Drilling A Hole Vs. Milling A Hole - Bit In Lathe Tailstock

[BillWood]

After reading a few posts on the internet I used an endmill to create a 12mm hole in a 15mm diameter piece of steel.

Two flute milling cutter in jacobs chuck in tailstock of lathe.

No Problem - easily and quickly done.

And yet if I had gone the drilling route ie pilot hole then increasing hole size with incrementally bigger drill bits in jacobs chuck in tailstock it would have taken several passes increasing the drill size each time, and I can tell that my little lathe (SB 9" clone - Aussie Hercus doesnt like the larger diameters and sometimes the MT2 taper will start to turn in the tailstock.

Why is it so easy with the Mill Bit and such a hassle with the drill bits ? I get the impression there is more to it than maybe the mill bit is sharper than the drill bits.

Reading between the lines of old books and magazines it not uncommon for the MT2 taper to spin in the tailstock when drilling - people discuss different ways of preventing this, with various "handles" sticking out to stop against the ways.

Oddly enough this lathe has no problems drilling small diameter holes yet theoretically it is well underspeed for small drill bits with a top speed of 720 rpm - If I use 100sfm for mild steel cutting speed then my criticial diameter is 0.53"

 

[T Bredehoft]

Out of curiosity, how close to 12 mm was your hole? And wasn't your Jacobs chuck on a MT2 driver? But it didn't slip? I have to ask, how hard were you pushing the end mill as compared to a 12 mm drill?

 

[Ulma Doctor]

I have a beautiful little 1976 Hercus ARH 9" lathe, the drill chuck will spin if you are too aggressive with a drill bit.
great, well made machines!!

for the same size tool, a drill bit will have more cutting edge exposed to the work due to it's cutting edge angle- whereas the 2 flute endmill would have a relatively flat cutting angle and less cutting edge contact
and endmills are usually a lot shorter too, less flex

 

[BillWood]

The 12mm hole was for a rough as guts collett which has how done its job and the original hole size is now impossible to determine - but I will do it again tonight in a fresh piece of scrap and report back.

I was fairly surprised that I didnt have to push the mill bit very hard at all compared to the drill bits, and yes it was on the same MT2 taper tailstock mounted Jacobs Chuck that I use with the drills.

I am too much of a newbie to know whether or not my drill bits are sharp enough and I need to learm nore about how to assess this and how to sharpen them, am currently reading about this. Maybe a good test for me at the moment is "If a milling cutter is easier than a drill bit then you need to sharpen the drill bit"

I was fairly surprised that I didnt have to push the mill bit very hard at all compared to the drill bits.

But I only seem to have problems with drill bits at diameters around and above 0.5" - smaller than that no problems whatsoever, and I do see these references in the older magazines and books to using drive dogs etc on the tailstock to stop MT2 drill bits spinning in the tailstock so it does seem to have happened to other folk.

 

[JimDawson]

Consider that the endmill has a different cutting geometry than a drill bit. It doesn't require as much pressure to remove material. But, a drill bit of the same size can remove material at a much higher rate than an end mill is capable of.

 

[Bob Korves]

It is worth drilling a small hole even when using a center cutting end mill. The cutting speed at the center of the hole is zero, and the end mill does not have a chisel edge to open up the hole like the drill does. End mills can plunge like you did there, but they don't like it. They can also spin in the drill chuck. Using a dog on larger drills to prevent rotation will stop the spinning in the Morse taper. It is also a good idea to check the drill tapers and tail stock socket for damage and the fit of the drill in the taper to see how good the fit is. A hardened Morse taper tool or bushing of good quality and in new condition can check the tapers using Permatex High Spot Blue for marking and scrapers for removing burs and high spots. It is a bit tedious and can take some time, but those tapers can be tested and repaired for solid seating and for concentricity with the quill. A Morse taper reamer can also be a good tool to use judiciously.

 

[Wreck™Wreck]

Why is it so easy with the Mill Bit and such a hassle with the drill bits ? I get the impression there is more to it than maybe the mill bit is sharper than the drill bits.
"

Part of the answer lies in your question, if you can plunge an end mill to size in one shot why do you not do the same with a twist drill? Unless the part requires a flat bottomed bore which a twist drill can not do. There is no reason to drill a pilot hole then increase drill sizes in steps, spot drill then push the full diameter drill bit in in one operation, pecking for chip control of course. Step drilling is an excellent way to pull the chuck or drill out of the taper.

 

[BillWood]

Part of the answer lies in your question, if you can plunge an end mill to size in one shot why do you not do the same with a twist drill? Unless the part requires a flat bottomed bore which a twist drill can not do. There is no reason to drill a pilot hole then increase drill sizes in steps, spot drill then push the full diameter drill bit in in one operation, pecking for chip control of course. Step drilling is an excellent way to pull the chuck or drill out of the taper.

Ive been doing the incremental increase because I'd read about that method before I read about the straight plunge with the mill bit.

What do other SB9 or any other owners of small lathes do ?

 

[John Hasler]

I usually spot drill, drill full depth with a small diameter drill, and then go directly to full diameter. I find this faster than going directly to full diameter, perhaps because most of my bits are dull.

 

[Bill Gruby]

I use primarily MT2 Tapered shank drills in holes over .500 in the lathe. I stay away from drills wit altered ( turned down) shanks for rigidity reasons. They tend to chatter loudly in the lighter lathes.

"Billy G"