Welcome to Setting Up and Using an Offset Boring Head.
This head is used on
a Bridgeport machine to perform a few different tasks.
The first and most common is to bore holes
that require a precise diameter in a critical location.
They're also frequently used for machining the external diameter of a boss,
counter bores, and chamfering holes, as well as adding a radius at the top or
bottom of a hole.
Let's examine the parts of the offset boring head.
The shank allows the offset boring head to be directly mounted into a machine spindle.
If the head has a straight shank, you'll need to put it into a holder and
tighten the setscrew before placing the entire unit into the machine spindle.
The body of the head is mounted directly to the shank.
It has a dovetail where the tool slide mount fits.
The body also has a micrometer tool adjustment screw and a
locking or clamp screw.
The tool slide has a dovetail on one
side that fits into the dovetail on the body.
The other side has holes for the cutting tools.
Each hole has its own set screw so you can lock the cutting tools in place.
The micrometer tool adjustment screw
adjusts the boring head by moving the tool slide back and forth.
There is often a marking on the dial to tell you each division.
In this example, each division
is one thousandths of an inch in diameter.
That means that moving the dial
one division, increases the diameter's hole by one thousandth of an inch.
An allen wrench is used to adjust the boring head.
Always make sure you're using the correct size
Allen wrench to avoid stripping out the adjustment screw.
The locking screw keeps the tool slide and
the boring head from moving while you're cutting.
Always make sure this screw is loose before adjusting the head and
always tighten the screw using an Allen wrench after you've made your adjustment.
Do not over tighten the screw.
The boring head can be used with a variety of cutting tools.
Some of these are made from high speed steel and others from
brazed carbide or include brazed carbide inserts.
These tools come in different lengths and diameters.
The job type determines the kind of tool you'll need to use.
It's a best practice to always use the shortest tool
you can to complete the work.
The longer the tool, the less rigid it is, which may cause
problems with cutting as well as leaving a good finish.
The boring head can also be used with
tools specifically designed for cutting a chamfer or a radius.
Before using the offset boring head, you must prepare the workpiece.
Begin by drilling a hole where you need the bored hole to be.
The diameter of your drilled hole
should be roughly 1/16 of an inch smaller than the final diameter of the
bored hole.
Once you've drilled your hole, you can set up the boring head.
Start by selecting one with a shank that fits your machine.
Next, select your cutting tool.
Pick one that's just long enough to reach the correct depth
with as wide a diameter as possible.
Always keep in mind that the larger the tool's diameter, the
more rigid it is.
Insert the cutting tool into the tool slide.
Rotate the tool until its cutting edge is in line with the center of the
tool slide movement axis.
It's very important to position the cutting tool
correctly to avoid having incorrect rake angles and clearance angles.
Next, tighten the set screw so the cutting tool is securely locked into the tool slide.
Make sure you don't over tighten the set screw.
Double check to make sure the tool is firmly in place
by trying to rotate it in the tool slide.
Now you're ready to position the head and adjust for the first cut.
Begin by mounting the boring head into the machine spindle.
Position the head where the hole needs to be and lock the x and y-axes
Move the boring head until the set screws are facing you.
Bring the quill down until the boring head is just above your workpiece.
Adjust the boring head so it's smaller than the diameter of the drill hole.
Do this by loosening the lock
screws and using an Allen wrench to adjust the micrometer tool adjustment
screw, which moves the tool slide.
Bring the quill down until the tool's cutting edge is below the top of the part.
Next, adjust the boring heads so that the
cutting edge just touches the wall of the drilled hole.
Move the quill up until the cutting tool is out of the part.
Adjust the boring head to remove roughly
ten thousandths of an inch in diameter off
your first cut and tighten the locking screw.
Now, you'll need to bore the hole.
Before you begin, calculate the
correct RPM for the machine using the diameter of the hole
and the type of cutting tool.
For example, if you'd like to bore a two inch diameter hole and
your cutting tool is high speed steel, you'd use this formula
to calculate the correct RPM.
Once you've figured out the correct RPM,
you can engage the power feed for the quill.
Next, select the feed rate.
Remember, the feed rate is measured in thousands per revolution
and there are three to choose from -
.0015, .003, and .006.
Roughing cuts are normally done with a feed rate of .006 and
finish cuts are done with either .0015 or .003.
The materials that make up your cutting tool
and your workpiece impacts feed rates.
The rigidity of the part and the tool can also affect the feed rate.
Set the direction you want the quill to feed,
then turn on the spindle and set the RPM.
Bring the tool close to the workpiece and engage the quill feed engage lever.
Allow the tool to bore through the part.
Disengage the quill feeding gauge lever and shut the spindle off.
Raise the quill until the tool is above the part.
If you do this while the spindle is still on, the tool will leave a groove in the part wall.
Measure the hole using a precision measuring tool, such as a telescoping gauge,
an inside micrometer, or a dial bore gauge.
Remember, if you're using a
telescoping gauge or an inside micrometer you need to use a calibrated
OD micrometer to get the actual size.
Once you know the size of the bore,
calculate how much additional stock you need to remove.
Complete your calculations so every remaining pass takes the same depth of cut.
When these depths are different, the tool
pressures on the cutting tool are also different.
This means you'll remove different amounts of stock on each pass
and it will be difficult to hit the desired size of the bore.
Adjust the boring head by the calculated amount.
Make another cut on the part and measure the diameter again.
Calculate the remaining stock and repeat the previous
two steps until you have bored the hole to the correct size.
You've completed: Using a Boring Head.