Replies

1. 
   DanH | Jan 27, 2019 06:05pm | #1

   You MIGHT get away with CAREFULLY grinding out the hole.  I wouldn't want to cut more than about 1/8", though.

2. 
   junkhound | Jan 27, 2019 10:46pm | #2

   Option 1:Heavily scribe the

   Put on your safety glasses. 

   Option 1:

   Heavily scribe the porcelain with a diamond tip glass cutter to about 7/8" diameter. Using a sharp center punch carefully chip off the porcelain out to the scribe. The porcelain will break evenly with the scribe. You need to MAKE SURE you do not have any scribe marks ENDING OUTSIDE of the scribed circle. Once you have chipped away the porcelain, drill or grind or file the cast iron.

   Option 2:

   Buy a 3/4" or 7/8 in diamond hole saw (for a few uses, the cheap ones from harbor freight work fine). The trick here is that you need to make a wooden or other jig to keep the hole saw centered - a piece of plywood with guiding hole (as in a drill bushing) clamped to the tub works OK. You can drill all the way thru with that but drilling the cast iron part works better with regular drill bit if you do not hit the edge of the porcelain. Have done this on the flat back of a CI sink, but not a tub - should work on tub also.

   Option 3

   Diamond blade on dremel or similar tool or even in a sidewinder. Saw kerf outside the area you want to enlarge the holes and drill. The kerf stops the porcelain cracks.

   REMEBER to  put on your safety galsses.  Or even a face shield - those porcelain chips can be sharp.. 

3. 
   florida | Jan 28, 2019 03:30pm | #3

   There is probably a 10% chance you could do this yourself without ruining the tub. There may be a pro out there who would be willing to risk it but I don't know. In know porcelain chips really easily. I think I'd work on reducing the pipes to 5/8." 

4. 
   Pagurus | Jan 29, 2019 02:09pm | #4

   Thank you! I really appreciate the thorough reply. Fast, too.

5. 
   cussnu2 | Jan 29, 2019 02:46pm | #5

   You might check in the tile area of your big box. They have drill guides in various sizes for drilling through granite for faucets. #1 they should have a guide for your size #2 the guides usually come with a diamond bit which should at least get your through the porcelain but if you aren't a stickler for a really nice hole (ie your not an engineer who is going to be endlessly bugged that the hole behind the Escutcheon Plate isn't round, then a dremel with a diamond bit will likely get you where you need to go. I would just make sure that you bevel the porcelain first and then bear down on the cast iron and repeat. I'm afraid if you go at it square you will chip or break the porcelain off so bevel the porcelain back first and then work the metal back square and repeat as necessary.