Don't assume your center drill is centered

[rixstix]

Last weekend, a Bosch engineer friend was here and giving me pointers to use in my metal lathe journey.

We went to drill a hole and checked the center drill/workpiece center and the tailstock was 20/1000 high. After a hour of fiddle-farting, we just compensated using shims under the ass-end of the tailstock for the sake of progressing to the next tutorial step.

The next day, I'm remembering that the tailstock was dead on using either dead centers in head/tail stocks or dead center in head stock and dead center in tailstock jacobs chuck.

We found that one side of the #3 centerdrill was 20/1000 off; the other side just fine. Well that explains why some of my drilling was fine and other times just felt half bubble off.

Moral of the story... Don't assume the centers to be proper. Check before wasting time chasing your tail. Either toss or grind the bad side to prevent future foul ups or wasted time.

I did learn quite a bit that will work when my skillset lets me scale down the lessons to pen dimensions.

 

[carlmorrell]

Yeah. Also, don't assume they are the diameter they claim to be. I needed some 1/8" diameter x 1/8" deep holes positioned accurately. I carefully used my optical center punch and a printed template to locate and mark the points. Then I switched to my Starrett punches to make very even looking centers. Then on to the center drill that was part of an Grizzly set and claimed to be 1/8. Nope. More like 1/8" + some slop forcing me to use epoxy glue instead of the press fit I was intending. After that I decided to just use the center drill to start the hole, and then on to my USA made, very old Craftsman drills, and I got exactly what I wanted. Lesson learned.

 

[rherrell]

When I drill holes I use a "spotting drill",

https://www.mscdirect.com/product/details/71330161

The ones I use have the same 118 degree tip as a regular drill bit which help keep the drill bit centered.
A "center drill" has a 60 degree angle and I only use those for putting centers in something I need to support with a live center.

 

[rixstix]

TNX for the drilling hint @rherrell Rick. In this case, we were prepping to use a live center to show taking 100/1000" cuts on acrylic.

 

[carlmorrell]

When I drill holes I use a "spotting drill",

https://www.mscdirect.com/product/details/71330161

The ones I use have the same 118 degree tip as a regular drill bit which help keep the drill bit centered.
A "center drill" has a 60 degree angle and I only use those for putting centers in something I need to support with a live center.

Dang, so much to learn. Thanks for the pointing that out. My machinist "mentor" is who recommended the optical center finder, and the center drills, he never mentioned spotting drills.

 

[Paul in OKC]

Drill chucks can also be an issue. Sometimes not 'true'. You can remove and turn a bit and reinstall sometimes takes care of it.