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pntrbl
07-02-2009, 01:52 AM
I keep having a problem drilling deep holes with S&D sized bits from the turret on my lathe. I am looking to get 3-4 inches in deep which for all I know is a stupid thing to do in the 1st place. The flutes get underwater so to speak so I keep carefully pecking away to clear the chips, easing it in there because I know it's risky, but even so, tonight I got an 11/16ths bit bound in there so deep it ain't ever coming out! That one's over!

The lathe in question is an 11" Logan Turret. 1018 Steel. I had just ran a 9/16ths bit and was stepping up to the 11/16ths on my way to 3/4" when the disaster happened.

The turret has a T-Handle to lock 'er down that I've been leaving loose. My thought was it'd follow the previous hole easier that way, but my thoughts have been wrong before. Let's not go by those.

No visual evidence of the drill wobbling on the way in. Everything's sweet until I get in there a few inches and then all of a sudden the belt slips on the countershaft and the spindle stops. Reversing has saved me in the past after fighting with it for a bit, but this time I can't even get that poor bit back out. I've killed another perfectly innocent cutting tool.:D

Any advice is, as always, greatly appreciated.

SP

oldtiffie
07-02-2009, 02:19 AM
This can happen with too much front clearance angle - particularly without a normal "chisel-edge" to slow it down - when progressively enlarging a hole.

You can feel it "pulling" instead of needing to be "pushed".

Reduce the front clearance angle and see how you go.

It can also happen if the drill "binds" in the hole if the drill/tail-stock centre is not very accurately aligned to the head-stock spindle axis. The tail-stock "error" can be "high/low" as well as "in/out".

Jim Shaper
07-02-2009, 02:21 AM
You're using cutting fluid right?

Moly Dee is the cat's pj's for hard cuts, but you should be able to do that hole with regular cutting oil.

DR
07-02-2009, 06:54 AM
I've had exactly this problem deep drilling 7075 aluminum. In that case the material is expanding, then contracting down onto the drill.

Flood the area with cutting fluid to lubricate the chips and keep the work cool. Short pecks.

Try a parabolic flute drill ($$$$$ compared to S&D).

J Tiers
07-02-2009, 09:26 AM
The lathe in question is an 11" Logan Turret. 1018 Steel. I had just ran a 9/16ths bit and was stepping up to the 11/16ths on my way to 3/4" when the disaster happened.


That's your trouble..... right there.

NEVER STEP DRILL.............................

At least never with a standard drill....... or if you must, use way bigger steps.

I'd drill with a web-width drill, then go full size. oddly, the torque on the bit seems to be often MORE with a step drill technique than with a drill from solid..... The step-drill system often lets the drill, especially in large sizes with tiny steps such as your 0.031, "screw itself in" and jam up solidly.

maybe if you dull the bit, as one does for brass, you could do that.

Fasttrack
07-02-2009, 09:48 AM
That's your trouble..... right there.

NEVER STEP DRILL.............................

At least never with a standard drill....... or if you must, use way bigger steps.

I'd drill with a web-width drill, then go full size. oddly, the torque on the bit seems to be often MORE with a step drill technique than with a drill from solid..... The step-drill system often lets the drill, especially in large sizes with tiny steps such as your 0.031, "screw itself in" and jam up solidly.

maybe if you dull the bit, as one does for brass, you could do that.

ABSOLUTELY! Exactly what I was going to say. They make "core drills" designed for enlarging an existing hole. Step drilling with ordinary silver-demming drill bits is asking for trouble. If you have to, use larger steps!! The most you should you need to do for a large drill bit is provide with a pilot hole - no bigger than the width of the web as JT says.

pntrbl
07-03-2009, 12:40 AM
1st of all, Thanx for the responses. I did get greedy one day and tried a big step, don't remember exactly how big, but I do remember it getting screwed up. Or was it screwed in? :rolleyes: Maybe it wasn't big enough!

I'll be looking into core drills, parabolics, etc. And I'll try one big step from the web width next chance I get ....

Thanx again. You guys are the best.

SP

BadDog
07-03-2009, 01:12 AM
I'm with the others. I would probably do that as 1/4 followed by 3/4. If your lathe lacks the power for that, then maybe 1/4, 5/8, 3/4 or so. No way would I be going by 1/8" steps. That's only 1/16 per side, just asking for an auger in. Night before last I was opening up a 2" long hole on a big cast iron table from ~5/16 to 3/8. I knew better than to try that with a regular bit, particularly with a hand drill I was forced to use (hard to get a 300 lb table onto the drill press). So I took a 3/8" bit and "drubbed" it to give a neutral (0*) rake land about 0.075 wide. Worked like a charm, 8 holes in about 2 minutes or so, maybe less, taking my time, no broken bits or hangs out of the lot.