drilling small holes

[havoc]

This evening I have been trying to drill 0.5mm holes. Made 1 hole and broke 5 drills. At the price they cost I guess I have to refine my technique before any further attempt

So far I followed this workflow:
- used the mill for everything
- put the piece in the clamp and tighten well
- with a center drill 1.5mm made a small centerpoint, it doesn't matter this is a bit larger than the to be drilled hole
- then with the 0.5mm drill in a collet, table clamped and the mill at top speed (1200rpm) I slowly start the hole.
- nice long swarf comes out
- after about 1 or 2 mm the drill breaks and cannot be removed as it is inside the hole.

I'm drilling in bronze brazed to brass and I need to go into the brass. Total depth is 3mm. Now I'm using normal twist drills (Dormer), before I have tried with a nameless twist drill from a hobby shop and another nameless one but that had a thicker shaft. Aparantly the brand of the drills is just that, only they cost about 3x as much.

Now I got to remove the rest out of those holes.

[kingsteam9]

Are you trying to feed the drill straight in without backing off frequently? It's just that the long swarf suggests that maybe a plunge in action is more than the drill can cope with, especially at that size. If I was trying this I'd be tempted to use a 'pecking' action with the drill and just let it cut a few thou deep then withdraw to let chips/swarf clear. Most bronzes seem pretty tough going for drills in my experience.

Robin

[Peter W.]

I'm no expert, but have you tried peck drilling ?
i.e. drill 1mm (or even less) then ease off, then carefully down again.....
That seems to work for 1mm holes. I've never tried half that !

Peter

[russell]

1200 rpm strikes me as rather too slow. You should be using at least 5000 rpm. With the lower speed the depth of cut per revolution is likely to be too high. You also need a very sensitive downfeed - is the milling machine sensitive enough.

Russell

[baggo]

As mentioned by Robin, bronze can be awful stuff to drill. Often the work/drill will get hot and expand causing the drill to bind in the hole. Try flooding the job with coolant, even if only squirted on, and take it easy with the feed, withdrawing the drill at frequent intervals to clear the swarf and let the job cool down between cuts.

John

[brozier]

If it was me I'd use my Minilor PCB drill as that runs at 10K RPM. There is a cheapy on ebay at the moment (300225943662) or one with a stand (170220854298) might be worthwhile if you drill a lot at this size.

Good quality Tungsten carbide PCB drill bits tend to have a stepped shaft so are less flexible and less likely to break.

Crownhill sell them for £2.29
www.crownhill.co.uk/product.php?prod=1865

A dremel or clone would also get the speed up. You could lashup a mount on the Milling machine head for it.

Cheers
Bryan

[cotswold]

I certainly agree that 1200 rpm is too slow and frequent relief (pecking) is essential. So is delicate 'feel' which I suspect you are not getting with a mill.

I don't like building tools but have never regretted building something based on a one-and-a-half sized version of the George Thomas sensitive drill. I say "something" because the business end owes everything to the late maestro while the base, pillar and table owe everything to bits from a 'Selecta Homemaster' general purpose tool (it never served any of its original general purposes very well). I use it for anything less than 2mm. The drive is an old 'Bridges' drill via a toothed belt - my one mistake was probably not stepping up the speed sufficiently.

[Shawki Shlemon]

3 mm deep is quite a lot for that size ,I have drilled down to no 80 with similar speed but good quality bit ( I don't know yours) ,using cutting fluid with bench drill feeding lightly and backing off often . It is easy to push little harder and break the bit , don't be hard on yourself , it is a tricky job .

[havoc]

Okay, so probably the speed wasn't high enough and I didn't remove the swarf oftn enough.

I'll try next with my pcb drill. Sadly I don't have any carbide pcb drills that small. I'll try that this weekend.

[alanstepney]

You may find this useful, or at least, interesting.

www.youtube.com/watch?v=q6-4oyIoku4

[missemmajade]

I spent a lot of time not so long ago drilling little holes in hard brass and alloys, and there is a lot written in watchmaking books about it, and usually they say that twist drills and brass don't mix at all, and I really do agree.

the best results are with an old fashioned flat drill in either a good archemedes drill or with a pulley and a bow. technology just hasnt been the answer for this particular job.

the way i was taught to do it was to use a holder, for the drill, and a pulley driver on it. You set the plate up vertically, and place the ring over the end of the drill holder. the ring is just a standard key ring or a propper brass ring if you have a good drill set, and it helps keep the drill at right angles to the job, it is quite easy to hold the drill to the work so that the ring doesnt move up and down the rod. (does that make sense?)

you have a bow with the thread wrapped once round the pulley, and move it back and forth with finger pressure on the end. its a very quick and easy way to drill holes in brass plates.

the drill is a piece of silversteel wire, sharpened up on a stone, after being turned up with a 90 deg point and some relief behind the widest part, for about the depth of the hole. then its made to a point with a file and stone, on two sides, so it is flat, and the cutting edges sharpened on all four edges. you will have to harden and temper it then, heat it till red, and plunge it into a wax candle.

the drill holder is a bit of 1/4" brass, it needs a hole in it, an easy way in the watch repair shop was to pinch a short bit of clock bushing, about 2-3" long. shellac (or superglue or loctite) the drill in the end, and and make a fancy knob for the other end, with a swivel, if you have time, or round it up for ur finger. make a pulley from wood to push on it, or brass or whatever you can find, mine are mostly nylon. a bow is good from carbon fibre, i think, but mine is brass welding wire. its strung with dental floss, doesnt need to be all that tight, just wrap it round again if it doesnt grip. I dont have a pic, as this stuff is in storage, but if you are going to drill a lot of holes, then this is the best way to do it. it won't break the drill when it breaks through , either!

is some history anyway, if this isn't much use to anyone, but I think its still a long way ahead of a twist drill.

*EMMA*

[freddo]

the drill holder is a bit of 1/4" brass, it needs a hole in it ......

Is this "There's a hole in my bucket dear Liza ...."?

Freddo --- bemused - confused! --- How do you make the hole for the drill that you need to make the hole for the drill .......

[missemmajade]

use a bit of 3mm steel for the drill, or something u have a drill for... and turn the last 10mm or so down to make the cutting edges.. clock bushing already has a hole in it..

*EMMA*

[steam4ian]

Thanks Emma

That was most illuminating. I can see that a spade bit would be superior on brass because you need a negative rake.

Regards
Ian

[missemmajade]

thanks ian. I did find a pic just now, it might give some more idea what it looks like. this one is under the 50 x microscope, so its a lot smaller than .5mm, but the idea is the same.



this pic is added for interest, its a round end drill, made the same way for drilling hardened and tempered steel.



*EMMA*

[GWRdriver]

I will pass this along for what it's worth . . . I designed a Ga1 inside cylinder block in bronze with an internal drain cock arrangement which required drilling two small (1/32") but deep (5/8"+) pasageways at each cylinder end which must pass just under the bores. All the usual preparations were taken, sharp drill, correct speed, etc. The first hole was pushed through in very small steps, not much more than pecking, and that went beauitfully. Emboldened by the success and ease of the first hole I pushed the second holes through a bit more quickly only to discover that the slight increase in pressure caused the drill to wander off-line by almost three diameters and right through a cylinder wall! Insert workshop Esperanto here.

[modeng2000]

I wonder, is this the way the holes are drilled in gas jets?

John

[havoc]

Emma, thanks for the explanation, but I fear that is above my ability. I do get the part about the bow, drill holder etc (I do know how a bow drill looks like and work), but not the part about the ring. Also I don't see why you put the workpiece vertically.

Lucky you added a pic of that drill because you got me lost in the proza.

Might try it for drilling gas jets. I got 0.2mm drills for that but I don't dare to use them.

[missemmajade]

:-[sorry it was a bit garbled. just a quick sketch here showing the ring and vertical workpiece. the only reason you use these is to get the drill straight, the idea is to hold the drill vertical so the ring doesnt move along the stem , its a simple guage to make sure its level.

www.flickr.com/photos/missemmajade/2514102025/

*EM*

[modeng2000]

Hi Emma,
Now that is lateral thinking!

John