How to cut square hole
- Thread starter BigDaddyGump
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The big secret is NEVER TRY TO CUT A SQUARE HOLE IN CAST IRON. Cast iron expands and contracts with temperature and a sharp corner is an invitation for a crack to appear after a few temperature cycles. If you look at any cast iron casting, openings will always have a smooth radius at each change in the direction where there is an internal corner. If you absolutely have to put in a non rounded hole, you need to put rounded corners and even then you are risking a future crack.
This is not just a problem with cast iron but any metal that is in cycling temperature or pressure service. Its the same reason ships use portholes and planes have oval windows, the rounded openings distribute the stress.
If you need a gas tight square opening, your best option is cut a rounded hole then put an insert in the hole and seal the interface with resilient temperature resistant packing that can allow expansion and contraction. In general trying to modify any casting after it is poured is risky as the casting is generally thinner in areas without holes and thicker where there are openings in the casting. In general use a cutting process that is not thermal and use lots of coolant. Then go through a series of slow heating and cooling cycles gradually increasing the temperature. Even with all this care the casting could start cracking.
This is not just a problem with cast iron but any metal that is in cycling temperature or pressure service. Its the same reason ships use portholes and planes have oval windows, the rounded openings distribute the stress.
If you need a gas tight square opening, your best option is cut a rounded hole then put an insert in the hole and seal the interface with resilient temperature resistant packing that can allow expansion and contraction. In general trying to modify any casting after it is poured is risky as the casting is generally thinner in areas without holes and thicker where there are openings in the casting. In general use a cutting process that is not thermal and use lots of coolant. Then go through a series of slow heating and cooling cycles gradually increasing the temperature. Even with all this care the casting could start cracking.
What he said.
Why do you want to cut a hole in your stove anyway
Why do you want to cut a hole in your stove anyway
tabner
Feeling the Heat
As far as the actual cutting - i cut a large rectangle in the top of a thick steel wood stove using an angle grinder. I think it was about a 3.5" or 4" disc angle grinder, i bought metal cutting blades, and just went slow. threw a lot of sparks, but worked beautifully. And i bought a thick grinding disc to clean up the rough edges afterwards.
not positive if cast iron will cut the same way or not, but i would think so.
(i'm not arguing with the round vs. square comments above, i just thought i'd weigh in incase you were looking for specific tool/technique suggestions)
not positive if cast iron will cut the same way or not, but i would think so.
(i'm not arguing with the round vs. square comments above, i just thought i'd weigh in incase you were looking for specific tool/technique suggestions)
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