anyone ever tried home brew EDM?

 

[BrownOut]

Aren't you a machinist? I am almost embarassed as a rank amature to offer advise to a pro, but here goes. The only way I know of to drill hard steel is to anneal, drill, retemper. For micro drilling, I would try a microscope mounted on a milling/dirlling machine. I'm sure you're going to tear my suggestions to pieces now

 

[JimB]

Home made EDM machines are quite popular in the model engineering fraternity.

I one saw one in action at an exhibition, it was quite impressive, removed a busted tap from a component in 15 mimutes or so, leaving a clean hole.

Try googling for DIY EDM or home made EDM, there is plenty of information out there.

JimB

 

[BrownOut]

PS I didn't pay enough attention to the size of the stock before I made my post. I have no reasonable suggestion.

 

[MrAl]

Hi,

The way this would normally be done is it would be drilled BEFORE it was carbonized. Cleanup later.

That's pretty hard stuff. Do they make a diamond bit that small? Take it to a machine shop

 

[squishy36]

Here's what I'd do if I was faced with this. You can find old used PC board carbide drills for sale; usually, they're on the order of a buck apiece. The key is that you want carbide if you're trying to drill hard steel.

You then want to chuck them up in a drill press that a) has as little runout in the spindle as possible and b) turns fast.

Most people (me included) turn small drills way too slow because our drills and drill presses won't do the requisite spindle speeds. You can estimate the required spindle speed with the approximation

RPM = (4*SFPM)/D

where SFPM is the surface feet per minute required for cutting, D is the diameter in inches, and RPM is the spindle speed. For cutting hard steel with carbide, the surface speed should probably be in the 500 to 800 surface feet per minute range. Thus, for drilling a 0.25 mm hole, that's about 0.04*(1/4) or 10 mils in diameter. Using 500 ft/minute for SFPM gives 200,000 rpm. Using 800 for SFPM gives 320,000 rpm. Few people have drill presses capable of those speeds. Some folks substitute Dremel tools to get around 20,000 rpm.

The problem with not using the right spindle speeds is that you'll very likely break the drill because it won't seem to be cutting fast enough. It's also worthwhile to use a lubricant of some kind; I'd probably start with something like a mixture of mineral oil and a solvent like mineral oil or kerosene. WD-40 is predominantly mineral oil and kerosene, so that could be a choice too.

EDM and laser drilling are two other ways of getting holes in hard steel, but you'll have to talk to someone experienced with those techniques. Of course, the machine tool industry also has more exotic drills like ceramic, diamond, etc., but you'll be paying a lot of money for those and will likely break them unless you have the proper equipment.

 

[BrownOut]

Some folks substitute Dremel tools to get around 20,000 rpm.

A friend of mine mounted his Dremel to the drilling head of his drill press. That way, he can use the tool as a micro drill press.

 

[Sceadwian]

Thanks for all the suggestions folks I just popped this one up as I thought of it at work before doing any Google searching and to allow me to follow up when I got home, figured I might as well ask if anyone else has done stuff like this.

BrownOut, I'm not a machinist, I'm a metal finisher that works at a machine shop, same scales of work, very different tools.

I have a solid drill press, but with the size of the stock the size of the hole and the fact that it's file hard metal I didn't think it'd be something I could get goods results on at home, the main problem being first how do I even get the drill started, it's not exactly practical to use a punch tool to mark something that small and I'd want a well centered straight hole, it being file hard would make a center punch impractical. I might pick up the bits just to try if I can get em cheap but my first thought was EDM/ECM which I'll definitely look into.

MrAl, I'm a glutton for punishment and I like to work with the materials I have and work the process to get the desired results around what I have, just my mentality. If I can't figure out how to do it on the cheap with what I have I won't bother, just another one of the hundred ideas I'll have and research the practicalities on just to learn more and maybe get something done. This one is something I'm willing to spend a bit of time researching though as what it allows me to do is pretty potent to some very small scale projects I've had in the back of my head for the last 5 years.

 

[Sceadwian]

where SFPM is the surface feet per minute required for cutting, D is the diameter in inches, and RPM is the spindle speed. For cutting hard steel with carbide, the surface speed should probably be in the 500 to 800 surface feet per minute range. Thus, for drilling a 0.25 mm hole, that's about 0.04*(1/4) or 10 mils in diameter. Using 500 ft/minute for SFPM gives 200,000 rpm. Using 800 for SFPM gives 320,000 rpm. Few people have drill presses capable of those speeds. Some folks substitute Dremel tools to get around 20,000 rpm.

That was some really good information and some nice approximations, any other references to various cutting methods/materials outside of drill bits? There has to be similar formulas for grinding, perhaps an approximation between equivilant friction/material removal?

 

[Sceadwian]

Looked into EDM a bit more, apparently the most common DIY methods use kersone baths, so I'm just gonna shy away from that from a general saftey standpoint, also the clearances for workpiece/tool distance are pretty tight. Looking more into ECM right now as that's related to plating anyways so something I'm far more familiar with. Seems doable, electrode construction appears to be a bit tricky though, if I ever get anywhere I'm sure I'll post. The nice thing about ECM as opposed to EDM is there is a LOT of detailed technical information about ECM methods and theory.

 

[Sceadwian]

Just started going through this PDF and already had one comment.

https://www.electro-tech-online.com/custompdfs/2012/01/Aevmacro.pdf

I have yet to see any PDF fill so well annotated and every microscopic bit of nomenclature is fully defined, with data everywhere. The people that write this way are my kind of people! (even though I personally never could)