Cross drilling

[IanN]

I have seen many designs for jigs and fixtures to assist with accurate cross drilling but apart from the fact that you end up building a special tool for the task, most designs use guide bushes and so a different sized bush is required for each size hole that you need.

The following method uses only a vee-block (which you would use to hold round stock for machining anyway) and avoids the use of special jigs and custom bushes.

In the following pictures securing bolts, clamps, etc have been left off to allow clearer pics - in reality everything would be secured of course.

Secure a piece of round, straight bar in the drill chuck. Push the bar onto the vee to centre the vee-block under the chuck.

At this point it is a good idea to rotate the chuck by hand through 90 degs, 180 degs and 270 degs, testing the location of the vee-block at each point to check the straightness of the bar (and the concentricity of the chuck!)

You now have the centre of the vee directly aligned with the centre of rotation of the drill chuck.

Bolt down the vee-block and place a centre drill (Slocombe drill) in the drill chuck. Secure the bar to be drilled in the vee-block and start the cross hole.

Once started with the centre drill, follow up with the required size twist drill.

I do not claim any originality in this method - it was taught to me, many years ago, by someone far older and wiser than myself.

Ian.

 

[Bogstandard]

Very good tip Ian.
You can get repeatability as well, and with any size.
Must try this out myself. I usually do it a long winded way with my miller and edge finder.

John

 

[ikif]

....poetry​

 

[Herbiev]

Thanks for the tip

 

[goldstar31]

Whilst I agree, there is yet another simpler system. Lay a short piece of sheet steel or a 6" rule on the top of the round and ensure that the drill keeps the rule horizontal.

Again, it is similar to using the technique as a quick way to set a lathe tool at centre height.

Further, nip a safety razor between centres- likewise.

After all, it is only school boy Euclidian geometry, isn't it?

Cheers


Norman

 

[deverett]

Very good tip Ian.
You can get repeatability as well, and with any size.
Must try this out myself. I usually do it a long winded way with my miller and edge finder.

John

Ditto.

For small diameters, I have a selection of steel blocks predrilled with the diameter of the bar and the cross drill.

Dave
The Emerald Isle