How to find opposite sides of a cylinder

[Southtowns27]

I need to drill two shallow holes on exact opposite sides of a cylindrically shaped piece of metal. How the heck do I get them exactly opposite each other?

 

[Cobra]

If you're using a mill, find the centre of each axis and the reference from the centre of the cylinder.
To find the centre of each axis just use an edge finder along a line for that direction, lifting the edge finder to get to the other side. Don't need to be on centre for either.

 

[Wreck™Wreck]

You can only get them a accurate as you can measure them. The fastest and easiest way is to mill/drill the first hole and then mill a flat for a reference surface for the opposite hole. If this is not permissible either build a fixture to hold the part or use an indexer.

 

[Shepherd]

Fixture...drill into a surface plate, install a ground rod. Drill first hole in cylinder on a v block, then instal hole on the rod on the surface plate....

 

[Southtowns27]

I don't have a mill, only a lathe and drill press. And I can't envision how that fixture is supposed to work...

 

[Wreck™Wreck]

I don't have a mill, only a lathe and drill press. And I can't envision how that fixture is supposed to work...

Square fixture with a round hole for the part, put part through tool and drill first hole, rotate part and tool 180 Deg. and drill opposite hole, done.

 

[Shadowdog500]

How big is the cylinder?

Wonder if you could clamp the cylinder into a v block.

Then put the v block into the drill press vise in one orientation to drill one hole, then put the vBlock in the drill press vise 180° and drill the other hole.

chris

 

[savarin]

Make a square block, scribe around 4 sides to ensure the line meets itself. drill through on the line to fit the cylinder dia.
Now drill through the other two faces to intersect the the first hole at the size you want the dimples to be.
Now drill from one end to the cylinder hole and thread it for a holding bolt.
Place cylinder in hole, tighten the holding bolt now use the other holes as a guide to drill the dimples.
I had to do just this last week
http://www.hobby-machinist.com/posts/274544/

 

[Shepherd]

I don't have a mill, only a lathe and drill press. And I can't envision how that fixture is supposed to work...

Drill press will work fine...by drilling the peg into the plate, you have a "male" fixture..., set it aside and drill the hole on one side, then place that hole over the peg in the plate and clamp it down...picture the peg as if it were a drill bit, on its way right through the cylinder...may not be nasa level, but if the hole and peg are drilled accurately enough, it should get you pretty close....
Or, find a square tube that the cylinder fits snugly in and tack it with a welder and drill away...

 

[Shepherd]

Or, Scribe a line along the length on either side using a height gauge set to half the diameter on a surface plate.....