Starting Holes On Domes and The Ends of Rods

[rgsparber]

A common way to get a drill to start at a specific location is to first use a spring-loaded punch to make a small divot. This holds the point of the drill in place until it can start cutting. If you have more than one hole to make, switching between drill and punch can get tedious.

Here is an alternate approach that can be fabricated in seconds. It handles a range of dome sizes and also works on the ends of rods.

If you are interested, please see

http://rick.sparber.org/Drill_Guide_...ome_or_Rod.pdf


Your comments are welcome. All of us are smarter than any one of us.


Thanks,

Rick

[suther51]

Will have to remember this. Now if there is a trick to starting a concentric hole in a broken bolt that would be the cherry on top!! Have usually had difficulty eyeing center when the broken thread makes the bolt shaft look oval. Thanks
Eric

[rgsparber]

Will have to remember this. Now if there is a trick to starting a concentric hole in a broken bolt that would be the cherry on top!! Have usually had difficulty eyeing center when the broken thread makes the bolt shaft look oval. Thanks
Eric

Eric,

I don't see why this tool wouldn't be able to center a drill on the end of a broken bolt as long as the bolt was not bent. The threads shouldn't matter.

Rick

[suther51]

Quite so if the bolt is proud of the surface, my difficulty has been more with flush or just recessed situation. Could be an indication of my impatience with such situations. Thanks
Eric

[rgsparber]

Quite so if the bolt is proud of the surface, my difficulty has been more with flush or just recessed situation. Could be an indication of my impatience with such situations. Thanks
Eric

I haven't tried these yet so they may be totally worthless:

What about placing enough 5-minute epoxy in the hole so it domes over. Drill a piece of scrap bar with the same diameter as the hole. When the epoxy is firm, place the scrap's hole over the dome. The dome should provide alignment in the hole. Then drill down until a divot is established.

A related idea is to use plumber's putty in the hole and strike the top so it is flush with the surface. Sight through the hole in the scrap to center. Then holding the bar firmly, start drilling the divot.

Rick

[DIYer]

Thanks Rick! We've added your Dome Head Drill Guide to our
Drilling and Drill Presses category, as well as to your builder page: Rick's Homemade Tools. Your receipt:

Dome Head Drill Guide by Rick Sparber

tags: drilling, guide

[Baddog]

Great idea for a handy drill jig!

Even if the bolt is proud of the surface, and the end flat, I don't think the cone will provide good centering because of the helical nature of the thread forming the locating surface. I would expect it to be off center by something less than a thread height. Maybe close enough, but less accurate than use on a dome or flat ended rod. But a similar purpose built tool could be made to encompass the threads for location (if enough thread).

I've used a similar approach to drill out bolts broken flush (or below) just by making what amounts to a limited use drill bushing with scraps of steel. The problem is holding location while starting the drill, so it's of limited use depending on context. Most often I've used a round bur on a die grinder to provide a pip for starting. And more often still, for larger automotive/tractor size bolts I mostly deal with, welding a nub buildup for grabbing with vise grips. Heat shock helps in many cases too.

In any case, I often find myself needing to remove/relocate brackets riveted to frames in my desert trucks. And pre-drilling the head for knocking off with air chisel is always a mixed bag for success, particularly when some areas don't have good open visibility and access. You can bet I'll be making one of those in steel for future use! I sure could have used this when I was cleaning up the frame for my current build a few months ago. Thank you!

[Baddog]

Wow, I saw this on one of the site emails, but didn't notice the date.