View Full Version : 135 Degree Split-point Drills and Chatter

01-14-2009, 09:58 PM
Anyone else notice that the 135* split points seem to chatter more on entry? I notice it only on my mill and drill press, although I suspect that is due to the part/drill not being held securely. My little Smithy mill is a piece of junk! The spindle walks around when you put a thrust load on it. In the case of the drill press, I rarely clamp anything down rigidly (its a dinky DP anyway). So, in these two cases, I've noticed that the 135* split points walk a triangle for the first .1" or so.

Although they take less effort to force through the material (especially important if your drilling through 3/4" steel with a hand drill!), I've had much better luck getting a nicer looking hole with 118* point drills.

Now, if I was really concerned with the quality of the holes, I'd be clamping stuff down, drilling under size and reaming or etc. I was just wondering if anyone else had noticed this. Perhaps it has to do with the fact that the spot drill or center punch mark is usually 60*. I seem to recall reading that the 135 split points liked a 90* spot drill. Is that right?

(Lane's thread about using a 90* spot drill to chamfer parts reminded me of this)

01-14-2009, 10:08 PM
I only use the 135degree and do not have that problem, I do use spot drills, not center drills and almost never punch marks, you want the spot drill to be as close to the 135 degree as possible for drilling, this will give you the greatest contact area.


01-15-2009, 07:25 PM
All I use are 135 chip point drills and never have a problen if the point is ground right and centered on the drill. also with the 135 drill you dont even need to center just go ahead and drill but part needs to be tied down.

Frank Ford
01-15-2009, 07:36 PM
Me, too. As soon as I could afford it, I replaced every 118 degree drill in my home shop with 135 split points, and have added more of them along the way. As to chatter, I can't recall any specific difference.

01-15-2009, 08:03 PM
I only notice it with new 135* drills. I got a set in trade for some work on a barn. It was a brand new Chicago Latrobe cobalt set. I noticed it with them and with a set of triumph thunderbits with the 135* split point. The common sizes on the thunderbits are working nicely now. I've used them enough they don't seem to chatter. It's almost like they're too aggresive. They just feel different when drilling and you have a damn hard time keeping the part from moving around. Like I said, when I use them in a "proper" mill, like the BP's at work, and clamp the part down, they do great! I had to poke a whole punch of 3/16" holes in some 304 SS .25" thick flanges (a total of 120 holes), and it cut it beautifully.

I dunno ... maybe I'm just loosing it ;)

01-17-2009, 01:50 AM
My tool catalog suggests that some drill point angles are more suited to drilling some materials than others. I believe the 135's are marked for the annealed form of some of the harder steels.

dan s
01-17-2009, 03:51 AM
I noticed it with them and with a set of triumph thunderbits with the 135* split point. The common sizes on the thunderbits are working nicely now. I've used them enough they don't seem to chatter. It's almost like they're too aggresive.

I use ThunderBits as well, and I find that I have to push them harder or they chatter for me as well. when i push them hard, they make nice little chips even in steel.

I'm still new to drill grinding terminology, but I think the angle of the secondary facet is really severe? According to the Triumph catalog the ThunderBits have a "quick penetration split point" maybe that has something to do with it.

01-17-2009, 03:56 AM

I think you may be right. This might help:


01-18-2009, 12:06 AM
As far as spot drill angle vs. drill angle, the spotting drill should have a larger angle than the drill you are using so that the drill starts cutting with at the center rather than farther out on the lips. I learned that HERE (http://www.practicalmachinist.com/vb/archive/index.php/t-159845.html). I still will spot with a 90* drill-mill when it makes life simplier (less tool changes) and I haven't bought any 140* spot drills yet but I have been using 120* spot drills lately and it works much better for 118* drills.

01-18-2009, 11:52 PM
Not refuting or disagreeing with what you are saying, however, that may likely be referring to or a spin off of indexable drills where a center start is required for best operation. The fullest contact will result in a drill having the greatest difficult in wandering.

In the end, I guess it is always what works for you that is correct.


01-19-2009, 11:05 AM

I am saying you want the spot angle to be equal to or greater than the drill angle, so I think we are saying the same thing. Trying to start a 135-drill in a big 90* spot will result in chatter. The whole PM discussion was about solid drills and there are definitly various opinions. The indexable drills I've used (not many) don't require a spot at all. Since switching to 120# spots, the 118* drills don't squeal when entering the spot. It's like when one is step-drilling a hole on a drill press, when the bigger drill first starts it wants to chatter as it catches on the lips.

FROM INGERSOL (http://pdf.directindustry.com/pdf/ingersoll-cutting-tools/hole-making-catalog/17869-11078-_93.html)

Now at work I spot to a depth that will leave a nice chamfer so another tool/op isn't needed. On manual machines with a small spot, the angle won't really matter that much.

As far as the OP, my guess is that it may be that being split-point they drill with less tool pressure and they need more feed.

01-19-2009, 11:39 AM
We are close to talking about the same thing but not quite, after looking at the Ingersol link it seems that I was just plain wrong, not so wrong that it caused troubles, but wrong none the less. My next spotting drills will be at a greater angle.



dan s
01-19-2009, 12:02 PM
who makes a 150 degree + spot drill? The highest i have seen is 120.

01-19-2009, 12:31 PM
If its chattering on entry you aren't feeding it hard enough, and in 304 that is the kiss of death.

01-19-2009, 12:46 PM
Thanks for the graphics, OT.

I did notice that they take a more aggressive feed to reduce that chatter issue, but I can't ever make it go away using my machines. I had no chatter issues with the SS. In fact, I found the SS to be very agreeable to the operations I was doing. I just had to slow it WAY down when I was facing the flanges in the lathe or it would start singing.

My cock-n-bull story is that the split point, not the angle, is causing the issue. I reckon it's too "aggressive" for a spindle with bad bearings or a work piece that isn't tied down.