Picking up the center?

How would you pick up the center of a rotary table on a BP with this set up? The head is tilted 45 deg and the cutter is a fly cutter with a 3/8 tool bit. The bit is not ground to it's center point. I need the bit to contact the work at the center of the table? ..........Bob

If I understand you rightly what you're setup to do is to cut a sphere. If that's the case you want to align the center of the ball on the spindle axis. To do that you'll need to mount a point in the center of the rotary table with the tip at the center of the ball, and a similar center in the spindle brought to the point of the center in the table. Lock the mill table and retract the quill for clearance. Mount the work and the tool and size the ball by advancing the spindle, keeping the swung diameter of the tool less than that of the work,

bhigdog said:

How would you pick up the center of a rotary table on a BP with this set up? The head is tilted 45 deg and the cutter is a fly cutter with a 3/8 tool bit. The bit is not ground to it's center point. I need the bit to contact the work at the center of the table? ..........Bob

Click to expand...

Rather eazy.... but you need a Tooling Ball and a way to mount it in the center of the table. To see what a tooling ball looks like go to MSC Corp's catalog and search for tooling ball

Does the table have a center bushing? I will assume it does or that you will bore one and press fit a hardened bushing.

Now to get the idea, set a tennis ball on the center of the rotary table...
You can see it's diameter, and you can see it's height above the tables surface.

Traming the ball gets your spindle pointed directly at the center of the ball.

You measure the balls diameter.
Move the tool to just touch a piece of paper between the toolpoint and the balls surface.
Now your tool point is a ball radius + a paper thickness away from the balls center, and it's how ever high the balls center is off the table...

You do the math knowing the Tooling Balls geometry...

If you are maching a sphere just make an extra one and use this for setting the rotary table and spindle on center. Line things up as good as possible by eye and start cutting. After one revolution of the sphere it will be clear which was the rotary table is off center because the tool will be cutting on only one side so you just move it to suit. When it is centered on the spindle the tool will leave a fine cross-hatched pattern on the sphere.

I'm not machining a sphere. I need to cut both circular "V" grooves in flat stock radiating from the center of the stock and a number of straight grooves. I need to use a rotary table and fly cutter. So I need to pick up the center of the table/work piece where the point of the tool bit makes initial contact. That my starting referance point. The head being set to 45 deg and the point of the tool bit being off center is whats throwing me...........Bob

If I've got the right end of the stick ?

Assuming you have the hed tilted to the left or right on X axis

You need to establish the swept diameter of the cutter, place an angle plate on the centre point of the rotab, clock true to X axis sweep cutter (BY HAND ) until it just brushes the vertical surface, rotate cutter 180deg to get cutter diameter, ( vernier calipers handy) divide diam' by 2 and track Y axis to that position = centre.

If head is tilted in the Y axis reverse Axis designations in above method