Replies

1. 
   JohnWW | Apr 04, 2004 08:04pm | #1

   Some blade geometries are better than others to prevent tearing when exiting the stock, but nothing beats using a backing board for 100% reliability.

   John W.

2. 
   forestgirl | Apr 05, 2004 04:53am | #2

   I'm sure someone will correct me if I'm wrong, but I think that negative-hook element is to help prevent kickback.

   Any reason you can't just slap a backer to your miter gauge?

   forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
   Another proud member of the  "I Rocked With ToolDoc Club" .... :>) 

1. 
   EricAnderson | Apr 05, 2004 05:10am | #3

   I suppose not.  I think I was just surprised at what happened at the time since the Freud 208 was pretty flawless up until that time.  When I used my Forest WWII to cut dados, I never had the problem.  I will be doing this again for the dresser I will be making next.  Whatever solution I use, I don't want to face this again.  Maybe the best solution is just a backer board, but when I tested my old Craftsman wobble dado from 30 years ago, it did not create this problem.  I tested it just because I did not remember having it doing this when I used it.  My memory was correct.  I guess I am just trying to see if there is a dado that does not have to have a backer board.  It may not seem like a big deal, but when you are on a roll, taking time out to but on another piece of hardware (the backer board, clamps, etc) that you are surprised that you need makes you wonder why.

1. 
   forestgirl | Apr 07, 2004 04:18am | #7

   Eric, I'll drop Charles-from-Freud a line and ask him to review this thread.  Sorry I couldn't do this earlier -- was in Oregon and didn't have access to my address book.  Stay tuned!forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)Another proud member of the  "I Rocked With ToolDoc Club" .... :>) 

1. 
   EricAnderson | Apr 07, 2004 04:26am | #8

   That would be really interesting.  So far I don't think we have had anyone that has real experience with the characteristics of a negative and a positive hook dado from the standpoint of design tradeoffs.  My old dados (both stacked and wobble) are positive hook.  Many of the new ones (but not all -- why??) are negative hook.  What is the change in philosophy?  Why would I want one with positive hook?  Why would I want one with negative hook?  Forrestk, as I understand it, has some of the cutting surfaces positive and some negative. 

1. 
   charlesm | Apr 07, 2004 01:14pm | #9

   Negative hook dado cutters are engineered to reduce splintering/chipping in manmade materials. The two drawbacks to this are increased feed resistance and potential blowout at the end of the cut. Positive hook blades have less of these tendancies but typically don't perform well in veneered plywood or laminate/melamine. If you never use manmade materials I highly recommend the SD300 series which has 15° hook. For the versatility of cleanly cutting all wood products I am not aware of a solution that doesn't require a backer board.Charles M

   Freud, Inc.

2. 
   EricAnderson | Apr 07, 2004 02:14pm | #10

   Now I think that is the answer I was looking for.  I will look up the SD300 series.  There are many times that a cabinetmaker is not using manufactured products.  If the top surface is not chipped (and I assume from your post that it should not be unless it is plywood), then it sounds like the SD300 would be a better choice for all around dado work.  It would not chip the surface, it would not blow out the end and it would have a flat bottom.  Is that correct?  Doesn't that answer all the typical concerns? 

3. 
   EricAnderson | Apr 07, 2004 02:24pm | #11

   Just took a look at the 300 series.  In the 8" blades, you have a couple of choices similar to the SD208 and SD508 choice.  SD308 has 24 teeth and the SD408 has 40 teeth.  Review for me if the end result in the cut is any better with the 40 tooth model or are we mostly talking about longevity or some other issue.  In this case, my concern is dadoing (across the grain) and not necessarily having to use a backer board.

   By the way, thank you Forrest Girl for getting Charles involved.

4. 
   forestgirl | Apr 08, 2004 02:52am | #12

   Your welcome, Eric, I'm glad he was able to help.  Since I'm a Freud girl though, I spell my name forestgirl -- [laughing, laughing, laughing!]forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)Another proud member of the  "I Rocked With ToolDoc Club" .... :>) 

5. 
   LeeEschen | Apr 08, 2004 04:59am | #14

   Eric, a positive hook blade will cause surface tearout, especially on very thin faced plywood, but will usually not blowout the back side of a board. A negative hook blade prevents this, but the price paid is that it will blowout the back of the board if you don't use a backer. The higher the angle either way, the more pronounced the effect. I suppose a 0 degree hook would minimize both effects, but I'm not aware of any blades or dados with 0 degrees.

   --

   Lee in Cave Junction, Oregon;

   Gateway to the Oregon Caves

6. 
   EricAnderson | Apr 08, 2004 06:43am | #15

   Well, I got an SD308 today and compared it with my SD208.  Just as Charles implied, the SD308 minimizes the blowout GREATLY.  Hate to have to have 2 sets for different purposes, but I guess that is the way it goes.  I am just about at the price the Forrest (sorry about that Forest Girl) blade would have cost, but I don't know if it would have been the answer for a replacement for the SD208 and SD308 anyway.  The SD308, of course, does not have the feed resistance that the SD208 does.  That will make a difference when I am cutting the drawer guide groove in the side of the drawer.  I will probably be able to do that in one pass now.  Before the feed pressure was much too high to cut the depth in one pass.

2. 
   LeeEschen | Apr 08, 2004 04:52am | #13

   You were in Oregon and didn't stop in for a visit? Shame on you, Jamie.

   I presume you were just around Portland and never got this far south. After all, I'm only 10 miles from the CA border.

   --

   Lee in Cave Junction, Oregon;

   Gateway to the Oregon Caves

1. 
   forestgirl | Apr 08, 2004 07:32pm | #16

   Someday I'm going to get down your way, Lee!  There are a couple other places I want to go that are way further south than Portland, but I was in Eastern Oregon and E. WA this weekend, helping hubby celebrate his dad's 99th birthday!!!!  I'll post a couple pics later in the Cafe.

   Thanks for the invite!forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)Another proud member of the  "I Rocked With ToolDoc Club" .... :>) 

2. 
   migraine | Apr 05, 2004 06:18pm | #4

   I would assume that datto sets are ground for the same reasons as a saw blade.  A negative blade(as in a melamine blade) are ground with a negative grind so that there is less downward cutting/removal, which decreases chipping on the bottom of the board. This also makes more force required to feed the material through the saw at the same time because the blade is "sort of" pushing the material back towards you.  A positive hook blade cuts more on the down stroke through the material causing more tear out on the bottom of the panel, but easing the ability to feed material through the saw.  Many of these characteristics are changed even greater as the positive/negative hook is increased/decreased

   Then threre are the high top ATB blades, blades with a Highland grind that have 2 different hooks ground on the face of each tooth, triple chips, hollow grinds, etc.  Just as you think you figured it out, something "better" comes along.

3. 
   Mach70 | Apr 05, 2004 07:25pm | #5

   I have this stack set.  It's not "high end" by any means.  The set seems fairly well made but I've found it chips the face of veneers so the flatness or tooth grinding must not be to a high quality.  Perhaps the chipping is due to the positive hook--maybe a bit TOO aggressive.  THat said I still like it better than any wobble dado I've tried & it beats the hell out of my old steel stack set.

1. 
   EricAnderson | Apr 05, 2004 10:11pm | #6

   It is just possible that I would want to use a negative hook (Freud 208) for plywood and a positive hook for situations where I don't want to splinter the side of a board that I exit when dadoing a solid board.  With that thought in mind, have you tried to make a 1/4 deep dado (with the Harbor Freight dado) across a board (say, oak) and see if it splinters the wood when it exits?