Drilling thru porcelain sink

Old 08-02-16, 09:29 PM
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Drilling thru porcelain sink

Hi All,

Im looking to drill into my porcelain sink to install a RO water filter. Just got a diamond headed drill bit and planning to create a water reservoir with plumber putty to keep it cool and duct tape to help anchor it in place.

Looking underneath there is a "knockout" hole to drill into, but there is a support that intersects with the hole. I am 90% sure the right answer is to drill a new hole (away from the supports and ignore the knockout hole) but I wanted to double check.

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Old 08-02-16, 09:39 PM
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Welcome to the forums.

If that's truly a knockout.... then it's in the wrong place.
I've drilled sinks before but have not used the knockouts. I've always been afraid of it not breaking out cleanly.

Don't forget.... wear safety glasses when drilling.
Old 08-03-16, 05:16 AM
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I literally did this on Saturday for 2 bathroom sinks.

Mine had those "knock outs" as well. But they're not really knockouts rather marks for where to drill in case the sink is to be sold as a 1 hole or 3 hole. From what I understand this is before the sink is glazed

Since I needed to drill a 33mm hole for the whole valve thing I had to use a hole saw. I used a tungsten carbide because the hardware store was out of diamond hole saws.

Here's I did

I used that knockout mark to drill a pilot hole. For this I used a regular 3mm masonry bit.

I then turned it over and drilled with the hole saw from the top down. This is important because no matter how I tried, I could not avoid at least some chipping of the glazed surface when the bit came through.

For lubrication and cooling I went with an assistant with one of those garden sprayers you use for pesticides. I considered the putty and well method but was recommended this by a plumber who said that constant clean cold water is better than just drilling in water.
Old 08-03-16, 06:01 AM
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Esand gives good advice. Your sink is porcelain coated, but is actually cast iron. You might find drilling through it difficult. Depending on the diameter, a diamond grit bit or hole saw might work.

If all else fails, do a search for cast iron sink hole cutters, or sink cutters. Here's an example:

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Old 08-03-16, 04:06 PM
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In that case take my advice with a grain of salt, the sinks I drilled were some sort of ceramic all the way through.
Old 08-03-16, 04:09 PM
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Also be careful that if you're using a hole saw that nothing touches that rib. I had to cut the base plate for the hole saw down with an angle grinder to be sure it wouldn't touch. It might not be a problem if the sink is iron centered but everyone warned me that the biggest danger with drilling porcelain is that one part gets hotter than the rest and the whole thing cracks open

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