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Old 06-22-2008, 06:35 PM   #1
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cutting large circles in marble


Hi, I am trying to figure out the best and neatest way to cut large circles in 30mm marble. Is there some sort of expandable hole cutter like for wood?

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Old 06-22-2008, 09:34 PM   #2
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cutting large circles in marble


I'm not aware of an expandable tool for cutting stone. How large are the holes you're cutting?

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Old 06-23-2008, 04:29 AM   #3
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cutting large circles in marble


Hi there, I am looking at cutting holes around 350mm - 450mm.
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Old 07-01-2008, 10:46 AM   #4
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Hi there, I am looking at cutting holes around 350mm - 450mm.
You are looking for diamond core bits. I've never seen one that is expandable. They can be found in all sizes for various applications. I've never really seen bit larger than 3-4" outer diameter used for drilling stone that is only 30mm thick. They do make them up to 30" diameter though.

If you were adventurous though, here's what you could do.

  • Get a high speed wet concrete core drill with a diamond core bit that is the desired diameter. You can likely get one at your local equipment rental shop for about $30/day.
  • Lay your marble out on a flat and very ridgid sacrificial surface. You don't want marble flexing at all, and the bit will ruin the surface underneath the stone when it cuts through, so obviously don't lay the stone on top of other slabs.
  • Clamp the slab down firmly to prevent it from shifting and drill through slowly with the drill.
Obviously this doesn't allow you to precisely specify a hole size, but instead you have to use the bits that are available. Also, this will be really messy, so you'll want to do it outside.

If that sounds like too much hassle, then you should do what is common practice. Use a grinder with a diamond cutting wheel on it to make the rough cut of the opening. You'll end up with a hole that is about the right size and shape but the holes profile will have crosshatch marks from the wheel.

You'll then want to get a zero tollerance wheel and use that to put a smooth straight profile on the cutout. Once the crosshatch marks are gone, you'll need to work your way through increasingly finer polishing pads to shine up the profile you just cut.
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Old 07-01-2008, 12:31 PM   #5
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cutting large circles in marble


What are you going to turn a 13"-17" hole saw with?
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Old 07-01-2008, 01:42 PM   #6
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cutting large circles in marble


a water jet works well if you have one

or;

a router with a bit designed for stone
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Old 07-01-2008, 01:43 PM   #7
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What are you going to turn a 13"-17" hole saw with?
A 12 volt Ryobi drill/driver should do the trick.
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Old 07-01-2008, 02:04 PM   #8
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a water jet works well if you have one

or;

a router with a bit designed for stone

A Jasper jig and a diamond router bit
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Old 07-01-2008, 02:15 PM   #9
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What are you going to turn a 13"-17" hole saw with?
http://www.csunitec.com/drills/cored...ic.html#14inch

This type of rig is what is generally used for coring holes larger than 6". I've done a 6" horizontal core through a 10" concrete wall with a handheld, but it was a pain. These rigs are better as they hold the drill in place and result in a more precise core placement. Like I said in my previous post, you need to make sure that the stone slab is well supported. Our local equipment rental shops have these rigs for rent on the cheap.

In any case, the OP would probs still have to use a zero tollerance wheel to achieve the desired profile after using the coring rig, so using a grinder with a diamond wheel might be a bit easier depending on how many cutouts there are. If I could get the right size coring bit and I had to make more than 3 cutouts, then I would probably rent a coring rig for $30. Sounds like the OP is just trying to make vanity sink cutouts which are usually done with a 5" diamond wheel on a variable speed angle grinder.

Last edited by Cache; 07-01-2008 at 02:17 PM.
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Old 07-01-2008, 02:26 PM   #10
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A Jasper jig and a diamond router bit

If you do it that way you are going to burn through some expensive bits very quickly. Better to just use a diamond cutting wheel. JMHO, but maybe you know of some plunge bits that cut well and don't cost very much.
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Old 07-01-2008, 02:30 PM   #11
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cutting large circles in marble


chances are no rental place is going to have a 350-450 mm core bit so that would mean he would have to purchase one. I have never priced one that large but hearing a price of a thousand dollars would not surprise me.

If he needs a custom size, I would think twice that would not be a surprise and definately removes the rental possibility.
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Old 07-01-2008, 02:31 PM   #12
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If you do it that way you are going to burn through some expensive bits very quickly. Better to just use a diamond cutting wheel. JMHO, but maybe you know of some plunge bits that cut well and don't cost very much.
sorry cache but I do work at a shop that uses this method all the time. How do you think they put an ogee on the edge of stone countertops.

rather than a plunge bit, you would drill a hole to allow a starting point
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Old 07-01-2008, 03:23 PM   #13
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Yeah, I said the OP wouldn't have the option of getting a precise diameter if using a rental diamond core bit. I was just offering a suggestion along the lines of the coring bits proposed.

I regards to your other method. An ogee profile is a bit different than routing out a sink cutout. The ogee only removes small amounts of stone at each pass, eventually achieving the appropriate profile. You're talking about a diamond finger bit making a 1 1/4" deep cutout in a single pass. That's great, but I'm wondering how many feet those bits are good for. Those finger bits are about $150 for a decent one. A 5" diamond wheel is about $20.

Admittedly, in order to profile a sink cutout from a 5" wheel I have to use a $120 zero tolerance wheel. Maybe I'll switch to a finger bit too. Do you have any recommendations on brand?

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