Little Help with Me First Boring Head - How to Set Boring Bar?

[Bolster]

Just received my first boring head, 2" capacity on an R-8 collet for use in my small mill. Also a set of Cobalt boring bars. Will be boring aluminum that's 1/2" - 1" thick.

I could use a little help. As I was assembling the boring head, I realized (for the first time) the boring bar itself could be rotated so that the cutting edge could encounter the hole being cut at an infinite number of angles of attack. How do I know when I have the boring bar set to the correct rotational angle? Should the face of the boring bar lie along the hole's radius line? Or does it need to be rotated a bit more to give positive rake? (Or negative?) If rake, how do you know when you've got enough? How accurate does one need to be with positive-negative-zero rake?

There must be some good shop wisdom on how to set your boring bar correctly into the boring head, care to share?

Wait, one more question: Do I want to remove most of the metal from the hole (with an end mill) before using the boring bar? Is the boring head for removing the last couple of .010s, or can you just sink the boring bar straight into the work like a drill?

Honestly, never used one before, so am trepidatious about how to start...

 

[Metal Butcher]

You defiantly want to drill or mill out most of the material and take light cuts with the boring head to bring the bore to final dimension. If you try to plunge cut like with an end mill the chatter will send you running for cover!I rarely take more than .010" per pass. I try to set up the bar with zero rake. It works for me on brass and aluminum. If the first pass has a lousy finish I check and re-adjust the bar.

Light cuts are best.

-MB

 

[Troutsqueezer]

I think you can take as much or as little out of the hole as you like before using the boring tool, it's just that it will take you longer to bore if you start with a smaller hole.

Boring is usually done at a relatively slow rpm as well. You will notice that making several passes without moving the bar in between passes still results in metal being removed with each pass. This is because the tool bit flexes, something to keep in mind if you depend upon the dial on the boring head for measuring.

 

[Bolster]

Hm, OK, I see. Thanks. So the boring head/bar is more of a finishing tool. How does one bore to a specific diameter...do you bore an undersize hole, measure it, then adjust to final size using the dial of the boring head? If so, sounds like I should have bought a set of hole gauges with my boring bar setup. All I have for measuring hole diameter is dial calipers.

And does the boring head dial give me results in radius or diameter? If I make a .001 adjustment, does the diameter increase by .002 or .001?

I was going to run the boring bar at about 1/4 the speed indicated by the diameter of the hole, is that OK?

I may have gotten in a little over my head here. Sorry for the noob questions. I'm starting to wonder if I should have just stuck to using my rotab with an endmill as I have before. You can get a reasonably accurate diameter that way by dead rekoning...you sink the endmill in the center, crank the X axis to the calculated radius (minus the end mill's radius), and spin the rotab.

 

[DaveH]

Bolster

Boring is a slow job, you can think of it as you would doing boring on the lathe, single point tool, slow speed and slow feed. Boring will give you a very accurate hole size and good finish.

Start at 200 rpm feed the tool as you would on the lathe, slow and steady. When you feel confidant zip it up a bit but you don’t have to, if you’re happy and the machine is happy the hole is looking good then everything is 100% ok.

Boring is a lot less stressful on your mill than cutting with end mills.

I think it might be a good idea to invest in some hole gauges.

The .001” or .010” is the depth of cut, as it is on the lathe.

You are definitely not in over your head.

Remember to lock the Y and X axis.

Give it a go then come back and tell us how easy it was.

Dave

 

[Bolster]

Thanks guys! Confidence restored. ;D

Still confused re: relation of boring head dial to hole size...at school I've used lathes that were both types...some dials gave you measurements in terms of radius (the actual amount the bit was moving into the work), others gave measures in terms of diameter (half the amount the bit was moving into the work).

Obviously I can figure this out by boring holes and measuring them, but thought I'd save myself the experimentation if possible.

 

[Lew Hartswick]

Thanks guys! Confidence restored. ;D

Still confused re: relation of boring head dial to hole size..

The scientific way would be, check the thread pitch on the feed screw and
compare that to the numbers on the dial.

ie. If the thread is 40 tpi and the dial has 50 div it is a diameter change.
...lew...

 

[Troutsqueezer]

The dial on my boring head reads from 0 to 40, each tick mark on the dial is .001" movement of the head position. So by moving the head one tick, the radius of the hole changes by .001". The change in hole diameter would then change by .002".

I think you'll come to appreciate your boring head as much as I appreciate mine. It's easy to use, doesn't stress the machine, bores accurate holes, straightens out crooked holes, bores outside as well as inside, you can take it slow and easy, giving you plenty of time to make your mistakes instead of making them instantly. :big: Just kidding, well worth the money spent.

 

[Bolster]

Hey anything that will allow me to make a mistake slowly, I'm all for it! :big:

Appears to be 20 TPI and 50 divisions, so I guess that's reading me radius.

OK, I'm off to give this a try. Thanks guys.

 

[mklotz]

Get some hole gages.

Calipers have minute flats on their inside measurement jaws. That means that you're always measuring the distance between two chords of your hole so the indicated measurement is always less than the true size of the hole.