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Jagged Countersinks

s10sakota

s10sakota

Well Known Member
I know I've seen a thread or two on this before, but the search didn't turn up the threads.

I am countersinking some holes in a piece of aluminum on a different airplane and they are coming out really jagged.

In the pic you will see the jagged hole, and the other hole I've smoothed out with the hand held debur tool.

But I've used the bit shown on the RV-7 and all the holes came out absolutely smooth and perfect.

What's going on now? Is the bit dull? I've tried high speed and low speed and the speed makes no difference. I've tried light pressure and high pressure and they all come out jagged. I can smooth them with the debur tool, but I'd rather them just come out smooth from the countersink tool!

Any thoughts?

Thanks

 
Generally when I've had chattering while counter sinking it has been when I'm not properly backing up the work piece. This allows the pilot to wander causing the results you're seeing.
 
I don't think that's the case here as I have two pieces of wood underneath the hole right up to the hole. So it's pretty solid under.
 
s10sakota said:
I don't think that's the case here as I have two pieces of wood underneath the hole right up to the hole. So it's pretty solid under.
Click to expand...

You know, right after I posted that, I looked at your signature and assumed you had covered that base:D. If every hole does it with that cutter, I would guess the cutter...
 
s10sakota said:
I don't think that's the case here as I have two pieces of wood underneath the hole right up to the hole. So it's pretty solid under.
Click to expand...

Try a piece of 1/8" aluminum instead. That worked for me. I'd let the countersink go into the aluminum, which was thick enough that the pilot remained constrained.

I use a very low speed for countersinking. I use a Dewalt battery drill.

The 1/8" aluminum part had other holes in it so that I could cleco it to the work using adjacent holes.

Dave
 
David Paule said:
Try a piece of 1/8" aluminum instead. That worked for me. I'd let the countersink go into the aluminum, which was thick enough that the pilot remained constrained.

I use a very low speed for countersinking. I use a Dewalt battery drill.

The 1/8" aluminum part had other holes in it so that I could cleco it to the work using adjacent holes.

Dave
Click to expand...

Same technique here - start very slowly and end fast once I know the cut has been initiated smoothly; always use the electric for this. Good call on using aluminum to back up the work. If countersinking a lot and using wood, I usually have to make a fresh hole fairly often as the hole quickly gets slightly enlarged and doesn't hold the pilot as well as necessary.
 
Chatter

s10sakota said:
I know I've seen a thread or two on this before, but the search didn't turn up the threads.

I am countersinking some holes in a piece of aluminum on a different airplane and they are coming out really jagged.

In the pic you will see the jagged hole, and the other hole I've smoothed out with the hand held debur tool.

But I've used the bit shown on the RV-7 and all the holes came out absolutely smooth and perfect.

What's going on now? Is the bit dull? I've tried high speed and low speed and the speed makes no difference. I've tried light pressure and high pressure and they all come out jagged. I can smooth them with the debur tool, but I'd rather them just come out smooth from the countersink tool!

Any thoughts?

Thanks

Click to expand...

Chatter is often the result of a combination of too high of a tool speed combined with too little cutting pressure. If you are already backing up your work with a piece of metal or wood, match drilled and rigidly clamped, then I would suggest using more pressure on the drill. Also pull the cutter off of the hole as soon as it bottoms against the stop.

Skylor
 
Countersink

The two flute piloted countersinks are prone to chatter for some reason. For years I favored the single flute but now favor a high quality multi flute. 2024 aluminum is less prone to producing countersink chatter than softer grades.
 
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