drill hole

[larry53]

Has anyone have the same problem I have had and found a solution?
I was drilling a 15/64 hole x 2 inches deep in 12L14 steel after centering drilling. All was done on a lathe. The hole was not concentric on the oppositive end. It had around .015 runout on the diamenter. I checked my tailstock and made sure it was inlined. Tried again with same results. I then tried a larger size hole that was 3/8 diamenter and it was true. The bit is walking to one side as it drilling. It is a new jobber length drill bit. What other drill bit would do better? The drill bit is high speed steel. Larry

[lakeside]

split piont drill

[DareBee]

Your problen is likely an improperly sharpened drill bit.
A perfectly sharpened drill bit is more important than most people realize, and I know a lot of journeyman that can't even get it right.

As Lakeside mentioned, using a new HQ splitpoint drill is guarenteed to work perfectly.

[HuFlungDung]

I'd classify the problem as "just one of those things" that you have put up with in a simple deep hole drilling operation. If drills always drilled dead true, we wouldn't have to drill, bore and ream to obtain precision.

But, there are steps you can take, if your drills look properly and evenly sharpened. Make sure the end of the stock where the drill enters is faced or setup so that the face of the part is running dead true. Any slight angular error of this surface can make the drill walk off center. While it might only be a miniscule amount at first, any error at the start of the hole tends to accumulate the further in you go.

For an accurate drilled hole, start the hole with a spot drill, not a center drill. This rule applies to drilling holes on the mill, so I don't see why it would not apply to lathe. This is because the included angle of the spot drill creates a starter hole that matches the drill angle, whereas a center drill makes a hole that does not guide the drill bit, but allows it to shake and rattle around until the drill penetrates and creates its own path, and who knows where that might be.

If you want to take the trouble, drill a slightly undersize hole, bore it or redrill it with a sharp endmill which will serve as a crude boring bar and will straighten the hole if it has gone crooked. Then, continue drilling with a drill that is the same size as the endmill, making use of the true part of the starter hole as kind of a drill bushing.

[Mike Mattera]

Guhring Drills are the best. I looked at some drill points under a microscope (1mm drills) and nothing compared to the quality and precision flute of the Guhring drills.

Mike

[william1970]

try a cobalt split piont (135 DEG.) drill. not sure what rpm's your running but maybe to high of sfm? also are you using any coolant or cutting oil? If still not working maybe try piloting hole.

[nathwil]

You can also spot drill a little deeper and bore just past the drill point depth. If you make the hole size close enough you can keep the drill from walking off center. This helps when the drill is a smaller one or the drill chuck is worn. If the drill is sharpend wrong nothing will help.

[One of Many]

Look into D-bit drills. These are like gun drill bits, but cutting load can be a little better since it is half flute verses 1/4 flute. They have many benefits with hole alignment and true size, some consider them D-bit reamers.

DC

[little bubba]

I've run into this problem a couple of times. Had a 3.25" deep hole .188 diameter. The way I cured that one was to keep decreasing the feed until the hole stayed centered, not great for productivity, but it got the job done. The other times, its usually a crappy or roasted drill, or the drill isn't centered and square.