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tear out using dado blades

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Forum topic by 3285jeff posted 03-29-2020 02:35 AM 523 views 0 times favorited 22 replies Add to Favorites Watch
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3285jeff

184 posts in 2454 days


03-29-2020 02:35 AM

this might seem like a silly question,,,but I just bought some dado blades and was planning on dadoing some shelves across plywood,,and this is my first attempt at it and it splintered really bad,,,the blades I have are not cheap,,i bought them from amazon and they had a good rating,,and I paid 90.00 for them,,,but the crosscut across plwood was terrible,,so I tried using a palm router and the cut was better but it seemed like a lot of effort on the router,,,can anyone help me or tell me what I was dong wrong,,,thank you


22 replies so far

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WoodenDreams

1038 posts in 647 days


#1 posted 03-29-2020 04:26 AM

Was there tear out along the whole dado cut or just tear out at the end of cut or blow out of wood at end of cut.

On each of the dados is to be made, I have cut each side of the dado with a 80 tooth blade, on all the dados to be made. Then change to the dado blade and cut out the remainder waste with a dado blade. One method. I have used painters tape, but didn’t always keep from tear out. Also feeding slower does help.

View RobS888's profile

RobS888

2829 posts in 2581 days


#2 posted 03-29-2020 04:30 AM

Could you score the cut lines first? Use a marking knife or exacto blade and make a shallow cut line A tiny bit on the outside of where the cut will be.

-- I always knew gun nuts where afraid of something, just never thought popcorn was on the list.

View Walker's profile

Walker

352 posts in 1209 days


#3 posted 03-29-2020 04:36 AM

Any chance your dado stack is the Oshlun SDS-0842? That’s the one I have, and I don’t have any issues with tear out. For the record I have the cheapest of all ridgid saws, the R4516 (in other words pretty terrible).

The things that reduce tear out on a dado stack are the same as a normal blade. Make several passes, use painters tape on edges of cut, add a sacrificial board on end of cut. (tough to accomplish on a table saw sometimes). Make sure feed rate is just right. A zero clearance insert will help. Beyond that, you may have some blade wobble, if the arbor is moving or if the stack is not tight. On occasion I’ve had plywood panels that are warped just enough to cause issues, i.e. not sitting flat on the surface of the table saw.

Could also be the quality of your plywood.

If you’re still having issues after all that, try undersizing the cut with the dado stack. Then widen to final dimension with your router.

-- ~Walker

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CaptainKlutz

3027 posts in 2231 days


#4 posted 03-29-2020 09:51 AM

+1 check quality of plywood, and/or try some other plywood

Can get cheap 4×8 BB plywood locally, and use it only for shop stuff due tear out issues. The top layer of veneer has crazy amounts of tear out, even when compared to cheap cdx pine plywood from BORG. Have to use brad point bits for holes, unless I want the hole to look my dog chewed it out.
If I need decent finish, have to buy Russian made BB plywood in 5×5 sheets, or use better quality hardwood veneer panels.

YMMV

-- If it wasn't for bad luck, I wouldn't have no luck at all, - Albert King - Born Under a Bad Sign released 1967

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tvrgeek

946 posts in 2386 days


#5 posted 03-29-2020 10:24 AM

Well, grain matters too. If cross cutting the surface layer, it is going to be highly susceptible to tearout as dado blades are ground like a rip blade. Flat bottom teeth.
Did you make a new zero clearance throat plate? A must for about every project.
Good deep scribe lines from a box knife.
Harder to get the depth right, but cutting with a sacrificial sheet under it can work. I have used hardboard.
Never had much luck with masking tape.
I have done rabbits by doing the cheek with my 80 tooth about half way, then changing to the dado set.

View Fred Hargis's profile

Fred Hargis

6186 posts in 3230 days


#6 posted 03-29-2020 10:52 AM

I suspect it may be more of an issue with the plywood, as opposed to the dado set. But making a zero clearance insert may help, so would scoring the cut lines.

-- Our village hasn't lost it's idiot, he was elected to congress.

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tvrgeek

946 posts in 2386 days


#7 posted 03-29-2020 12:05 PM

Don’t blame the material for the technique. Know your material and then use the appropriate technique.

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3285jeff

184 posts in 2454 days


#8 posted 03-29-2020 01:48 PM

i never said I was blaming the material,,read what I said,,i was asking for advice

View Gene Howe's profile

Gene Howe

12128 posts in 4165 days


#9 posted 03-29-2020 01:59 PM

Two things come to mind. #1 You could securely tape the path of the dado. Or, #2 you could, using a sharp knife and straight edge, scribe the outside of the proposed dado cut.
I find #1 to be the easiest. I use good masking tape and a brayer (a handled rubber roller) to insure it’s stuck tight.

-- Gene 'The true soldier fights not because he hates what is in front of him, but because he loves what is behind him.' G. K. Chesterton

View Tony_S's profile

Tony_S

1323 posts in 3819 days


#10 posted 03-29-2020 02:00 PM

Did you take any pictures of the tear out?
What type of plywood was it?

-- “Wise men speak because they have something to say; fools because they have to say something.” – Plato

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3285jeff

184 posts in 2454 days


#11 posted 03-29-2020 02:18 PM

no I didn’t take any pictures but the plywood was 3/4 maple

View splintergroup's profile

splintergroup

3667 posts in 1959 days


#12 posted 03-29-2020 02:44 PM

Tape along the cut will help immensely. It’s more work, but you can also take a very shallow skim cut before raising the blade for the full passes.

View bilyo's profile

bilyo

1081 posts in 1839 days


#13 posted 03-29-2020 04:33 PM

As stated by others, the problem could be with the quality of the plywood you are cutting. However, the first thing I recommend is to check all alignments of your blade with the fence and miter groove. Also, my dado set has outer blades that have an inner and outer face. Check to see if yours are the same and are facing the correct direction (mine are stamped with “this side out” on the blades). Having checked all else, it is possible that you have a defective set. I wouldn’t jump to that conclusion too quickly, however.

View MNgary's profile

MNgary

318 posts in 3154 days


#14 posted 03-29-2020 04:49 PM

I think what bilyo is saying is to check if each of your outer blades is labeled for left of the stack or right of the stack. The set I have has one of the outer blades stamped right and the other stamped left. If they are labeled you may need to experiment whether that means R/L while you are facing the blades or if that means R/L as the blades face you.

-- I dream of a world where a duck can cross the road and no one asks why.

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therealSteveN

5583 posts in 1311 days


#15 posted 03-29-2020 05:53 PM

I like to use painters tape over a scored cut line to diminish frizzz at the edges. Blowout at the end of the cut can be stopped by backing up to exit with some scrap.

For me though the thing most aggravating would be if the bottoms of the dado were not squared. Lesser blades will give you a cupped bottom, so your inserted piece has a smile below it. Not desirable.

I would call this cheapazz plywood. With a really thin outer veneer, it just frays. Scoring is all that will help here. The outer ply is so thin it just chips off.

I would call this a cheap blade set. Note the cut edges are fairly crisp, but the bottoms aren’t clean. A good blade would eliminate this.

I consider these to be the best dado blade available today. It’s that 6 tooth chipper set.

https://www.infinitytools.com/dadonator-stacked-dado-blade-set-with-5-8-bore

-- Think safe, be safe

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