Enlarging "reaming" sink hole in kitchen basin

Forums › Home Workshop DIY › Enlarging "reaming" sink hole in kitchen basin - seeking conical drill bit

Hatch

797 posts

Ultimate Geek

#198331 5-Jul-2016 01:11

It's time to replace our leaky kitchen mixer. I purchased a decent flexible head mixer from Bunnings requested by the boss. However the original sink hole is approx 34mm and the new fitting requires a hole of around 38mm.

Conical drills or step drills are the tools to do the job, but they are quite expensive for the size I want.

Does anyone have one lying around I could borrow or alternatively an ideas on how to accomplish this task without said tool?

I'm probably going to end up do this by hand with a semi circular file. I have a Dremel clone but the dremel bits I have are too soft for stainless steel.

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8953 posts

Uber Geek

#1586006 5-Jul-2016 06:39

If you have the right size holesaw, clamp a piece of wood to the bench for a guide then use that.

andrewNZ

2487 posts

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Inactive user

#1586007 5-Jul-2016 06:57

A step drill really isn't the answer. They hate stainless, and you'll probably kill it.

The real answer is either a holesaw, or a chassis punch.

nickb800

2715 posts

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Trusted

#1586009 5-Jul-2016 06:59

Yeah stainless steel sinks suck for drilling holes. If you use an unsuitable drill bit such as a bimetallic hole saw you risk overheating the sink and causing discolouration.

I ended up getting a plumber in just to borrow his holesaw. Might be cheaper to get an appropriate bit off Amazon?

frankv

5680 posts

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Lifetime subscriber

#1586013 5-Jul-2016 07:02

Agree with AndrewNZ. Or get a small drill bit and drill a whole lot of holes around the edge of the circle you want. The flange on your fitting should hide the messy edge.

Mattmannz

471 posts

Ultimate Geek

#1586143 5-Jul-2016 09:21

As with any metal cutting work you want to use a variable speed drill and also some cutting lubricant or paste which will assist with cooling and also increase the cutting speed. Go slowly and don't let things overheat.

The suggestion around clamping timber over the existing hole is a good idea and works well.

Cheers

Matt.

Hatch

797 posts

Ultimate Geek

#1586148 5-Jul-2016 09:25

andrewNZ: A step drill really isn't the answer. They hate stainless, and you'll probably kill it.

The real answer is either a holesaw, or a chassis punch.

The thing is the sink is already installed and I don't see anyway to use an appropriately sized holesaw to shave off the 2-3mm off the edge of the existing hole.

If a step drill was cheap I wouldn't mind buying and ruining it for this single job, however they're expensive at that size.

DarthKermit

5346 posts

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Trusted

#1586167 5-Jul-2016 09:49

I totally blunted one of my good quality bi-metal hole saws trying to drill a hole through a stainless steel laundry tub. When I went to the tool sharpening guy, he said that bi-metal (which is tungsten carbide fused onto steel) isn't suitable for cutting through stainless.

He recommended these types of hole saws:

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MikeAqua

7773 posts

Uber Geek

#1586174 5-Jul-2016 09:59

Drill a hole dead centre on your existing plug (use a nail punch to make a dent to start drilling in).

(I'm assuming one of those stainless plugs with a rubber rim and raised centre).

Insert the plug.

Use a holesaw with a central drill bit to drill the new hole.

Stick the drill bit into the hole in your existing plug and use this to keep the holesaw centred as you cut.

Mike

ubergeeknz

3344 posts

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Vocus

#1586178 5-Jul-2016 10:07

or in this case clamp wood underneath (you might have to remove the sink) and use it to guide the centering bit on the holesaw. Get a holesaw made for stainless because it is hard and use some kind of cutting fluid (light machine oil is fine). Go as slowly as you can and keep things cool.

MikeAqua

7773 posts

Uber Geek

#1586188 5-Jul-2016 10:28

You can buy cutting fluid in a spray can. When I used the method described in my previous post I used dish-washing detergent as a lubricant.

Mike

Adamww

48 posts

Geek

#1586191 5-Jul-2016 10:33

Since you mentioned you have a dremel clone I would suggest shopping for a Tungsten carbide burr for it. The genuine dremel ones are pricy ~$30 but you should find cheaper ones for about $10. When you say "the dremel bits are too soft for stainless", that would probably indicate the one you tried was just a "high speed steel" or worse "Chinese HSS" that would overheat and soften quickly.

Bung

6477 posts

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Subscriber

#1586199 5-Jul-2016 10:53

MikeAqua:
Drill a hole dead centre on your existing plug (use a nail punch to make a dent to start drilling in).

(I'm assuming one of those stainless plugs with a rubber rim and raised centre).

Insert the plug.

Use a holesaw with a central drill bit to drill the new hole.

Stick the drill bit into the hole in your existing plug and use this to keep the holesaw centred as you cut.

You've got the wrong hole as the actress said to the Bishop. There are probably many different grades of stainless but the last mixer hole that I drilled was just done with a cheap Fuller saw. A lot of modern sinks are really thin. As an alternative to centering with the drill bit you can cut a hole through something else and use that to guide the outside edge of the saw.

ubergeeknz

3344 posts

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Trusted

Vocus

#1586202 5-Jul-2016 10:58

Adamww:

Since you mentioned you have a dremel clone I would suggest shopping for a Tungsten carbide burr for it. The genuine dremel ones are pricy ~$30 but you should find cheaper ones for about $10. When you say "the dremel bits are too soft for stainless", that would probably indicate the one you tried was just a "high speed steel" or worse "Chinese HSS" that would overheat and soften quickly.

Have you ever tried this though? I have found that the burr just works itself loose, and this was on regular steel, but maybe I'm using it wrong.

BTR

1527 posts

Uber Geek

#1586209 5-Jul-2016 11:11

This made mad laugh given your username is bung and we are talking about holes.

Bung: You've got the wrong hole as the actress said to the Bishop.

MikeAqua

7773 posts

Uber Geek

#1586231 5-Jul-2016 11:36

Bung:
As an alternative to centering with the drill bit you can cut a hole through something else and use that to guide the outside edge of the saw.

Works nicely if you can hold the guide in place. I suggest that may be difficult on an installed sink.

Mike

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