# Creating a 'trench' in a wooden frame



## jf1 (Nov 8, 2008)

Hi!

Great forum..I've learned a lot from just reading up on here already!

I'm pretty much a newbie to all this so please bear with me..

I won't bore you with all the details but i need to create a 25mm wide by 15mm deep trench running the lenght of some redwood that's 28mm thick.

The lengths of wood are 1m 20cm (L) x 10.6cm (W) & 45.5cm (L) x 10.6cm (W). I'm going to be building a frame out of this & need the trench to run as uniformly as possible all the way around the interior of the frame once it's put together.

The question is - would a router be the best bet for this job? And if so, what type of router would be the most suitable & would i need a table for it ect..? I'm going to need to make 15 of these frames to start with & possibly more down the road.

I've already built some frames to this size (without the trenches) but just drilled & screwed the wood together & added L backets internally in opposite corners to provide extra strength. This time i'd like to give the frames a better finish & have been looking at mitre & dovetail joints ect.. but really don't know where to even start with that! 

Any help or advice would be very much appreciated!

Thanks in advance 

Joe


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## dovetail_65 (Jan 22, 2008)

If I understand you the trench is a rabbit, correct? You can do this with a table and rabbit the pieces before construction or make the frames first and rabbit along the interior after. Make sure the frames are secure when passing the router over the frames.

A rabbit bit like this is nice: http://www.mlcswoodworking.com/shopsite_sc/store/html/smarthtml/pages/katana_bits3.htm


Nick


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## Mike (Nov 22, 2004)

Nick, a trench is a dado cut or groove, depending on the direction of the grain. A groove runs with the grain, a dado crosses the grain.

Joe, you can cut your desired trench by using an oversized base plate with two bearings or guide pins attached. To get the idea click here: http://www.rockler.com/product.cfm?page=17847&filter=mortising plate


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## dovetail_65 (Jan 22, 2008)

Mike said:


> Nick, a trench is a dado cut or groove, depending on the direction of the grain. A groove runs with the grain, a dado crosses the grain.
> 
> Joe, you can cut your desired trench by using an oversized base plate with two bearings or guide pins attached. To get the idea click here: http://www.rockler.com/product.cfm?page=17847&filter=mortising plate


You are saying a trench is a generic term for a dado and a groove. I
never heard the term trench, is that from the other side of the pond from me.

He said on the interior edge and on the edge it would be called a rabbit not a dado or groove, no matter the direction of the grain, then yes its a groove depending on the cut of the lumber. 

Unless he means the trench is for the center of the edge of the stock.

Its semantics and the question confused me because if it is a trench on the edge of the piece and it is quarter swan lumber then technically it is a dado. If it is flat sawn and the trench is on the edge of the lumber then it is a groove.

Hey I now understand why there is a term called a trench!


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## bobj3 (Jan 17, 2006)

Hi jf1



"trench to run as uniformly as possible all the way around the interior of the frame once it's put together."

I would suggest using a slot cutter or a T & G bit for this job.

http://www.mlcswoodworking.com/shopsite_sc/store/html/smarthtml/pages/bt_slot.html

Two Piece Tongue & Groove Set
http://www.mlcswoodworking.com/shop.../bit_tongue_groove.html#tongu_assembly_anchor


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jf1 said:


> Hi!
> 
> Great forum..I've learned a lot from just reading up on here already!
> 
> ...


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## jf1 (Nov 8, 2008)

Thanks guys..appreciate you taking the time to respond.

Yeah it definately looks like the dado cut / groove is what i'm needing to do as opposed to what the rabbit cut looks like.

That mortise centering base seems like it'd do the job great in keeping the cut straight to, although i really don't know where to start regarding what type of router would be best to use with this or if i'd need a router table as well?

Mike - would i be needing any kind of special bit to get the diameter (25mm) & depth (15mm) of the cut that i need to make? 

I've been having a quick look at routers & tables & spotted the Erbauer ERB210C 2100W router & Wolfcraft RT460 table, which are both within budget for what i'm looking to spend. Do you think these would do the job ok, or do i really need to be looking at something better / different?

Thanks again!


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## dovetail_65 (Jan 22, 2008)

That's what I would use, I have the cmt and its nice. Then again you can use a table and straight bit before assembly and zip them through pretty quick or a table saw too.


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## jf1 (Nov 8, 2008)

Thanks guys..appreciate you taking the time to respond.

Yeah it definately looks like the dado cut / groove is what i'm needing to do as opposed to what the rabbit cut looks like.

That mortise centering base seems like it'd do the job great in keeping the cut straight to, although i really don't know where to start regarding what type of router would be best to use with this or if i'd need a router table as well?

Mike - would i be needing any kind of special bit to get the diameter (25mm) & depth (15mm) of the cut that i need to make? 

I've been having a quick look at routers & tables & spotted the Erbauer ERB210C 2100W router & Wolfcraft RT460 table, which are both within budget for what i'm looking to spend. Do you think these would do the job ok, or do i really need to be looking at something better / different?

Thanks again!


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## jf1 (Nov 8, 2008)

Not sure why that double posted? no doubt related to me being up at 2am thinking about router bits!

Anyway, cheers for all the info on that everybody. So would the best way to go be to use a slot cutter or T&G bit AND the mortise centering router base for extra precision / repeatability of cut?

Also, if you do have any recommendations for a basic router setup for that'd enable me to get started i'd really appreciate it.

I'll no doubt be back with more daft questions as i get into this more 

Joe


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## bobj3 (Jan 17, 2006)

Hi jf1

This is what I would suggest, now that it's glued up, put in on a router mat on the work bench, pop in the bit and set the depth of the bearing so it can run on the inside of the frame, fire up the router and go all the way around a time or two..you may want to add some support blocks around the out side of the frame to support the router so it can't tip..

You may also want to run a test board 1st. to get it set just right..b/4 you touch the frame with the cutter .. 



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jf1 said:


> Not sure why that double posted? no doubt related to me being up at 2am thinking about router bits!
> 
> Anyway, cheers for all the info on that everybody. So would the best way to go be to use a slot cutter or T&G bit AND the mortise centering router base for extra precision / repeatability of cut?
> 
> ...


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## Mike (Nov 22, 2004)

Joe, we need to know your location for the best advice. Trench is either UK or Oz speak. Please fill in your profile with state/provence and country.
You said you need 25 mm width of cut, are you sure the size will be uniform the entire length? Here is why I ask: If it is exactly 25 mm you can use a 25 mm cutter making one pass about 8 mm deep, then a second pass for the remaining 7 mm of depth. This conforms to the "1/4" cut in a single pass" rule to ensure a clean cut. This method requires you to be centered on the board, and that is where the two guide pin system really shines. Bob and Rick Rosendahl developed a simple jig for centering a board and it provides stable side supports for the oversized base plate to ride on. I'm sure BJ knows the location of the post showing how to do this. The jig and oversized base plate with two guide pins will cost far less than a table. You will want a plunge router to make this job easy.
You can also do this job on a router table with a fence. You would lay out the location of the cut on each end of your board, then use a 14 or 15 mm cutter set to the line closest to the fence. Again make a pass at 8 mm followed by a pass at 7 mm to get your depth. Next you flip your board end around and repeat the process to get the rest of the trench. This method will allow you to adjust the width of cut a bit if needed. Your cut should be perfectly centered.
Either way you choose the cutter should be a solid carbide spiral up cut bit, they tend to stay sharp longer and give the cleanest cut. Do not try to cut costs on this, it will bite your wallet in the long run. If the wood you are cutting is hard like Oak be sure to let the bit cool down between passes. A cool bit lasts a long time, once a bit has been overheated it will lose it's edge quickly and be scrap. Once we know where you live we can tackle the router choice question.


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## bobj3 (Jan 17, 2006)

" I'm sure BJ knows the location of the post showing how to do this."

http://www.routerworkshop.com/2equalparts.html

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## harrysin (Jan 15, 2007)

It sounds to me like framing for trellis is required, something that I've made a lot of over the years. If this be so, then a table mounted router is the safest way to do it. use the largest diameter straight cutter and if necessary, move the fence for a second cut to widen the trench to the required 25mm. The depth should be in two or three cuts.
If it needs to look pretty, then mitres held with two screws at 45* is very strong as well as neat.


I've just realised that amongst the very low cost cutters that I recently bought from saw & bits on line, (which have been praised by all who have bought them), there is a 25mm straight cutter, so depending on where in the world you live, $5.50 Australian, about $3.75 US, could be a low cost way for you to obtain a good range of cutters at a low start up cost.


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## jf1 (Nov 8, 2008)

Cheers for the above link Bob, that seems to be exactly what i need to do. 

I've pretty much got it clear in my head now what type of bits could work & understand the 'multiple passes' for getting to the required depth of 15mm (which would need to be the same right around the inside of the frame).

I'm based in Manchester in the UK by the way, hope that helps narrow things down a bit in terms of what could work kit wise, which again i'd be really grateful for some advice about if possible. I'm looking to spend up to £200 ($300ish usd? not sure what is now?!) if i can get a setup that'd work for that.

I'd also prefer to use a table if it's likely to be safer as i play bass guitar, so want to do as much as i can to keep my fingers in tact!

In case anyone's wondering the frames are for building sound absorbers for my home recording studio..i do a lot of mixing (including for lower budget films) from there so the frequency response of the room needs to be as even as possible. I've already built quite a few of these & they look nice enough (once sanded & varnished ect..), but i'm trying a new type of filling material for the new ones, which should save on some labour time - hence the 'trench'.

Anyway - thanks again to everyone for the advice so far, it's really helped to give me an understanding of how to do this, not to mention what a router actually does!

Joe


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## Mike (Nov 22, 2004)

Joe, I'm sure one of our members from your area will chime in with router suggestions and pricing. International favorites would include the Hitachi M12 and Makita 3612 plunge routers, both outstanding machines.


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