How do I find center of a hole I want to bore, on an LMS 3960 mill?

Doug, if the hole simply needs to be enlarged I throw a drill blank the size of the existing hole in the chuck and move the X-Y table around until if slips in without contact. This will get you close enough for rough work.

If you need more precision then the easiest way is with a coaxial indicator if you have one. Using a center finder or even a wiggler will also work but it is more operator-dependent as far as how accurate it is. You can also use toolmaker's buttons or even a ground dowel pin; these have tips of a known size and when combined with a center finder you can get very close.

As to whether to use a drill bit or not, it depends on the fit you need. If all you need is a through hole then a drill bit will do. If you need closer tolerances or a finer finish then a reamer or boring head is called for. This is especially true if you need to have the hole on-size AND straight.
 
mikey said:
Doug, if the hole simply needs to be enlarged I throw a drill blank the size of the existing hole in the chuck and move the X-Y table around until if slips in without contact. This will get you close enough for rough work.

If you need more precision then the easiest way is with a coaxial indicator if you have one. Using a center finder or even a wiggler will also work but it is more operator-dependent as far as how accurate it is. You can also use toolmaker's buttons or even a ground dowel pin; these have tips of a known size and when combined with a center finder you can get very close.

As to whether to use a drill bit or not, it depends on the fit you need. If all you need is a through hole then a drill bit will do. If you need closer tolerances or a finer finish then a reamer or boring head is called for. This is especially true if you need to have the hole on-size AND straight.
Click to expand...

Thanks Mikey. That's very helpful.
Thanks everyone!
...Doug
 
All 3 ways I would do it have been mentioned more or less. If it needs to be nuts on I would use a test indicator. If it can be off and the parts in the vise I would use a drill, endmill, or the like. If it's not in the vise I would use conical finder and have the part on parallels but not tight. Bring the quill down and the taper will pull the part to center.
 
Why explain it when you can show it :) Not my video.

[video=youtube;VY2crpjhL3E]https://www.youtube.com/watch?v=VY2crpjhL3E[/video]
 
Thanks, Andre - as they say, a picture is worth a thousand words...but a video is worth half a book!
...Doug
 
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