Is this dado operation safe?

[Mark Katz]

I have a few dados to cut in plywood panels that I'm a bit worried about.

First of all, I know I could build a jig to make these with a router, but I'd rather not take the time to build that jig right now. The dado needs to be for undersized 3/4" plywood but a 23/32" router would be too tight and a 3/4" router bit too loose. Therefore, I'd need to use one of the several exact-fit methods and I just don't feel like dealing with that right now.

Also, I could build a dado sled for my table saw. That would be safe but also take time and effort to put together. I do have a dado set and the shims needed to get the right width of cut.

My pieces are 16" wide by 34" long. I want the dados to go across the width of the piece 2" from each short end. That means that the 16" ends will be against the fence and the piece will extend about 32" to the left of the blade. Or I could move the fence to the left of the blade and the piece would extend to the right, resting on my extension table. In either case, I'm worried that the piece could rotate during the cut because there is so much more extending to the side than against the fence.

Am I right to be worried? Or should the 16" along the fence and pair of Grr-rippers for pushing the stock through the cut be OK? Would my miter gauge with an auxiliary fence help the situation?

Thanks, Mark

[Adam Tracy]

i don't know man, i'd probably try to bang out a sled for that kind of operation. if you had more width relative to the length of the piece registering off the fence would seem okay. think about it this way, you might be able to make a cross cut sled for this project that you will without a doubt be able to use in the future. i'd take a simple sled. peace of mind.

[Todd Mason-Darnell]

I am not an expert by any long shot, but I would be worried about the 32" either to the left or the right of the blade. That is a really big lever perpendicular to the blade. Any little twist as you move across the blade, you will get a kick back.

Can you do two miter gauges with an auxiliary fence between them?

[Doug Hepler]

Mark,

As I understand what you wrote, you should think of this as a crosscut, not a rip. Don't use the rip fence. Make an accessory extension for your miter gauge that is about as long as the piece you are cutting (34 " or so) Screw it to the miter gauge. Make it wider than the dado is deep so that it will remain intact after the dado stack cuts through it, say 2" wide. You can clamp the workpiece to this extension if you don't feel that you can slide it straight. BTW, if you have not already done so, you probably should calibrate the angle of the miter gauge to ascertain that it is cutting close enough to 90 deg. (This for accuracy rather than safety.)

My practice is to take the time to make whatever jigs and fixtures I need to make an operation safe and accurate. You seem to be in a bit of a hurry, but do not compromise your safety.

Doug

[Josh Kocher]

I agree. use your miter gauge with a board, even a stop block to reference off...

You can build that as fast as it takes to joint a piece of scrap, cut it to length and screw it to your miter gauge.

[Mark Hennebury]

If you are worried then it is not safe...for you.
Being nervous about an operation makes it dangerous.

[Marshall Harrison]

Mark,

As I understand what you wrote, you should think of this as a crosscut, not a rip. Don't use the rip fence. Make an accessory extension for your miter gauge that is about as long as the piece you are cutting (34 " or so) Screw it to the miter gauge. Make it wider than the dado is deep so that it will remain intact after the dado stack cuts through it, say 2" wide. You can clamp the workpiece to this extension if you don't feel that you can slide it straight. BTW, if you have not already done so, you probably should calibrate the angle of the miter gauge to ascertain that it is cutting close enough to 90 deg. (This for accuracy rather than safety.)

My practice is to take the time to make whatever jigs and fixtures I need to make an operation safe and accurate. You seem to be in a bit of a hurry, but do not compromise your safety.

Doug

Yes, definitely keep the rip fence out of the equation when the area against the fence is significantly smaller than the length of the piece.

A long extension for the miter gauge is the best approach in your case. I would though put a short spacer block on the rip fence to register against for getting the "across the width of the piece 2" from each short end" spacing for your dados. Make sure the spacer block is short enough so that the piece you are cutting isn't touching it when the blade starts cutting into the wood. that allows you to set your fence to 2" + the thickness of the spacer for lining up your cuts. If I didn't make that clear enough let me know and I'll try to find a drawing or a video demonstrating this.

[tom lucas]

yep. miter gauge, auxiliary fence on it, and clamp it down. If you support it well and clamp it, it will be very safe.

[Michael Rector]

I was picturing the cut in my head and then wandered out to the saw to see how I'd do it and here are my observations.

1) Definitely not against the rip fence even with a spacer block because you'll never clear the spacer block by the time you engage the blade, there's not enough room in front of the blade.

2) I can get my miter gauge into the slot barely if the work piece is almost touching the blade, but I only have about 6-7" of the bar in the slot and the gauge isn't resting on the table when I would be starting the cut so I certainly wouldn't rely on that.

3) This cut is easy in my sled plenty of sled on the table and room to push the work through.

In my shop this would definitely be a cut for the sled or a router, I wouldn't use the miter gauge or the fence.

[Leo Graywacz]

I do that sort of operation all the time. But woodworking is my profession. If you are a bit uneasy doing this use your miter gauge or build a sled. If you have a few of these to do you might want to keep them wide, do the dadoes and then cut them in half. That way you'd have matching dadoes too boot.

I normally do this this way. I'd set the fence so the dado is 2" away. Then I have a support that is essentially just a board length supported by two legs that is the same height as my tablesaw. An extension to support long stock.

So I'll put the pc up against the fence and put my hands on the front and back of the pc making sure to never be over the dado set while pushing. I use my hip to help push the board. Just make sure the table and the extension is well waxed so things move easily.

You can see the table extension to the left, in front of the trash can. I use this to support long boards/plywood off the left side of the tablesaw.

http://www.fototime.com/02DDF68DD2A781F/orig.jpg

[Jim Becker]

I'd use a sled for sure. Running the narrow end of the panel along the fence, despite it being 16", brings risk that I'm not personally comfortable with for this operation. A movable sled to the edge of the dado blade with a stationary panel fixed to the table on the other side of the blade will help retain somewhat of a "zero clearance" situation and keep chatter to a minimum as you make each cut. It also makes it easy to line up for each groove or rabbit.

[Edwin Santos]

When I was faced with a similar task, out of caution I decided to take the time and make a dado sled. What is amazing is how frequently I have reached for it since then. Someone gave me the good idea to put a t slot groove into the fence and using it I can attach a replaceable face to the fence. This created the opportunity to make a face with a moveable index key for repetitive cuts. This key could also be your moveable stop block for the cuts you need to make. Also, the dado sled is bigger than my normal sled, so I reach for it for normal crosscutting when cutting a larger piece or panel.
Edwin,

[John TenEyck]

Frankly. I wouldn't give it much thought. I'd put the fence on the right, 2" from the dado, support under the overhang, and use a rubber pushblock to hold the workpiece down on the table and against the fence. I always have outfeed support, too. But that's me, and if you aren't comfortable find another way. A handheld router and edge guide would work fine.

John

[David M Peters]

I'd propose going back to your router. Being that the two dadoes are only 2" from the edge, you could use your guide fence and too-small bit to take two passes. The first could clear out 99% of the width with the second pass sneaking up on the perfect fit.

[andy bessette]

Two passes with a 1/2" router bit. Quick and EZ.

[Leo Graywacz]

Just dadoes sides for 9 cabinets. 3/4" dado. For the uppers the space was 3/4" from the fence to the dado. For the lowers the space was 5 1/4". I had 2 cabinets that are 49" tall and had a center dado. The upper cabs are about 14" deep and the lowers about 23"

Just setup the fence and pushed them through.

You could have been done already.

[Martin Wasner]

Just setup the fence and pushed them through.

You could have been done already.

That's about how I feel about it. It's about as easy a dado operation as you can get.

I'll catch hell for this, but I do a climb cut pulling the material over the head to score the material when going across the grain, then push it through. But that's not for amateur hour.

[Peter Christensen]

I'll catch hell for this, but I do a climb cut pulling the material over the head to score the material when going across the grain, then push it through. But that's not for amateur hour.

I assume you have the blade lowered to where you are just beyond scratching the surface so you don't have much to fight against. Still not a practice for beginners or the clueless. Not that there are any of those around except the ones making youtube videos. ;)

[glenn bradley]

I always have plenty of time and energy to do something a safer way. I can also still count to ten ;-)

A super simple dado jig and a 3/8" bit would be my preference.

383272

Literally two "L's" out of scrap will do the job.

[Von Bickley]

I have started cutting most of my dados with a smaller straight router bit and then cut rabbets to match the dado. I can get a much better fit by doing this.

[Mark Katz]

Thanks everyone. Here is what I finally did.

As I was looking around for a suitable board to use as a base for a sled, lo and behold I spotted an old, single-runner sled I had forgotten about. It was designed to run on the right side of the blade and extend to the right over my extension table. To re-purpose it, I turned it around, ran the dado through it (checking first that the screws holding the fences weren't in the way) and added a little auxiliary fence segment on the left end because the original fence was pretty short. It worked great. Pics of the new old sled and the end result are attached.

Thanks again!

383275

383276

[Martin Wasner]

I assume you have the blade lowered to where you are just beyond scratching the surface so you don't have much to fight against. Still not a practice for beginners or the clueless. Not that there are any of those around except the ones making youtube videos. ;)


I tried to edit, and deleted by accident.


I keep it at full height. If I have to run a job with a thousand dados in it, no way am I raising and lowering the head each time.

Like I said, it's not for amateur hour. You better be real comfy with what you're doing before you start playing that game.

If you want to try it, so it on a rabbet where if something goes wrong, nothing really happens.

[Peter Christensen]

I tried to edit, and deleted by accident.


I keep it at full height. If I have to run a job with a thousand dados in it, no way am I raising and lowering the head each time.

Like I said, it's not for amateur hour. You better be real comfy with what you're doing before you start playing that game.

If you want to try it, so it on a rabbet where if something goes wrong, nothing really happens.

No sweat Martin. I'm not about to try a climb cut that deep even with my SawStop. Assuming again that it is 3/8" or 1/2" deep you're talking about and not some of the 3"deep cuts I've done. I'm not a production woodworker so have different needs. I thought you were scoring the veneer before going to depth to prevent tear out, like a scoring blade on a slider, but you do the whole operation in one go. I get it.

[Pat Barry]

I tried to edit, and deleted by accident.


I keep it at full height. If I have to run a job with a thousand dados in it, no way am I raising and lowering the head each time.

Like I said, it's not for amateur hour. You better be real comfy with what you're doing before you start playing that game.

If you want to try it, so it on a rabbet where if something goes wrong, nothing really happens.
Sounds like a pretty dumb / scary way of doing things. Care to share a video of your technique?

[Bradley Gray]

[QUOTE]Sounds like a pretty dumb / scary way of doing things.[QUOTE]

Sounds like a "somebody who uses a table saw every day" way of doing things to me.

[Martin Wasner]

Sounds like a pretty dumb / scary way of doing things. Care to share a video of your technique?

For some, yeah scary. Hence the disclaimer that's been started twice. For those that do this 70+ hours a week, not so much.
I need to wack some parts out for a vanity tomorrow, I'll try and remember to video some of it.



No sweat Martin. I'm not about to try a climb cut that deep even with my SawStop. Assuming again that it is 3/8" or 1/2" deep you're talking about and not some of the 3"deep cuts I've done. I'm not a production woodworker so have different needs. I thought you were scoring the veneer before going to depth to prevent tear out, like a scoring blade on a slider, but you do the whole operation in one go. I get it.



I just score it going backwards. I'm usually getting about 1/16" of penetration. Finish the operation forwards in the standard way

I am talking 3/8 deep dados though. Big deep ones usually aren't in large pieces of plywood with mass and distance from the cutter in your favor.

[Edwin Santos]

I just score it going backwards. I'm usually getting about 1/16" of penetration. Finish the operation forwards in the standard way

I am talking 3/8 deep dados though. Big deep ones usually aren't in large pieces of plywood with mass and distance from the cutter in your favor.

Martin,
I'm having trouble getting this. I'm not questioning your procedure nor turning this into a safety issue. Pretty much everyone here knows you know what you're doing, and you gave the disclaimers.

But why is there only 1/16" of penetration when you're not lowering the blade set? Is that just what happens regardless of blade height because the stock is basically climbing over the blade? Are you standing right in front of the blade and pulling the workpiece toward you, then immediately pushing it back to finish the cut?
I doubt I'd ever try this but I'm still interested to know your technique. Thanks
Edwin

[Martin Wasner]

But why is there only 1/16" of penetration when you're not lowering the blade set? Is that just what happens regardless of blade height because the stock is basically climbing over the blade?

Yep, it's just floating over the blades and chippers. It's 3/4" wide, and with a dado set made for plywood it doesn't want to dig in because teeth all have a negative hook to them. If you slowed way down or put down pressure on the part it'd probably start to grab hard since you're engaging a larger arc of the head.





Are you standing right in front of the blade and pulling the workpiece toward you, then immediately pushing it back to finish the cut?
I doubt I'd ever try this but I'm still interested to know your technique. Thanks
Edwin

Most of the time, I'm standing off to the side of the saw at the end of the material. I've got a table off to the left side of the tablesaw. There's about a 40" gap between the saw and the table. If there isn't enough room for my body and the part, then I'm stuck holding it from behind.

[Scott Bernstein]

I would use my Incra Miter Sled, which has an extra-long bar and can handle cross cuts in wide stock.

[Martin Wasner]

Care to share a video of your technique?


There you go.


https://youtu.be/luxwwxBY3mk

Don't like it, don't do it.

[Peter Christensen]

Can't see the video. Message says Video Unavailable. You pull it?

[Martin Wasner]

Can't see the video. Message says Video Unavailable. You pull it?


Try it now. I had it under "private" when I think I wanted "unlisted"

[Michael Rector]

Very nice!

[Dave Zellers]

WOW! That is awesome. I have got to try that technique. Been making cabinets for 40 years and never seen that.

"Don't like it, don't do it." That's your bottom line right there.

The only thing in danger is the plywood, if you screw up.

But I have to ask- why do you do 3/8" dados? Even 1/4" seems overkill to me, but I like them because the math is easy. :D

[Martin Wasner]

But I have to ask- why do you do 3/8" dados? Even 1/4" seems overkill to me, but I like them because the math is easy.

Easy math. Really it'd be no different if it were 1/4" deep, but I'm just used to the 3/8" depth.

I am kicking around when a cnc does land at the shop switching though. I think it'd be marginally better for nailing things together.

[Peter Christensen]

The thanks Martin. Learned something new that never would have occurred to me. Probably forget the next time I need it since I don’t do much dado work.