smaller blades for ripping FYI

[Mike3206]

I'm not sure if I saw a post on this forum, or another, but the suggestion was made to cut/rip plywood with the smaller 7 1/4" saw blades. they're cheaper and pretty much disposable, as opposed to a $100 blade, or even a $20 sharpening.

Thought I would mention that HD has Freud 7 1/4" 24 T blades for $9.99 and it comes with a free one. (only $5 each) The blades are pretty nice and have the same features as their higher end table saw blades. the kerf is also very thin, even for a 7 1/4" blade. smile.gif

[daveferg]

Think your first consideration is the number of teeth and if the results are good for plywood. However, when you switch from a 10" to smaller blade, the rim speed of the blade (number of inches of circumference/sec.) will drop, possibly making for more effort to cut the stock---and, of course, the smaller blade will dull faster for the same number of cuts--since each tooth has to cut more frequently.

[Dave Arbuckle]

What would the benefit be?

Dave

[Mike3206]

yes, you may have to cut slower, and the blade may wear faster, but... For $10 you get two disposable blades.

The cost of a sharpening on a standard 10" blade is around $20 depending on where you go. Sooo, for the same cost of one sharpening on the 10" you get 4 disposable carbide tipped blades to use when you rip thinner stock (I believe thickness would be about 1" or less)

I for one don't want to wear out a 10" blade when I can pop in a cheap smaller one for the job. Besides, I normally rip the wood close, then do finish cut with the smaller, more manageable pieces.

[hammerman]

It would seem to me that if i am building a project, like furniture or cabinet out of a good wood, that an extra $30.00 or so for a good 60 or 80 tooth blade wouldn't hurt my budget that much that i would sacrifice the quality of the project.
Your quality is only as good as the tools you use.

[Steve L.]

I have and do use 7-1/4" blades for ripping. Since the blade is smaller it will spin faster than a 10" (less rotating mass). The faster spinning blade should cut better than a similar larger one but it would also dull faster. Like Mike3206 stated, the price is right. So far, I cannot afford to spend $75++ for a blade. The Freud blades that I have used still required jointing/sanding. Stay away from teflon coated blades. The lubricative properties of teflon is never utilized because the teflon coating never touches the wood.
Steve

[Dave Arbuckle]

Since the blade is smaller it will spin faster than a 10" (less rotating mass).

I would like to challenge this statement. Most tablesaws use synchronous induction motors that have a nearly fixed speed that derives from line frequency. As well, once a blade is spun up to speed, it's mass has nothing to do with the power required to sustain it.

The cutting tip speed of a smaller blade will be lower than a larger one, because the circumference of the blade is smaller.

Dave

[Steve L.]

Simple physics my friend. If the motor shaft speed is held constant, as blade diameter increase the speed at the blade tips will decrease. Larger blades will have to travel through a greater distance - circumference.
Mass also has a lot to do with cutting. Rotating mass provides the momentum that helps your saw cut through thick or dense wood. Smaller blades with less mass will stall quicker than a larger blade. If rotating mass was not important than no car with a manual transmission would have flywheels. I think you are confusing mass with torque.
My knowledge of synchronous induction motors is very limited so I cannot discuss them.
Steve

[Dave Arbuckle]

You have me entirely confused, as you are contradicting yourself, and stating things backward.

-----------------------------------------------
Regarding speed:
-----------------------------------------------
Quote one, Steve: Since the blade is smaller it will spin faster than a 10" (less rotating mass).

Quote two, Dave: The cutting tip speed of a smaller blade will be lower than a larger one, because the circumference of the blade is smaller.

Quote three, Steve: If the motor shaft speed is held constant, as blade diameter increase the speed at the blade tips will decrease. Larger blades will have to travel through a greater distance - circumference.

In quote three, your first sentence is stated backward. The second sentence is correct.

Let's use an extreme example to see the effect more easily. We have two disks, each revolving at one r.p.m. One of them is one inch in diameter, the other one is fifteen feet. A dot on the edge of each will pass a given point one time each minute. During that minute, the dot on the small disk will have traveled roughly 3.14 inches (circumference = diameter X pi). The dot on the large disk, in the same time, traveled over 565 inches, about 180 times faster. Since fifteen feet is 180 inches, this isn't surprising.

-----------------------------------------------
Regarding mass.
-----------------------------------------------
Smaller blades with less mass will stall quicker than a larger blade.

I agree. But, don't you think this is counterexample to your first post, where you imply the smaller blade is better?

Dave
Next, let's do centrifugal force vs. centripetal acceleration... ;)

[daveferg]

Steve---sorry but I fully agree with Dave A.---it's that darned "Dave Thing" again ;) The rim speed (where the teeth are) is the issue and Dave's example is correct.

As to flywheels, and Dave can correct me, but they are used to sustain speed under load, and if my memory on this is correct, that's another point if favor of a 10" blade.

[Steve L.]

I did goof up a bit. I will follow up with a clearer explanation when I get off the company clock.
Steve

[JPM]

Another simple way to think about blade speed(speed of teeth). [Speed(velocity)=distance/time]
With a constant rotation you have constant time. What is changing is distance. As Dave and others have established, a larger blade has a larger circumfrence. So increasing the distance in the equation will increase speed. With an RPM of 3450, a tooth on a 10 inch blade travels 102.6 MPH. With 7 1/4" blade the speed is only 74.4 MPH. I'd have to dig out my Dynamics book to enter into the centrifugal discussion!

[Mike3206]

Wow, sorry about the can of worms.

Yes, the blade rim speed will be slower with the 7 1/4, and as I mentioned, you would have to feed slower. However, I have yet to see a quality 60 tooth blade for less than $40, and since I always cut a little larger when ripping, (so I have more control over final cut) I think it makes sense to get something cheap that will do the job.

I would have to disagree though with the point made about the mass of the 10" blade making it spin better or cut better than the smaller one. The difference of mass in a blade that narrow doesn't do that much. Now, if the blade was say... 2 pounds, then I would agree about spinning mass making a big difference.

[Dave Arbuckle]

if the blade was say... 2 pounds

Hmm, maybe there is a market for blades with tips of depleted uranium? ;)

Dave
Goofy toward the end of the day

[daveferg]

Heard they sell those blades in North Korea :D

[Steve L.]

I do not think that a smaller blade is better for cutting but it is more affordable and regardless of what size or type of blade I use there is normal some time spent jointing/sanding etc.I do own a 10" Freud 60 tooth blade that I am very fond of.
:D
Irregardless of blade radius and blade mass the ts motor will maintain 3450 rpm? How?? I do not dispute that if the larger blade makes one rotation in the same period as a smaller blade than the larger blade is traveling faster at the blade tip. The statements that I made previous did not assume constant rpm or negligable mass. I theorized that a large heavier blade cannot be spun at the same rpm as a smaller, lighter blade utilizing the same motor. I find it difficult to grasp that regardless of size or mass of a blade that the rpm of the blade remains constant.
In theory, a larger diameter blade, that has more mass requires more power to accelerate and maintain rotation at any given rpm then a smaller blades. Now, if the motor shaft maintains 3450 rpm then that doesn't mean that the blade will. Power will be lost in maintaining the rpm of the blade. Less power will be lost on a smaller diameter blade. This lose may or may not be significant. I do not know that answer (nor am I conducting a physics experiment on my TS). Disclaimer: If the motor maintains a constant rpm regardless of blade radius and mass then it's Miller Time. Now momentum is a different story.

Steve

[Mike3206]

Steve, the motors on table saws are at least 1 and a 1/2 HP. With a motor that size, it would have no trouble turning a 7, 10, or even 12" blade at a constant RPM. Remember, saw blades don't weigh all that much, so the keeping the mass moving at 3450 rpm isn't all that hard.

At work, I have a few 3 and 5 horse motors that turn large exhaust fan cages that weigh in excess of 50 pounds without a problem. (of course they are 3 phase, and I'm just waiting for one to need "upgrading or bearing replacement." ;) Problably never happen though as I take really good care of the stuff.)

Dave A, maybe the army could use some of those blades?? Perhaps you could sell them for the same cost as a toilet seat?? :D

[Dave Arbuckle]

Disclaimer: If the motor maintains a constant rpm regardless of blade radius and mass then it's Miller Time.

Remember, no shop time after beer.

Not a chance in the world I could explain why a synchronous speed motor works the way it does. But, there are lots of things in that category, that work even though I can't explain them.

<quote>
Calculating Synchronous Speed:

AC motors are considered constant speed motors. This is because the synchronous speed of an induction motor is based on the supply frequency and the number of poles in the motor winding. Motor are designed for 60 hz use have synchronous speeds of 3600, 1800, 1200, 900, 720, 600, 514, and 450 rpm.
<end quote> citation: http://www.elec-toolbox.com/Formulas/Motor/mtrform.htm

If an inductive motor of this type is run at a lower speed, as by applying too large a load, it will burn out. If it is run with no load, it will run at synchronous speed (less bearing drag and other minutiae).

So, there you go. Happily, we never touched on centrifugal force or centripetal acceleration, because I never did figure that dang stuff out. ;)

Dave

[Cutbuff]

Steve,

I'll not get involved in the speed, mass circumference physics debate, I got lost on that halfway down the thread. But your comment on not using Teflon Coated blades since the main portion of the blade doesn't come into contact with the wood.
It's my understanding that this coating, which also appears on a number of Router Bits, is an attempt to prevent the buildup of pitch and resin, and nothing to do with helping the blades/bits through the material.
Is this not so? :confused:
David

[daveferg]

Steve---let's put it another way---if you had a motor which DID significantly increase in rpms, with a smaller blade, you'd really notice it---a motor so reactive to a minor change in the mass and size of a saw blade, would barely cut butter, let alone wood.

I'd say this---if someone gave you a box full of 7 1/4" blades for free---by all means knock yourself out---but on economics, buy the 10". A good carbide tipped 10" will outlast many 7 inchers.

[Steve L.]

Well this has been an excellent conversation. I must (finally) agree that the mass is negligable. I calculated the velocity of the blades at 3450 rpm for both blades and besides some rounding and significant fiqures came up with the same results as JPM. When changing rpm for the 10" to 3000, the blade still had a velocity of 89.6 mph.
It was nice dusting off my ole physics books. Let's drink some beer. Thanks for all your input and patience. Now, where can you order those depleted uranium tipped blades again????? :D

Steve

[Steve L.]

Cutbuff,
I feel it is more gimicky then practical. If pitch is accumulating on the face of your blades, then pitch is likely accumulating on your teeth too. Personally, I haven't seen much in the way of accumulation on the face of the blade. Most of the accumulation occurs on the teeth. I just make it a blanket policy to clean my blades after I complete a project or if a see a noticeable degradation of blade performance. I keep my 7-1/4" blades clean too. Now, what does everyone use to keep their blades clean?? Oven cleaner, baking soda/hot water, commerical cleaners??

Steve

[JPM]

I know this topic has been beat to death, but, the suggestion that a heavier blade will require more power/energy to maintain a constant speed goes against a very basic physics law. An object in motion will stay in motion until acted upon by another force. The forces acting on a SPINNING blade should not be affected by size. Sure, there will be a little more weight on the bearing(negligible), and the larger blade will have slightly more surface area, so more air friction, (also negligible). As to weather more teeth would increase drag, I think that would need to be tested, but I'm sure the effects are small. What you might notice with a smaller blade is a reduction in start up time(acceleration). I'm done.
As for cleaning off pitch, Simple Green works great.

[daveferg]

Agree---Simple Green is fantastic---err, sorry, that's another product :D Works in a few minutes. Also, I use it to clean my cast iron tops, followed by good coat of paste wax.

Steve---yea, let's spill a little beer on the physics book :D

[Dave Arbuckle]

Steve L. writes: I feel it is more gimicky then practical.

Steve, I'm not picking on you, I swear. But, your profile here says you are a Scientist. I am too, of sorts.

Would you agree with me that "feel" is not a particularly scientific word? Have you tested teflon coated blades to determine how well they work in comparision with plain steel ones?

I haven't either. But, a friend works for Freud, and they have. Oddly, a teflon coated blade experiences lower heat rise in testing than a plain steel one. Chrome plated did even better, if I recall correctly. Why? I don't know, because the way you "feel" makes sense to me too. But, the tests don't support it.

Dave

[KellyC]

Steve, I felt the same as you and posted the same thing about the same blades in my old Delta bench saw on another forum. The same result was thrust upon me and I also had to agree with them. The fact did remain though, that the result they spoke of was under NO LOAD....when you toss solid Maple into the discussion, the drag on the larger thicker blade slowed the tip speed down to UNDER that of the thin kerf 7.25" blade with the same feed rate. That's why the stock goes through easier and the cut bogs the motor down less.

While this was tested in real life and found to be true, the more powerful the motor, the less this would matter. On a 13 amp bench saw, the difference was stunning...on my 15 amp belt drive Ridgid, it was a little less prominant...on a cabinet saw with 3 hp? I'd say it wouldn't matter.

So under a load such as solid Maple or Oak, the tip speed of a thin kerf 7.25" blade can out perform that of a thick kerf 10". The drawback though...none of those thin kerfs are made for smooth edges....

[woodslayer]

“on my 15 amp belt drive Ridgid, it was a little less prominant..”

Kelly, yours is a little more powerful than mine “Emerson 1.5 HP, 13/6 Amps, 120V-240V Induction/Capacitor Start & Run”. This thread has been very entertaining, thanks.

Woodslayer

[Steve L.]

Don't sweat it Dave A. My mind is always open. I can guarantee you that my official reports that I produce do not contain the word feel or guess.
My question is this how does teflon help dissipate the heat? Does your friend know how or why the lower temperatures are created? Is the differences only measureable in a laboratory? How would this affect all of those non-stick cooking pans?? Teflon has a well established lubricative quality that reduces the friction between moving parts. Teflon is a man made polymer created by DuPont. Lower friction levels mean less heat. But, how much contact occurs between the teflon coated surfaces and the wood? Most carbide tipped saws cut a kerf that is wider than the metal blade. If that is so then there should be minimum contact with the side of the blade. Most of the heat should be generated at the teeth. Freud website states that, "Permanent red Teflon coating on some Freud blades guarantees less working friction and less resin adhesion while preventing the development of rust." I clean and oil my blades regularly. If you regularly clean the pitch out of the carbide teeth, how much extra effort would it take to clean the face of the blades? I have never had a blade rust. I also do not believe that the friction reduction they speak of is measureable by the average woodworker or is worth the extra expense. That is why I feel it is gimicky. If it worked so well, why isn't everyone doing it?
Steve tongue.gif

[Steve L.]

I guess the rate I'm going I will never get one of those neat little stars under my name.
Nice to hear from you Kelly. There are more variables at play but I think I fired Dave up enough this week. :D

Steve

[Dave Arbuckle]

(Dave hangs himself at mention of the "if it's so great why doesn't everyone do it" argument ;) ) My car is supercharged, it runs great and gets better gas mileage than it should for its size and the way I drive it. Why aren't all cars supercharged?

I will ask my friend for more details. I haven't a clue why it reduces running temperature, and he probably doesn't either. With luck, maybe he can find out.

Teflon is a man made polymer created by DuPont.
How does this snippet add to the conversation, please? Teflon is the registered trademark of the DuPont company for polytetrafluroethylene (assuming I spelled that anywhere close to right). IIRC, it was discovered serendipituously by a researcher trying, humorously, to develop a better adhesive. But that has nothing at all to do with its use as a sawblade coating, it is just additional background noise.

Dave

[KellyC]

Originally posted by woodslayer:
Kelly, yours is a little more powerful than mine “Emerson 1.5 HP, 13/6 Amps, 120V-240V Induction/Capacitor Start & Run”. This thread has been very entertaining, thanks.

Woodslayer I stand corrected...checked the manual and it's 13 & 6.5 amps...mine's a 220 now so it's 6.5 amps.

[Steve L.]

Dave,
As a part time wrench turner, a supercharger is way to produce more power from a smaller displacement engine. We can chat later about the feasibility ($$) of supercharging a small engine versus putting in a larger engine with the same power output. Personally, I would choose the larger engine. There is no replacement for cubic inches!
My point about the industry gravitating towards teflon coatings is simple. If it was truely as good as they claim every saw blade manufacturer would be producing them. For example, all quality saw blades have expansion slots. Expansion slots have been proven to work and every quality blade manufacturer uses them on their blades.
Regarding the snippet about teflon, I thought it was worth mentioning. And apparently YOU thought it must of had some value because you expanded on my point. I could have gone into it's coefficient of friction, etc. but I choose to avoid it.
:D
As a side note, if your car has a roots style supercharger, it has been proven that teflon coated rotors produce lower aircharge temperatures and slightly higher boost pressures.
Steve

[Big Johnson]

I'm canceling my subscription to "Popular Mechanics"... This thread is much more exciting to read and it's free...

Waiting for the trend to the right subject so I can chime in... :D

Great discussion guy's...

[Henry Anthony]

This snippet does not add to the conversation but, Teflon was discovered serendipituously by a researcher at Dupont trying to develop a new COOLANT. Not an adhesive.

Best regards and sorry for the noise smile.gif

Henry

[Vigs]

Not sure If I really want to get in on this one, but what the heck.

Steve L.
But, how much contact occurs between the teflon coated surfaces and the wood? Most carbide tipped saws cut a kerf that is wider than the metal blade. If that is so then there should be minimum contact with the side of the blade.

It depends on how much lateral force you are exerting on the wood. I would guess that if you are crosscutting a rail, there will be almost no contact. If however you are ripping, I would bet that there is a great deal of lateral force, which is why you should have a splitter at the back of the blade.

Dave Arbuckle:
Why aren't all cars supercharged?

Because a good number of them would blow a rod.
It so happens that some engines handle heat better than others, and it so happens that the Honda Civic and the Subaru WRX Wagon are a couple cars with an engine block that can dissapate heat very very well. It is for this reason that these cars have been embraced by rich kids who love to make them look like low-riders and street race them. A very light car can produce very high hp without blowing up. It's kinda cool, really. Like a motorcycle on 4 wheels.

But I still agree with Steve L.
There is no replacement for displacement.

[Jerry Jensen]

Alright, what the heck...

I don't know how much you are cutting that you want to spare your blades that much wear, but for me, I rough cut large plywood panels with a hand circular saw (Makita cordless, lightweight and sweet) and then go to the table saw where I just bought a Forrest all purpose blade. First times I cut with it I think I had a religious experience. If you have not tried one and have heard all the rhetoric, its true. I am going to send them my old blade and dado set for sharpening and see what I get back. Based on this experience, I don't think you'll see me downgrading to $10 blades any time soon.

I think those cheepies are probably great for cutting framing lumber but they wont see my TS2424.

[Andy B.]

so is the smaller blade safe to use?

[KellyC]

I think those cheepies are probably great for cutting framing lumber but they wont see my TS2424.

I hear ya there, I use a Freud in mine (but am wanting to upgrade to a Forrest soon) and the small ones don't even see time anymore in my jobsite saw. Since buying the 2400, I've been using the Freud Framing blade in it with great results. I still want to upgrade from that for trimwork on my bookcase work to eliminate more saw marks. I only used the little thin kerfs in my Delta portable (which I no longer own).

[Dave Arbuckle]

Andy, I don't see any safety hazard, with one exception. The blade should be speed rated, most 10" blades are rated to 6000-9000 rpm, even though the saw is doing less than 4000. I've never paid any attention to the rating on the small blades.

Dave