snapped centre drill

[kayzed1]

  snapped a centre drill in a lump of Brass starting a 2mm hole, is it start all over again or is there a way to remove said tiddly bit of steel? i do hope so as it was the last of 12 tapping holes and no room to move the hole...Ta!
Lyn.

[awemawson]

Of course I'd say use a sinker EDM machine as I have one 

... but you need to research if anything will dissolve steel and not adversely affect the brass - though nothing comes to mind


(or you could quickly make a 'tap dis-integrator'  - they are very simple - google them ) At the simplest, a vertical armature with a copper tube running through it is attracted upwards into an electro-magnet. As the copper tube was resting on the victim and making the circuit, the armature falls back and the cycle continues - just like an electric bell or buzzer (though they use springs rather than gravity)

[Ed ke6bnl]

I have herd that for aluminum and maybe brass Alum placed in the hole and maybe a dam for containing the fluid will eat away the steel. Never done it,never found the alum. maybe available at the pharmacy. EDM can remove it. and lets here from the ones who know. Found this on wikiAlum solution has the property of dissolving steels while not affecting aluminium or base metals, and can be used to recover workpieces made in these metals with broken toolbits lodged inside them.[5] As considerable expense and/or effort may have gone into machining a specialist part, this can be a worthwhile exercise.

[krv3000]

hi well you can skim so much of the end of the brass bar to expose so much of the broken bit to get hold of it with sum thing to remove it or set to with a diamond coted bur that goes in a dermal and grind it out or get sum acid car battery acid works well stand the bare up right and mack a well  to hold the acid and pore sum in and lave fore a week

[Stilldrillin]

Lyn.
 Can you drill through, from the other side?
Then tap the ensuing hole. Loctite/ solder in a screwed plug, and re drill.

I rarely use centre drills. Always use a spotting drill...... http://www.ebay.co.uk/itm/3mm-HSS-Co8-90-DEGREE-NC-SPOTTING-SPOT-DRILL-EUROPA-OSBORN-8214020300-D25-/271833566150?hash=item3f4a8b0bc6:g:THIAAOxyrx5TjwAq

David.

[Joe d]

soaking it in a warm to hot alum solution will (albeit slowly) work.


Here's a picture of my set up the last time I needed to do this


It will give your brass a nice weathered look, so brasso may be your friend afterwards.

Joe

[Ed ke6bnl]

where did u get the Alum

[Joe d]

I bought it at the pharmacy, where it is stupidly expensive.  If you have a WELL equipped grocery store
in terms of pickling and preserving supplies, you will get a much larger container for far less than it cost me...

[woodguy]

Bulk Barn Franchises carry it.

[kayzed1]

Many thanks one and all, David, i can not go through from the other side as it is a Cylinder with a flat one side for the valve chest.
I will give the Alum a shot in the week.
Lyn.

[sparky961]

Bulk Barn Franchises carry it.

That's cool... never seen it there. How is it sold? Bulk powder, boxed, liquid?

I took a few minutes to read about it and it seems to have so many uses you wonder if they all have merit.

[Will_D]

Alum is Aluminium Sulphate.

Aluminium Sulphate is used and sold as a "Styptic Pencil". This is used to stop the nicks bleeding when you wet shave. Most pharmacies should still have them (I bought one only a few years ago for a couple of €)

You will get about a 1" long by 3/8" diameter piece of Alum. Crush it up and disolve in hot water.

[borriss]

I read this on another forum so cannot give credit but it works.
You already have the solution at hand. Get the broken centre drill and using a cut off wheel on your angle grinder cut a groove the same width as the broken tip straight into the end of it deeper than the length of the broken tip. Then put your ground centre drill in the lathe and attack the end of the brass. You will effectively trepan around the broken piece and it will be easy to pick it out. Use the next size centre drill and recut the centre and Bob is my son's name!!!!
Borriss

[borriss]

PS I just reread your thread. If this was done in the mill or drill you can still use this method but it will involve clamping it down rigidly.
A tip: Always run centre drills speed as per the tip diameter.
Hope you have success,
Borriss

[SteveT]

This some times works, try heating the brass as it will expand more that the tip of the centre drill and give it a good tap from the back, also try gently moving the tip back and forward as it can some times release the trapped swaff. Best off luck

[Jonny]

Even easier just break up the broken centre drill or what ever in the hole, works every time.
Blind holes can be more intricate certainly small items ie 7BA.

[Arbalist]

Next time try using a spotting drill. 

[kayzed1]

I think i may have some spotting drills in some far away draw mind i did wonder what they were for when i got them some years ago. I will give the heat a try tomorrow while i await the Alum i ordered from Eblag..
Many thanks all. Ow! i forgot to say, i can not do photo's as my broadband is so slow, around the old dial up speed as i live in the back of beyond BUT. we are getting Fibre very soon, then you can look out it'll be pics every where.
Lyn.

[Stilldrillin]

Lyn.

Centre drills, are for drilling holes, for centres.

Spotting drills, are for spotting drilling positions. Also, for leaving a chamfer, around the finished hole.......

David.

[sparky961]

Lyn.

Centre drills, are for drilling holes, for centres.

Spotting drills, are for spotting drilling positions. Also, for leaving a chamfer, around the finished hole.......

David.

I've been baffled by how many professional experienced machinists are oblivious to this fact. I've even been told at the very beginning (while using a spotting drill) that I should use a center drill to start the hole.

[Stilldrillin]

That's quite true Sparky!

Anyone who has any drilling finesse. Will feel the drill chatter, as it opens out the small diameter, before settling into making it's own hole......

David.

[ieezitin]

Spotting drills makes a concentric hole to drill through the zero axis of the job. Center drills are for prepping for a job between centers giving the lead angle for the taper nose. A two for one. The end of a center drill is a spotting drill.

spotting drills give the concentric axis and taper for the drill to follow, a drill bit will follow an askew lead if off center, hence why spotting drills are short or stubbed, a sturdy force over less length.

QED.

Anthony.

[sparky961]

The end of a center drill is a spotting drill.

While technically this may be true, this statement strikes me as a bit misleading to those with less experience.  The end of a centre drill is way too small and fragile to use for every day spotting of hole locations.  Not to mention that if you penetrate the material deeper than the cutting lips of the small point, you've defeated the purpose of spotting/"centre drilling" in the first place.

Does it work?  Sure it does.  I'll even use a centre drill to spot holes if it isn't too critical and I have one sitting right there beside me.

Would I trust it for anything I wanted to be absolutely "spot" on?  Nope.

But I'm digressing horribly from the original topic of this thread.  In this instance the best reason not to use a centre drill is that you're making an operation more risky than it needs to be.  If you break off the tip of a centre drill occasionally, that's par for the course.  Been there, got the T-shirt.  If, however, you break off the end of a spotting drill in a part..... well, worrying about the drill wandering off a few thousandths this way or that is the least of your problems.

An option I favour that hasn't yet been mentioned is to use "stub length" or "screw machine" drills.  They are much, much more rigid than their "jobber" counterparts.  Most of the time you aren't drilling more than a few times the diameter anyway so the extra length is just extra length.  They're stupidly expensive to purchase, but making your own set by cutting a regular length set is excellent practice in drill bit sharpening.  With care, properly sharpened stub drills can be used on their own for all but the most critically located hole.

[awemawson]

Don't forget that if you do cut jobbers drills down to stub drill length, the diameter won't be accurate as drills taper slightly to create clearance. They will cut slightly under size.

[Arbalist]

The end of a center drill is a spotting drill.

While technically this may be true, this statement strikes me as a bit misleading to those with less experience.  The end of a centre drill is way too small and fragile to use for every day spotting of hole locations.  Not to mention that if you penetrate the material deeper than the cutting lips of the small point, you've defeated the purpose of spotting/"centre drilling" in the first place.

Does it work?  Sure it does.  I'll even use a centre drill to spot holes if it isn't too critical and I have one sitting right there beside me.

Would I trust it for anything I wanted to be absolutely "spot" on?  Nope.

Agreed. I've had holes go off centre on very small parts in the Lathe by starting holes with a centre drill. Using a spotting drill proved far more accurate for me so I'm not sure the point is the same. Many folks, particularly newcomers don't know what a spotting drill is though much less have several in the cupboard. I should add that unlike some I don't use mine for deburing or countersinking, I use a countersink for that!