Enlarge existing hole, how to do it with a hole saw?

[RichardRR]

Got assistance with drilling and unfortunately not all holes turned out as expected. How do I easiest adjust existing holes (lightweight concrete)? It's partly about changing the "angle" of some holes, and other holes need to be slightly enlarged or adjusted in height/sideways. I can't get a grip with a regular hole saw with a pilot bit. Should I try to attach a temporary backing that the pilot bit can grip onto to guide the hole saw, or how do you do this?

Best regards, Richard

 

[tobben87]

How many degrees do you want to change them? Are we talking a few degrees or tens of degrees? I would try to attach some form of wooden construction in the existing hole. A couple of beams screwed together to fit in the hole. If you can get the center drill to grip them so you can start drilling the first centimeters into the light concrete, you should be able to continue that way.

How sensitive is it around the hole? Another option is to drill with small drills around and then chip out the excess with a chisel or a demolition hammer.

 

[RichardRR]

How much of an angle do you want to change them by? Are we talking about a few degrees or tens of degrees? I would try to attach some form of wooden construction in the existing hole. A couple of beams screwed together that fit in the hole. If you can get the center drill to grip them so that you can go the first few centimeters in the lightweight concrete, you should be able to continue that way.

How sensitive is the area around the hole? Another option is to drill with small drills around and then chisel out the excess with a chisel or a demolition hammer.

The existing hole was 200mm, so I first used a 200mm hole saw and angled it to make the hole a little larger. Then I took a 210mm hole saw and adjusted a little more. Since it's blue concrete, I made the final adjustment with a long rasp.

Best regards,
Richard