castiron brazing

[cessna]

I made a couple of steam cyls but cut the intake and exhaust slots slightly off, I brazed them shut and tried re cutting. I broke two 1/8 end mills and one drill bit, even drilling into the brass is really tough. My question is does cast iron and brazing rod become very hard after brazing? I did'nt seem to have any trouble cutting the first time before brazing.
Terry

 

[portlandron]

As you have found out yes it does. Try heating it to red then cool off slowly.

 

[gbritnell]

Hi Terry,
I don't know the measurements or configuration of your cylinder but it might be possible to take a cut from the face, say .062, and make an intermediate plate with the port location corrected.
gbritnell

 

[mike os]

the composition & structure of the metal changes quite a bit in the HAZ, you may be able to bring it back aif you can heat & cool very slowly, but probably less work to either remake or take more time machining

 

[cessna]

Thanks for the replies, I have considered making up an intermediate plate as suggested, I just found it amazing how hard even the brass became.
Terry

 

[Mainer]

If the cast iron cooled rapidly, it may well have hardened. I can't explain the brass though. Are you sure it's not bronze? Some bronze alloys can be a bear to machine. The bronze alloy locks up all the slip planes in the microstructure so there are no natural cleavage lines.

 

[cessna]

No I don't think it would be bronze, it was just ordinary flux coated brazing rod. I put the cyl in my small forge and heated till red, shut the forge down and closed it up with the cyl inside to allow it cool slowly, I then tried drilling the brass again and promptly broke another drill bit. I am doing as George suggested and milling about sixty thou off and making up a plate to cover the poor machining I did.
Terry

 

[Maryak]

it was just ordinary flux coated brazing rod.

Terry,

If memory serves me correctly, (and that's not a given these days), the above is tobin bronze.

Best Regards
Bob

 

[cessna]

Thanks Bob, I wasn't aware it was bronze, maybe that explains my broken tools.
Terry