Any tips for making this easy? 100m diameter round duct have a 102 holesaw. Plasterboard is not up yet, ducting is. Other than measuring a lot and hoping I'm within 2mm on a sheet (not likely) is there a simpler way of doing this?
Only thing I can think of is a larger square hole and then patch with a smaller bit of board with the hole cut so if I get it wrong not a whole sheet cocked up.
Any other ideas? Stuff is pretty heavy solo so not easy to offer up....
Short length of flexi stuff between duct and fan unit? Cardboard template?
flex pipe connection
Measure twice?
Failing that, can you cut a bit of ply or something to fit snug into the duct with a nail dead centre (compass mark) then offer up the board, give it a tap to give you a centre mark?
Just thinking out loud.
Cut a smaller hole, say 75mm by measuring. Then mark the 100mm more accurately now you can see/measure to the duct in place. Enlarge the hole with a Stanley or a jabsaw. If you really want to use the 102mm holesaw then cut a 102mm hole in some ply, screw it to the ceiling and use that to guide the holesaw.
I could use a flex hose I suppose but it's a very short run till the adaptor. say 15cm or so, was hoping to get away with a simple straight bit of pipe. shortest flex pipe from screwfix was something like 2m....
smaller hole then enlarging sounds a good idea as does some way of marking.
I was quite surprised at the weight of a sheet of plaster board. not easy to get to ceiling height on your own
Flexi.
I put one in a bathroom recently, wouldn't dream of doing it any other way.
Flex pipe about £4 if i remember right
<p>Drive a nail through the centre of where you need to be then mark it with a compass on the other side. Either that or just drill it from the "easy" side as it'll presumably get skimmed if it's new board so any small tears will get covered.</p>
make a small hole then cut it with a pad saw, much easier to be accurate that way
Cut a bit off the plasterboard sheet small enough to handle, large enough to reach the ceiling joists. Offer up, make exploratory holes, take down and cut out
I just did this on a boarded up window.
Managed to get 2x vents through it lined up perfectly! Just measured it very carefully.
Scrap template (bit of wood, plasterboard or even thick cardboard), square against the two closest sides/joists. Mark out and cut to make sure it fits, then trace over the plasterboard and bob's your mother's.
Magnets. Fix a magnet to your centre point before the plasterboard goes up. Use another magnet to "find" this point one plasterboard is up. Recover magnets once hole is cut.
I have done something similar by running 2 string lines from opposite walls overlapping to form an X at the centre of the duct. Mark the walls where the string lines need to start so once the boards are up you can put the string lines back on these points and you have your same X.
Not sure that makes sense reading it back...
I would measure as accurately as possible, trying several ways to ensure I can repeat to within 25mm. Then fix the plasterboard and mark the assumed centre. Then cut four small holes 25mm from the centre (leave the centre area in place) and poke bent wire through them to measure exactly where the duct is. Plot the duct location, mark the exact centre and use the hole saw.
Oldskool methods without using lasers.
String two pieces of string from marks on the opposing walls to cross on the centre of the duct. Remove string, sheet ceiling, restring from the same marks to find your centre as suggested by hooli
or.....
Hang a plumb bob from the centre of the duct and mark the floor where it touches.
sheet the ceiling and rehang the plumb bob from a drawing pin to touch the mark on the floor to find your centre point again.