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Forum topic by SawDustMaker54 posted 06-05-2017 02:18 PM 746 views 0 times favorited 15 replies Add to Favorites Watch
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SawDustMaker54

5 posts in 191 days


06-05-2017 02:18 PM

I just started using the 8” Diablo dado stack. It’s described as being able to make flat bottom cuts. Right now I can only use the 2 main blades and a shim (I have to make a dado throat plate still). The blades themselves alternate flat topped teeth and angled teeth. I am cutting 3 inch wide grooves to do 1/2 lap joints that are cross grain. The resulting cuts are nowhere near what I would call flat, very visible ridges that would take a lot of sanding to make flat.

My question is how “flat” are the dado’s truly going to be?
Is this more from me having to use a smaller stack set and making multiple passes?
Is going cross grain not helping the situation?

This is my first time trying this and it just seems really odd.


15 replies so far

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WhyMe

909 posts in 1396 days


#1 posted 06-05-2017 03:31 PM

Is the shim the reason you are getting ridges? The teeth on the two blades should be overlapped when rotated correctly to each other. You are not going to get a mirror finished bottom cut anyway. Can you post a picture of the blade setup and a cut?

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Rick_M

10610 posts in 2215 days


#2 posted 06-05-2017 03:36 PM

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pintodeluxe

5459 posts in 2648 days


#3 posted 06-05-2017 04:28 PM

Your results are typical with dado sets. A single-pass dado or groove, say 3/4” wide should have a fairly flat bottom. The corners will have small relief cuts or “bat ears” because the main blades are slightly deeper at the outside edge. This is by design and prevents surface chipout when cutting cross grain dados, especially in plywood.

If you take multiple passes, you will get scoring lines. The 8” diablo set is pretty good. My Infinity Dadonator is a little better for hardwood joinery, but I’ve made nice half-laps with the diablo as well. Usually the marks are hidden by a half-lap joint (if the intersection occurs at the middle of two parts), but it will show with a half-lap at a corner (like a cabinet door made with half-laps). You will just need to cut the parts a little thick, then use a sanding block or shoulder plane to clean things up.

The only truly flat dado sets I am aware of are marketed as box joint sets. They may cause tearout with plywood though (not sure as I haven’t used one yet).

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

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SawDustMaker54

5 posts in 191 days


#4 posted 06-05-2017 10:43 PM

Blades overlap and the resulting wood cuts.

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pintodeluxe

5459 posts in 2648 days


#5 posted 06-05-2017 11:54 PM

Yeah, that’s not normal.

You have something else at play here. Check to make sure the saw insert is perfectly flush with the saw top.
Is the stock flat and true?

Even downward pressure on the board?

At any rate, start with a new dado insert and try again. For a joint like that, a full dado stack should be used.
That may kill two birds with one stone.

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

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Rick_M

10610 posts in 2215 days


#6 posted 06-06-2017 12:41 AM

That looks terrible

-- http://thewoodknack.blogspot.com/

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WhyMe

909 posts in 1396 days


#7 posted 06-06-2017 12:41 AM

Do you have the blades installed in the right direction?

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SawDustMaker54

5 posts in 191 days


#8 posted 06-06-2017 11:51 AM

Blades are going the right way. I am going to make a custom dado insert this weekend to see if that helps at all.

Could it be bad blades? Looked them over and didn’t see any chipped/ missing teeth.

There was little downward pressure on the board when cutting. I had it braced against the fence on my incra 1000se with a sacrificial fence. The tear out on the back side was trrrible with out it.

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Gene Howe

9754 posts in 3263 days


#9 posted 06-06-2017 12:27 PM

The results on that half lap are not good. Two conditions seem to be in play. First, it looks like inconsistent down pressure was applied. Second, it appears that your cutters may be of slightly different circumference.

For the down pressure, a fence mounted feather board and/or miter gauge clamp would help.

I had my cutters and chippers professionally reground….first to remove the bat wings and second to insure consistency of their circumference.
As pintodeluxe suggests, the box joint sets are the only ones with true flat bottom blades. And mine are prone to tear out, too. Backers and ZCI will help, but that doesn’t seem to be your problem.

-- 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

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TungOil

744 posts in 330 days


#10 posted 06-06-2017 02:49 PM

You might get better results on a half lap joint using a tenoning jig. Like this one:

http://www.rockler.com/heavy-duty-tenoning-jig?utm_source=google&utm_medium=cpc&utm_term=&utm_content=pla&utm_campaign=PL&sid=V9146&gclid=CjwKEAjwpdnJBRC4hcTFtc6fwEkSJABwupNiq6lLSBa-dZ-618yQ_Sor_eJL42LYyKl1ULwJYS7w2BoCb8bw_wcB

-- The optimist says "the glass is half full". The pessimist says "the glass is half empty". The engineer says "the glass is twice as big as it needs to be"

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splintergroup

1694 posts in 1057 days


#11 posted 06-06-2017 04:48 PM

For half laps, the seam where you grooves show will typically be hidden by the mating piece of wood. Of course they can still be seen if the ends of the joint are exposed.

For the unevenness in the picture, that is due to inconsistent downward pressure on each pass. I’ll typically make several passes for each position to eliminate this common problem. The “grooviness” as stated is from the outer cutters. Some blade sets are better at controlling it then others.

I’ve basically given up on dado sets for many of these types of cuts and instead I have switched to a “box joint” blade set. I have a Freud brand (about $60 a few years ago), but there are others on the market now. You basically can cut either a 1/4” or 3/8” wide grove. Wider grooves can be done with extra passes.

The beauty of this blade set is perfectly flat bottom grooves. The blades have flat top grinds and square side profiles. No chip out with a backer board on the miter gauge.

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xeddog

173 posts in 2842 days


#12 posted 06-06-2017 04:56 PM

When installing the set, how snugly does each blade fit onto the arbor? I had an old Craftsman table saw that would yield cuts like you show until I found that if I wrapped the arbor with just the right amount of packing tape, the cuts improved dramatically. When I upgraded to a PM66, the blades fit quite sungly onto the arbor and the dadoes I cut are FLAT bottomed. Except, of course, for those #$&** DEVIL EARS from the two outer blades.

If I need good half laps now, I do one of two things. Use some sort of tenoning jig and rip blade as already mentioned, or after I have cut the entire width of the dado I will go back again and move the wood back and forth left to right moving forward in small increments after each pass. That gets rid of most of the devil ears.

Wayne

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SawDustMaker54

5 posts in 191 days


#13 posted 06-07-2017 01:39 AM

The tenoning jig would be nice, but I was doing the half lap in a T lap at some points so the jig wouldn’t work there.

I am going to try and rig up some kind of feather board to keep pressure on the board over the blade.
On a few pieces I did do a “secondary” pass where I would slowly work the board back and forth over the blades like xeddog described. It helped but there was still noticeable lines.

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EricTwice

228 posts in 368 days


#14 posted 06-07-2017 02:27 AM

Dado blades have a tendency to leave things pretty rough (stepped and ridged like the photo) Most of the sets I’ve used have cut like that. Go back over it another pass or 2, or clean it with a rasp or chisel. You might talk to your sharpening guy. He might be able to fix it for you. You should save a piece to show what the cut looks. He might want to see.

I just got the Tenryu GMD-20340 Gold Medal 8 inch set, and was pleasantly surprised by how flat on the bottom of the cut is. probably won’t when it gets sharpened though. I need a new sharpening guy,

-- nice recovery, They should pay extra for that mistake, Eric E.

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Rick_M

10610 posts in 2215 days


#15 posted 06-09-2017 03:44 AM

I have a Freud dado blade but never used it before today. I don’t cut many dadoes and I’m too lazy to break out the stack for a few minutes work. While waiting on some glue to dry I did some test cuts.

Freud SD208: This is the best crosscut I could get. No tearout but the bottom of the dado looks like ass. Rip cuts look great, better than the glue line rips I bought a few weeks back. This is 2 outside blades + 1 shim.


Here is a review of the same blade with cut examples. Definitely a better cut than I’m getting.
http://www.table-saw-guide.com/dado-saw-blades.html

This is a wobble blade someone gave me – dull, blade covered in rust and pitch. There is no brand on it, nor on the packaging. This is the worst cut from it. I was able to improve it a little by running it through again a little offset.


-- http://thewoodknack.blogspot.com/

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