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Old 03-09-2012, 01:46 PM   #1
tpolley
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Default dadoing plywood

i need to dado an edge around a 4x8 sheet of plywood. probably 1/16 of an inch deep and an inch or so wide all the way around.

i'm worried that the dado blade will tear the crap of the plywood. is there anything i can do to help minimize the damage?

i have, at my disposal, a radial arm saw. i'm thinking i can turn the blade 90 degrees to the fence, set it to the correct height and run the plywood thru in a ripping fashion.

what say y'all?
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Old 03-09-2012, 01:52 PM   #2
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Default Re: dadoing plywood

i was just thinking about doing this the other day, i want to put angle iron around the top of my work table, but i want it flush with the plywood top.
how i would do it, is get a friend to help, set my table saw up with the blade sticking up an inch, set the fence at 5/8" from the blabe (i'm using 3/4" plywood), the kerf of the blade is 1/8". this should daddo it 1/8". then stand up the sheet on its edge and run it through. this would be the quickest and easiest way unless someone has a better idea.
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Old 03-09-2012, 01:53 PM   #3
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Default Re: dadoing plywood

Put a "sacrificial " piece on top and dado through that, Or use a plywood blade and move the saw over a 1/8" at a time after every pass. How neat does it have to be?
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Old 03-09-2012, 01:54 PM   #4
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Default Re: dadoing plywood

Stick a piece of wide masking tape in from the edges so that the blade is cutting through the tape into the wood underneath. This will reduce splintering a lot. You've really gotta be careful doing this with a radial arm. Beg, borrow or steal a router. It's the best tool for the job.
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Old 03-09-2012, 01:56 PM   #5
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Default Re: dadoing plywood

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Originally Posted by atotalnincompoop View Post
i was just thinking about doing this the other day, i want to put angle iron around the top of my work table, but i want it flush with the plywood top.
how i would do it, is get a friend to help, set my table saw up with the blade sticking up an inch, set the fence at 5/8" from the blabe (i'm using 3/4" plywood), the kerf of the blade is 1/8". this should daddo it 1/8". then stand up the sheet on its edge and run it through. this would be the quickest and easiest way unless someone has a better idea.
He's got a radial arm saw. With a table saw it's a lot easier. I would just make several passes moving the fence over a little bit at a time and knock what's left out with a chisel. Standing a sheet of ply on end would be a bitch.
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Old 03-09-2012, 01:57 PM   #6
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Default Re: dadoing plywood

Maybe scribe a line with a utlity knife. Should cut down on the rip out.
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Old 03-09-2012, 01:58 PM   #7
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Default Re: dadoing plywood

how about i go in an inch and make a 1/16th inch deep cut all the way around with a regular saw blade, then dado the rest out to the edge. would that reduce splintering?

i have a router, but i don't have any blades for it. the RAS is the only stationary saw i own.

it doesn't have to be beautiful. its going to be hidden. but i don't want it to look like ray charles did it, either.
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Old 03-09-2012, 02:04 PM   #8
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Default Re: dadoing plywood

If you feed it slowly it usually isn't to bad. You could use painter's tape on it and see how that goes.
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Old 03-09-2012, 02:04 PM   #9
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Default Re: dadoing plywood

You should be fine, but try a piece of scrap plywood first. I know I have used my stack dado head cutter on my RAS, but I was only making a 1/4" wide channel. It worked fine for what I was doing.
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Old 03-09-2012, 02:08 PM   #10
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Default Re: dadoing plywood

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Originally Posted by ratdoggy View Post
Maybe scribe a line with a utlity knife. Should cut down on the rip out.
This, has worked best for me. Scribe your line with a sharp utility knife. Also get a plywood blade, big difference in saw blades, the more teeth on the blade the better.
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Old 03-09-2012, 02:08 PM   #11
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Default Re: dadoing plywood

Wait, the whole sheet and feed it? I have never done that and I don't know if I ever would. That is a long feed. How would you control the plywood during feed? I think your cut would be wavy in every direction. I'd go with the router and a nice long straight edge. Do the cross grain cut first to reduce splintering and you should be golden. A router bit is cheaper than having to buy a second sheet of plywood.
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Old 03-09-2012, 02:16 PM   #12
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Default Re: dadoing plywood

I'd start with a 1/2" spiral router bit on your router table and cut the final dimension of the groove. Or, you could just cut the cut with a normal saw blade. Then clean up the rest of the material with the dado. Dados can make a mess of veneer.
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Old 03-09-2012, 02:43 PM   #13
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Default Re: dadoing plywood

How about gluing an 1/16" thick sheet on top already cut to the dimensions you want?
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Old 03-09-2012, 02:50 PM   #14
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Default Re: dadoing plywood

Quote:
Originally Posted by tpolley View Post
i need to dado an edge around a 4x8 sheet of plywood. probably 1/16 of an inch deep and an inch or so wide all the way around.

i'm worried that the dado blade will tear the crap of the plywood. is there anything i can do to help minimize the damage?

i have, at my disposal, a radial arm saw. i'm thinking i can turn the blade 90 degrees to the fence, set it to the correct height and run the plywood thru in a ripping fashion.

what say y'all?
I would not try what you suggest with the radial arm saw. They work like shit for ripping. Chances are, best case scenario it will try to suck the wood in faster than you feed it, spit it out the other side, screwing up your work in the process. Or if you're a little less lucky, it will climb up the workpiece at the same time and screw up every setting on the saw. Or even worse, it can create a missile out of the work piece, (but this is not likely with a big panel. It WILL happen with any thin strip you want to rip.) Hopefully you won't get hurt.

How about using a router instead of a saw???
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Old 03-09-2012, 02:53 PM   #15
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Default Re: dadoing plywood

I agree with skyline, I would use a router too. Fast, easy, neat and clean.
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Old 03-09-2012, 03:01 PM   #16
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Default Re: dadoing plywood

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Originally Posted by smschriefer View Post
Wait, the whole sheet and feed it? I have never done that and I don't know if I ever would. That is a long feed. How would you control the plywood during feed? I think your cut would be wavy in every direction. I'd go with the router and a nice long straight edge. Do the cross grain cut first to reduce splintering and you should be golden. A router bit is cheaper than having to buy a second sheet of plywood.
it's a 4x4 section of plywood. so there would be four 4 foot cuts, maybe only two, i can't remember. the plan is to line the dado blade up with the fence to keep the plywood straight and set it to the correct height..

should i decide to go the router route, what bit should i use?

Quote:
Originally Posted by ddawg16 View Post
How about gluing an 1/16" thick sheet on top already cut to the dimensions you want?
because i f**ked up and bought too thick of plywood (harbor freight folding trailer).

i can't fold it all the way because the plywood just barely touches and keeps it from folding all the way. you're probably familiar with that trailer, its made of 4 foot sections of c channel. well, there is a lip on either side where the c channel over laps preventing the plywood from laying completely flat. if i carve out enough around the edge so the plywood will lay flat it may just be enough to allow the trailer to fold up all the way

Last edited by tpolley; 03-09-2012 at 03:04 PM.
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Old 03-09-2012, 03:08 PM   #17
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Default Re: dadoing plywood

1/16 inch deep dado/groove/rabbet along an edge (on the "face" of the plywood and near the edge, or actually on the "edge" of the plywood?)?

Hmm, 1/16 inch deep and ~1 inch wide, that says unless you have some really-really-really thick plywood you actually mean a shallow 1/16 inch deep dado/groove/rabbet on the face of the plywood near an edge.

OK, big question is "Why?"

That said, I'd go with either a tablesaw with a good 'high-end' dado set or a router (probably with a down-spiral bit to really miinimize edge chipping/fuzzing on the inboard edge of the cut line, and then just use a decent bit to cut the rest of the rabbet/groove/dado).

A big No-F'ing-Way to using a radial-arm saw for what I think you want to do. <shudders>

Down-spiral carbide router bit is about $20 or so for a 'name brand' one (1/4 inch diameter solid-carbide 1/4 inch shank, the 1/2 inch shank ones are -much- pricier. Flat-bottom mortising bit is about the same.

http://www.woodcraft.com/Product/208...-1CL-14SH.aspx

http://www.woodcraft.com/Family/2080...uter-Bits.aspx


A 'high-end' dado set (Freud, Forrest, etc) to make nice -flat- cuts is easily $100-$200+. A 'wobble' dado typically ain't going to cut as smoothly or neatly or with a nice flat bottom (sometimes curved bottoms are nice such as in some of the other Free-Parking threads, but not in a dado/groove/rabbet) as a 'good' dado set.

http://www.woodcraft.com/Family/2005...-King-Set.aspx

http://www.woodcraft.com/Family/2020...-Dado-Set.aspx

YMMV.
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Old 03-09-2012, 03:12 PM   #18
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Default Re: dadoing plywood

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Originally Posted by tpolley View Post
it's a 4x4 section of plywood. so there would be four 4 foot cuts, maybe only two, i can't remember. the plan is to line the dado blade up with the fence to keep the plywood straight and set it to the correct height..

should i decide to go the router route, what bit should i use?



because i f**ked up and bought too thick of plywood (harbor freight folding trailer).

i can't fold it all the way because the plywood just barely touches and keeps it from folding all the way. you're probably familiar with that trailer, its made of 4 foot sections of c channel. well, there is a lip on either side where the c channel over laps preventing the plywood from laying completely flat. if i carve out enough around the edge so the plywood will lay flat it may just be enough to allow the trailer to fold up all the way
Ahhh. Remove hinge and reset/reposition it to allow 'proper' folding of the trailer. While welding hinges in place, check and redo all the OEM factory welds as needed.
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Old 03-09-2012, 04:04 PM   #19
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Default Re: dadoing plywood

Router is the best tool for this. But, if you must use the radial arm saw, pivot the blade to horizontal, set it behind the fence just sticking out the inch you need the dado width to be. Then set the height so that you get the 1/16" depth into the plywood. Fast and easy, BUT be sure that you have an adequate way to hold the wood to the table and feed against the blade's rotation.

I've done lots of edge cuts like this on the radial 'cause it's much easier than standing a big slab of ply up on the table saw.
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Old 03-09-2012, 04:10 PM   #20
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Default Re: dadoing plywood

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Router is the best tool for this. But, if you must use the radial arm saw, pivot the blade to horizontal, set it behind the fence just sticking out the inch you need the dado width to be. Then set the height so that you get the 1/16" depth into the plywood. Fast and easy, BUT be sure that you have an adequate way to hold the wood to the table and feed against the blade's rotation.

that's pretty much the plan. i just didn't know if it was going to splinter the crap out of the wood.
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