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OT: Problems drilling 360 brass

Ron Hofer

Hot Rolled
Joined
Jul 7, 2007
Location
Brookfield, WI
Trying to drill 360 brass, which I thought would be easy peasy, on three different lathes, the largest of which is an old Clausing. On each, the spotting drill and/or the numbered drill would stop cutting pretty quickly, each having built up a 'point' of brass on the tip, stopping each from drilling further. I tried to search this in the PM archives, but didn't find anything in the last ten years. Any tips please? Thanks in advance.

Ron
 
Drills for most materials have a positive rake at the cutting lips. Brass wants a neutral or even slightly negative rake. Take a small slipstone or diamond paddle, and hone a small flat on the lips in a plane passing through the centerline of the drill. This will give you neutral rake.

Your description suggests you've got metal building up on the chisel tip of the drill. Try splitting the point on your drills. You can do this by hand on a grinder whose wheel is dressed to a sharp corner. Also, try lubrication or cutting fluid. (Not the same thing, but either one may help prevent buildup.)
 
If it's really 360, you should be able to go through it even with the spindle in reverse. Can you post a picture of the affected drill, with the buildup? Something must be off, like bad drill grind or badly off center tailstock, or ?

I agree with dubbing a drill for brass, but regular grinds work too as long as you prepare for the potential "grab" on breakthrough. If possible drill right to size, don't try a smaller, then larger drill - this invites grabbing.
 
The real problem with drilling brass is that it cuts too fast and the drill gets pulled into the work. So it grabs because it tries to take too big of a bite. That's why you need the reduced rake angle. As for buildup on the cutting edges, I would first dubb them as described above. You don't need a very large face at the zero rake angle, 1/64" to 1/32" wide is enough. When you do that, use a fine stone and some oil to give that new rake face a polished finish. And use some cutting oil when drilling. Peck to allow the oil to reach the cutting edge.
 
Thanks, folks, for the tips. I'll try them tomorrow. But one last question--I've been using a spotting drill to start. Is that bad practice? Thanks.

Ron
 
Depends, but unless you're removing the chisel edge from the drill it'll invite grabbing. If you have a split-point drill you can avoid the spot drill. And is it an actual spot, or a center-type drill?

And I'd still like to see a picture of the drill that was giving you problems...
 
Milland,

You're right; it's a center-type drill. And I can't post a pic because I lost the cable that connects my phone to my computer.


Ron
 
Get yourself a quality split point drill and see if that makes life better. Stub-length SP drills are what I use most, even though they're more expensive than the regular jobber drills. When I factor in time and accuracy benefits they're worth the money.
 
I agree about the rake is to much and it takes to much per rev. I have been either grinding or stoning the sharp edge off for years. Works well when hand drilling to in any soft material. Sorry for the fuzzy pic's
 

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definitely dont want a positive rake with brass as it will pull on drill especially if you have a pilot hole,.
.
morse taper drill or morse taper tool holder (drill chuck) will pull out often fast and rapid with things breaking and metal pieces going flying through the air.
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even if doesnt pull out of taper it will often go fast into part and stall motor. inertia of heavy moving parts stopping suddenly can easily do some damage
 
The positive rake and the chisel point can make brass difficult to drill. if you can face bump the edge to be no-rake/flat to a tad negative and run that same grind to near center so most/some of the chisel point is gone.

Then the brass flakes off in chips with not sucking the drill in to the stock.
 








 
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