Off-center lathe drilling jig - GIF

**Altair** · Jul 19, 2020, 09:51 PM

Off-center lathe drilling jig.

Previously:

Brutal machine shop safety signs - photos
Glowing hot hard turning - GIF
Lathe cutting oil system from motorcycle chain oiler - video
ER20 lathe toolpost milling/drilling fixture - video
Powered lathe top slide - video

**nova_robotics** · Jul 20, 2020, 09:39 PM

Two of these jigs, one inside the other, and you could put that hole anywhere you want.

**Tonyg** · Jul 21, 2020, 02:59 AM

You would really have to be making a lot of parts to warrant making a jig like that.

**nova_robotics** · Jul 21, 2020, 05:34 AM

Originally Posted by Tonyg

You would really have to be making a lot of parts to warrant making a jig like that.

I have to drill off centre holes all the time. Most people just use a 4 jaw chuck or a drill press. But if you only have a 3 jaw then you do what you gotta do.

**mklotz** · Jul 21, 2020, 08:41 AM

For one-offs the 4jaw is the way to go but, if you lack a 4jaw, shimming one of the jaws on the 3jaw works, though the setup is less than secure. The ECCENT program on my page does the math to calculate the offset required.

A much safer approach is to use a tubular jig. Here's the description from the webpage archive...

Imagine a tube bored to be a sliding fit on the parent stock. A slot of sufficient width to pass one of the three-jaw chuck jaws is milled in this tube. The parent stock is inserted in the bore and the whole thing clamped in the three-jaw chuck such that one jaw passes through the slot to seat on the parent stock while the other two jaws seat on the circumference of the tube. Obviously the centerline of the parent stock is offset from the lathe spindle axis and turning will produce an eccentric. If we know the OD of the parent stock and the amount of the offset required, it's possible to calculate the OD of the tube needed to produce just that offset when clamped as described above. That's exactly what ECCENTUB does.

and the associated picture...