Lathe drill not cutting

I need a 1/2 hole in a 5/8 OD 2" long piece of steel so I center drilled it then drilled a 5/16 hole with no issues. When I try to finish with the 1/2 drill bit, it just squeals and overheats after less than 1/8" deep, no long curly chips. Also tried a 31/64 bit with same result. Both bits are sharp but behave like they are dull.

If its squeeling screaming and smoking, I'm going to guess you are running it a bit fast.

2nd thing. As a general rule, drills don't like going down drilled holes. My general rule is never stick a drill down a hole that is bigger than 1/3 its diameter. Ideally pilot drill just enough to clear the chisel point or the web of the drill.

You should probably pilot with something smaller than 3/16, and you'd be ok.

IF you must try stuffing a drill down a big hole. Putting a chamfer on the corners seems to help it quite a bit.

Thanks. I am only running about 350rpm. I did try progressively larger bits in 1/32 increments from the 5/16 with some success but the 31/64 still squealed and overheated. I think the thin wall has alot to do with it. probably flexing and just rubbing the bit instead of cutting. Anyways I got to about 7/16 and bored the rest out with the entire piece inside the chuck jaws.

Quick and dirty

Personally I would just spot drill the piece just enough to prevent the drill from wondering and go right through with the final diameter. No sense messing about with pilot drills. Just as previously mentioned, if the chisel on the final dia. is larger than the pilot your gonna have problems. I suffer from the same problem too a lot I make things more complicated than needed, I get the work done, yes, but could eliminate a lot of measuring and scribing. I guess it dependes no how tight the tolerance is in the end.

Best of luck

martik777 said:

I need a 1/2 hole in a 5/8 OD 2" long piece of steel so I center drilled it then drilled a 5/16 hole with no issues. When I try to finish with the 1/2 drill bit, it just squeals and overheats after less than 1/8" deep, no long curly chips. Also tried a 31/64 bit with same result. Both bits are sharp but behave like they are dull.

Click to expand...

Your "Piece of Steel" is not low carbon and you work hardened the outer edge when you started drilling with the 1/2". To prevent this you have to slow down considerably when starting the hole. Never use a light feed rate and let the bit linger on the surface.

To fix if you work harden another one. Grind a bit of a negative on the leading edges of the larger drill, slow way down and use a heavy feed to break thru the hard surface. If you have extra stock length then face off the hard surface.

When starting a hole from solid or c'drilled we can use a decent feed rate right away. When opening up an existing hole we have to baby the feed in order to get a clean start. This is where the problems begin.

Walter A.

Hello Markit777
I agree with those above. Eliminate the pilot hole = eliminate the problem. This seems to be a common problem. Lots of people think it will be easier if they step up the size of the drill bit instead of doing it in one pass. It's not.

Disclaimer: I'm not an expert, just passing on information on what works for me.

Regarding pilot holes...

Although this mainly applies to much larger drills, and is common knowledge among the many working machinists who are forum members, many of those new to the trade could use some extra information.

Pickup a drill and point it toward your face. You will notice that in the middle there is a section shaped like a chisel. This center area of the bit is the web. If you use a drill bit to drill a shallow hole you will see that the center of the hole looks a little rougher than the outer surface. This is because that chisel section cuts with a rotary chisel action that works just like it sounds.

Pick up several drills and look at the ends. You will find that the thickness of the web changes along with the drill size. Small drill= small web. Pushing the web through the material takes much of the available spindle torque and with very large drills that is considerable. With small holes most machines have more than enough torque to push the bit through and you just need to use a combination center drill or a spotting drill to get the hole on location. Just keep in mind that what will work in one machine may not work in a smaller machine (or by hand).

In theory, if you drill a pilot hole equal to the larger drill's web thickness, then the larger drill needs less torque to turn (& cut). In actual shop conditions there are other factors in play such as spindle rigidity, material type, set up conditions, drill grind angles, etc. On a large radial drill I can push a 4" drill through material with only a 3/4" pilot hole and get no chatter. But, only up close to the column. When the hole is 6 to 8ft away from the column I then get chatter and have to adjust feed, speed rake angle or all of those. I also may need to "Thin" the web but that is a whole different skill.

Start with the theory and figure out what works for you in each situation.

Some who are new to the trade do not take the time to learn how to sharpen drill bits or how to properly drill holes. With a decent drill press a good machinist can drill holes on size and accurately located. Take the time to learn more about drilling and it will serve you well.

Walter A.

All good ideas and things to check. The first thing that came to mind is the grind of the drill. Even if the drills are factory, there is a good possibility that they are not ground for what what you are doing.

Quit sneaking up on the finished dia. Want a 1/2" hole, use a 1/2" drill. If is a fussy dia drill 1/64" under and ream. If you want less drilling pressure, thin the web. Sneaking up on a hole size is a recepe for disaster. Peter

Thin the web of the drill and ram that drill hard and fast. if you cant drill a .500 hole then you might try cooking hot dogs for a living.

this thread is pathetic.

While you're taking a break from the hot dogs, if the steel is 1018 drill at around 600 rpm it it's alloy steel drill at 400 rpm. Use coolant. Soluble oil and water between 50 to 1 and 100 to 1. Oil is the small # Peter