Router for deep cuts...

I need a router that will allow me to cut 2.5 inches. We make precast concrete countertops that are 2.5 inches thick. We use dense foam for our sink knock-outs in various shapes... ovals, circles, etc. Up til now we've used the nail and string method, a band saw, and a lot of sanding. But I would like to use a router with an oval jig. I'm thinking that this would really improve the process.

The only router that I have found that has a plunge depth of at least 2.5" is the Festool. Are there any others that might do the trick? DC is an important consideration.

I guess you'd be using a flush trim bit of some sort that can cut concrete? If so, you can get 1/2" collet straight bits up to at least 2" long, so you really only need to plunge an additional 1/2". Or do you really need 2.5" of travel?

Are you just cutting the foam? If so, why not cut the foam close with a bandsaw and use a template and long bit to finish off. It's not clear why you would need a plunge router.

Greg

Yeah, we cut the foam... not the concrete. We build a form 2.5" deep to precast the top. We use a high density foam that comes in 2.5" thick sheets to shape knockouts where the sink opening will be. After everything is set up in the mold we pour the concrete. After it has cured we flip it and remove it from the mold. Then we knock out all of the foam inserts.

We start with the sink the customer has chosen. If its a new sink with a template we use that... but often we don't have a template. If its an oval sink we just measure the x and y axis and then using the two nails and string method draw out the oval that we need, cut it a little large on the band saw and then sand it to size.

I was thinking that a plunge router with at least a 2.5" plunge in combo with a 2.5" straight bit mounted on a jig like this would make the job fast and accurate...
http://www.rockler.com/findit.cfm?page=17282

Am I nuts? Seems like it would work great.

I don't know a router with that much plunge capability, but you could also do it in two passes by adjusting the router bit 1/2" out of the collet or you could buy a fourfluted end mill that is 2-1/2 inches long or longer. In most applications an end mill will work just like a router bit. You can get end mills over 3" long.

Steve
Several years ago I helped a friend build an airplane. We used a HOT WIRE to cut the hd foam. Worked great with virtually no dust.

I think Lee may have hit the nail on the head. You should be able to get a fluted end mill (doesn't even need to be a 4 fluted unit, can get 2) that in essence is a spiral up or down cutting bit.

mike

The hot wire mentioned above is probably the best solution for cuting the foam. You can cut two templates out of thin material, one for each side, and then just rum the wire around the templates. There is lots of good info on the net about wire cutting foam. Some folks even set up CNC machines to guide the wire.:)

The hot wire is probably the simplest. If the wire is set up like a bandsaw or a scroll saw, you'd probably need a template only on the top.

The end mill SOUNDS like a good idea, but for 2.5" cutting length, the mill would have a shank larger than most routers accept. Since the foam is a lot softer than materials usually used with an end mill, you could turn the shank down to 1/2", provided the mill is dedicated only for that application. Next issue then is to find a router with sufficient plunge depth, and it might be necessary to modify a conventional one. And even after all that, there's dust control.

Many, many years ago, I worked in the precast concrete industry (product design and plant engineering), so I can feel your pain. I'd go with the wire.

Joe

You really dont need the full 2.5" of travel if you're just cutting foam. You should be able to take a fairly aggressive first pass then make additional cuts until you're through. You will need a 2.5" bit which I believe can be found easily enough.

I appreciate the hot wire suggestions but that is something that we previously considered but rejected.

2.5 " bits are not hard to find and I was hoping to be able to make the cuts without having to readjust the bit in the collet.

The Festool seems to be up to the task. I was just wondering if there were any other options.

Steve,

The Freud FT2200E and FT3000VCE both have plunge capacity of 2-9/16". That's bare minimum for what you wanted but should work. They also come with a vacuum adapter that surrounds the bit at the base.

http://www.freudtools.com/c-77-routers.aspx

Quote:

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Originally Posted by Steve Ash II

I appreciate the hot wire suggestions but that is something that we previously considered but rejected.

2.5 " bits are not hard to find and I was hoping to be able to make the cuts without having to readjust the bit in the collet.

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You dont have to adjust the bit in the collet at all if you have the right bit. At a minimum you will need a 3" bit. Take your router down all the way as far as it will go and install the bit with your needed 2.5" protruding. Now take the router up until about 1/2" to 3/4" is protruding. Make your first cut. Now you will only have to plunge the remaining 1.75"-2" at whatever increments you want to finish the cut. See? You're starting with some of the bit already out so the actual plunge depth is not the full 2". Most any router will go 1.75"-2" and cost alot less.

Quote:

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Originally Posted by joe greiner

The end mill SOUNDS like a good idea, but for 2.5" cutting length, the mill would have a shank larger than most routers accept. Since the foam is a lot softer than materials usually used with an end mill, you could turn the shank down to 1/2", provided the mill is dedicated only for that application. Next issue then is to find a router with sufficient plunge depth, and it might be necessary to modify a conventional one. And even after all that, there's dust control.

Joe

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There are lots of end mills with a length of cut between 2-1/2" and 3' that are 1/2" diameter. McMaster Carr has at least 50 in their catalog and other end mill suppliers have similar numbers. Price isn't cheap, but they are available.