JDługosz

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

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?

Mike

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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Mike
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harrysin

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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Harry

bobj3

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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Joe Lyddon

Joe Lyddon

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.

JDługosz

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.

JDługosz

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!

Mike

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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