drilling in spring steel

Hi, may I pick brains please......I need to drill some holes in hardened spring steel and I've just ordered some carbide drills 1.4mm diameter to help me do it. Luckily these have a 3mm shank so I can use the drill chuck in my Wabeco mill. But its speed only goes up to 3000~3500 RPM.

Will this speed be sufficient and should I use any lubricant ?

Also, I would guess for such a small drill, I don't want to apply much force. Can any give me an idea as to how much I'll need on the bit (and I'll work that back to a hand force) ?

The machine is more than fast enough for heat treated spring steel even at that diameter. You might want some suds but not oil as spring steel is prone to glazing, a form of work hardening the surface.

How does a person guess the load? A kilo?

As has just been said your speed range should be enough, main thing is to have relatively feed pressure and keep cutting, until just before the drill breaks through. The job needs to be rigidly mounted and if the spring steel is thin needs supporting close to the drill so it cannot flick up at break through.

Bear in mind that carbide drills dont bend or flex and they need to run dead true. I hope your Wabeco chuck is an Albrecht!

Small carbide drills with 3mm shanks put PCB drills in mind, nothing wrong with PCB drills but they all seem to have large flutes compared to drills intended for cutting metal. The large flutes leave only a small web which means the drill is nowhere near as strong as a normal drill so is not good at taking downward pressure.

Some time ago a drilled quite a few 1.5mm holes in both hardened and stainless steel. I broke quite a few carbide drills some of which I resharpened freehand. I was surprised to find that about 2 out 5 of my inaccurately sharpened drill worked better and lasted longer than brand new drills.

IanP

In one of the Machinists Bedside Readers Guy Lautard has an article on a drilling system for hard materials that uses low speeds with standard drills but high pressure. If I get a moment I could try to find it. There was a US made tool looking like a large gee clamp, with a mandrel that had an acme screw to force it down on the workpiece. The chuck was driven by a socket from a portable drill or even manually. So maybe an alternative worth trying is to use low speed and high pressure? You would want the minimum amount of drill protruding from the chuck to minimise the risk of breakage, and use hss rather than carbide.

I would immediately think of using a Spark Eroder (EDM)

Just a thought

Ray

Not tried either of these methods myself yet but they may be worth bearing in mind for some situations.

Downloaded an old book on gunsmithing recently that is my coffee break 'browse' currently. I'm not interested in gunsmithing per-se but some of the machinists methods used are of interest to me. One thing I spotted was a method to drill into hardened parts (rifle barrels) by locally annealing the spot to be drilled. He used a small diameter carbon rod with an arc welder - and just touched the spot where he wanted the hole. Apparently the intense local heat generated anneals the area enough for it to be drilled with "normal" drills. Don't see why it wouldn't work with thinner hard materials too.

Alternatively (and I cannot find the reference) I also recall reading a method of drilling thin spring material (for loco springs) by punching it with a centre punch to form a small 'pip' which was then filed (or perhaps ground?) off - leaving a small hole which can then be opened out using normal dills. I think the usual caveats about drilling thin materials would still apply so rather than just drill it (which might work OK) I might be tempted to further (progressively) deform & grind the hole out to size with larger punches/dies. Must admit I don't relish drilling thin materials at the best of times.

Regards,

IanT

If you heat spring steel it won't be springy at that point any more.

Perhaps it might "dremel" out?

Agreed Capstan - but I think this idea is that only a small area is effected..

IanT

> 2 out 5 of my inaccurately sharpened drill worked better and lasted longer than brand new drills

Because they were shorter so less leverage to break them?

Drills 1mm or under seem to work whatever sort of tip you manage to put on them.

Neil

Most of the ones that broke did so at the transition of flutes to shank so not really sharpenable. I put the improved performance down to reduced work hardening because each edge was cutting at a different point.

With two identical cutting edges more pressure is needed to ensure that both edges keep cutting before the opposite edge comes round and skids over it. With unequally ground edges not only is it a full revolution before an edge comes up against the surface it has cut, that cut surface has changed! so it just keeps on cutting. I feel a patent coming on! (Oh dear, I've just told everybody)

Ian P

I've used dental turbine handpieces.. 300K RPM with their burs to pop holes in surgical stainless. The handpieces aren't that expensive and the burs are cheap. There would be the nuisance of hitching up an air and water supply and making up a clamp for the accuracy one might need compared to hand held.....

I have only ever dealt with spring steel in rod form. Is it harder to drill than stainless generally?

Well the 'blue' steel spring that I've tried to drill in the past certainly was a pretty quick way to blunt a drill Nick. I ended up grinding a hole in it with a Dremel but I was far from happy with the resultant hole (it wasn't circular for a start).

Stainless is not really a problem to drill provided the drill is really sharp and you adjust the speed down (about half the rate of free cutting steel). I'd guess there are quite a few different kinds of "spring" steel too, so what might work on one - might not on another.

Regards,

IanT

I have used a diamond coated point (from a cheap set) mounted in my Dremel at max rpm to make small holes in springs for model D-T timers. One good source for small sharp cutters and grinding tools is your friendly local dentist; - very good quality and they throw them away.

* Danny M *

Thanks all for the useful information and great food for thought. There is such a depth of experience on here ! I'll let you know how it goes.

Gerry