What size dado bit for 3/4 ply? - Woodworking Talk - Woodworkers Forum
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post #1 of 16 Old 01-02-2018, 04:40 PM Thread Starter
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What size dado bit for 3/4 ply?

Never used dados before. What size bit do I use for 3/4 ply? Considering 3/4 ply isnt really 3/4...

Sorry for the amateur question. Making a bookcase and dont want to ruin it.
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post #2 of 16 Old 01-02-2018, 05:08 PM
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there are router bits made 1/32 under nominal to accommodate the not-really 1/4-1/2-3/4 plywood.
Amazon and eBay have singles and sets.

a more generalized solution is:
http://www.rockler.com/rockler-perfe...ntractor-clamp
it uses a 1/2 bit and the router mounts/adjust slightly off center - cuts any width.
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post #3 of 16 Old 01-02-2018, 05:13 PM
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It used to be 23/32", but plywood seems to be all over the map now. Probably best to measure the plywood to be sure. 23/32" bits are available, but if it's different than that, you may need to make two passes using a 1/2" bit. That's probably what I'd do anyway, so you can sneak up on it and get a precise fit.

Also, some plywood is in millimeter thickness and of course bits in metric sizes are also available.

As always, experiment on scrap.


http://www.rockler.com/undersized-pl...SABEgJof_D_BwE
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post #4 of 16 Old 01-02-2018, 05:31 PM
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Good luck with a one size fits all, best to adopt a 2 pass solution and get an exact fit.

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post #5 of 16 Old 01-02-2018, 06:12 PM
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The dado blade is adjustable enough with spacers and paper shims to give you a proper fit regardless of the size needed up to about 1. I always use scrap to test the width and fit of the dado before cutting the dados for the project. On 3/4 plywood you can cut your depth from 1/4 to 3/8 deep for a strong joint.
Your fit should not be loose but it should be loose enough to fit without force.
A 6 diameter dado set or carbide Wobbler dado is enough for most work.
Have you already bought your dado?

If you don't have time to do it right the first time, when will you have time to do it over?
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post #6 of 16 Old 01-02-2018, 09:40 PM
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In addition to what is noted above on testing the fit, and that not all plywood is the same size, I had a sheet of prefinished plywood that was 1/64+ thicker than the other sheets. All came off of the same pallet and the codes showed all as the same batch. I had my dado set dialed in for a good fit without forcing the ply into the dado. When I started using this one particular sheet, it just wouldnt go into the dados without significant tweaking with a dead blow mallet. Drove me nuts until I started checking everything with calipers. It was the only thicker sheet out of 9 sheets. Now I check every sheet with the calipers and do a new test fitting on scrap before the good material gets cut.
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post #7 of 16 Old 01-03-2018, 03:01 PM
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@Microscopes is asking about a "bit", so I assume he/she wants to use a router.

I don't have experience using a router for dados. Based on a comments above, I assume that you must have a router bit whose width is an exact match for the plywood, and plywood width is not always predictable.

I use a table saw and a Freud SD208 dado set. I would measure the plywood with calipers, configure the dado set, run a trial cut on scrap. and finally adjust the dado set width if necessary.

If you have a table saw and decide you want to buy a dado set, be sure to read the table saw manual first to make sure it is compatible with a dado set that is wide enough for your plywood. You may need a zero clearance insert and maybe a special washer or other fastener. (My table saw uses a special bolt for wide dados, for example.)

Regardless of whether you use a router or a table saw, first run a test cut on scrap to see how it fits the actual plywood. After that, you can adjust accordingly. If you are using a router, hopefully you have found the correct matching router bit. Good luck!
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post #8 of 16 Old 01-03-2018, 07:20 PM
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Using a router, if your bit is smaller than needed, you would just adjust your fence or straight edge and make a second pass.

If you don't have time to do it right the first time, when will you have time to do it over?
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post #9 of 16 Old 01-03-2018, 08:24 PM
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Quote:
Originally Posted by Toolman50 View Post
Using a router, if your bit is smaller than needed, you would just adjust your fence or straight edge and make a second pass.
and screw up untold amounts of stock doing that . . . . and really get in some practice cussing if the job has 3-4 dados in a single piece of stock and you screw it up on the 3rd or 4th one . . .
yes, it can be done but the measuring routine does not lend itself to lots of error free repeats.

which is why I got the doohickie from Rockler. it rides in a slot of the 'fence' clamp - then you flip it around and since the router is adjust slightly off-center, you get a wider dado.

I also have the undersized bits for when they are right for the job - even with them I always use the plate and the slotted fence guide - it minimizes those little 'oops' moments when the router veers off a plain straight edge.
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post #10 of 16 Old 01-03-2018, 08:29 PM Thread Starter
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Thank you everyone.

I was planning on using a router, but it sounds like everyone prefers the table saw method?

I figured router would be easier, as I could line up both sides of the cabinet and router the dado into both sides at the same time.

That way, I would know they're perfectly lined up.
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post #11 of 16 Old 01-04-2018, 06:50 AM
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Quote:
Originally Posted by Microscopes View Post
Thank you everyone.

I was planning on using a router, but it sounds like everyone prefers the table saw method?

I figured router would be easier, as I could line up both sides of the cabinet and router the dado into both sides at the same time.

That way, I would know they're perfectly lined up.
Table saw with a dado stack will cut faster and generally cleaner. Cutting a 3/4 wide dado would usually require several passes with a router to get to depth, a table saw will be able to take it all in one go. As for the cleanness of the cut, 9 for 10 the table saw will leave less tearout.

Don't get me wrong, a router will work fine, but for my money id rather have the dado stack. More that 1 size of dado, can get the exact size you want every time, faster cuts. If you want to use a router, I'd look into an exact width dado jig. Basically 2 parallel fences set to the exact thickness of the stock, then a bearing guided pattern bit used to make the cut.

https://www.thewoodwhisperer.com/vid...idth-dado-jig/
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post #12 of 16 Old 01-04-2018, 09:19 AM
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Quote:
Originally Posted by Microscopes View Post
Thank you everyone.

I was planning on using a router, but it sounds like everyone prefers the table saw method?

I figured router would be easier, as I could line up both sides of the cabinet and router the dado into both sides at the same time.

That way, I would know they're perfectly lined up.
Quote:
Originally Posted by epicfail48 View Post
Table saw with a dado stack will cut faster and generally cleaner. Cutting a 3/4 wide dado would usually require several passes with a router to get to depth, a table saw will be able to take it all in one go. As for the cleanness of the cut, 9 for 10 the table saw will leave less tearout.

Don't get me wrong, a router will work fine, but for my money id rather have the dado stack. More that 1 size of dado, can get the exact size you want every time, faster cuts. If you want to use a router, I'd look into an exact width dado jig. Basically 2 parallel fences set to the exact thickness of the stock, then a bearing guided pattern bit used to make the cut.

https://www.thewoodwhisperer.com/vid...idth-dado-jig/
Speaking only for myself, I prefer dado blades on a table saw for several reasons, all personal, and nothing to do with what might be the best solution. (1) My first dados were made with a dado blade on my roommate's radial arm saw. I made many dados with it, so I got used to using a dado blade for dados. (2) When I finally got my own table saw last Spring, I bought a dado set for it, because that was what I knew from the deep past. (3) My router is an old hand-me-down with a 1/4 inch collet. and (4) I don't have much experience with routers. I need a lot more practice, a router table, and in truth, a better router.

I am impressed with the simplicity of the router jig in the Wood Whisperer video that @epicfail48 mentioned.

Going forward, I will still use the table saw for most dados and rabbets, because that's what I know, but I like that router jig for when the dados are stopped inside the work. Accurate plunge starts and stops are easier to do with a router.
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post #13 of 16 Old 01-04-2018, 09:23 AM
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Avoid a single wide bit!

A router guide for dados like epic posted uses a narrow bit that travels on each side of the guide. This allows for less material to be removed, easing strain on both the router and the cutter. The first pass is just slightly below the surface to minimize tearout. Then succeeding passes remove the waste down to the desired depth. Yah, it's a lot more work, but you will get a nice finished dado.


Table saw dados are cutting from the bottom side up, a "blind" cut, since you can not see what's happening. You will not know if the cutter path varies because the workpiece has lost registration with the fence.
Ya gotta pay attention when using the table saw and hold the work snug against the fence. Then, make all your same dimension dados at that fence setting rather than resetting the fence for each new measurement.
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Last edited by woodnthings; 01-04-2018 at 09:26 AM.
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post #14 of 16 Old 01-04-2018, 12:09 PM
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and screw up untold amounts of stock doing that . . . . and really get in some practice cussing if the job has 3-4 dados in a single piece of stock and you screw it up on the 3rd or 4th one . . .
yes, it can be done but the measuring routine does not lend itself to lots of error free repeats.

which is why I got the doohickie from Rockler. it rides in a slot of the 'fence' clamp - then you flip it around and since the router is adjust slightly off-center, you get a wider dado.

I also have the undersized bits for when they are right for the job - even with them I always use the plate and the slotted fence guide - it minimizes those little 'oops' moments when the router veers off a plain straight edge.
This has not been a problem for me. Ive increased the width of a dado or a rabbet many times with a router. Because I have the tools, I cut most of my dados with a saw and most of my rabbetts with the router. I rarely use the jointer to cut a rabbet but it does a good job too.

If you don't have time to do it right the first time, when will you have time to do it over?
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post #15 of 16 Old 01-04-2018, 12:25 PM
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Quote:
Originally Posted by epicfail48 View Post
Table saw with a dado stack will cut faster and generally cleaner. Cutting a 3/4 wide dado would usually require several passes with a router to get to depth, a table saw will be able to take it all in one go. As for the cleanness of the cut, 9 for 10 the table saw will leave less tearout.

Don't get me wrong, a router will work fine, but for my money id rather have the dado stack. More that 1 size of dado, can get the exact size you want every time, faster cuts. If you want to use a router, I'd look into an exact width dado jig. Basically 2 parallel fences set to the exact thickness of the stock, then a bearing guided pattern bit used to make the cut.

https://www.thewoodwhisperer.com/vid...idth-dado-jig/
Epic,
Some will disagree on this but a good carbide tipped Wobbler dado gives me very satisfactory results for most dado applications. I also have a multi-blade set-up but its not carbide and I tend to reach for the Wobbler because the set up is so much quicker.
Also, regarding your statement above on making multiple passes with a router, I cut my dados in one pass because Im only cutting 3/8 deep. Sometimes only 1/4
deep. For most dado cuts I will lay out my lines and score the lines with a knife to prevent tear-out. Im a dodo making fool. I think its a great joint.

If you don't have time to do it right the first time, when will you have time to do it over?
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post #16 of 16 Old 01-04-2018, 04:30 PM
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Originally Posted by Toolman50 View Post
Epic,
Some will disagree on this but a good carbide tipped Wobbler dado gives me very satisfactory results for most dado applications. I also have a multi-blade set-up but its not carbide and I tend to reach for the Wobbler because the set up is so much quicker.
Also, regarding your statement above on making multiple passes with a router, I cut my dados in one pass because Im only cutting 3/8 deep. Sometimes only 1/4
deep. For most dado cuts I will lay out my lines and score the lines with a knife to prevent tear-out. Im a dodo making fool. I think its a great joint.
A perfectly fair point. My rule of thumb is 1/4" depth passes with a router, so if you're only cutting a 1/4" dado you kinda bypass the need for multiple passes. I figured it'd be worth mentioning for those times where you may need a deeper dado.

The only thing I've got against the wobblers is they don't make a flat bottom. Sure, that's probably not an issue for most things, but if you wanted to cut some box joints, well, it's an issue. I find the stack setup to give better results, at the expense of extra setup. Personal preference though, I don't doubt the wobble blades work just fine

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