I was drilling some (13) holes is a 10mm titanium plate and everything was going fine and dandy until I wore out the last 4mm (.1575") 5% kobolt drill I had. I then switched to straight HSS. It broke in the first hole, about 1mm below the surface. The plate is on a fixture of aluminium and I "can't" remove it because I am pretty sure I can't get it back on with exactly the same rotation.
How do I remove the broken drill ?
I have 2 ideas:
1. Plunge 6mm carbide endcutting endmill on top of it and straight thru. The hole is going to be 8mm in the end so I have got room to spare.
2. Build a dam of model clay and use some kind of acid to remove the drill, but what acid ?
I would try the carbide. Put it in the mill, touch your carbide tool to the top of the broken piece of drill, then set the depth stop so it won't allow the quill to move down any farther, then peck while winding the depth stop down 10-15 thou per peck. That will keep you from digging in if you catch the tool. Don't be afraid to get your 6mm endmill up to about 800 rpm. Keep the chips blown away and you should make quick work of it.
As GREEN says, a carbide end mill should work. Hand y to have some "dull" carbide end mills around just for "digging" out broken stuff. We usually use carbide or "supertanium" drills on titanium.
I will try the endmill with depth stop [img]smile.gif[/img] Thank you.
Any strong oxidising acid won't attack titanium. Concentrated nitric would do a good job and also won't attack the aluminium, but keep it well away from your machines and yourself. Use gloves, rubber apron and face shield, and do it outside or in a fume cabinet. When you wash it off make sure it is diluted quickly because dilute nitric acid will attack aluminium and titanium. It could be neutralized with sodium bicarbonate. One of those odd bits of practical chemistry, concentrated nitric acid can be kept in aluminium containers because a layer of aluminium oxide prevents the acid from attacking, but dilute acid will dissolve the oxide, and then the metal. Same applies to titanium.
A carbide cutter is more practical unless you have access to a chemistry laboratory and are familiar with some elementary chemistry.
- Mike -
use a carbide anything at HIGH SPEED (saftey glasses)
preferably something around the root dia. of whats stuck
just plunge in a little at a time 'till it gets itself in the center...
and bore away.. chip away at it with no reguard t whats happening to the "cutter"
you will get the broken whatever out
i've done this millions of times and it works out great.. taps, end mills whatever is in the way
save broken carbide endmills, reamers, drills, whatever
and use them to remove the other broken stuff that gets in the way
it works (no coolant)
If you soak the tap in ferric chloride it should eat the tap away without hurting the Ti. I'm not sure what it will do to the aluminum though.
You can get ferric chloride in radioshack. They sell it as circuit board etchant.
I feel sure the carbide endmill will do the trick for you.
Just for future reference, though... I had a retired machinist come out to the museum one day and bring a pile of drill bits for me. He picked up a couple of really odd-looking butchered bits and asked me if I knew what they were for. I had no idea. "Broken tap removers!" he said.
The basic principle was the same as a non-center cutting endmill. The center of the endmill does not cut and neither did the center of these drills. He had used a tool grinder to remove the point and web of the drill about 1/4-3/8" up, leaving two teeth on either side... kind of a core drill. You straddled the broken tap (or drill bit in your case) and cored the metal out around it, leaving enough to chip out with a punch or grab with pliers and back out. Those bits now live in a very special place nobody else knows about.
Ferric chloride PCB etchant will eat aluminum even faster than it does copper. With a large enough surface area, the reaction is quite violent, with all matter of smoke and fumes given off....
If it would be easier to remove the broken drill with the Ti plate off of the machine, you could always use two or three existing holes (before you wore out your cobalt bit) and re-drill them into the alum fixture and then insert pins. The portion of the pins above the alum. fixture would probably have to be relieved a half a thou or so to ease removal and replacement of the Ti plate. Would keep you pretty close to your original set-up. As for removing the broken drill itself, follow what some of the others have already said.
Just a thought!
That's a smart idea murf. Thank you!
I will do that if the carbide endmill shouldn't work. I should have thought about that myself