Drilling brass conumdrum

[Eric CoxParticipant @ericcox50497]

We've probably all had it happen at some time or other and that is have a drill run off centre when drilling brass. but why does it happen in brass and not in mild steel.

[Eric CoxParticipant @ericcox50497]

[Anonymous]

No idea, because I've never had it happen. Assuming the same drills and setup are used for steel as brass all I can think of is some anisotropic characteristic of the material.

Andrew

[JasonBModerator @jasonb]

As brass likes sharp cutting tools it may be that your drill that seems OK for steel is not cutting well in the brass and that is making it wander. Also look at the current thread on wandering holes

[HopperParticipant @hopper]

If you use an ordinary bit to drill brass it has too much rake and can hook into the brass and do nasty things. Try reducing the rake angle on the drill bit to zero by rubbing the cutting edges on an oilstone for a while. Or very gently touch them on the fine grinding wheel. That way instead of an acute cutting edge where the helix of the flute meets the cutting edge, there is a small flat spot parallel with the drill axis. (It may be clearer to google a drawing!)

[HopperParticipant @hopper]

Heres a link **LINK**

[Michael GilliganParticipant @michaelgilligan61133]

Can’t say that I recall it happening, Eric … but

A conventionally ground twist drill has an excessive rake angle for brass … so it seems likely that one flute of yours is grabbing, and this is pulling the drill.

Apologies if this brief post has been overtaken by events : I had to take a telephone call between starting and finishing.

MichaelG.

.

Edit: and so it was

Edited By Michael Gilligan on 22/05/2020 10:48:19

[SillyOldDufferModerator @sillyoldduffer]

Posted by JasonB on 22/05/2020 10:25:08:

As brass likes sharp cutting tools it may be that your drill that seems OK for steel is not cutting well in the brass and that is making it wander. …

+1. I keep two sets of drills, one reserved for Brass only. Brass likes tools to be sharp, and although I've never bothered, a different rake angle as per Hopper's advice.

Using a drill once on steel can be enough to reduce it's effectiveness on Brass, but drills too blunt for brass still work well on steel. So when I've knackered a steel drill I replace it from the Brass set, and the Brass set gets a brand-new one.

Same with files.

Dave

[Thor 🇳🇴Participant @thor]

Hi Eric,

I have never experienced your problem when drilling brass. As Hopper and Dave recommend, I use special drills for brass – they never touch steel.

Thor

[Anonymous]

At one time it was possible to buy zero rake drills for use on brass. So hardly 'sharp' in the conventional sense. I have a selection of slow helix drills for use on brass in the sizes I use most.

If you think brass is bad for snatching try bronze.

Andrew

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Andrew Johnston on 22/05/2020 11:09:22:

[…]

zero rake drills for use on brass. So hardly 'sharp' in the conventional sense.

.

An interesting distinction, Andrew … and worthy of discussion sometime

i.e. Is a 90° corner with no perceptible rounding ‘sharp’ ? … or not

MichaelG.

[Anonymous]

Posted by Michael Gilligan on 22/05/2020 11:16:58:

i.e. Is a 90° corner with no perceptible rounding ‘sharp’ ?

In a strictly mathematical sense yes; the curve is discontinuous and the derivative will be infinite. In the sense of sharp like a scalpel no.

Andrew

[Nigel McBurney 1Participant @nigelmcburney1]

Are you marking out ,then using a prick punch followed up with a centre punch and what size hole are you trying to drill,? or are you you trying to go straight in on a milling machine.

[JasonBModerator @jasonb]

Andrew, by sharp I meant not worn, I'm sure your zero rake drills would not perform if the actual cutting edge had become worn and rounded

I'd don't stone my drills or keep a special set, if enlarging a hole then I will add some drag from the tailstock lock if on the mill or feed using the handwheel on the mill not the lever feed, which seems to stop the problem.

[old martParticipant @oldmart]

I fully agree with Jason's method of keeping a firm control on the feed, it stops the drill from getting out of control, and should drill straighter. Try and find a new drill rather than a hand sharpened one.

[Anonymous]

Can't say I've noticed any difference between new and old (worn) drills when drilling brass. The last hole I drilled in brass was 1.5" deep and tapping size for 1/4" BSF. That's a drill I use a lot so it's pretty worn. The drilling was fine. The thread was only a 1/4" deep, but I took the opportunity to drill deeper to remove material that was going to be milled away later to form a slot. As far as I can tell the drill didn't wander, certainly there are no witness marks on the slot after milling. Apart from using slow helix drills the best antidote to snatching is to drill the hole in one pass, no stepping up in increments.

Andrew

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