Posted by clogs on 18/06/2016 17:45:58:
HI all,
I have to drill hundreds of 6 and 8mm with the odd dozen or so 10mm holes in concreted in 50×50 angle iron……and I don't really have the facilities to sharpen the drills in the field…literally……..
If I had hundreds of holes to drill like this, I would rig up a bench grinder on a plank of wood or whatever was available at the site. You can buy cheapie 6inch bench grinders for hardly anything these days.
Then grind the drill bits so they have a bit more clearance (relief) angle than normal. They cut better and faster that way. Yes, they wear faster too, but if you keep a few in your pocket and change them as they go dull, you can sharpen them as a batch at smoko break etc.
And for a 6mm drill bit I would be spinning the drill at more like 1500mm and the 8mm at least 1000rpm. With today's variable speed drills you can slow down a bit if/when you feel it hit a hard spot. HSS bits will not burn out at these rpm IF THEY ARE GOOD QUALITY. Which I guess is the next thing I would do: use only top quality drill bits for jobs like this. They make life sooooo much easier.
On tough stuff, or drilling way overhead where you struggle to get good pressure on the drill, a smaller pilot drill, even down to 1/8" but more often 3/16", works well too.
That's the way we did it when I worked engineering construction in a former life, and being a lazy sod I worked hard at finding all the easy ways!.