# Problem Rabbeting Plywood



## JDługosz (Sep 10, 2007)

I'm working on a couple "fine" cabinets, and ran into a problem. I've got too much material cost and effort invested in order to ruin it now!

The outside sides are made from high-quality ¾" cherry plywood. Now I need to rabbet the back edge to accept the back, also a piece of ¾" plywood. So I'm making a rabbet that is ¾" deep and 3/8" wide. 

I'm using a CMT rabbeting bit with a 5/8" bearing to give me the 3/8" cut I want, and I'm making it with two passes for depth because the teeth are not quite 3/4" long. On the first pass of about half the final depth, to my horror the plywood is blowing out! Huge gobs are torn out, making a mess of all my previous work!!

Even scribing the cut line with a carbide wheel marking gauge set to the actual depth of the first pass, it still rips out!

I used that wheel cutter (Veritas' "Graduated Micro-Adjust Marking Gauge") for other operations on the same wood, and it prevented tear-out when making dadoes on the router table. I thought I knew how to handle this wood by now.

I wonder if it has to do with balancing the router on the 3/4" ledge? Would a little side-to-side rocking cause tear-out beyond what I've set up to deal with? If I can be confidant that that is the cause, I could make a super-wide router base that spans the entire cabinet, or clamp a wide ledge against the edge, or otherwise stabilize the router.

But I don't want to guess at this late stage. I'm hoping for some expert advice in what I suppose to be a common operation.

—John


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## vapochilled (May 2, 2007)

do you have a table saw?
With a tall fence, or sliding MDF jig, you might find it easier on the saw than the router? I know this is a router forum, and I'm all for using the router, but sometimes it's easier to use another tool than risk ruining good wood?


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## Mike (Nov 22, 2004)

You would have better luck cutting the plywood with a carbide down cutting spiral bit. This type of bit pushes the cuttings away from the router and into the cut. You can chuck it up in a router table and run your sides, top and bottom through with no wobble.
Note: Plywoods and laminates use a spiral down cut for rabbets or dados. Solid wood uses a spiral up cut for rabbets or dados. If you are cutting the entire side of a plywood or laminated piece you would use a compression cutter which actually squeezes the layers together, such as with a pattern.


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## harrysin (Jan 15, 2007)

vapochilled said:


> do you have a table saw?
> With a tall fence, or sliding MDF jig, you might find it easier on the saw than the router? I know this is a router forum, and I'm all for using the router, but sometimes it's easier to use another tool than risk ruining good wood?


Another possible way would be to cut the 3/4" on the table saw and because of the panel size, instead of this being done on the TS,(which if possible would be best) why not a slotting saw on the router table, this way both cuts are done with the panel flat on a table as shown.


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## bobj3 (Jan 17, 2006)

Hi John

Just one more way to do it...

Make a chip breaker for your router table..

Use some 3/4" thick MDF/Plywood,etc., cut it the same size as your fence size, once you have it cut and clamped to the fence pull it up to the bit and mark around the bit with a pencil,,, once you have done that unclamp it and take it to the band saw (jig saw) and cut out the pattern,,,out of the new fence ,,once you have that done take it back and put it in place and check it so the cutters of bit are just proud of the front face,(not to proud) make sure the bearing and the top of the router bit can come out flush, once you are sure clamp it back on the main fence, now with care power up the router and pull the fence into the bit..

This will make a chip breaker,,, and should stop most of the rip out on the plywood...when you make the 1st.pass only cut 1/16" deep or less , this will give you a nice clean sharp edge....

Something like the pictures below ▼


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JDługosz said:


> I'm working on a couple "fine" cabinets, and ran into a problem. I've got too much material cost and effort invested in order to ruin it now!
> 
> The outside sides are made from high-quality ¾" cherry plywood. Now I need to rabbet the back edge to accept the back, also a piece of ¾" plywood. So I'm making a rabbet that is ¾" deep and 3/8" wide.
> 
> ...


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## Joe Lyddon (Sep 11, 2004)

*W e l c o m e . . A b o a r d !!​*


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## Joe Lyddon (Sep 11, 2004)

JDługosz said:


> I'm working on a couple "fine" cabinets, and ran into a problem. I've got too much material cost and effort invested in order to ruin it now!
> 
> The outside sides are made from high-quality ¾" cherry plywood. Now I need to rabbet the back edge to accept the back, also a piece of ¾" plywood. So I'm making a rabbet that is ¾" deep and 3/8" wide.
> 
> ...


Perhaps using a "V bit with an acute angle would work...
Make a scribing cut close to the line...
Using Bernie's Epoxy Cocktail along the line...
Then, maybe another V cut pass slightly deeper but still close to the line.

If that doesn't work...
Take it to the Table saw that has a Forest WWII blade in it... set the ht. to very low... maybe 1/64" and cut a pass TO the line... raise the blade 1/32" and make another pass... Hey, then raise the blade to 1/32" shy of full depth of rabbet and make another pass.

Routing it now should work just fine...

... but, by now, you just might finish it up on the TS!   

Just writing what comes to my mind... to try...

Good luck... Let us know how yoiu did... OK?

Thank you.


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## JDługosz (Sep 10, 2007)

vapochilled said:


> do you have a table saw?
> With a tall fence, or sliding MDF jig, you might find it easier on the saw than the router? I know this is a router forum, and I'm all for using the router, but sometimes it's easier to use another tool than risk ruining good wood?


The box is already assembled, and I'm cutting the rabbet after so that the corners are right and the rabbet lines up across all the pieces after glue-up. In any case, it would have been difficult to do stopped rabbets on the table saw.


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## JDługosz (Sep 10, 2007)

Mike said:


> You would have better luck cutting the plywood with a carbide down cutting spiral bit. This type of bit pushes the cuttings away from the router and into the cut. You can chuck it up in a router table and run your sides, top and bottom through with no wobble.


Hmm, routing on the edge (not the face) pushing away from the motor would just encourage chipout, wouldn't it? Pulling toward me would help.

I contemplated using the router table, but the cabinet is too large. It is considerably larger than the router table top!


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## Mike (Nov 22, 2004)

Ok, so far you have learned that you cut your rabbets before you assemble your cabinet. A stopped rabbet is easy with a router. To cut the rabbet once assembled will be tricky but it can be done. You will want an edge guide with some wood attached to ride on the outside of the cabinet and keep you square. In this application you would use an up cutting spiral bit. Scoring the plywood with a utility knife will also help prevent tear out with this method. It takes very steady hands to edge rout. Take your time and make shallow cuts.


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## Joe Lyddon (Sep 11, 2004)

OK, how about a Dremel type tool...

Already assembled?! 
... that's a real curve ball...

Good luck.


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## JDługosz (Sep 10, 2007)

Here is a photo of the bad rabbet:

(( it did not let me post an image!! How did other people manage it? So paste it together the hard way: the domain is
three w's, the domain name "dlugosz", and the most COMmon top-level-domain with dots added, and the file is "files postings 2007 9 bad_rabbet.jpg" with the spaces replaced by slashes))

The line _was_ scribed before routing.

Since the blowouts are associated with wavy cuts, I think the wobble of the router has a lot to do with it.

My plans are to make a router base that spans the whole box width so it will be steady, yet still be easy to make multiple passes. Clamping edges around would have to be done piecemeal. I'll also take smaller bites in the horizontal direction (start with larger bearings).

Also, thanks for the tip of rabbeting half depth and doing the same for the back panel.

—John


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## JDługosz (Sep 10, 2007)

Joe Lyddon said:



> OK, how about a Dremel type tool...


I have a mini circular saw blade for the Dremel. But I don't have a router-like base for it, and freehanding would not work for me.

I wonder, does anyone make 1/2" router shaft mandrels that can take various Dremel tool disks?

--John


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## bobj3 (Jan 17, 2006)

Hi John
I tried to find your picture on your web site but didn't find it, here's link to it

http://www.dlugosz.com/

if you fill in the rest of the address in your post it should pop up

or your can do this way

dlugosz.com/bad_rabbet.jpg



just drop the 1st.part of the address


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JDługosz said:


> Here is a photo of the bad rabbet:
> 
> (( it did not let me post an image!! How did other people manage it? So paste it together the hard way: the domain is
> three w's, the domain name "dlugosz", and the most COMmon top-level-domain with dots added, and the file is "files postings 2007 9 bad_rabbet.jpg" with the spaces replaced by slashes))
> ...


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## bobj3 (Jan 17, 2006)

Hi John

Dremel, Yes they do, http://grizzly.com/ but I'm not sure what you mean by "shaft mandrels"


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JDługosz said:


> I have a mini circular saw blade for the Dremel. But I don't have a router-like base for it, and freehanding would not work for me.
> 
> I wonder, does anyone make 1/2" router shaft mandrels that can take various Dremel tool disks?
> 
> --John


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## JDługosz (Sep 10, 2007)

bobj3 said:


> I tried to find your picture on your web site but didn't find it, here's link to it
> 
> http://www.dlugosz.com/
> 
> ...


(omitted first parts) dlugosz.com/files/postings/2007/9/bad_rabbet.jpg


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## JDługosz (Sep 10, 2007)

bobj3 said:


> Dremel, Yes they do, http://grizzly.com/ but I'm not sure what you mean by "shaft mandrels"


The Dremel router base isn't for the cordless models. It has a more melted "ergonomic" shape rather than a neat cylinder.

By "1/2 inch router shaft mandrel" I mean a mandrel that fits in a 1/2 inch router collet. But instead of a bit, it would have a screw on the end.


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## JDługosz (Sep 10, 2007)

Thanks all for the comments.

I got it to work this weekend, by keeping the router level and cutting 1/8" at a time.

Because I was going to make three passes, I didn't want to keep moving and reclamping an edge. I made a router base that was as wide as the cabinet, and bridged the large gap. It worked beautifully.

Also, I went to full depth but changed guide bearings three times, to take 1/8" at a time in that direction.

I still scribed the line first, too.

—John


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## bobj3 (Jan 17, 2006)

Hi JDługosz

Not that I know about but you can get a Adaptor, then just push in the Dremel tool mandrel into the adaptor...I use it this way when I need to use the SMALL router bits with the 1/8" shanks..the bits are about 1/4 the size of the standard router bits..But I also use the mandrels in my Dremel router table for doing fine work...also and in the Colt router table...

-----------
Steel Adaptor Bushings

Part niumber #273 1/2" to 1/8"

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


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JDługosz said:


> The Dremel router base isn't for the cordless models. It has a more melted "ergonomic" shape rather than a neat cylinder.
> 
> By "1/2 inch router shaft mandrel" I mean a mandrel that fits in a 1/2 inch router collet. But instead of a bit, it would have a screw on the end.


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## Rard (Nov 9, 2007)

Mike when you said "use an edge guide with some kind of wood attached" I assume that you mean wood attached or clamped to the outside of the case which would not only keep the edge guide from riding across the cabinet case but would serve as a wider platform for the router to ride on to help keep it square?


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## Mike (Nov 22, 2004)

You got it right. Most routers have so much torque it is difficult to work on a narrow edge. By adding more support to the outside of the "case" you eliminate a great deal of the wobble effect. The large base plate that straddles the cabinet width is a good fix too. Perhaps the first obstacle beginning routers have to overcome is the tendency to tilt the router while working on an edge. Adding an extra board for support while edge routing greatly improves results.


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## bobj3 (Jan 17, 2006)

Hi Guys

Here's a little tip for routing PLYWOOD and Veneer plywood on the router table...

Run the stock by the bit in the climb way, that's to say backwards from the norm..
But this should only be done 1/4" deep max for each pass...

This will hold/push the chips/saw dust into the slot and hold plywood in place when the bit goes by the slot unlike the normal way when the bit pulls the chips/saw dust out of the cut...

Do this for a quick test, cut some scrap plywood up , say 6" wide and about 18" long, run it by the bit the right way then flip it around and pass it by the bit in the climb cut way,,you will see the climb is clean with almost no rip out...this also works for dados and groove cuts..



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## Hamlin (Dec 25, 2005)

I've seen this done a time or two... use painters tape along where the rabbit will be.


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## woodcarver (Dec 12, 2007)

Relate to the subject of routing plywood: Has anyone had success using a drawer lock bit on half inch Baltic birch? It does fine going with the grain, but creates a lot of tear out going cross grain. By cross grain I mean in relation to the top veneer. I tried scoring, using painters tape, wetting the plywood and multiple shallow cuts. The bit is of good quality and new. I tried three different bits. All the bits do well in solid wood.


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## Hamlin (Dec 25, 2005)

For ply, I'd think you'd want to "score" before you make the cut. Or make "relief" cuts.


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## bobj3 (Jan 17, 2006)

Hi Ken

http://www.routerforums.com/63871-post2.html
http://www.routerforums.com/63885-post3.html



http://www.routerforums.com/table-mounted-routing/6895-drawer-lock-baltic-birch.html#post63885

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