Off Setting Stock in a 4 Jaw Chuck

[Nerdz]

I decided to practice using my new 4 Jaw chuck. I can find guides everywhere on the net as to how to center stock, But how exactly do I offset stock by a certain Amount?

Example: I have 0.750 Square Stock, and need to drill a hole thats 0.56 from one side, but centred in the middle of the stock (Its the valve body for the EZ engine )

How exactly do I do that?

 

[Philjoe5]

Look at the face of the square stock like so:

-----
l--- l
l--- l
-----

Now consider the 4 sides of the stock at 12, 3, 6, and 9 o'clock.
As I understand it you want the hole centered between 12 and 6 o'clock and offset 0.75 - 0.56 = 0.19" from center between 3 and 9 o'clock.

Put the stock in the 4 jaw chuck and place the end of a dial indicator under some load against the side at 12 o'clock, lift the DI rotate to 3 o'clock and adjust the work to the same reading on that side and continue doing all the sides to get the same reading off all sides. You are now centered on all sides.

To put in the 0.19" offset, loosen the jaw on the 3 o'clock side and tighten the jaw on the 9 o'clock side. Do this in small increments until the difference in DI readings on those sides is 0.19" * 2 = 0.380".

You are now offset 0.19". Check the 12 and 6 o'clock readings to make sure they're the same.

In the time it took me to type this out you could have actually done it a few times.

I hope this was not confusing

Phil

 

[Nerdz]

Nope! Not in the least, Thanks for the advice I'll Try it tonight!

 

[bb218]

I usually try to put a small center drill at the location I want using the mill then indicate the center drill hole while in the 4 jaw. Mike

 

[RonGinger]

I have a centering rod that I find very helpful- Its about 10" long, has a center point machined on one end. The other has a spring loaded plunger with a travel of about 1/4". The plunger has a center drill in its end.

I would layout the block either on a surface plate or by putting it in the mill and drilling a center hole in the correct location.

The part is then loaded into the 4 jaw, with the offset just close. The center rod has its point inserted into the center mark, and the tailstock brought up to slightly depress the spring loaded plunger. Now I can place a DTI on the rod, just behind its point, and indicate in the usual way to align the part to its center.

 

[weez]

I have a centering rod that I find very helpful- Its about 10" long, has a center point machined on one end. The other has a spring loaded plunger with a travel of about 1/4". The plunger has a center drill in its end.

I would layout the block either on a surface plate or by putting it in the mill and drilling a center hole in the correct location.

The part is then loaded into the 4 jaw, with the offset just close. The center rod has its point inserted into the center mark, and the tailstock brought up to slightly depress the spring loaded plunger. Now I can place a DTI on the rod, just behind its point, and indicate in the usual way to align the part to its center.

This is also how I do it.