Tools, Sharpening and Power Machinery - Can't keep drill bit in chuck

A disreputable contractor replaced a section of my foundation and poured concrete all over the yard, leaving an unbeleivable mess. There is at least 5 inches of concrete where I want to dig a 15 in. dia. sump pit. I tried a few different ways and decided to drill a few holes. I'm using a 3/4" masonry bit in a 3/8 drill. Working fine for awhile and then the bit won't stay in the chuck; it keeps coming loose after a few seconds. I got a brand new drill and it does the same thing. What's going on?

have you tried a new bit ?

personally I would rent a heavy duty hammer drill something like a hilti , save yourself lots of grief cut right thru it

Also I don't believe that some of the new keyless chucks tighten as well as the old chucks. I have a cordless with a keyless chuck, every now and then I go to install another screw only to find that my bit is still attached to the last screw :wall:

I agree with mango man, I believe a heavier drill will work better. Personally I would try drilling part way and then use a chisel and sledge hammer - it might be a little faster.

The 3/4" bit is overpowering your 3/8" drill to begin with. Check to see if the bit has a round shank or a hexagonal shank. If hexagonal, when you tighten it up, make sure the chuck teeth lay flat on the sides of the bit shank. After installing the bit in the drill give it an extra twist to ensure proper seating of the bit. But, the best method of doing what you want will probably require the use of a Hilti hammer. Rent it and be done with it.