cutting wide dado's in sheet stock

[Scott Driemel]

Haven't done much dado'ing on my tablesaw, usually clamp up a straight edge and use a router. But I just set up a 2nd saw in my shop to be dedicated for a dado saw. So I haven't built any cross sleds yet for it which are certainly around (lots of plans). Especially complete with the concept of replacing the bottom with 1/4" hardboard pieces to create 0 clearance for the basic sizes I'll be using.

So without having one, here's what happened the other day.

A pal comes over & says he wants to build a bookcase for his Church as a donation and arrives with a couple sheets of 3/4 oak ply (4x8 size). He asks me what depth the shelves should be. I suggest a foot or so. He says he'd like to have them at least 16" deep.
So using the concept of cutting the dado right across the piece of 32" plywood then ripping the side in half to enable perfectly lined up heights, we go about it. He wants the bookcase 76" high as well. After setting the dado and the fence I'm looking at this 32" wide 76" long slab of plywood and wondering how I'll keep it against the fence to make a clean - non wavy = butchered cut. The 1st one goes okay but it was close. I saw a small gap appear against the fence appear at least 2x. As I got to the other dados, (he wanted a bunch of shelves), the difficulty in keeping the end against the fence didn't improve. At one point my friend thought he'd help and pushed the panel which of course immediately butchered the dado and had me visioning a 30lb chunk of plywood coming off the table at me. (but it didn't) whew.
The 32" width negated me using my miter guage to start the cuts as the panel was over the edge of the table to engage it.

I think this is one of those cases where a dedicated dado sled would have been the answer, (if it was wide enough) My question is do any of you cut dado's on wide panels on the tablesaw and if so, how large have you made your sled & to what level of success? Or ... is this just a "not to do again" and on wide panels to use the straight edge & router method?

[Jay Jolliffe]

To do something like that I use a plunge router with a jig that you use a bushing against a stop.....Here is a pic of one:http://s142.photobucket.com/user/garrettfrench/media/MEAckerman_Router_Dado_Jig_DSC01397.jpg.html

[glenn bradley]

I avoid long dado cuts in sheet goods on the tablesaw. The irregularity of the material is amplified by the large flat table reference surface. A router is the tool for this job IMHO.

294956

The smaller reference surface of the router assures a more consistent depth of cut (example greatly exaggerated, of course :D). I do cut a larger piece of material and then rip into parts to assure alignment as you describe.

[Peter Quinn]

If you joint a long board, clamp that to your fence to extend your edge reference, and you make sure to square up your stock before you begin, you stand a chance of success, if a very thin one. You need more infeed and out feed fence to reference a cut that long, and a good smooth well waxed surface. Say 3' before and after the blade? Having two guys that both know what they are doing and work well together is helpful too. Scariest thing to me is having a person jump in that doesn't know what they are doing. Can get risky. Generally I'd avoid making dados that long, just do all the dados in the 16" partitions each off the same stop and be done with it. The router jigs work well on larger pieces where you have to do it monolithic, and I have dadoed multiples then ripped, but if it feels risky it is, so move on to another idea.

[Mark Ashmeade]

Longarm radial arm saw. A 5 minute job. A table saw is not the right tool for that, IMHO.

[Vince Shriver]

Kreg makes a jig for ripping sheet stock. I've used it for that purpose, but thinking you could make multiple cuts to make a dado. It's not very expensive and works great for ripping, but don't know if it would be accurate enough to plow a dado. Give it a look.

[Peter Quinn]

Longarm radial arm saw. A 5 minute job. A table saw is not the right tool for that, IMHO.

In theory that sounds great, and simple. But if he can't find a good used one in his area a new one like original saw will set him back almost $5k, the 8"-10" dado stack with 1" arbor another $375....that's a lot of cash to cut a few dados for the church group. I'm thinking something like a small grizzly 10" slider would come in around $3200, he can use the dado he owns and and be ahead almost $2k! Maybe is because I'm from New England, home of the frugal Yankee......but I'm always asking myself what is the most cost effective solution. And RAS is not it unless he already owns one. I happen to own a dewalt GR with 24" cross cut and have a dado for it, I see your point about effectiveness clearly. Perhaps if he has a standard RAS with 18" crosscut he could rip the sheets and dado off a stop? Or a good router bit comes in around $20.

[jack forsberg]

In theory that sounds great, and simple. But if he can't find a good used one in his area a new one like original saw will set him back almost $5k, the 8"-10" dado stack with 1" arbor another $375....that's a lot of cash to cut a few dados for the church group. I'm thinking something like a small grizzly 10" slider would come in around $3200, he can use the dado he owns and and be ahead almost $2k! Maybe is because I'm from New England, home of the frugal Yankee......but I'm always asking myself what is the most cost effective solution. And RAS is not it unless he already owns one. I happen to own a dewalt GR with 24" cross cut and have a dado for it, I see your point about effectiveness clearly. Perhaps if he has a standard RAS with 18" crosscut he could rip the sheets and dado off a stop? Or a good router bit comes in around $20.

I have to agree with both Mark and Pete. Mark is right that RAS is king for dado's and on the used market there a dime a dozen. tooling cost can get up there but who pays retail in the used market? even with a slider doing work upside down is less than ideal with large sheets. In the end there is a lot a hand held router can do and it is very compact as pete said. that said it not always cheaper:p:p I picked up a Wadkin CC 18" RAS with 3 sets of 2" wide dado stacks for $400 . so used RAS is not costly buy any means and is just a pleasure to cut dado's with if you have the room.

here is one of my 16" dado stacks to compare with the 8" set for the General 10" saw. The wadkin CC cross cut will take wider than a 2" stack, in fact has 4.5" under the nut and will take shaper/tenoner heads of 1 1/4 bore.

http://i927.photobucket.com/albums/ad111/tool613/wadkin/16dado001_zpsfeb39648.jpg

http://www.practicalmachinist.com/vb/attachments/f79/89766d1383404809-sure-am-glade-ras-dime-dozen-imageuploadedbytapatalk1383183956.095126.jpg

[Ethan Melad]

If you had ripped your cabinet sides to width first (i think you said 16"?) using a sled on the table saw would be no problem at all, and for sure faster than setting up a straight edge guide for a router. screw on a temporary, extra-long fence to the back of the sled for stops, and you've got repeatable, accurate cuts. the down side to a sled is once you cut a 3/4" dado, you can't cut a smaller dado without a good chance of veneer tearout and chipping.

[Steve Rozmiarek]

Good sliding saw will do the trick quite well too of course, in slightly less style than one of Jack's Wadkin's though. In my limited dado on conventional saw experience, the problem is the length of the workpiece causing it to rack as the friction of sliding it across the top changes, and not having enough bearing surface on the fence to counteract it. Just a limitation of the saw.

I'd personally dado a whole sheet, which would give you a longer bearing surface against the fence, then trim off the strips you want. Keep the widest part between the fence and blade. Forget the jig, it's useless in this particular instance.

[Bill Orbine]

I've done dado cuts on large sheets with very few issues. Generally, larger sheets requires helping hands. I've always had extra hands around. And it helps that you keep the table saw clean and wax so the materials slide easily. There's usually one saw operator who pushes and guides the material while the "hands" offer support an go with the flow.

[Kent A Bathurst]

The idea of dado into double-wide sides, then rip, is enticing. But - IMO they got too big to handle. With a stop/fence, you can dado them as a pair, and the dados will align.

The narrower width makes it possible to use a sled or a good-quality miter gauge across the TS.

However - I have done the same thing at a friend's "shop" - no TS. Router and straightedge. IN that case, I was concerned with alignment, so we did them double-wide.

[Paul M Miller]

I use an attachment for my DeWalt track saw that lets me use a router with the track. Very quick, accurate, and easy.

Paul

[Rich Engelhardt]

I've done a dado like that with my track saw.
It wasn't all that slow & it turned out well enough that I'd do it again in a heartbeat.

In my case it wasn't a matter of choice since it was a jobsite & all I had with me was the track saw.

[Scott Driemel]

Well thx to everyone. I'm rather pleased it wasn't a "you got to be kidding ... you did WHAT?" kinda' response. Which on occasion I certainly no doubt will deserve! I'm not about to lay out big cash, or even medium cash for a so seldom type of job tool. (too many other tools still to buy and now Jessem has that new fancy angle gage I'm coveting .. I digress) The lure of perfectly lined up dados from a single cut got the best of me. I think from all the comments I'll try the cut to width (if much wider than 24") then utilize some stop blocks for the matching line up. Although I try to be careful when routing on a straightedge as I tend to on occasion, wander. Sorta' like being on the edge of a roof and feeling your going over the edge no matter what you do - I think it's an actual condition... any pschologists want to say?
Looks like it's more sled building. I did like the thought of the long reach RA saw but it ain't going to happen. I can barely swing a cat in my shop now. (not that I do for you cat lovers)

[Bill Huber]

Scott, I have done dados like your are doing with my router, I used 2 straight edges, strips of 1x6s. I put one on each side to trap the router, that wondering thing was a problem with me. Then I would put a strip of wood on one side to match the distance I had to move the router over to complete the dado.

[Kent A Bathurst]

Scott -

Dude - don't overdrive your headlights here.

At the end of the day, it is simply a plywood carcass. NOthing more, nothing less.

You can measure for each dado from a known reference point [I usually pick the top], and go down making accurate pencil marks to use as alignment points for your router-based straight edge. Measure each dado location from the top of the side - NEVER measure dado-to-dado. Cumulative tolerance error, and all that.

You will absolutely be less than 1/32" off of dead-level.

The construction of the carcass will not give a good goldang about that amount of offset.

I have done this multiple times in friends' shops that were less sophisticated than yours.