I’ll swear I’ve put every blade in my arsenal on my table saw trying to find one that cuts a good flat bottom kerf. The kind you want for cutting finger joints and/or tenons. They all either cut a kerf with those ever so slight turned down ears at the corners, or have a slight depression in the middle of the kerf bottom.
Any recommendations for mfr., grind description, etc., would be appreciated. Any particular brand(s) would be welcome as well.
Replies
Forrest makes a version of their woodworker II blade with teeth ground and set for a flat bottom. Call them and ask for it, they'll know what you want (I think they call it their finger joint version). It's a little more expensive than the stock blade, but if want an absolutely flat bottom...
They have another blade with reduced grooves, but not perfectly flat. Make sure you aren't getting that one.
Paul
Most manufacturers offer ripping blades with flat grind (ours is the LM72 series - 10X24T). We also now have the SBOX8 which is two blades that stack to make either 1/4" or 3/8" grooves for box joints and they can also be used for tenon cuts.
Freud America, Inc.
Charles -Thanks for the reply.I may have missed trying out my Freud rip blade in my search last night. I'll give it a go tomorrow. I did do a search of the archives on 'flat bottom kerf' and realized I had asked this same question almost a year ago. Th bulk of the replies are as you note, rip blades ordinarilly, or at least often, have flat bottom cutting profiles overall of the kerf. None of the rip blades I tried last night produced a truely flat bottom, though. I'll re-try my Freud, perhaps I overlooked it.
The only Freud blade that has a flat tooth grind is their LU72xxx. This is a full kerf (1/8") 24 tooth rip blade.Howie.........
Howie,The Freud LU72 is not the only FTG Freud makes. The LM72 is a flat top grind.http://www.right-tool.com/freudlmteffi.htmlRich
"The only Freud blade that has a flat tooth grind is their LU72xxx." Nope. See my post above. 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" .... :>)
Freud also make an excellent 1/2" top-bearing hinge mortising bit that I use in a laminate trimmer to cut an absolutely flat bottom with square corners in dados. I have an excellent Dimar dado set, but the outside blades leave a small slice cut on each corner. The Freud bit, set to take off about 1/32", leaves a perfect dado. Regards,Ron
Wouldn't a dado blade give you a flat bottom?
A single dado chipper would make a flat groove except that they are not designed to run indivudually. Many do not have side relief on the tips of the chippers (they are not side ground). A stacked dado set will have bevel teeth on the outside saws to score the fibers/laminate so it will not cut truly flat.
Charles M
Freud America, Inc.
I was refering to the blade. Thought it might give the results he was looking for. Thanks for the info.
Timberrattler -The "instructions" that came with my Amana dado set speak specifically to the issue of *not* using one of the outside blades independantly. The top angle of the outside blades are ground to only one side (angle). Thus their designed to cut either the right or left side of the dado, not both sides.
As timberrattler sugested a single dado blade would work in a pinch. There are a lot of flat ground blades out there that should work well. But I wonder why it is so importaint to you. If it is only for the shoulder cuts then the scoreing lines will not be visible. In fact my uncle will actually deepen the shoulder cuts a little more that the cheek cuts to create a place fot the excess glue to go. Though personaly I dont like that idea.
Mike
mudman -I didn't plan on getting into the specifics of the particular project for which the joinery is so fussy (for me, at any rate) But to explain, I'm making a series of bread cutting boards which consist of a shallow box about 18" x 9" x 2+_" deep. The top of the box consists of 3/8" wide slats spaced 3/8" apart. You cut your bread on the top slats and the crumbs fall in the box below. Nothing original on my part, I'm just playing with various design options.The design of the slatted top I've decided to use consists of a 1/8" tongue on the end of the 3/8" slat pieces which will fit into a 1/8" deep plough in an end cap piece which holds the slats together. I realize that for most box construction, particularly hand cut dovetails and box joinery, incised layout lines are often viewed as a sign of true hand crafted work. To which I would agree. But in the case of the pieces I'm working on, my goal, if only to prove to myself I can get that far, is to have perfectly closed joints.
I thought you might have an aplication like that, where the flatness of the kerf mattered. I have tried to use 1/8" router bits (amana up cut solid carbide). It cut very poorly, compaired to a saw. If it is a big deal and you cant find what you want, try either a custom blade from forrest or find a sutable old blade (flat grind) and have it ground flatter at a saw shop. This should cost around $25. I am interested in what you come up with, keep us posted.
Mike
Mudman -I've decided to take one of my lesser blades and have it re-ground as you mentioned. This is a time filler type project so it will be an off and on kinda thing with respect to reporting back.Thanks for the reply, though.
Dennis,
About a year ago, I needed a blade to do exactly as you have asked. On the advice of CharlesM from Freud, I have used the Freud LM blades in 8" and 10". They cut a perfectly flat, 1/8" kerf. They perform beautifully.
I recommend getting a new LM blade,rather than having a lesser blade reground. The LM is a known quantity, it's a professional piece of gear, and you'll probably wind up spending as much for regrinding.
Rich
To expand on your suggestion, the LM's are ripping blades. If they get put to use for this purpose (rather than the grooving purpose), here's the scoop. The LM72 is a flat-top grind recommended for material 3/4" to 2-3/4" (24-tooth in the 10"). The LM74 is a triple-chip grind, 32T, recommended for 1/8" to 1" material. I don't think it would provide a flat-bottom kerf due to the height of the triple-chip teeth.
Which one(s) did you get, Rich?
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" .... :>)
Edited 10/8/2005 11:52 am ET by forestgirl
FG,
I think it's the LM 72. I'm at work. I'll check when I get home.
Rich
Two words: Router table ;-)
Freud just came out with a new offering. It is a pair of 5/8" arbor X 8" dia. table saw blades designed specifically for cutting box joints.Installed back/back they cut 1/4" box joints; assembled face/face 3/8" box joints.Item "SBOX8"Arlington, Texas (The dash in Dallas-Fort Worth)
Practice...'till you can do it right the first time.
Dunwright -I need a 1/8" (more or less) wide kerf. The router table was suggested but I'm more accustomed to making these kinds of joints on the table saw with a sled. I seem to get smoother cuts with less tear out but that's probably due to my limited experience using a router for this kind of application.One idea I've come up with is to take one of my older carbide blades and have it re-ground for a flat bottom kerf. I'd pop for the Forest blade another reply mentioned And although is most likely worth it's price, it's not really justifiable in my case.
You always wanted a Sorby Rosewood Chisel 1/8 inch did you not?I would use a router BUT just make the kerf with what you have and either get a 1/8 paring chisel or grind down a 1/4 inch to make one.
Cut a 90 degree guide guide block of the width you need. Clamp it down and pare away the bottoms. Take longer to set up the guide block than square off the bottoms...Just me though.. YES.. I am NOT above using a guide block when paring.
Do you have a particular project in mind for this finger joint?The reason I ask is; while the thought of 1/8" fingers may seem appealing, look at it from a production point of view. Choosing the 1/8" fingers, you'll need to make 4 passes per lineal inch, while 1/4" fingers need only 2 passes. For the four corners on a 2" high joint, that's 32 times through, verses 16 passes.
My preference is to make the "fingers" as close as possible to the stock thickness. To my eye, 1/4" th. stock with 1/4" fingers look balanced, as does 3/4 fingers using 3/4 stock.Arlington, Texas (The dash in Dallas-Fort Worth)
Practice...'till you can do it right the first time.
Freud has a new set up just for 1/4" and/or 3/8" box joints.
I guy used to be able to get combination blades with 4 atbs and one flat top raker. I still have some from Oldham. You can get those resharpened for about $.25 a tooth around here, or you can send them to Forrest, for used to be about a buck a tooth, (maybe more now), and ask them to leave your chisel raker, flush, or just a hair proud of the bevel teethe. They can do that. Most of these tool and cutter grinders like being asked for grinds a bit out of the ordinary, I believe, because I am sure the same old grinds get pretty tedious for them.
How wide do you want/ need your kerf to be for your finger joints? For tenons, you probably want to touch up your cut with a shoulder plane, or use a good crosscut blade to finish your tenon so that it mates upnicely to your mortise. You won't care if your rip cut is square bottom, as it will be buried.
FG,Yes, they're LM72R.Rich
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