Chain drilling remarks

[mklotz]

Rick Sparber's chain drilling guide, detailed here...

http://www.homemadetools.net/forum/c...ng-guide-73254

provides a very clever way of laying out hole locations closely so that hole-to-hole breakout is avoided when drilling.

I wanted to add some remarks but didn't want to intrude on his thread so I started this one.


If laying out holes around a curved, rather than straight, contour, making a drilling guide may be more effort than is practical. In this case a spacing punch, such as the Starrett #118, photos here...

https://picclick.com/Starrett-Spacin...176136104.html

may be more practical. Building your own version of this is straightforward. On the rare occasions when I've chain drilled, I've used the beam compass I made...

http://www.homemadetools.net/forum/t...-verburg-27353

although far simpler designs are possible if only the hole spacing function is required.

A row of holes can be drilled on the mill. One approach I've read about is to drill every other hole in the line using the spacing function provided by the accurate mill table screws. Then go back and drill a second sequence of holes between the first sequence. The idea is that, with a hole on each side, there will be less tendency for the drill to wander toward either. I've never tried it so I can't testify to its effectiveness.

If I were to do it on the mill, I would use an endmill to make the holes. An endmill is much stiffer than a drill and consequently has less tendency to wander. Of course, if the workpiece can be mounted on the mill to chain drill a straight series of holes, why not just use the endmill to mill a long slot? Generally, chain drilling is a type of last resort for workpieces too large to fit into machine tools.