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Drill Bit Chatter?
- Thread starter randyjaco
- Start date
that's a complicated question to answer due to the variables unknown to me.
a few things come to mind....
drilling speed, is it too fast, too slow for the bit? large bits need to turn slowly, small bits need to turn faster.
are you using a pilot bit of at least 1/2 the size of the intended hole?
is your bit sharp, does it have sufficient clearance?
are your bits 118*,135*?
what hardness is the material being drilled? is your bit hard enough for the work?
are you using a lubricant during drilling operations?
What condition is the drill in? worn quill bearings?
what condition is the drills' table in, is it square and perpendicular to the quill?
do you hold the work in a vise, or mechanical hold down studs or does the work free float?
what materials are you drilling into?
as you can see the variable stack up quickly.
if you eliminate problems above 1 by 1 you'll get your answer.
these are by no means the only possibilities, merely a quick inventory of possible anomalies.
i hope this info helps out!
mike
)
a few things come to mind....
drilling speed, is it too fast, too slow for the bit? large bits need to turn slowly, small bits need to turn faster.
are you using a pilot bit of at least 1/2 the size of the intended hole?
is your bit sharp, does it have sufficient clearance?
are your bits 118*,135*?
what hardness is the material being drilled? is your bit hard enough for the work?
are you using a lubricant during drilling operations?
What condition is the drill in? worn quill bearings?
what condition is the drills' table in, is it square and perpendicular to the quill?
do you hold the work in a vise, or mechanical hold down studs or does the work free float?
what materials are you drilling into?
as you can see the variable stack up quickly.
if you eliminate problems above 1 by 1 you'll get your answer.
these are by no means the only possibilities, merely a quick inventory of possible anomalies.
i hope this info helps out!
mike
)
Lots of factors but need more info on what's happening in your case. What material are you drilling, what type of dill bit, 118°, 135°, flute type, drill bit material, hole & drill bit size, spindle speed, on a lathe, mill, handheld drill, etc.?
Let's just start with a nearly new 1/4" jobber's drill bit drilling half inch cold rolled at about 300 rpm with no coolant. Hole started with a center drill. Until the drill clears the center drilled hole it chatters like crazy. Then drills smooth as silk.
Randy
Randy
Mostly what I have found is that the age old solution to reducing chatter (decrease speed, increase feed) works here. Try putting a little more pressure on when you first contact (don't slam it in, but don't dally either). You may also check your center drill vs the drill point angle. A lot of people use combined drill and countersinks like so http://www.use-enco.com/CGI/INSRIT?PARTPG=INLMKD&PMPXNO=16720050&PMAKA=619-2294, even though that's really not what they are for, and they don't work particularly well (I am guilty of this too, but I am getting better about it... slowly). The problem is most of these are a 60 degree included angle, meant for lathe centers. Standard twist drills are 118 degrees, IIRC. Really you want your starter to have a wider angle than your drill. If not, then the edges of catch first, and the drill pirouettes around the edge of the starter hole and makes that great "kududududdududududud" noise until you you get some engagement.
I have started using a spotting drill more often, which is the "right tool for the job" and the results are much better.
Here's one like what I have been using
http://www.use-enco.com/CGI/INSRIT?PARTPG=INSRAR2&PMAKA=891-6781&PMPXNO=3906254
I have started using a spotting drill more often, which is the "right tool for the job" and the results are much better.
Here's one like what I have been using
http://www.use-enco.com/CGI/INSRIT?PARTPG=INSRAR2&PMAKA=891-6781&PMPXNO=3906254
USE THIS STANDARD MACHINE SHOP FORMULA:
| [SIZE=px"2"] Cutting speed (CS) X 4 [/SIZE]Diameter of cutter (D) |
70X4=280 =1120 RPM
.250 .25
I HOPE THE INFO HELPS OUT!
MIKE
)
The bit must be stabilized by one of two means, preferably both. First, the center of the bit, where the webbing is. If you have a pilot hole, you don't have a good center bearing point, and the flutes are free to float and grab. Every time they grab, the drill till torques against the rotation until the cutting forces exceed the grab strength and the bit will "unwind" and spin slightly faster until it tries to grab and twist up again. This repeated over and over and cause a noise much like chattering.
If you don't have a pilot, and on a 1/4" drill there certainly isn't a need for it, and if it is sharpened off-center the least bit, only one flute is doing the majority of the cutting, and this can be seen in the difference between the chips made by each cutting edge. This results in a hole that is oversized, and you lose support of the side of the hole against the bit. This is a loss of stability that can allow the drill to find it's resonant oscillation frequency and chatter and squeal.
When using a standard center drill, you don't need to go very deep. 1/16" is plenty. You don't need to go all the way to the full body diameter, that's for sure. At first, it's as I described in the first scenario. Then when you get the center support from the drill's web, things smooth out.
If you don't have a pilot, and on a 1/4" drill there certainly isn't a need for it, and if it is sharpened off-center the least bit, only one flute is doing the majority of the cutting, and this can be seen in the difference between the chips made by each cutting edge. This results in a hole that is oversized, and you lose support of the side of the hole against the bit. This is a loss of stability that can allow the drill to find it's resonant oscillation frequency and chatter and squeal.
When using a standard center drill, you don't need to go very deep. 1/16" is plenty. You don't need to go all the way to the full body diameter, that's for sure. At first, it's as I described in the first scenario. Then when you get the center support from the drill's web, things smooth out.
Most people do not realize that a regular drill bit has two cutting edges directly across from each other. ( 180 degrees apart) Once one edge grabs the tip jumps across the hole and the other cutting edge grabs creating a harmonic or chatter. If you had a drill bit with an odd number of cutting edges it would be less prone to chatter. Starting a drill bit in a center bit hole already creates a bit of a problem because the entrance to the hole is a bit large. Try spotting the location with that same center bit but do not use the 60 degree tapered part. After all what you need is a small lead hole the diameter of the web of the bit. For a 1/4 diamter bit you only need an approximate 1/16 th pilot hole.
Hey I am always putting my center bits in too deep creating a too large entrance and the bit chatters a slight amount. I get aggressive and the chatter is gone is a second. Also too large a pilot hole damages the cutting edge since the edges are overloaded on the corner of the pilot hole.
Hey I am always putting my center bits in too deep creating a too large entrance and the bit chatters a slight amount. I get aggressive and the chatter is gone is a second. Also too large a pilot hole damages the cutting edge since the edges are overloaded on the corner of the pilot hole.
Maybe I'm way off base here but drill-bit chatter happens on & off. Sometimes yes, sometimes no. Once in a while, it comes & goes while drilling the same hole. My theory/hunch: Uneven density of the metal in the workpiece.
All my bits up to this point have been TiN coated but I just bought 2 sets of black M2. I'll keep an eye open to see if things seem different over time. Maybe that will uncover more clues. -Just a thought.
Ray
All my bits up to this point have been TiN coated but I just bought 2 sets of black M2. I'll keep an eye open to see if things seem different over time. Maybe that will uncover more clues. -Just a thought.
Ray