# Chatter after Pilot Hole



## EmilioG (Oct 26, 2014)

I'm very new to machining but learning quite a bit quickly from all the great posts and info here.
I've been drilling holes in 1018 steel with a drill press using a hole starting bit or spot/center drill.
Sometimes I get chatter when I start the next size drill up after a shallow pilot hole.
I;m thinking that I may be using the wrong point angle, i.e. 135° drill after a 118° starter hole drill.

Do I need to follow the correct sequence of point angles or is the chatter from something else?
The holes are 1/2" in 3/8" thick 1018 steel.  Could it be a speed problem? Not sure of the RPM's
on the last attempt.  The drill press is very old with a lot of run out. (I saw this when I reamed a few holes
the other day and the long reamer showed how bad the run out is).  The holes don't come out elliptical
but clearly not even close to round).
Thanks. I'll take all the help I can get.


----------



## chuckorlando (Oct 26, 2014)

Never used one after the other so I dont know. But in thinking, seems the 135 would  start out only cutting on the very out side edge of the pilot till it sits all the way down. When you step up make sure each step is no bigger then the web of the next step.

Think of it like sticking a triangle inside of another triangle. If the same angle the larger triangle will still fit in snug till it bottoms.

If the first triangle is smaller angle the larger one will hit the sides at the top but touch nothing under that edge

If the first is larger angle then the second one will bottom out but have side clearance all the way up. So only the point seats.


----------



## John Hasler (Oct 26, 2014)

Try a lower speed.


----------



## Terrywerm (Oct 26, 2014)

It is not uncommon to experience a little bit of chatter as you start a drill bit into a pilot hole. This can happen when one cutting edge encounters the work before the other one does. This is a common problem if your chuck has quite a bit of runout, the drill bit is bent or mounted incorrectly in the chuck, or can happen if you do not have the pilot hole centered beneath the larger bit. In many cases, getting the drill bit working faster (increasing rate of feed) will resolve this problem. This does not mean running it at a higher speed, however. Many times reducing the rpm of the drill will help also.


----------



## Pat of TN (Oct 26, 2014)

Hmm. I find that, if drilling with a pilot hole, a slower speed is necessary than if going without a pilot. Now, a _spot_ is different. A small dimple or very shallow hole to make sure the drill remains centered, but with nothing through the part, is a spot. A pilot drill would be, say, drilling through the part with a .125 drill and then with your 3/8 drill.

Just to clear up any misconceptions!

I also find that, if one is drilling with a pilot hole, the drill will seem to chatter until it gets down into the part a ways. 

Although... Having a loose drill press certainly doesn't help either though, and may indeed be the source of the issue entirely...

I would add more, in concurrence with monsieur Terrywerm above me here, that the rule of thumb when chatter is experienced is very simple - reduce your cutting speed (RPM), increase your feed.


----------



## EmilioG (Oct 31, 2014)

Pat of TN said:


> Hmm. I find that, if drilling with a pilot hole, a slower speed is necessary than if going without a pilot. Now, a _spot_ is different. A small dimple or very shallow hole to make sure the drill remains centered, but with nothing through the part, is a spot. A pilot drill would be, say, drilling through the part with a .125 drill and then with your 3/8 drill.
> 
> Just to clear up any misconceptions!
> 
> ...





Thank you all very much.
I did manage to get past the chatter and finally drill through.
I did notice that my final 31/64" drill bit got a tiny chip on one of the cutting edges.
On this old drill press, 
I will not use pilot holes. Just shallow spots.

I will also use the Bridgeport with the Jacobs chuck from now on.
Can I save the drill bit?  I was going to use it for brass next.

I've read that a bit used on steel shouldn't be used on brass, true?
I'm thinking that I can use the bit after a dull the cutting edges, which in this case
has the tiny chip which can be dulled back.
Thanks again!


----------



## NightWing (Oct 31, 2014)

Standard practice in screw machining is using a stubby 90° spot drill that will leave a chamfer on the edges of the drilled hole.  Most finished parts call for a 45° chamfered hole.

Anyway, the hole to be drilled will have a greater angle than the spot drill, 118° or 135°.  That drill will start cutting on the outer lips against the 90° seat which will cause the drill to track true and make a hole before the chisel point meets the work.  The chisel point on long drills is what makes the drill wobble when contacting the workpiece.  Having it supported and stabilized by the hole it drills before the point gets involved gives straight holes.


----------



## Dave Smith (Oct 31, 2014)

One trick to eliminate the chatter is a small section of cloth between the bit and hole---not a big rag and just let go of the small cloth piece as soon as the bit grabs it and starts drilling---I know it doesn't sound safe but it sure works--the cloth piece shouldn't be larger than 3'' so your fingers can just release it when the bit grabs it----if you don't feel comfortable or safe trying this method then don't------Dave----I don't know why this works but it does--especially in thin metal


----------



## Ebel440 (Oct 31, 2014)

You should have the hole either spotted or countersunk to a diameter larger then the drill your using. If the hole has square edges it can cause chatter or chipping of the drills edge.


----------



## EmilioG (Nov 1, 2014)

Thank you.
I will try these different methods on scrap metal to try and test, even the 3" rag trick.
So if want to end up with a 10 mm hole, start with a punch mark, then a spot or center drill.
Then move up to the 10 mm drill bit? This would require quite a large spot drill. I've read that a spot drill should
be 70% of the final drill size. (Guhring website).  I've also seen machinists use a countersink.
I will have to buy a countersink set. Keo?

Last, I think I made the mistake of drilling my spot and starter holes too deep. Shouldn't I keep the
holes shallow? All thoughts welcome. Thank you.  This site and it's members are knowledgeable and generous.


----------

