Chain drilling remarks

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.

I'll post a video on stitching cast iron which shows more chain drilling.

Quote:

---

Originally Posted by 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.

---

Marv when it is necessary to drill overlapping or holes so closely spaced that the risk of break out to either hole side is not only possible but highly probable. When you can do is to drive in sacrificial dowels. once the holes are all drilled then unless they are blind holes just drive the dowels out.
If the intent is to use the holes to stich repair a crack what I've done in the past was to drill a small hole at each end of the crack then drill out 1 hole then tap it but not tap all the way to full cleanout normally I would use a starting tap but not one that had a long starting taper just a taper of a few threads Plug taps work as well but the taper is too short for my next procedure which is to screw in a non graded non coated bolt until it twists off then dress down the surface and drill the next hole encompassing half of the bolt and repeat the procedure until the end of the crack. I've done it on aluminum as well using aluminum bolts. No fancy jig or special tools required other than a drill motor a few bits a tap, some bolts and a grinder.

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

I always enjoy learning about things I didn't know are available.