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Boring head

G

Garyt

Active Member
New to milling. I have drilled a hole in my project using a twist drill held in a er32 collet, that went as expected nice hole seems centered on the spot. Now I need a counter bore so I set up my new boring head, it cuts OK but does not make a hole centered on the drilled hole (by quite a bit). What am I missing?
Gary
 
Do you mean the boring head hole is nice & round but displaced from the pilot hole center? Or the BH hole is not round - oblong or whatever? The fundamentals:
- work is locked in place, it cannot drift in between tool swaps. (Maybe you have a round column mill & it is not re-centering after lifting the head to tool swap?)
- BH cutting tool orientated & turning in correct cutting direction (it happens!)
- BH lock screw is snugged to prevent drift along the dovetail? (most wont move much on their own but its considered good practice)


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Nice round hole offset in x . My table is locked, the head dovetail is locked and I have not moved the mill head.
I think the cutter is oriented correctly (it cuts ok)
 
The millhead is locking bolts are tight so can't move.
The head dovetail I referred to is the boring head dovetail.
I'll attempt a photo later.
 
Photos
My first attempt at pictures
 

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Rats.... images as attachments don't work for me.

What exactly are you attempting to do? Looks like an AL casting your attempting to bore out? To what size?
 
Yes an al casting. Counter bore about 3/4 inches but it needs to be concentric. I was hoping to not move the table to make this feature. If the boring head does not cut on center it is going to be a problem later in the project.
 
I downloaded your pics while we continue to struggle with our issues

Hard to say. If the mill is dovetailed, no way it should be displaced like that. I wonder if the surface of your casting is related if it is curved or maybe asymmetrical at that mark? Are you starting the drill with a center drill or just plunging? (ie maybe the drill is off & the CB is concentric?). But hard to imagine its walking that much unless the part is shifting?

Some of those brazed cutters are notoriously wanky tool tip geometry, but I would expect it to plough through aluminum & leave a bad finish at worst. Unless it was catching one surface first & getting dragged over. But unlikely. You should have all kinds of tool rigidity.

OK any chance that the boring head body is not concentric to spindle axis for whatever reason? Is it like an integral R8 BH or a screw on?

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A drill will start and drill where it likes. The boring head will correct small errors caused by the drill wandering away from the spindle centre. This will be several thou to a dozen thou from a drilled hole.

The way I like to drill holes: Locate the hole. Use a spotting drill to start the hole's Vee. I mark it to 1/2 to 1/3 the diameter of the next drill to follow. The spotting drill will match the angle of the following drill. For instance, you can buy spotting drills at 120, 135, and 90 degrees.

If I have to make the hole larger, I almost never follow one drill with another. I respot the hole making the correct angle chamfer, then follow with the larger drill.

Using a spotting drill this way stops drills from wandering *too far* from the centre line of the spindle. That said, you can only expect to bewithing about .003 of the centreline. The boring head will correct any deviation from there.

FYI a reamer will follow the drilled hole, and doesn't do any substancial correction of hole location.
 
How did you start the hole? Did you use a spot drill and ideally mill a small flat first?

The tip of the boring head will always be perfectly concentric to the spindles axis - just by its nature as a single point tool ...... something moved or the drill didn't start where you wanted it to.

You can probably recover by picking up the hole location (not the counterbore), centring that to the spindle and then re doing the counter bore
 
My process
Mill a flat
Spot drill with drill held very short in er collet
Drill with twist drill the same as the larger diameter or the spot drill
Drill up to final size
Start to bore for counter bore
Now I need to find what went wrong.
Gary
 
Can't fault with any of that, somehow, the head/column or work piece must have moved. Maybe there's another possibility but its not occurring to me.
 
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Assuming all the info is correct, it's the weirdest thing I've ever seen..

The whole concept of a rotating spindle is a single axis of rotation for everything.

Oscillating boring head?

If you are in a hurry to get the job done just recenter the head.

Then take your time to figure it out later. But please let us know what you find. My curiosity is killing me.
 
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