# I need to cut a 7/8" deep rabbet joint



## WVHick (Apr 7, 2015)

I am new to woodworking and have recently purchased a Bosch router as one of my first investments. I am building an 18" home theater subwoofer and bought a well known (in home theatre) box kit that I glued up, sealed, sanded, and painted the other night and now I am ready to mount the driver. 

I have now decided that I want to flush mount the subwoofer, and the current cutout is a 16.75" diameter hole. In order to flush mount the driver, I need an 18.5" cutout. So I need a bearing guided rabbeting bit that will cut a 7/8" deep rabbet but I can't find any. Any ideas? The max I can find is 3/4".

Thanks for the help.


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## hwebb99 (Nov 27, 2012)

I don't think a rabbiting bit will work because there will be nothing for the bearing to ride on. I would make a template, and use a pattern bit to enlarge the hole.


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## WVHick (Apr 7, 2015)

The rabbeting bit could ride on the face of the existing hole, right? This is how my box sits right now. I just want to cut a 7/8" rabbet about 3/8" deep around that hole.












So that I end up with this:


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## hwebb99 (Nov 27, 2012)

Yes that would work. I thought you were trying to cut all the way through.


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## ryan50hrl (Jun 30, 2012)

I've never seen a 7/8 bit....and a quick search didn't turn up any results. You might be sol on a bit that large.


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## WVHick (Apr 7, 2015)

hwebb99 said:


> Yes that would work. I thought you were trying to cut all the way through.


Which brings up the million dollar question...any bearing guided bits out there that will cut a 7/8" rabbet?


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## bauerbach (Mar 25, 2012)

take the 3/4" rabbit bit, cut a 3/4" rabbit from the top. Then drop the bit 1/8" and cut again.

boom, 7/8" rabbit.

edit: maybe I have my dimensions backwards.... you want 7/8" thick...

well... thinking outside the box... make a plate for the router. On that plate, mount 2 dowels (or bearings if you have them). 

attach the router to that plate where you can make it so the 2 pins ride against the opening, and the router bit sits 7/8" outside.


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## Toolman50 (Mar 22, 2015)

WV
Could you cut another board 3/8" thick and make the hole 1 3/4" larger (giving you the equivalent of a 3/8" deep X 7/8" wide rabbet). Overlay this board over the face of the other.


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## woodnthings (Jan 24, 2009)

*maybe, but ....*



WVHick said:


> Which brings up the million dollar question...any bearing guided bits out there that will cut a 7/8" rabbet?


You need a rabbet bit, diameter large enough to suit, with a bottom bearing, diameter small enough to suit. The right combination is what will work.

Like this one, but a larger diameter cutter:
http://www.ebay.com/itm/Amana-49340...744?pt=LH_DefaultDomain_0&hash=item5662fb0a18

If all else fails and you can't find a larger cutter...I couldn't and I search pretty well, then what? ....
You can use a top bearing on a cutter to remove material from the bottom of the surface leaving a ride path for the reverse setup, a bottom bearing with the correct diameter to get your 7/8" rabbet ....ultimately. :blink: That would be a 2 step operation.


Another option would be to use a slot cutter with a bottom bearing riding on the material like this and then space the cutter up progressively as you go to get your offset down from the top:
http://www.ebay.com/itm/CMT-822-332...456?pt=LH_DefaultDomain_0&hash=item3cf6937448

I don't know how many cutters you can stack on the arbor to get more offset, or rabbet depth, but that may work with more than one cutter.... I donno?

http://www.toolstoday.com/c-333-slot-t-slot-cutting-router-bits.aspx


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## FrankC (Aug 24, 2012)

Bauerbach's last suggestion with the plate and two pins will work, you will have to make at least two setups, one for each pass to cut 7/8" wide, depending on the bit you have. Fortunately only the last pass is critical.


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## bauerbach (Mar 25, 2012)

I think you could cut 7/8 in a pass... might want to swing a pretty big bit, but its doable.

Id still make the jig adjustable, it could be a useful rabbiting jig for any application.


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## WVHick (Apr 7, 2015)

Thanks for the help, guys. Haven't decided yet what to do. May go ahead without flush mounting for now until I have a little more experience.


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## Pcride (Jun 4, 2012)

make a circle template like everyone is saying to cut the outer most dimension, then free hand the remaining 1/4 in. Shouldn't be hard at all. A steady hand is all you need.

I think you mean 7/8" wide, not depth.


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## Pcride (Jun 4, 2012)

Or just cut another top from 3/8 ply, cut the circle to the size needed using a jig saw and template, then glue it on top of the box front, so the front will be a bit thicker than the other sides, carpet the box and you won't see it.


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## Pcride (Jun 4, 2012)

Its easier this way than spending $50 for a bit you are only going to use once. I have a lot of those bits in my tool box from over the years 

OR take it to a local shop and have them do it, might cost about $50.


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## Zircon (Aug 1, 2009)

Here is a setup that should work. Put a 3/4" straight bit in the plunge router with depth set to 3/8". Install the guide that is meant to follow curves 1/8" away from the bit so the edge of the bit will cut 7/8" away from the hole. If you hold the router tight to the workpiece you will be left with a 1/8" wide and 3/8" high piece around the hole. If you have a steady hand you can hold the router away from the piece and waste the remainder or else remove it by hand planing or chisel.


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## FrankC (Aug 24, 2012)

Zircon said:


> Here is a setup that should work. Put a 3/4" straight bit in the plunge router with depth set to 3/8". Install the guide that is meant to follow curves 1/8" away from the bit so the edge of the bit will cut 7/8" away from the hole. If you hold the router tight to the workpiece you will be left with a 1/8" wide and 3/8" high piece around the hole. If you have a steady hand you can hold the router away from the piece and waste the remainder or else remove it by hand planing or chisel.


Only having one guide point will make it more difficult to keep a consistent distance from edge of hole as the guide has to be kept exactly perpendicular, it will work though.


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