Cutting holes in ground insulation for 110mm waste pipes

[Chanmenie]

Hi

Anyone got any tips for the best way to cut 110mm  holes in 100mm PIR for the waste pipes, I can’t find any hole saws deep enough to go through the 100mm Celotex 

[JohnMo]

I just used a small saw blade in a Stanley knife blade handle.  Foam filled any gaps

[Conor]

Plasterboard saw. Cut it big and rough then just foam around.

[Jacob]

I found a wood jab saw from screwfix £4.99 , 300mm long to cut my 250mm slab insulation. Same as a pb saw but longer if needed. 

[PeterW]

I’ve got a 110mm hole saw somewhere that got “modified” with a slot cut into the top and then the edge bent down to cut through EPS as it basically acts like a food processor blade and chops the core out as it goes - it’s not pretty but works ..! Now if I can remember where it is ….. 

[Chanmenie]

Some great ideas there, thanks guy’s 

[Bonner]

Jigsaw with these blades. Bit bendy but work surprisingly well.

https://www.amazon.co.uk/Festool-Jigsaw-Blade-155-204345/dp/B07M6PKLCS/ref=asc_df_B07M6PKLCS/?tag=googshopuk-21&linkCode=df0&hvadid=412285882712&hvpos=&hvnetw=g&hvrand=7100560651268759544&hvpone=&hvptwo=&hvqmt=&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=1006876&hvtargid=pla-872783453695&psc=1&th=1&psc=1&tag=&ref=&adgrpid=85363719810&hvpone=&hvptwo=&hvadid=412285882712&hvpos=&hvnetw=g&hvrand=7100560651268759544&hvqmt=&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=1006876&hvtargid=pla-872783453695

[TonyT]

Old school pad saw for me.