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  • Problem Rabbeting Plywood

    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 (see http://www.leevalley.com/wood/page.a...33&cat=1,42936 ) 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

  • #2
    Re: Problem Rabbeting Plywood

    I'm trying to vizualize exactly how you are trying to make the pass but it sounds like you are trying to take off too much material at a time. Try making multiple shallow passes taking of a little bit at a time instead. Wood generally doesn't like it when you try to get too agressive with the router in one pass, which will generally ruin your work. You will definately need some sort of larger base to stabilize the router. A balancing act on a 3/4" edge will not give adequate support or results. Personally I hate rabetting bits. I prefer using a straight bit with a fence or guide.
    Last edited by Velosapien; 09-10-2007, 11:33 AM.

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    • #3
      Re: Problem Rabbeting Plywood

      John -

      I've put rabbets on plywood without a major problem like you describe. There are the obvious considerations: use a sharp bit; make multiple passes with small cut per pass; use slow feed rate...

      ...but your comment "balancing the router on the 3/4" ledge" makes it sound like you are running the base of the router on the edge of the material. That would be a difficult cut. Are you running the router along the face of the wood with the bit bearing running along the edge, like so: Click Me?

      - djb
      sigpic

      A Democracy is 2 wolves and 1 sheep voting on what to have for lunch.

      Restore the Republic.

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      • #4
        Re: Problem Rabbeting Plywood

        It sounds to me like he has the router base resting on the 3/4" edge of the plywood.

        You will never keep the router stabil like that. I am assuming you have no choice and have already but the carcass together at this time.

        If so, I would clamp something to the sides and give yourself a decent base for the router to rest on.

        Even then, take it slowwwwww, and make shallow passes.

        Regards,

        Biscuit

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        • #5
          Re: Problem Rabbeting Plywood

          Using the router as shown by DJB will greatly reduce the chipping of the veneer. If you have no choice but to route on edge use a slow feed rate and if possible a higher bit speed (within safety limits). If it is just the veneer that is chipping then cut it with a knife and remove it with a chisel

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          • #6
            Re: Problem Rabbeting Plywood

            I agree with previous post it sounds like carcass is already complete so he has to route the rabitt on the edge. I also don't understand the 3/4 inch depth. There should be 3/8 rabitt on the perimeter of the carcass and 3/8 around the back. That way they nest together. Now for the carcass you need to clamp a 2 by 2, or larger, along the edge to provide support for the router. Good luck and keep us posted.

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            • #7
              Re: Problem Rabbeting Plywood

              (first try this on a scrap)

              but move the router backwards in comparison to what a normal cut would be, instead of pushing the router pull it, so that the bit is cutting into the ply wood not cutting out of it, (in other words make the router bit cut going the wrong way into the material).

              you will need to be careful so it does not catch and run with you
              Push sticks/blocks Save Fingers
              ~~~~~~~~~~~~~~~~~~~
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              attributed to Samuel Johnson
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              PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and oil...plus the current state of the economy............the light at the end of the tunnel, has been turned off.

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              • #8
                Re: Problem Rabbeting Plywood

                OR, score the edge of your rabbit with a box-knife/x-acto blade/marking knife prior to cutting that way the wood knows where to break at. . .

                OR put tape over the line where you're about to rabbit to reduce breakage

                OR do both (score first then tape)

                You'll see HUGE improvements.

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                • #9
                  Re: Problem Rabbeting Plywood

                  Originally posted by TerryD View Post
                  I also don't understand the 3/4 inch depth. There should be 3/8 rabitt on the perimeter of the carcass and 3/8 around the back. That way they nest together.
                  I tried that. I had to redo it.
                  With nesting like that, a crack is visible inside along the perimeter of the back. With a rabbet on the case only, the visible seam is made from two pieces at right angles, and it fits perfectly if they are both flat. With nesting, the visible parts have parallel edges and even with supercritical control over dimensions it looks bad.

                  —John

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                  • #10
                    Re: Problem Rabbeting Plywood

                    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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                    • #11
                      Re: Problem Rabbeting Plywood

                      That is one reason I rarely dado any veneer sheet goods. Most of them, even the "high dollar" sheets, are so poorly glued up that splintering is a real problem. MDF core and particle board cores are a little better but I steer clear of them due to the weight. Trying to manage a 3/4" thick MDF core Alder sheet is almost impossible at darn near 100 pounds. Not to mention if the project takes 4 or 5 sheets, trying to move, load, unload and install it is a real killer. Even my 24 year old son won't help me on those anymore!! LOL

                      Mark
                      Congratulations to Mr. "the sky is falling" Al Gore, nominated the new Village Idiot!

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                      • #12
                        Re: Problem Rabbeting Plywood

                        Originally posted by JDługosz View Post
                        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
                        Sounds like you made a success out of impending disaster. That's what it is all about: Being able to make it work with the materials and tools you have. That's what the artisans and craftsmen did 1000, 100, and 10 years ago. In addition, I'll bet you learned some lessons and a few new skills you won't ever forget. Don't ever let someone tell you you "can't" do something. Just keep looking and you will find a solution.

                        Happy Woodworking!!

                        Go
                        Last edited by Gofor; 09-18-2007, 08:52 PM.
                        Practicing at practical wood working

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                        • #13
                          Re: Problem Rabbeting Plywood

                          Be sure to post some pics when they are done.
                          ‎"I've never let my schooling interfere with my education" -Mark Twain

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                          • #14
                            Re: Problem Rabbeting Plywood

                            John, Glad everything worked out okay...........as previous post said post some pictures when done.

                            Terry

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                            • #15
                              Re: Problem Rabbeting Plywood

                              Originally posted by The Wood Meister View Post
                              That is one reason I rarely dado any veneer sheet goods. Most of them, even the "high dollar" sheets, are so poorly glued up that splintering is a real problem.
                              So what do you tend to use? If I wanted something less common, I'd have to veneer a plain panel myself. Commercial veneer is quite thin, but does gluing it properly help?

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