Best blade to cut a 1.75" deep swath 3.5" wide, across the grain - Woodworking Talk - Woodworkers Forum
 
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post #1 of 18 Old 04-03-2008, 02:25 PM Thread Starter
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Best blade to cut a 1.75" deep swath 3.5" wide, across the grain

I'm using a 10" Radial Arm Saw to make sign posts out of 4x4 pine. For the T, I notch each piece 1.75" deep 3.5" across. I started out using some old funky single blade that cut 3/4" at a time. It was carbide tipped, but it made a mess of the edge of the cut and just wasn't clean. So now I'm just using a standard finish cut blade making however many passes it takes to do the 3.5". I'd like to get a DADO blade, but am wondering how clean a cut you guys get out of them, because even the DW7670 only has 24 teeth, which doesn't seem to be all that many to me. Or can I just use 2-3 finish cut blades together and put my own shims or washers between each one? Arbor length isn't a problem, there is plenty of room. I also need to be able to do the entire 1.75" deep in one pass, so I don't have to reset the depth for each post. Any suggestions? TIA.

PS: Referring to the "old" blade above, I mean probably designed 10+ years ago, it's only been used once in it's life and is in like new condition still though.

Last edited by xjaz; 04-03-2008 at 02:47 PM.
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post #2 of 18 Old 04-03-2008, 03:16 PM
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A dado set will give you the best results. If tearout is a concern, just tack a piece of sacrificial wood to the piece being sawed. It would be best to do this operation by utilizing many passes taking a small amount of depth with each pass.

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post #3 of 18 Old 04-03-2008, 03:26 PM Thread Starter
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The sacrificial wood would work for a couple, but since I'm doing 24-36 posts at a time and will be producing hundreds ultimately, it's not efficient to tack another piece of wood or to take the depth down slowly, cause once I set the depth measurement I use it for all 24-36 to get them through quickly. I appreciate the response though. Anybody used multiple, normal blades together, separated with shims or fender washers or something?
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post #4 of 18 Old 04-03-2008, 06:07 PM
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Well, I am not sure I would choose a radial arm saw to do this, HOWEVER, that is the saw you are using. You don't state what size saw it is, but it must be pretty big to have an arbor that will take a lot of dado blades! I wouldn't make a cut that was 1.75" deep and 3.5 inches across in one cut, not with a normal radial arm. That is a lot of wood to remove in one cut. Remember when a radial arm is pulled into the work, it "wants" to pull into it pretty vigorously. You can get blades that don't have as much aggressive cutting, but I don't think you can find such so easily in dado blades. Anyway, here is what i would do. Get a decent dado blade. (I love my Forrest dado, but I like my Freud too) Set up the radial arm for a dept of cut of 1.75 inches. (This assumes that all the posts are the same dimension and that is why I would rather do it on a table saw with a sliding table). Then put up a sacrificial piece of wood against the fence that is high enough so that it fully supports the 4X all the way to the top or past the top) Then cut thru that fence with the blade. Now you are ready to figure out your stops. Let's say you are cutting the bottom of the cut 1 foot from the top of the post. Make that cut carefully and put a stop with a clamp such that you can repeat this cut many times, just by putting your post up against the stop. Now make the other end of the cut. Your post end will now be short of the stop by 3.5 inches, less the width of the cut. Cut a block of that lenght that you can put between the top of the post and the original stop.
Course if you have flip stops or the like you can set the two. But if not, this will work easily and is pretty failure proof. as to the amount in the middle, just rip that out with a two or 3 more passes. Once you have set this up, make the first cut with your block infront of your stop, then remove the block and progress toward the stop. The one piece of sacrificial lumber is the same piece every time, no need to change it, it just supports the edge of the cut.
Hope this makes sense.
If you still want to do it in one cut, and have the machine to do it, the same thing goes, just that you make only one stop. Remember not to leave the stop all the way to the bottom, or bevel the bottom of the stop, so that sawdust doesn't change your mark every time.
best
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post #5 of 18 Old 04-03-2008, 06:48 PM
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You can use a stacked dado blade set to do that job, if you need a really smooth bottom do not use a wobble dado, due to the wobble design it doesn't leave a perfectly flat bottom when cutting 3/4 wide. I don't see why you couldn't use several saw blades with shims between them. Like Paul said, that isn't the best tool for that job, I'd use a table saw and a sled with stop blocks so I could cut 4 at a time. Stacking blades creates a mass of metal spinning has a lot of force, and the way a radial arm saw works is the teeth are spinning in the direction of saw movement making it want to dig and pull through the wood. You have to move real slow or the blades could grab the wood and catch rather than cut, the saw would rise and come to-wards you on its own (danger!!). The added blades would add mass making it potentially more dangerous. I believe thats why the reduced the diameter of dado blades to 8 inches and using chipper blades rather than full circumference blades stacked, it reduces the rotating mass allowing more control. I hope this makes sense.
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post #6 of 18 Old 04-03-2008, 07:51 PM Thread Starter
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I'm only using the radial arm saw cause it was the best tool for the job out of the ones that I already have (no tablesaw). My dad and I typically work together making the posts, and we've got the stops all figured out, although the exact size of each piece of wood varies slightly so we pair each one to make sure it has a tight fit. I'm not looking to do the entire 3.5" cut in one swath, but doing it in 3/4" swaths vs. my current 1/16" or whatever it is swaths would be nice. Thanks for the information guys.
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post #7 of 18 Old 04-03-2008, 10:26 PM
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I've been thinking, why couldn't you start with the saw closest to you and move the saw to wards the back? This would minimize the saw catching and throwing itself to wards you since it wouldn't have anything to grab onto. You could also start with the regular 1/8" blade and make your first cuts on all your pieces, then run the dado to remove the bulk.
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post #8 of 18 Old 04-03-2008, 11:15 PM
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Sounds like Century 21 sign posts LOL. Setup a good blade with dual stops and cut every one for finished width, then put dado blade on and remove the rest.
And YES cut the way MrRodeo suggested. Pull saw all the way OUT, put pc on, KEEP THE ARM LOCK SLIGHTLY SNUGGED.
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post #9 of 18 Old 04-04-2008, 12:15 AM
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[quote=xjaz;29340]I'm using a 10" Radial Arm Saw to make sign posts out of 4x4 pine. For the T, I notch each piece 1.75" deep 3.5" across. I started out using some old funky single blade that cut 3/4" at a time. It was carbide tipped, but it made a mess of the edge of the cut and just wasn't clean. So now I'm just using a standard finish cut blade making however many passes it takes to do the 3.5". I'd like to get a DADO blade, but am wondering how clean a cut you guys get out of them, because even the DW7670 only has 24 teeth, which doesn't seem to be all that many to me. Or can I just use 2-3 finish cut blades together and put my own shims or washers between each one?


A dado set up would be the best way to go, but you can stack a few blades together if you dont have a dado. Dont use spacers between the blades though. Just stack the blades making sure you stager the teeth so the blades will lay flat against each other. And NEVER pull the saw to you while cutting. Always start with the saw all the way out and cut the wood by pushing the saw back. It is also best to set a little drag in the travel. Take your time. Wood working is much more fun using all ten fingers.

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post #10 of 18 Old 04-04-2008, 11:06 AM
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You got a lot of good suggestions, but understanding a bit more, I might another comment or two. Yes, don't use a wobble dado, use a decent stacking one, and if you have the stops figured out, and use that same backer board, sounds good. As to pushing the saw back in, definitely it is a bit safer, as it won't grab. However with a big stacking dado, it does still have 2 drawbacks.
1. if you push it quickly it will tend to "raise" the post slightly. Probably not a big deal, as it is a post after all.
2. perhaps more importantly, as I understand it, you are mass producing these and want the fastest way to do it. When speed is involved, I would get a bit concerned about pulling the saw out, sliding the post behind the saw, then pushing it back in. You have a big saw spinning at the end of the travel, too close to you while you are manipulating a big piece of wood. You might get too close to it, and the piece of wood also is able to slide and hit that saw too. yes, you could make a "track" that would keep the post in its groove, but be careful. Radial arm saws are not known for their safety. My late father in law (a contractor) wore a glove on his left hand, to cover up where he had sliced off 3 of his fingers, on a radial arm saw.
So while I agree that pushing rather than pulling is less likely to bind, I worry about the act of moving the wood in and out behind a saw blade, same in moving the stops. If you do this, remember to move the stops while the blade is behind the wood. Good luck
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post #11 of 18 Old 04-04-2008, 12:00 PM
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Paul; I believe everyone here PRESUMED he was smart enuf to turn the damn saw off before moving material HOWEVER Sorry if I did'nt mention it. Your point is very good.I haven't used my radial for years, almost new, runs great just useless since the tablesaw
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post #12 of 18 Old 04-04-2008, 08:41 PM
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Yes, I hoped he was too, but if he is in "a hurry" and wanted the fastest way, maybe he wouldn't. As to radials. I remember being mighty impressed with my dewalt 16" radial, a great saw, but it sits in the shed to be used only about once a year for cross cutting timbers that my chop saw doesn't want to do. Funny thing is, that on a 16" saw, it doesn't cut much deeper than a 12" chop saw, in that the body of the saw takes up more depth. Yes, a sliding table on the table saw, and a good chop saw, and that meant the demise of the radial arm for me.
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post #13 of 18 Old 04-06-2008, 02:25 PM Thread Starter
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I do pull the saw toward me with my right hand while holding the long board steady with the left hand. Sometimes I turn the saw off in-between cuts, but not always, and for that reason it seemed safer this way. Created 15 more yesterday with 2 rip blades stacked and it went about 4 times faster than it previously did with just one finish cut blade. I agree a Dado blade would be sweet, but based on comments here and from a friend of mine who owns a carpentry business, I was concerned that it would be even that much harder to control due to the depth of the cut with a 3/4" wide dado vs. a 1/4" wide double blade stack (that & the cost difference). I did use a very thin washer in-between the blades, but since the carbide tips stick out farther than the center of the blade, there was no gap. Speed and efficiency are important because of the volume of these I'm doing, but obviously I'm being very cautious while operating the saw also. Thanks for all the help.
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post #14 of 18 Old 04-06-2008, 06:26 PM
 
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I would make the two "end" cuts with the radial arm saw with a normal blade, and then make 3 or 4 kerfs in-between to the full depth of 1-3/4" and then use a hammer and big chisel to chisel out the lion's share of the waste, then clean up the little waste that remains with a dado blade.

If you need to cut a lot of them, I would break it down: First make all the end cuts and the 3 or 4 relief cuts in-between on as many posts as you need to do. Then get your hammer and chisel and chop out as much of the waste as you can on all of them. Then put the dado set in your saw and do cleanup on the full run.

Chopping out the bulk of the waste with a chisel will make your saw blades last a lot longer, and it shouldn't really take that much more time, since the saw is cutting across the grain and the chisel work will be "with" the grain.
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post #15 of 18 Old 04-07-2008, 02:37 AM
 
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Maybe this will work...

A few years ago I built a Gang Rip Machine to rip 8/4 Maple into 2 x 2 squares that didn't work so well. I ended up with 10 - 7 1/4" Rip blades hanging on my wall. Later I needed to cut some 3/4" dados in Maple plywood. My Freud dado set left a choppy bottom and produced a fair amount of tearing on the surface. So I went and bought two 40 tooth fine cross cut blades and set the rip blades between them as chippers, I used the shims from my dado set to fine tune the width and presto, my own fine cutting dado set.

From your description, I think this will work nicely for you. The set-up cuts very smoothly with an almost perfect edge and bottom and because it uses 7 1/4" blades, the rotating mass is about the same as my dado set, and the cost is cheap compared to a high end dado set. Just buy 2 good quality carbide trim/crosscut blades then stack whatever they have on sale for ripping blades between them. The best part is thick kerf blades are usually cheaper than thin kerf so it won't break the bank to do. I still use this setup when I need an extra smooth cut, even though I've gotten a nice router table since then, it's almost as smooth as my router, but way faster.

BTW. You would want to look for blades that have a flat top grind for the chippers and a triple chip for the outer blades, this combo makes for the best quality of cut, and double check that the blade diameters are identicle, 7 1/4" seems to be an estamate. Also, I'd recomend Pushing the cut as a stack of small diameter blades has more leverage, traction, and a shallower angle of approach, all making it more likely the saw will "ride up" rather than cut.

Definitely push the cut, I took a few minutes to setup and try the cut on my Rigid brand Radial Arm Saw, It tractioned right up and over a Pine 2 x 4 I setup as a test cut. Pushing it cuts like butter though, I cut a 7/8" wide by 1" deep cut with almost no force.
Anyway, best regaurds.
Randy.
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post #16 of 18 Old 04-07-2008, 07:17 AM
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Stacking blades will only work if they're all identical. A stacked dado is a more logical choice. Systimatic makes a 42T dado set...~ $300. Holbren sells the Oshlun 42T for around $70 shipped....surprising well made for the price.

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post #17 of 18 Old 04-24-2011, 01:39 AM
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More years ago than I like to think of I worked for a co. that made mailbox posts. we used a 10 inch and a 16 inch radial arm saw with jigs with a hinge to make a custom fit arm, cutting the arm and post at the same time. Make one pass use arm to mark post and arm line up pencil marks and make final passes. Always pull through the work with a pull but ready to push if it gets grabby. We used dado blades all sharpened at the same time for smooth cut. BTW the more power the safer it cuts insted of grabbing. we cut full depth in one cut. Hope this helps.
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post #18 of 18 Old 04-24-2011, 06:54 AM
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Push or Pull?

http://www.woodworkingtalk.com/f12/ras-push-pull-15784/
Check out this thread for "opinions" regarding pulling or pushing the saw into the work. Briefly stated, pulling the saw into the work allows the teeth first contacting the work to press it down, into the table and fence, safely.
Pushing the saw into the work allows the teeth first contacting the work to lift it off the table surface. Now you really have to be pressing it down to keep it from lifting off. Kinda like if you hand held your circular saw a few inches off the work and then started your cut. The work would snap up into the saw base.

It's not about "opinions", it's about the physics involved. Pull the saw. BTW, if you pull the saw your left hand is pressing down on the work and resisting the travel toward you. If you were pushing it, you have no leverage to resist the forward travel, since both hands are pushing forward. More physics.... bill

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 04-24-2011 at 06:59 AM.
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