Drilling small holes

[Darren]

How do I drill small holes of less than 2mm, or even 2mm for that matter.

I'm trying to make the eccentric straps for my little engine from brass.
I've snapped so many 1.5mm drill bits trying I've given up. I've tried normal cheap drills, titanium coated and cobalt and it's no go.
Mill is at highest speed of 2,000 rpm, I'm being gentle with pressure ect, peck drilling and all that.

I then tried my little drill  at 2500 rpm and still it's a no go.

So guys, what's the secret when drilling brass? There must be something I'm missing here?

[NickG]

Brass does tend to snatch badly but you should still manage. I don't usually use such a high speed even with drill bits that small, when drilling brass I find it useful to nip the spindle slightly, I think it's the drill being pulled in too quickly that snaps them. Obviously keep withdrawing it after every few mm depth to clear the swarf too. Clean the drill off too if it's getting swarf stuck to it.

Can't think of any other tips and you've probably tried all of these! 

[bogstandard]

Hi Darren,

My heart really bleeds for you over this one, as unless every detail can be shown, it is very difficult to find a cure for your problem.

It is of no solace to you to know that I have no difficulty in any small drilling operations, and only yesterday I was drilling 0.8mm holes on my large mill using a big chuck and normal feed handles, drilling thru 2mm brass rod.

Is the problem when you are breaking thru or actually half way down the hole?

Because you have used a variety of drills, I don't think your problem is because your drills are too sharp (that is a normal problem when drilling brass) and is usually cured by stoning the cutting face to give zero rake.

Are you sure, because of suspect sources of materials, that you haven't got a piece of alloy in there that looks like brass, but in fact could be a bronze alloy. That would account for the drilling difficulty, as bronze can turn into a rock hard face at a moments notice, and no amount of trying will get you restarted in cutting the hole, and will give the symptoms you describe. You have to cut bronze with a continuous pressure, and by peck drilling it could have allowed the cut face to chill and become very hard.

Was the swarf produced like very fine dust (brass) or any sign of a curled swarf (more copper in the material pointing to another alloy, like phos bronze) ?

I know it is difficult to notice things like that when drilling small holes, but all clues point to maybe the reason for the problems.

Your technique is perfect for the expected brass, but it might not be the right technique for the material you have.

John

[sbwhart]

Darren

John just beet me too it the only thing I could add is regarding your drill chuck is it slightly bell mouthed:- it could be holding the drill only at the back, does the drill look as if its running true. Try making a small holder for the drill in the lathe loctite the drill in then grip the holder in your drill chuck and have another go.

Stew

[Darren]

Ah, I think Johns hit it here

It's got swarf and I'm getting problems when about 4-6mm in.

Now then, I paid a lot of money for this so called brass some time ago for another project. Basicly, (to give a bit of history that may or may not help) it was a full sheet of 4mm brass sheet that I paid several hundered pounds for. It was then cut up into parts on a water jet.

Am I now to find it wasn't brass at all and some sort of alloy? It looks more yellow than other brass I have.....

[sbwhart]

Darren

The best brass for machining is called leaded brass it as a small % of lead in it that gives it better maching quality a lot of the bar brass you buy is leaded brass.

Now with sheet brass thats a different kettle of fish basically the more yellow the brass looks the higher the zinc content the more coppery it looks the more copper content I suppose thats obvious.
Some of the these grades of brass can be a bit gummy to machine especialy when you get around the 70/30 which is called cartridge brass this brass has got good deep drawing qualities but it doesn't turn so well.

Also sheet brass is sold in different hardnesess,  basicaly what they do is work harden it as John said this could be happening, its quite easy to anneal it back just heat it up to cherry red hold it there for a few minutes and let it cool down or just quench it either way you'll end up with a softer material.

Hope this helps

Stew
 

[Darren]

Am I now to find it wasn't brass at all and some sort of alloy? It looks more yellow than other brass I have.....

I just realised wot I said there  Brass is always some sort of alloy....

Anyhow, leaded brass, I have a bit of that and yes it's nice to machine. Not tried drilling it though.
Mine is round bar, does it come in other forms?

Stew, if I anneal this brass, should it last the course whilst I drill it before work hardening?

[bogstandard]

Darren,

Now the full story is known, Stew has got it in one.

Good explanation Stew.

To allow him to shine even brighter, I will let Stew answer your question. He is the super expert on drawn brass.

John

[sbwhart]

Anyhow, leaded brass, I have a bit of that and yes it's nice to machine. Not tried drilling it though.
Mine is round bar, does it come in other forms?

Stew, if I anneal this brass, should it last the course whilst I drill it before work hardening?

Leaded brass you can get it in most forms:- square, round, hex its a CZ spec I think its 133 but I can check

Annealing the brass depends what your going to do to it it will take a lot of machining to get it hard, but if your going to bash it and bend it it will soon harden up again.

Cheers

Stew

[bogstandard]

Just a little extra onto what Stew has said.

Most of the copper based alloys will age harden all by themselves, so don't worry about the parts you have to soften, just by a bit of time and handling, they soon become strong enough to use in your normal situations.

I would now like to make clear about a statement I made in my earlier post

is usually cured by stoning the cutting face to give zero rake.

Brass, when machined, likes to have no top rake on the cutter, and in the C-o-C I have shown the difference between lathe tool profiles to give you an idea of what I was on about. Don't get me wrong, most brass will cut with a top raked tool and give very acceptable results, but under certain conditions and types of brass, a zero rake tool will give superior finishes, so I keep one in my arsenal for those certain times.

It is the same when it comes to twist drills. You will have to excuse my rendition of a twist drill, I can never sketch helix correctly.

Sometimes, twist drills need the same sort of treatment, and is is very easy to do. Holding the drill vertical, rub up and down a few strokes with a stone or diamond lap against the cutting edge, again in a vertical motion. No need to go overboard, just a couple of swipes is enough. This gives the drill version of zero top rake, and you should find that brass cuts a lot easier with no snatching.
I used to have complete drill sets treated in such a way, but after a time I used to get them mixed up with my other drills, and so started having problems drilling into normal materials. So now I use normal ones, and if needed, modify a spare to get the job done.


Bogs

[Darren]

Thanks guys, 

I have quite a few pieces of this left over 4mm brass, enough to last me out I'm sure. I only remembered about them yesterday being tucked away in a box.

I could cut some 16mm brass bar that does machine nicely, and drill, but that seems such a waste. So I will try annealing either later today or tomorrow.

John, would you treat a drill bit this way for this type of brass that produces swarf? I'd guess not but thought it may be better to ask as I've already ruined four pieces and a few drill bits.

Thanks 

[bogstandard]

Darren,

The brass drills are really only for the normal yellow brass that comes off as fine dust or chips.

I think you will have to resign yourself to only being able to drill your sheet stuff thru it's thickness, as it looks like it is work hardening the deeper you go.

It should make good cover plates and engine mounting plates though. So all is not lost.

John

[Darren]

Thanks Guys,

I should have realised that there was something different about this plate brass as I've drilled other brass with tiny holes with no problems at all.

It just didn't occur to me last night in the frustration.

Live and learn as they say, all good fun 
It's good to now have it categorised for future ref 

[Darren]

Stew,

I found this chart, did you mean CZ121? That seems to be the most common brass available.

CZ133 seems to have tin added.......nice chart, maybe put it in the reference section?

http://www.cnc.me.uk/brass.html

[bogstandard]

Now you know why it is so difficult to categorise the brass we get from the scrappies, we take a chance on it being a good one, most times it is OK, sometimes it can cause the sorts of problems you are having.

John

[sbwhart]

Stew,

I found this chart, did you mean CZ121? That seems to be the most common brass available.

CZ133 seems to have tin added.......nice chart, maybe put it in the reference section?

http://www.cnc.me.uk/brass.html

Yes thats the one 

Stew

[kellswaterri]

Hi Darren, hows about trying these...Spade drills... I have found them extremely useful when drilling small holes...I found that the twist drill type tended to pull themselves in to brass or gunmetal a little too quickly for my liking.

http://www.cousinsuk.com/catalog/6/1074/1587.aspx

All the best for now,
                           John.

[Darren]

Thanks for the link, unfortunately they don't seem to stock them anymore.

Could we make these from Silver Steel rods? Bit small maybe?

[kellswaterri]

Hi Darren, yes I think that they would be a little difficult to make at that size, although I have made them out of sowing needles on occasions, here is another link you might try...

http://www.eternaltoolshorology.com/spade-drills.htm

All the best for now,
                           John.
P.S.
Well worth watching the video on the home page if you are going to use the sherline.

[Darren]

Thanks John K, all interesting stuff I will look into those spade bits...

I did try annealing this hard brass to cherry red but it didn't make any difference, still snapped the bit off. I had a look at another damaged bit and it was rounded off. I think there are two things going on here. One is the drill bit tip is being grabbed solid and on other occasions the brass is work hardening almost in an instant as suggested. It must go pretty hard to do that to a drill bit.

I have now started the parts again with some hex stock, it's a bit tight due to the size I have, but I think it should work out ok.
I have drilled the small holes with no mis-haps, amazing, I have learnt a lot about brass these last couple of days.

Can someone tell me the dia and height of 2mm allen screw heads please, I have my mill set-up and it would be better not to disturb it until I have this info. Why I didn't put some 2mm screws on my last order I don't know. I'd like to counter bore the heads if I can.

Thanks for all the help here guys, really appreciated... 

[Darren]

John K,

Though it's hard to tell from the picture those drill bits look very much like these http://madmodder.net/index.php?topic=853.msg6724#msg6724

[Darren]

Just thought I'd pop this in, 

I took an old 1.5mm drill bit and ground the "other" end to form a D bit.
It went in ok and didn't snap or anything, but what it did do was push it's way through rather than drill. It's not very clear in this pic, but you should be able to see how the sides of the piece have bulged out.

I realise it's not a proper D bit but thought I'd show and tell all the same.....



It's of no matter now as I have started with some new material that is behaving itself