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[gondolier88]

Centre punching small diameter holes- you need a brand new punch- very acute angle and save it for non ferrous to save the tip.

Using a brand new stanley knife scribe the centre lines you wish to use, then hold the work to the light, the brighter the better, and PUSH the punch into the centre- this will suffice for 0.5mm-1.5mm- it does for me anyway

Greg

[dodgy geezer]

Dodgygeezer

Dentist's burrs sound great - but do they go down to 0.5mm?

Mike

Smallest tip I have is .003 inch tip (0.07 mm), and a couple of .008 inch (0.23 mm). At 0.5mm I have quite a selection, including ball end and inverted cone. So in theory (if I could see or hold to that precision) I could drill a 0.5mm hole and undercut it inside to 0.25mm. Ask your dentist about them....

[Bunkerbarge]

I use standard HSS drills and hold small ones in a pin vice.  I haven't seen a mention yet of my own technique, which is to hold the majority of the length of the drill in the chuck, thereby not allowing the drill to flex as much.  To start off such a hole I would only have a few millimeters of the drill outside the chuck and then might extend it a couple of times during the process to keep the free length as short as possible.  This allows the use of HSS drills and therefore reduces the likelyhood of a tungsten carbide bit shattering.

Obviously lubrication and very regular clearing of the swarf play thier part but I don't normally bother with lubrication on such a cut but do very regularly remove the drill to clear the swarf and cool the drill.

[stallspeed]

You call it a technique,Bunkerbarge.I call it common sense.

All it needs is a drill with decent torque and proper chuck that you can run at low speed or doesn't leave 2" of twist drill flapping about at 5,000 rpm.

[derekwarner]

I must agree here

1) accurate center punch marking  is required
2) accurate stability of the work piece is a must
3) the suggestion by 'bunkerbarge' ....which is to hold the majority of the length of the drill in the chuck, thereby not allowing the drill to flex as much is naturally the preferred option

A ........45:1 ratio of effective drilling depth to diameter is totally achievable with care............. ....Derek

[Corposant]

Greg

Thanks again - yes, I use a Swann Morton blade to score the centre line. I'll have a scout round for a suitable centre punch.

Dodgy Geezer

0.003" Wow! - I really must find a dentist!

Bunkerbarge

I've always been reluctant to grip the fluted part of a drill in the chuck - but I see the logic of it. For the current problem (now over!), the chuck of my pillar drill is too chunky - so I'll have to try and find a pin vice that spins true.

Derek

Thanks for your confirmatory input.

Many thanks to you all - I'm most grateful

Mike

[tigertiger]

I cannot remember what I saw or where, but this problem rings a bell.

Perhaps what I write will ring another bell with someone else.

I think for brass you need to chamfer the cutting edge of the drill bit. Otherwise it digs in and bites, maybe why they snap. By taking of the sharpest part of the cutting edge, this is avoided.

Like I say I can't remember what exactly I read, but I am pretty sure it was about drilling brass.

[wideawake]

I cannot remember what I saw or where, but this problem rings a bell.

Perhaps what I write will ring another bell with someone else.

I think for brass you need to chamfer the cutting edge of the drill bit. Otherwise it digs in and bites, maybe why they snap. By taking of the sharpest part of the cutting edge, this is avoided.

Like I say I can't remember what exactly I read, but I am pretty sure it was about drilling brass.

Yes TT you're right.   It seems to be standard advice in Model Engineering books to do as you suggest when drilling brass or gunmetal.   Unchamfered, the drill has a tendency to snatch as it breaks through and break under the twisting force.   I also believe (but may be wrong) that when a wider range of kit was available than now, slow spiral drills were preferred for brass.   i have read of serious model engineers who keep a separate set of most-used sizes (tapping drills etc) modified for brass drilling.
If the drill is breaking earlier in the hole then too much pressure and/or not withdrawing often enough would seem to be the most likely cause.

In terms of cutting fluid it's possible to get small bottles of purpose designed oil quite cheaply.

HTH

Guy

[HS93 (RIP)]

I have just rember'd drilling some hard brass recently and found that dormer drills where the only ones that would touch it, the cheap ones where just skidding and getting hot, the brass was B+Q best wont buy that again no wonder it is so cheap.

peter

[wideawake]

I have just rember'd drilling some hard brass recently and found that dormer drills where the only ones that would touch it, the cheap ones where just skidding and getting hot, the brass was B+Q best wont buy that again no wonder it is so cheap.

peter

Yes Peter I think someone highlighted the problems with "brass" further down the thread or somewhere else.  Unless purchased from a reputable metal supplier and with a designation then what you get is fairly unpredictable in it's machining qualities.   Not knocking B&Q, I've used their stock myself at times for odd jobs.

The other thing your experience highlights is the desirability of using a rigid spotting drill or centre drill to form a dimple in which to start the normal twist drill.   Even the smallest size centring drill is far more rigid than a twist drill!

HTH

Guy

[HS93 (RIP)]

Yes Peter I think someone highlighted the problems with "brass" further down the thread or somewhere else.  Unless purchased from a reputable metal supplier and with a designation then what you get is fairly unpredictable in it's machining qualities.   Not knocking B&Q, I've used their stock myself at times for odd jobs.

The other thing your experience highlights is the desirability of using a rigid spotting drill or centre drill to form a dimple in which to start the normal twist drill.   Even the smallest size centring drill is far more rigid than a twist drill!

HTH

Guy

Yes it was me

Peter

[wideawake]

Yes it was me

Peter

OOPS!   Morgan - Rearrange the following, "Suck teaching eggs grandmother your to" and write out 100 times   

Guy

[Corposant]

Tigertiger, Guy, Peter

I know that brass comes in various hardnesses but, in my ignorance, I thought that it was the "bees knees" in terms of "workability". Your comments are very interesting - and helpful. I'm sure a major factor in the problem is using a pillar drill fitted with a 1/2" chuck. Whenever I use it, I think that a micrometer feed would be nice! - and that is why I don't have the problem using the lathe, because the feed can be done very delicately.

Thanks again,
                   Mike

[tigertiger]

Hi Mike

It is very workable, or so they told us in school.
Just a matter of having the right tools. 

[Corposant]

And a bad workman always blames his tools!

[tigertiger]

I seem to remember brass clogging files at school, and warnings about exploding grinding wheels.  

Trickey stuff, that brass.

[Corposant]

Tigertiger

That's certainly true of aluminium but really surprises me with brass - especially exploding grinding wheels! Explosions like that usually result from a collection of fine, combustible particles causing a chain reaction. It used to be a problem in flour mills - and the exposions are very violent! I used to work with a biochemist who had previously worked as a forensic scientist. He told the tale of a chap who went into work alone one Saturday morning to do some machining using magnesium. The fine dust he created ignited. My colleague said all they found of him was his shoes!

Mike

[gondolier88]

Bunkerbarge's advice is sound- i found this out after drilling brass funnily enough- the bit snapped, however the tip was left intact for a length of about 1.5inches- I put this back in the chuck and it worked perfectly.

Greg

[Corposant]

Greg

Bunkerbarge's advice is always sound! (especially good at pointing out pitfalls.) I'm very glad I posted my shortcomings, it's been very educational!

Mike

[tigertiger]

I thiink the exploding grinding wheel was not the gaseous like particles (e.g. lead powder), but the fine particle of brass clogging in the grain of the grind stone (possibly a build up over time) and then these particles expanding with the heat caused by friction. The expansion of the brass in the stone of the wheel causes the stone to rupture/shatter, whilst rotating at high speed. So less of a chemical explosion, but certainly high speed debris in all direction.

Well I think that is what our metal work teacher was saying.  I was possibly bored at the time , looking forward to another double period of planishing my caddy spoon.

[Corposant]

I'm sure your teacher was right - they usually were! I hope you've still got your beautifully planished caddy spoon!

Mike

[derekwarner]

mmmmmm grinding brass?  ...in lay terms .......we have aluminium oxide wheels for ferrous metals & silicone carbide wheels for tungsten or tipped tools

Were we not taught  , never grind brass on a grinding wheel  .......but maybe something newer has been invented............Derek

[samuel15g]

We also have to consider the rake and clearance angles when drilling brass.
Correct Rake and clearance angles are essential when drilling different materials.
Brass, cast iron and perspex will "snatch" if you use drills ground for mild steel. If your works not properly clamped the drill will snatch, grab and break.
With a large drill there's a chance it'll take your fingers out too.

To find the recommended angles search the web to find a myriad of stuff , however , it can take years of grinding experience to do this in a home workshop.

Kind regards

[Corposant]

Samuel

Many thanks for your advice. Sadly, adjusting the rake and clearance of a 0.5mm drill are beyond my capabilities! - and I don't have enough years left to gain "grinding experience in a home workshop"!! I'll certainly have a rummage on the "net".

Mike

[Angusc]

Hi

Nothing to do with working Derricks but I have just bought the caldercraft puffer as a first model. Have you any advice you can give me? On opening the box I felt a littlebit overwhelmed.

Thanks

Ancusc