How do I properly use a boring bar on the lathe?

[ScrapMetal]

(Massive ignorance on display ) I've already checked for a Tubal Cain vid but came up blank. Here's the setup - I have some round stock chucked up in the lathe and I have faced the end of it. Now, I would like to start boring an accurate hole.

How do I start and proceed?

-Ron

 

[irishwoodsman]

you need to drill a starting hole with a bit, they recomend not boring under a inch but i think it depends on your lathe and boring barhttp://www.youtube.com/watch?v=ThVprkb2w6g

 

[irishwoodsman]

1 drill you a hole in your stock by placing a drill bit in your tail stoc, drill your hole, smaller than what you want your finished hole, now use your boring bar in your tool holder make sure she is square to your work and centered, now run your boring bar into hole this is with the machine off, bring your cutting tool up against the side of hole once it touches bring your bar out of the hole now turn machine on and turn your cross feed backwards a couple 1000ths then proceed to enter the hole you will see it start to cut, if your machine is like most when you turn your dial 1000th it will be cutting 2000th hope this helps:biggrin: mac

 

[goldenchips2]

put a dial indicator on the toolpost to see where you are.
working on the Internal Diameters ( ID ), you cant see much and it is too easy to make a really bad mistake.
Avoid crooning your neck to " look into the bore " and see what is happening...
a bad accident waiting to happen.....
learn to trust your dial indicators for telling you the tool position.
Good Luck...

 

[Tony Wells]

<snip>
Avoid crooning your neck to " look into the bore " and see what is happening...
a bad accident waiting to happen.....

Especially if you left your drill bit in the tailstock or chuck.

 

[ScrapMetal]

Especially if you left your drill bit in the tailstock or chuck.

I haven't done it with a drill bit but I have tried trepanning my skull by impaling it on a ball-bearing center in the tailstock. The machine was off at least. :biggrin: I bent over it to see if my cutting bit was on center and learned that I need a ten foot bed so I can move my tailstock WAY out of the way. :biggrin:

Now, as to the feed. What do you do in the case of a blind hole? Do you only feed by hand then?

Another issue that comes to mind is with measuring and arriving at the proper hole size. You start with a drilled hole that may or may not be a certain size but it is "close" to the final size. Do you just go ahead and guess on the first cut that it will still be under sized so you can measure it and get more accurate from that point on or is the hole you drill so undersize that won't be an issue? (0.030" sounds like cutting it close I'm sure I could bugger that up in a heartbeat). Not sure if that's very clear but I'll see what kind of answers I get and adjust my crummy description accordingly.

Thanks,

-Ron

 

[Tony Wells]

Leaving 0.030" is fine as long as the drilled hole is running true. If you can't get the hole in straight, you need to leave more stock.

The way I do it is drilling about 0.030" under for a little ways, about 1/4", then observe the runout. If it's less than 0.015" I measure the hole with dial calipers, then touch off the drilled hole with the spindle running, and making allowance for the runout, take a cut. If you do it right, you will clean up the drilled surface before you get to your desired size. Never touch off with the spindle stopped, especially if you are using carbide. Using the caliper measurement as a base, dial off 0.010-0.015 and take the cut, as long as that is still undersize.

As far as depth goes, I feed up to within 0.050 max, then hand feed until you hit your depth. This can be determined by your DRO, or a dial indicator set up at the end of the cut.

 

[irishwoodsman]

if i know what depth you want i put a o-ring on my boring bar and measure from tip of cutting bit back to the desired depth then slide the o-ring up, once i get close to o-ring then i use a depth gage:biggrin:

 

[ScrapMetal]

Thanks guys. I think I have a better idea of what I am going to do now. I do have one little question though, Tony, (Hope this falls under the "no stupid questions" umbrella :biggrin what exactly does the term "touch off" refer to? Is that when you move the cutting tip against the work piece then adjust for depth or is it something a bit different? As much as I read here and in books some of vernacular still gets me with a "Huh?" factor from time to time. I want to be clear about what I'm supposed to do before I ruin a perfectly good boring bar. Once I understand I can then destroy it with confidence. :biggrin:

-Ron

 

[Tony Wells]

Sorry Ron.

Touching off merely means easing up to the moving part or material, just until the cutting edge barely touches the work. Done carefully, you get a position that is at most a few tenths away from the true surface location. Then you can zero out your DRO, or dial indicator, or your machine dial. And you may as well get used to the term "tenths" meaning not tenths of a mile, but tenths of thousandths. It's just a much easier way to express it, and since most machine speak (in Imperial Land) is in inches, it is accepted as that. In Metricville, of course, it doesn't work the same.