Core drilling tools for bolt replacement

HowNot2 sells them and has a product description that includes a video explaining which size fits what:

https://hownot2.com/products/core-drill-bits

bmdhacks wrote:

I go 16mm for removing 3/8in or 10mm wedges and sleeves.  12mm core drill will shear when it catches.  13mm will work if you're extremely careful.  But like timothy says, just use 8mm twists and drop them in a 16mm hole and then the core drilling will easily go around the bolt and be much faster.  The core drill is about 10x slower whenever it hits metal and about 10x more likely to break in the hole.

Thanks for the input

8 mm twists in 16 holes sounds like a good idea. 

After core drilling do you roughen up the 16mm hole with a regural rock drill bit ?? 

Thanos Pap wrote:

After core drilling do you roughen up the 16mm hole with a regural rock drill bit ?? 

Not intentionally, but I do have a 16mm SDS drill bit to do any clearance I need if the twist bits are a little picky about fitment.
I'm pretty sure the porosity of the rock allows for adhesion so you don't need mechanical roughing, but it would be an interesting test.
I tend to semi-notch my placements anyways just to insulate against rotational forces (and I think it looks better)

Thanos Pap have you ever tried a red neck  or hybrid core drill? Drill some small holes right next to the bolt. For me that is a standard tactic when i have trouble with a wedge bolt. The small drills will dig into the steel and often break the expansion clips. You get the added benefit of plenty of abrasive material in the hole and a great path for water if you need to spin. I think that might be helpful with the double wedge bolts. Then you could drill to 12 or 14mm after. 

Timothy , bmdhacks

Thanks for the info !!

When core drilling, do you have any info about your drills rpms, and how long should it take on average to drill say a 16mm hole around a 10mm bolt? 

Thanks !!!