I want to fit a number of 44mm fire doors where the existing doors (and rebates) are only 35mm.  To get the depth a hammer and chisel would take too long and be too uneven so I'm thinking of either a router or a combination of a mini-circular saw to cut down and a multi tool to cut in.  Once I have 44mm I can plant a strip of 8mm batten alongside the edge to deepen the stop from 8mm to 16mm.  Anybody tried anything else to achieve the required end?

Thanks

Ari

If you are fitting new fire doors you should use fire door sets which are the door and frame that has been tested together. Consequently there will be no modification to the frame required and it is more likely the enforcing officer will accept it more readily.  

Thanks Tom but there will be no enforcing officer as the house doesn't fall within the HMO category.  I'm doing the doors just for peace of mind and the budget is a factor.  I've found it  very difficult to find FD30 doorsets, and impossible to find ones at a reasonable price compared to putting a bog standard FD30 door in and adding surface mounted seals.

Ari

I was thinking more about building regulation, material changes, I understand your problems but your proposals seems to present many difficulties and using new frames may be a better solution, despite the additional cost.