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Forum topic by Nadrek posted 04-20-2021 08:39 PM 394 views 0 times favorited 15 replies Add to Favorites Watch
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Nadrek

3 posts in 26 days


04-20-2021 08:39 PM

Hello,

New member to Lumberjocks, been lurking for a while.

I am making a small wall cabinet and was trying my hand at box joints for the first time. I am using a freud dado set that was passed to me when my father in law passed away a few years back. It is the SD508 set. I am getting chip out/blow out on the back side of the cut. Something I don’t notice or get when doing regular dados in plywood. I am using poplar for my testing since that’s what the cabinet will be made of.

I am wondering if the chip/blow out is normal for poplar or if maybe the dado stack is dull? My father in law got it from Home depot probably 15-20 years ago and I cant think of him ever using it. (He worked there and I believe it was return. He would just buy stuff that he didn’t as long as he thought it was a deal.) I used it on a project once probably 15 years ago and a few times in the last year since I am just getting into the hobby again.

Can Dado stacks be sharpened? I am in MN and having a hard time finding anyone that says they sharpen saw blades let alone a dado stack.

I was looking at possibly purchasing a different dado stack if I can’t get those sharpened properly. Do they all leave the little bat ears at the corners? If they do maybe I will just look into the box joint blade sets and keep using this one for regular dados since it seems to work fine for that.

Thanks,
Steve


15 replies so far

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splintergroup

5133 posts in 2306 days


#1 posted 04-20-2021 09:17 PM

You need a backer board that prevents the chipping on the outfeed side of your cuts.

If you are using a miter gauge to feed your parts through the blades, slide the miter fence over so that a fresh, uncut section is positioned to pass through the blade. As long as you don’t change the width of your cut or lower the blade, you should be able to cut all your parts cleanly (be sure the part is held firmly against the miter fence).

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Nadrek

3 posts in 26 days


#2 posted 04-21-2021 01:33 PM

I’m am using a sled. I did some initial test pieces with 3/4” plywood. When I went to do my test pieces with 1/2” poplar I noticed the big blow out after the first cut. First cut on the left side of the image. I then made a backer board and proceeded with the rest of the cuts. They all still have more tear out then I guess I would expect. Maybe that is normal? But that’s what makes me wonder if my blades are dull?

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Madmark2

2662 posts in 1672 days


#3 posted 04-21-2021 01:36 PM

Use a router.

-- The hump with the stump and the pump!

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controlfreak

2131 posts in 685 days


#4 posted 04-21-2021 01:59 PM

It looks like the slot in your sled (backer) may be higher than the top of the box joint.

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brtech

1128 posts in 4007 days


#5 posted 04-21-2021 02:05 PM

You definitely can have your dado set sharpened. Whether it’s worth doing it depends on what they will charge you. I have a local sharpening shop, so shipping isn’t an issue for me, but there are plenty of mail order sharpening services. If it hasn’t been used much, that’s not likely it. Agree that you shouldn’t be getting that much tear out.

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splintergroup

5133 posts in 2306 days


#6 posted 04-21-2021 03:02 PM

Before blaming the blade, I’d consider CF’s comment. You can see the wood fibers folded back at the top which looks like the slot in your sled (good choice BTW!) is too high or your parts were not held firmly against the fence (use a clamp).

Try a sacrificial piece of temperboard (masonite) behind your boards, just place a wide enough piece onto the fence so you can effectively reduce the height of the blade kerf hole.

With the wood fibers supported by the fence/backer board, they should not flake off like that, even with a dulling blade

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Nadrek

3 posts in 26 days


#7 posted 04-21-2021 05:15 PM

Thanks for the responses.

I have thought about trying it on the router table. Went with the table saw method to start since it seemed quicker/easier for me to do it.

As for the backer board you see in the picture. The slot on the left was cut at the 1/2” blade height along with the poplar. The slot on the right was just to slide over the pin on the jig.

How about the bat ears? Is that common on all dado stacks? Even the higher end ones? I understand what is causing them, I just don’t understand why they wouldn’t make the flat tooth on the outer blades cut as deep as the beveled ones.

Thanks,
Steve

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splintergroup

5133 posts in 2306 days


#8 posted 04-21-2021 06:19 PM

A router works well, just as prone to chipping as the TS however (and a tad harder on the cutters compared to a TS blade)

Looking back on you photo, the three rightmost cuts are not really chipped out, just some “fluff” left in the cut. A light pass with a file (outside – in, forcing the fluff into the cut to avoid it pulling out) should clean those up well.

The bat ears are common with dado sets, the side blades do the shearing cuts and are ground like an ATB blade to make the sides of the cut smooth. The tips protrude to insure a square shoulder to the dado (usually these bat ears are hidden in the dado and do not matter).

You can get other dado sets where the side cutters are ground to avoid the ears (or get your set custom re-ground).

For finger joints, since the duration of the cut is limited, you can also just use the dado sets chippers (no side blades) for a truer “perfect” notch, which is essentially what a box joint blade set does.

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BurlyBob

8859 posts in 3350 days


#9 posted 04-21-2021 09:17 PM

Definitely need a backer board.

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pintodeluxe

6378 posts in 3897 days


#10 posted 04-21-2021 10:30 PM

I have had dado blades sharpened before, but they never come back from the sharpener cutting quite as good as new. I think I pay about $75 to have a full set sharpened. New sets are $100-300 usually, and you’ll pay more for a higher tooth count. 24 tooth outer blades will leave a smoother cut than 12 tooth blades. Likewise for the chippers, which range from 2-12 teeth per blade.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

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Madmark2

2662 posts in 1672 days


#11 posted 04-21-2021 10:55 PM

New carbide router bit is $15 or so.

Router gives dead flat square corner cuts that look lots better in box joints where the joint is featured. In casework shelving bat ears are mostly invisible esp. if painted as many pieces are.

$75 to resharpen an under $150 blade set doesn’t make economic sense. For the same $75 I can buy 5 $15 router bits.

I’ve made literally hundreds of box joint boxes and a router is fastest and best way to cut — esp. if gang cutting.

Yes, both the router and saw box joint cutting needs a backer board.

You indexing peg is too tall. It should be shorter than your cut depth.

A box joint isn’t really a dado. Conventionally a dado is a slot significantly longer than it is deep or wide. A box joint, is well, a box joint. Saw based dado cutters are generally preferred for the long runs, but the router cutting box joints is cutting inches and not feet at a time. The superior perfect corner cuts of the router bit tip the scales to the router.

Tip:
  • Box joints are easier to cut and generally look better if the stock width is a multiple of the tooth spacing. Your test sample has an odd width slot on one side. That makes assembly harder and looks crappy unless there is a reason for an odd tooth.
  • To make production faster, gang cut all four side-ends at once. Clamp all pieces and the backer snugly and only the last piece needs the backer. Use a fresh backer for each set. This works for both saw and router. If the width is a multiple of both a gap and a tooth, then all four gang cut pieces become interchangeable and can be assembled any which way — greatly simplifying final assembly.

-- The hump with the stump and the pump!

View 18wheelznwood's profile

18wheelznwood

143 posts in 114 days


#12 posted 04-21-2021 11:11 PM

Freud Super Dado stack with proper sized hole in backer board. If the backer is even an eighth of an inch too tall the tear out will be significant. Cut the backer board only after you have established the final height of your blade.

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AlaskaGuy

6573 posts in 3393 days


#13 posted 04-21-2021 11:18 PM

Dado Blade

-- Alaskan's for Global warming!

View splintergroup's profile

splintergroup

5133 posts in 2306 days


#14 posted 04-21-2021 11:18 PM

I just completed these with a Freud box joint blade set.

As the cuts are made, one face shown is the infeed side of the cut so it should show no chipping. The other face is from the outfeed side.

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bigblockyeti

7258 posts in 2805 days


#15 posted 04-22-2021 02:00 AM

I don’t think you need anything sharpened, but you do need a backer board as others have stated and the work needs to be tight against it. You can use a router too but the cut is slower because the cutting edge is going slower.

-- "Lack of effort will result in failure with amazing predictability" - Me

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