wrong size hole (too small ) for new air vent help!!

[whitehaven]

Hope someone can help.

I bought a blackhole airvent 127mm that i wanted to fit once i had knocked a hole through the wall because i had fitted a log burner.

Asked my plumber mate if he had a core drill for the job which he kindly lent me.
After spending some time drilliing the hole ( & much mess) I then went to fit the new black hole air vent only to find that the core drill bit that i used had drilled the hole too small - 100mm diameter.
Thus realising that my mate obviously uses his 100mm for soil stacks & the like.
SO, problem is, if i get hold of the right sized core drill, how can i knock the hole out bigger? as the normal masonary drill but in the middle of the core drill will have nothing to purchase on!
In the meantime i have stuck a vent over the inside & outside wall until i can drill the hole bigger to acomodate the 127mm blackhole air vent.

thanks in advance

 

[Alastairreid]

I would stitch drill around the perimeter till you get your required diameter.

 

[whitehaven]

I would stitch drill around the perimeter till you get your required diameter.

what is this please, my house is 9 inch brick (no cavity) if it makes any difference

 

[RMS]

Draw round the air vent. Then using a drill with a smallish masonry bit, drill a series of holes through the marking on the wall. Follow the line drilling lots of holes close together. This is where the term "stich drill rr chain drill" comes from.

Once you have done this then use a hammer and chisel to break out the hole. Repeat the same process on the other side of the wall.

 

[big-all]

it may or may not work because its masonry i don't know

but on wood you drill an outer ring and use that as a guide maybe that will work with a 12mm ply screwed properly in at least 4 places possibly in the area covered by the face plate

 

[RedHerring2]

Once the core drill has penetrated a few millimetres, there's no need for the pilot drill.
So using big-all's approach, once started you can dispense with the ply guide.

I must admit to never having tried it and I suspect that there's a real danger of the core drill sticking regularly or even going off-course.

 

[ColJack]

mortar the core back into the hole.. then use the hole that's already in the center of it..

 

[Sureitsoff?]

mortar the core back into the hole.. then use the hole that's already in the center of it..

could you put the core back into the hole and use wedges to centralize it and hold it in place to start off the bigger core drill

 

[wotan]

If you can't discern the difference between 100mm and 127mm, maybe
you should have left it to someone who could.

 

[diy001]

Mistakes happened.

 

[big-all]

If you can't discern the difference between 100mm and 127mm, maybe
you should have left it to someone who could.

to be fair its the thickness off the concertina walls that make up the difference
although you would never drill a 100mm hole it would always be 110mm plus for clearance