Looking at this bathroom sink from below a round area is visible in the middle where the material is thinner. Is there a safe way to drill a middle hole there (to install the faucet recommended at https://diy.stackexchange.com/a/18330/7480)?
I would not recommend treating the area in the center rear of the sink as a "knock out". Trying to remove that portion of the sink with a hammer is foolhardy at best and could lead to splintered and cracked procelain on the top side of your sink.
You would be far better off to apply a hole saw made for this type application. Here is an example of a diamond grit hole saw that may be suitable:
Link to tool on Amazon:
Hole saws of this type are often used with a 0.25 inch diameter drill bit acting as a centering agent to keep the hole saw in its cutting track. It is often a good idea to pre-drill the guide hole for this before deploying the hole saw. Look for a diamond dust drill bit for drilling this hole.
Use of the hole saw will likely require the adding of water into the cut area during the cut process to keep down the heat buildup on the hole saw.
If it was my project - I would drill the guide hole from under the sink first in order to get it centered properly and then come back and drill out the necessary larger diameter hole with the hole saw from the top side.
Last Comment - Before investing a whole lot of money in tools for a one-shot project you owe it to yourself to investigate the cost of a complete sink replacement that has the appropriate hole configuration to meet your needs. You may find that a retailer may offer a good deal on pricing if you purchase a sink and faucet at the same time.
2Note that cutting with a bit like this is not the kind of cutting you normally think of. Consider it sanding in a circle shape till you sand your way through the entire thing. Sep 28, 2012 at 18:31
@EdwinBuck - You are indeed correct regarding how this type hole cutting tool works. They go relatively slow but do make a nice hole. I have even used then for making holes through the steel frame on my van for running a wiring harness.– Michael Karas ♦Sep 28, 2012 at 23:28
I bought one of these bits (a 3" one) specifically to bore holes in the back of some very nice furniture which (despite not having holes) looked like it was an entertainment / TV stand. They do work nicely, I just didn't want the guy to think it wasn't cutting, because, well it doesn't cut in the traditional circle saw sense. Sep 28, 2012 at 23:31
1In this case, the shoulder of the indented section will direct the hole saw without needing a pilot hole, just keep even, centered pressure, pausing regularly to dip the bit in water.– HerrBagSep 18, 2013 at 15:37
The thinner part is a knockout. Give it a firm tap in the center and it should break out cleanly.
EDIT: Four upvotes to Five downvotes... Interesting ratio. I'm curious of the downvoters: What do you think that thin circle, in the center of the area where a faucet would go, with a formed center tapping point... is?
1And if it doesn't? Sep 27, 2012 at 19:18
2@TheEvilGreebo Keep tapping, until it all chips away. Sep 27, 2012 at 19:22
2I was thinking more what if it breaks too much out. Sep 27, 2012 at 19:23
1@TheEvilGreebo Then you whacked it way too hard. Use a smaller hammer, and don't follow through. Sep 27, 2012 at 19:28
2Every porcelain sink with knockouts has looked just like that... I've never had to drill out a hole and I've never had chipped finish.– MatthewSep 28, 2012 at 20:07