[Metrology] Finding The Center Of Jacobs Chuck...?

[EmilioG]

Hi,
I need to drill a 3/16" through hole in the center of my Jacobs 14n drill chuck body to punch out an arbor.
I have access to a BP mill with a DRO at work. I have an edge finder, .200 dia. tip.
The dro is old and doesn't have a midpoint function. How do I find the center? I can't really use the chucks
ID because the jaws are there, I need to touch off on the nose, (all 4 sides?).

What's the best way of doing this? Thanks

 

[Ed ke6bnl]

can you put the arbor in a vee block to hold upright and put the largest dowel pin in the chuck and center on the dowel pin? I am new and that is just the thought that came to me. Lathe would be simpler though if you can hold on to the arbor depends on the type of arbor.

 

[kd4gij]

My 14n had a drill point in the bottom I drilled it in the lathe chucked the arbor in the chuck and drilled it. It is soft and not real thick a hand drill would be fine also.

 

[RJSakowski]

+1 on the dowel pin.

You can use the edge finder to find the center of the dowel pin. Come as close as you can to the centerline in the y direction. Approach the pin from the left and note the position where the edge finder deflects. Zero the x DRO if you can. Now approach from the right at the same y position and note the position. Take half that nuber if you zeroed, Otherwise average the two positions. Move to the averaged position and zero the x DRO and repeat on the y direction.

Or, place a pin in the mill chuck and tighten the 14N on the pin leaving the shank free. move a vise with a vertical vee block while closing the jaws until the shank touches on the two sides of the vee and the vise jaw. Tighten in the vise, remove the pin, and drill.

 

[Bob Korves]

Chuck up a dowel pin or similar that will fit one of your collets in the drill chuck, install the collet on your mill, put the pin and chuck into the collet and tighten the drawbar. You are now centered on the work. Now figure out a way to mount the drill chuck arbor to your mill table, your method will depend on what tooling you have for setup and your imagination. A couple vee blocks in the vise to grip the arbor comes to mind. It is important that you not introduce side or angular loading to the chuck, arbor, and pin while you are securing them. When the chuck and arbor are mounted securely to the table, lock the table in X and Y, release the collet, drop the table down, remove the collet and pin, replace with second drill chuck and drill bit, back off the chuck jaws to their largest opening on the chuck you are drilling, and drill your hole. This project does not need to be this precise, but it is good practice for setup problem solving and for achieving a nicely centered hole.

 

[EmilioG]

All great suggestions. Thank you.
I think the lathe may be the best way to go. I have a Hardinge at work.
Thanks, happy holidays to you all!

 

[Bill C.]

You might consider once you get the arbor off taping the hole used to drive the chuck off for a jack screw. Just an idea. Hope you have a great week.

 

[Silverbullet]

If you have a rotary table at work they usually have a morse taper in them . Sleeve to your chuck drop in , locate your dowel pin and drill . All done no problem.

 

[Bob Korves]

Once you have the hole drilled, sometimes you can get lucky by inserting a hex nut in the drill chuck jaws, tighten firmly but do not over tighten. Then put a long threaded bolt into the chucked nut and use it for a jack screw. Tapping on the bolt head while it is tightened will sometimes help break the arbor free. Do not bang on it with a big hammer or gronk on the chuck key. You want a usable chuck for the new arbor. Remember to use your brains more than your biceps. There is usually no emergency needing the job finished immediately. There is always another method to try, and eventually you will win.

 

[EmilioG]

OK. Remember, this is 3/16" size hole. I don't want to go much larger.
I've also drilled a hole for a cross pin to then use the wedges, and this has always worked.
I'm trying to save the arbor. It's a vintage 1/2" stub arbor, looks case hardened.

Do you think any holes in the arbor will affect it's accuracy? I'd rather have a small spot on the arbor tip
by drilling through the chuck body. The metal between the taper hole and chuck body is about 5/32".
Thanks