Boring on the lathe with a step drill

[strantor]

I figured out a cool trick yesterday and thought I would share. I'm sure I'm not the first, so if anyone has been doing this for 40 years, feel free to chime in.

When I need to do some boring in a fresh blank, my usual process to get the hole big enough for a boring bar is the long and tedious drilling with a small drill, then a medium one, then a large one, then a really large one, then the boring bar, unclamping and moving the tailstock back each time, opening the Jacobs chuck, sliding the tailstock back and clamping, which altogether takes a minute or more for each but change.

Machining is just my hobby. My livelihood is building electrical panels, so I have lots of step drills laying around, which I have only ever used on sheet metal (to make knock-out holes for conduit and pushbuttons) and I assumed that's all they're good for. But I decided to try and use one to bore out a 1.5" hole, 3" deep, so I can go from [no hole] to [boring bar sized hole] in 1 step. I figured the bit would probably be destroyed, so I used the cheapest one I had, from Amazon. I used plenty of cutting fluid (CRC foaming cutting fluid in aerosol can) and much to my surprise it actually worked like a champ. It was several times faster than my usual approach, and what surprised me the most is that despite the fact it's cutting several holes at once, it was no harder than drilling a single hole. The resistance and the amp draw on my motor was about the same as drilling a 3/4" hole to 1" using large twist drills. Boring that hole took only a couple of minutes and the step drill was no worse for wear.

This step drill will remain part of my lathe tooling from now on, and this will be my new method until I find some reason for it not to be.

 

[Ken from ontario]

This sounds interesting,
Did you complete the task of drilling a 1.5" x 3" cylindrical hole ? if so where did you start the boring process? did you start at the smallest diameter or the widest (1.5)"? I wonder if this method would give you the exact dimensions you had planned to achieve.

 

[BaronJ]

Hi Strantor,

Did you actually drill all the way through ?

 

[strantor]

Hi Strantor,

Did you actually drill all the way through ?

Yes, through 3" of solid steel.

This sounds interesting,
Did you complete the task of drilling a 1.5" x 3" cylindrical hole ? if so where did you start the boring process? did you start at the smallest diameter or the widest (1.5)"? I wonder if this method would give you the exact dimensions you had planned to achieve.

I did not mic the hole to verify that it was exactly 1.5000" nor did I use an indicator to verify that it was exactly cylindrical, but it definitely was a 1.5" hole, 3" deep. My goal was to get in there with a boring bar to achieve a 2.000" cylindrical hole, and the step drill got me to where I needed to be, to get a boring bar in there.

I started the boring process with nothing but the step drill. I might have used a center drill to put a divot in it first, can't remember. But if I did, it wasn't necessary. The step drill is very stout, no flex, like a center drill, and I doubt it could possibly drift like a twist drill.

The step drill starts out with 1/8" I believe, and then goes up by 1/8ths until 1.5"

 

[Jason5555]

That is an interestingly intelligent approach. I'm not going to lie though, i was a little excited when I read the title about a step drill on the lathe. I might have been able to use one of the many monster steps drill i stumpled across. The two on the left are the range in size from 5/8 step to 7/8, and 1.270 step to to 1 3/8" STRAIGHT SHANK!

 

[mickri]

I am going to have to give this a try when I make more tool holders for my norman style qctp. It would save a ton of time.

 

[Bob Korves]

The two on the left are the range in size from 5/8 step to 7/8, and 1.270 step to to 1 3/8" STRAIGHT SHANK!

Core drills.

 

[magicniner]

I use a U Drill to open up for a boring bar.

 

[MrWhoopee]

I like this! I've been trying to acquire MT 2 drills big enough to start boring a hole. Step drills are much cheaper. I have some, but this never occurred to me even though I have used them for other unconventional jobs. Looks like I'll have to get a couple of the big ones.

Oh, not to pick nits, but the process is drilling. Boring is done with a single-point boring bar. When I opened this thread, I thought it was about using a step drill to enlarge a hole by mounting it on the tool post and offsetting from center.

 

[Jason5555]

What is the max mt2 drill bit size? A little over a 1/2" is all I've been able at aquire thuse far. Luckily my tailstock is mt2 so I use an mt2 to mt3 but ofcourse loose a few inches in doing so.