Spot Drill Not Aligned With Hole

[richardsalzman]

Quick question.  I used a spot drill to spot before drilling a hole and create a chamfer at the same time.  I then drilled the hole.  I have done this exact routine on a total of 6 different parts.  All worked great except the last two parts.  The last two parts have similar round geometry.  The problem is that the drilled hole is not concentric with the spotted divot.    When the problem happened the first time I thought it may be operator error.  When it repeated, I realized I have a problem.  I could actually see the drill bit coming down and sliding over as it hits the divot.  

Since I am using a Mill that I converted to CNC, I wanted to rule out machine error.  As a test, I repeated the spotting operation and watched the spotting drill drop down exactly on center with the previously spotted divot.  This proves to me that the machine is operating properly.  

Is it possible that I am doing something wrong in Fusion and somehow selecting the hole centers differently for the spotting operation vs. the drilling operation?

I have attached the two Fusion file and an image of one of the parts where the hole and spotted divot are not concentric.

Thanks... Richard

[engineguy]

@richardsalzman 

Is your G Code correct ?

I generated code for those two operations and they are the same coordinates so the machine should go to the same points, if it doesn`t then most likely a setting at the CNC control ??

[seth.madore]

Is your vice firmly bolted to the table, or did it shift over, or did the part shift in the vise? Do you have an indicator that you can use to verify the outside diameter is where it should be?

[richardsalzman · Accepted solution]

Thaks so much guys!

Engineguy, as soon as you proved that both operations have the same coordinates, I immediately checked the tram of the head.  Somehow the head was way out of tram.  Maybe I did not tighten the bolts enough.  I trammed the head and did a test pattern and everything is aligned perfectly now!  Thanks so much for your help.  I need to learn a bit more G-code.  The image below shows how far out of wack the tram was.

Thanks again to both of you for your help!

Richard

[seth.madore]

Glad to hear you sorted it out!