Finding the center of a bore using G55

I've found that finding the center of a bore while setting up a G55 offset to be very cumbersome and a lot of math and prone to simple mathematical errors. Is there a simple solution to this such as the example below modified to account for the difference of part G54 and using machine position used for G55?

This is the method I use to find part center of a bore using the standard part setup screen (G54).

Finding the Center of a Part

1. First check spindle RPM
2. Press the Manual Machine Mode Button
3. Press the Manual Function Set Up soft key
4. Look at spindle speed and change if needed
5. Press the Input Button
6. Press the PART SETUP Soft key
7. Put in an edge finder in the spindle – load your part in vise
8. Press the Spindle On then the flashing START CYCLE Button
9. Using the Hand wheel Jog over to the left edge of part with edge finder “When Close to Part Use Hand Wheel Only”
10. Look to see that cursor is at Part Zero X
11. When cursor is at Part Zero X press the Store Position button above hand wheel
12. Your Part Zero readout in the position display should read X 0.000
13. Jog the Edge Finder to the right side of the part, look at the Part Zero X position and take note of the number. On a 6” part is should be around 6.200”
14. Verify the cursor is at Part Zero X and type the value in the Part Zero Readout Display of X and math functions as follows… 6.100 / 2+Enter. The Part Zero Position for X should read half the value it was. You just split the difference in the X axis.
15. Now using the Hand wheel again jog over to the front edge of part…When Close To Part Use Hand Wheel Only”
16. Look to see that cursor is at Part Zero Y
17. When cursor is at Part Zero Y press the Store Position button above hand wheel
18. Your Part Zero readout in the position display for Y should read Y 0.000
19. Jog the Edge Finder to the Back side of the part, look at the Part Zero Y position and take note of the number. On a 3” part it should be around 3.200”
20. Verify the cursor is at Part Zero Y and type the value of Part Zero Readout Display for Y and math functions as follows…. 3.100/2+Enter The Part Zero Position for Y should read half the value it was. You just split the difference on the Y axis.
21. Press the Spindle Off button
22. Jog the Z up
23. Remove the tool from the spindle

How would you modify this procedure for use with G55?

Without getting too specific as to what kind of machine, etc,.....why are you using a edge finder to find the center of a cylindrical part? Use a spinning indicator like a Blake CoAx or a simple test indicator that you hand rotate? You split the error in half every adjustment, rotate, note differential, adjust, repeat. When you are happy with the accuracy, zero your machine in that spot.

I am having trouble understanding your definition of G54 and G55, To me G54 through G59 they are the standard machine G codes used to establish your part zero, ie, 4 part set-ups on one machine, part 1 being G54, part 2 being G55, part 3 being G56, ect. On most of the machines I use I would do exactly as eschless says, then just press the "x zero measure" "y zero measure" soft keys for the desired work coord (G54 thru G59) or on an older machine key in the machine position manually in the work offset page into the desired work coord (G54 thru G59). Either way, with the part properly clamped, a bore can be trammed in about 1 minute or less, from chucking your indicator to sending the machine home after tramming. Very little math and little room for error unless you transpose a number using option 2.

As for starting the spindle, setting the rpm's and using the hand wheel to move the table part zero, that is pretty standard and I don't know how to get around doing that

I hope this helps

I should have edited that example since I'm using a Haimer 3d taster not an edge finder. With the Haimer you just touch the edge and move till the indicator reads zero and its on the edge regardless if it a square of cylindrical.

Demo of the Haimer: [nomedia="http://www.youtube.com/watch?v=RTzxebz9xkQ&feature=mfu_in_order&list=UL"]YouTube - ‪Simplicity of Use‬‏[/nomedia]



9. Using the Hand wheel Jog over to the left edge of part with the indicator “When Close to Part Use Hand Wheel Only”
10. Look to see that cursor is at Part Zero X
11. When cursor is at Part Zero X press the Store Position button above hand wheel
12. Your Part Zero readout in the position display should read X 0.000
13. Jog the indicator to the right side of the part, look at the Part Zero X position and take note of the number. On a 6” part is should be around 6.200”
14. Verify the cursor is at Part Zero X and type the value in the Part Zero Readout Display of X and math functions as follows… 6.100 / 2+Enter. The Part Zero Position for X should read half the value it was. You just split the difference in the X axis.

I'm just adding a bolt circle to these parts not trying to re cut the bore so +/- .001 is close enough. one part in each vise. The above example works well for the first part G54 but not the second part G55.

When using the work off set page the G55 will not zero but shows the machine position, write down that number. jog to the other side and write down that number. divide by 2 then add to the smaller number and jog to that position and hit store. There must be a better way.

I always use a coaxial indicator on my HAAS machines. Spin it about 90 rpm and jog X and Y to find center, then you're done.

Looks like the coaxial indicator will be the easiest and fastest way to do this, I'll run over to MSC and pick one up this morning.

Picked up a coaxial indicator at lunch time and it sure did make things much more simplistic . Thanks for all your input.

No problem. I use one every day at work for anything round. I.D. and O.D., small and large. We have a selection of arms for ours that can indicate in pretty large material or very small items or holes. Works like a champ, glad you got one.:D