Chattering counter sink with brass

CODEMAN

CODEMAN

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I'm using center drills to countersink brass. It chatters pretty bad. Is that because I have drilled a pilot hole, or is it because of the rake of the center drill? I've ordered some diamond files to change the rake of my set of drill bits as I've been having issues with chattering, especially when I move to larger bits like 1/4". Are there countersinks like burrs rather than drills that I should be using?

Steve
Sudbury, VT
Big time noobie
 
Try slowing the rpm way down for brass. T usley run about 60 rpm or so.
 
Steve, what machine are you using. Brass tends to fight and bite if you don't have a rigid setup and machine through a pilot hole.
What screws are you countersinking for? Screws with a 90* (included angle) head? Most center drills have a 60* angle.
If you are using the type of center drill that I think you are then then yes, the rake angle in the flutes will help it to bite into brass.
 
One trick I have used is to place a small piece of cloth or heavy paper over the hole before running the counterbore in. It seems to dampen the vibration a bit. Of course the general fix for chatter is increase feed and/or decrease speed.
 
I'm using a bench top single speed drill press, so no way to change the speed that I'm aware of. I suppose I could use a hand drill and slow it down, but then I'd be risking an off kilter countersink. I got a heavy duty screwless vice so the work is held down pretty good while I'm drilling but I'll try clamping it down as well.

What size pilot hole should I use to drill a 1/4" hole. What are the rules for pilot holes in relation to finished hole size?

Steve
 
Shorten everything up as much as possible, feed the countersink very slow, spin your chuck by hand or a pin or the key, not under power, you should be able to clean up the chatter.
I've found for brass that the countersink's you get for wood with the single flute seem to work well.
A pilot hole usually works well if you don't go bigger than the web of the finish drill.
If your only option is that center drill for a countersink right now go to the depth you need with the CD first, then open up the hole.:))

Edit: I wonder if a light dimer would work for slowing down that single speed drill press when you need to, or if that would be to hard on the motor?:thinking:
 
Last edited:
CODEMAN said:
I'm using a bench top single speed drill press, so no way to change the speed that I'm aware of. I suppose I could use a hand drill and slow it down, but then I'd be risking an off kilter countersink. I got a heavy duty screwless vice so the work is held down pretty good while I'm drilling but I'll try clamping it down as well.

What size pilot hole should I use to drill a 1/4" hole. What are the rules for pilot holes in relation to finished hole size?

Steve
Click to expand...

If using a CD for counter sinking DonB is correct, countersink first, then finish drilling to size. Also CD's are a 60* included angle. Most screws are 82 or 90 degrees. Get a set of single flute countersinks or the ones with a hole through them (pilotless countersink), when you can. I bought a set of Hitachi single flute counter sinks from the local big box store, they were ground incorrectly and are useless in metal, never tried them in wood.

For deburing and and non-accurate countersinking I keep a countersink in my hand drill on my bench. Low speed range, and variable speed, turn it slow.

Normally a 1/4 hole and smaller does not require a pilot, and many times I will drill up to a 1/2 hole with out a pilot hole depending on the material and conditions. In general, you want a pilot drill that is just smaller than the web for the finish drill.

I wonder if a light dimer would work for slowing down that single speed drill press when you need to, or if that would be to hard on the motor?
Click to expand...

A light dimmer will not work for an induction motor. It may work for a universal motor (brushed type AC motor). A fan controller might work on a very small drill press motor, in that you would be able to turn the motor down after starting it at full speed, but the speed regulation would be very poor because a drill press is a variable torque device. And there would be a chance of burning up the motor when you drop into the start windings by running too slow.
 
For drilling brass NO pilot hole drill what ever size you need in one shot.Same goes for plastic's.
 
Countersinks with only ONE cutting edge cut smoother than those with multiple edges. There are also the "0" flute countersinks,which still have only 1 cutting edge. I just use the single cutting edge ones,as they can be sharpened readily,and they will do smaller holes than the "0" flute ones(which have a hole drilled through them to produce the cutting edge. You will have no trouble with a single edge countersink.
 
Ok…plenty of single flute countersinks on Amazon. So what degree? 60, 82, 100? I'm using it for typical #8 wood screws.

STeve
 
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