Core drilling a partially filled, existing 100mm hole, to a 150mm hole, through an outside wall.

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There are 3 holes in a room I have, all at 100mm wide. Rather than cut a fresh hole at 150mm, I thought it would be best to expand 1 of the current holes, so as not to look a complete eyesore from the outside.

On the inside, you would never know they were there, but on the outside, they still have the old vents attached. Looking into the vents, they have patched the internal wall, maybe a few inches deep.

Would this be enough to pilot a 150mm core through to expand the hole? The holes are approx 350mm long.

I would guess an alternative should this not be possible would be to stitch drill around it?
 
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Filling the 100 mm hole wth a wooden plug would ensure the pilot drill stayed in the right place long enough the get 150 mm hole cutter established.

A plug could be made using a 110 mm core drill to core through a thick piece of timber. The inside of a 110 mm core drill is approx 100 mm Or a 100 mm core drill and then wrap soemthing round the plug to make it a tight fit in the hole to be enlarged.
 
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Could I not use the few inches of filling from the inside of the hole for this?

How far in do you have to use the pilot?
 
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Could I not use the few inches of filling from the inside of the hole for this?

It would have to be strong enough to keep the pilot drill in the right place. If it is just mortar and bits of brick then it might be OK if it is just plaster then it will crumble and not keep the pilot in place.

How far in do you have to use the pilot?

The pilot is there to stop the core drill from sliding around on the surface. Once the core drll has cut into the surface and that cut is deep enough that the material is not breaking away but guiding the core then the pilot drill is not so important
 
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The is the hole.
 

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If you drill a 150mm hole you'll foul the other 100mm hole alongside it. You'll need to move at least 25mm, but probably better 50mm away from the other hole.
Move 75mm and you're into virgin territory for the pilot drill.
 
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Attach a piece of wood to the wall on the inside and then use that to support the pilot drill.
 
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Yes, rather than plugging the hole with a 100mm cutout, cut a hole in plywood that's 150mm diameter.

Attached the piece of ply, with hole in it, to the wall where you want to core drill. Use 4 red rawl plugs and screws into mortar and fill them afterwards when you take the ply away.

Guide the entire core bit, not the pilot.
 
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