Does anyone use a large circular saw? - Woodworking Talk - Woodworkers Forum
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post #1 of 24 Old 04-28-2016, 12:29 AM Thread Starter
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Does anyone use a large circular saw?

For most of our woodworking like cutting thin boards and plywood, a standard size 7-1/4" handheld circular saw works OK. However, sometimes these saws get stuck in thicker material such as hardwoods. So I was wondering if using a larger circular saw with a 9" blade would not be better in such cases?


Does anyone find a large circular saw (9" or higher) useful? Thanks.:smile3:

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post #2 of 24 Old 04-28-2016, 01:14 AM
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If it is getting "stuck" it is likely not powerful enough. I have never had my Skil wormdrive saw fail to cut anything I've used it on. These have a lot of torque and will serve you well (there are other brands besides Skil but that is the one most folks relate to). A larger blade is only useful if you have the need to cut thick material, but it will do nothing to help cut thru hardwood in and of itself.

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post #3 of 24 Old 04-28-2016, 01:37 AM
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If I think there's going to be an issue with binding with a cut, I'll keep a wedge handy to slide into the kerf.
I've got a 10-1/4" saw for 4x4 material, and I need to make sure that saw doesn't bind up.
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post #4 of 24 Old 04-28-2016, 03:16 AM Thread Starter
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Quote:
Originally Posted by ChiknNutz View Post
If it is getting "stuck" it is likely not powerful enough. I have never had my Skil wormdrive saw fail to cut anything I've used it on. These have a lot of torque and will serve you well (there are other brands besides Skil but that is the one most folks relate to). A larger blade is only useful if you have the need to cut thick material, but it will do nothing to help cut thru hardwood in and of itself.
I don't have a wormdrive saw and I thought a larger saw usually comes with a higher power. I don't cut anything thicker than 3" but even 2-1/2" hardwood binds up a less powerful saw.


I am looking at a Makita N5900B 9" saw rated just under 3HP.

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post #5 of 24 Old 04-28-2016, 09:46 AM
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I would guess you either have the wrong or a dull blade, and/or, faulty technique. It doesn't have anything to do with the size of the saw or blade. Should be plenty of power with all but the lowest quality circular saws. My largest portable circular saw runs a 16 5/16" blade, much more capacity but not necessarily any more powerful than my ordinary saws.
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post #6 of 24 Old 04-28-2016, 10:00 AM
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I've never seen any corded CS that pulls more than 15A, even the bigger ones like Hammer mentioned.

If the saw is getting stuck or the blade is stopping either the material isn't being supported correctly, the saw is cheap and underpowered or you have an extremely dull blade.
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post #7 of 24 Old 04-28-2016, 10:25 AM
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Quote:
Originally Posted by Chamfer View Post
I've never seen any corded CS that pulls more than 15A, even the bigger ones like Hammer mentioned.

If the saw is getting stuck or the blade is stopping either the material isn't being supported correctly, the saw is cheap and underpowered or you have an extremely dull blade.
.... Or the material is releasing internal stress, and binding up.
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post #8 of 24 Old 04-28-2016, 04:01 PM Thread Starter
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Thanks for all the replies!


The wood I am cutting is very hard and highly figured, and sometimes the grain direction changes abruptly. That's why even a new blade gets stuck which normally does not in soft wood.

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post #9 of 24 Old 04-28-2016, 10:48 PM
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Quote:
Originally Posted by Jig_saw View Post
I don't have a wormdrive saw and I thought a larger saw usually comes with a higher power. .
'Rated Power' of the electric motor is usually about the same as a regular circular saw with the ones I have used but once you get that big ass blade up to speed - Their IS a 'difference' in how it is going to act in the same piece of wood as a smaller blade. The bigger blade has a lot more mass / weight behind those teeth as it is spinning around and it is going to take a good bit more force to stop that from 'spinning'.



That big / heavy ass blade spinning around at operating speed is a wicked source of 'stored energy'. A heavy blade will want to keep the momentum going.

Same concept as a flywheel.

Same concept as a Tormek for that matter... It may take that puny motor a few seconds longer than it would take with a larger and more powerful motor to get started and get up to speed - but once you do have that big heavy ass wheel spinning around at speed - It takes a good bit of effort to stop it and you really don't 'need' a larger motor to keep it going when resistance is added during normal use.

With tools like that you want to play it safe and get the dog out of the way before doing your cuts. 10" blade or under and you are cool...

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post #10 of 24 Old 05-01-2016, 09:22 AM
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The PHYSICS of a larger diameter blade

It is very important to recognize that the diameter of the blade and the power of the motor are two different things entirely.

A saw with a larger diameter blade, but having the same motor power as a saw with a smaller diameter blade, has LESS cutting torque at the teeth! Let me explain.

The purpose of a more powerful motor is to provide more power. The purpose of a larger blade is NOT to provide more power, but rather to provide more cutting depth.

And "power" is an interesting thing. A "more powerful" motor cannot necessarily cut more wood per second than a less powerful one.

The formula relating power and torque is:

Power = Torque at blade x blade rpm / (numerical constant factor = 5250 if power is measured in "horsepower")

So Torque = Power x 5250/rpm

Let's say our first saw has a motor that turns at 3500 rpm and is "rated" at 2hp.

Then Torque at blade = 2 x 5250/3500 = 3 ft lb

Let's say our second saw has a motor that turns at 5250 and is also "rated" at 2hp.

Its blade torque = 2 x 5250/5250 = 2 ft lb.

It's got only 2/3 the torque at the blade that the first saw has, even though the "power" rating is the same.

Which saw do you think is going to cut through harder woods better?

Now, let's imagine we have two saws, each with a 2hp 3500 rpm motor. They each then produce 3 ft lb of torque at the blade.

But one has an 8" blade and the other has a 12" blade.

Torque = force x (distance from center of rotation that the force is being applied)

So, force at the blade teeth = Torque / (distance from center of rotation that the force is being applied)

On the 8" bladed saw, force at the blade teeth = 3 / (8/12 feet) = 4.5 lb force.

On the 12" bladed saw, force at the blade teeth = 3 / (12/12 feet) = 3 lb force.

So, the saw with the SMALLER blade applies more cutting force at the teeth, meaning it can cut harder wood before it stalls.

To get the SAME cutting force at the teeth, the saw with the larger 12" blade must have a motor that produces 12" / 8" = 1.5 times the power of the smaller bladed saw.

So, when buying a saw, look at:

- Does a saw with a larger diameter blade have a correspondingly more powerful motor?

- Does the motor have more power via more torque or via more rpm? If via more rpm, it will NOT cut through harder or thicker wood. It must have more TORQE at the teeth to cut through harder wood or thicker wood.

Also, "worm drive" circular saws have a reputation as being "powerful" than a saw of same rated power but direct drive. That is not strictly true. The worm drive saw actually has more TORQUE at the blade teeth because it uses internal worm gears to "reduce" the rpm of the blade below the rpm of the motor, thus increasing the torque at the blade teeth. This means it can cut through harder and/or thicker wood than a direct drive saw OF EQUAL POWER.

However, the SPEED at which the saw can be pushed through a cut is still controlled by the POWER available (That's basic physics). The worm drive saw won't cut any FASTER than the direct drive saw. But, it WILL be less likely to stall.

One DISadvantage of a worm drive saw is it is notably heavier than a direct drive saw, because it needs that "gear transmission". This can be tiring if you are doing more than just single or few cuts at a time.

Jim G
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post #11 of 24 Old 05-01-2016, 10:23 AM
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Circular saws are used on 120 Volts

With rare exceptions, most circular saw are designed for use on 120 Volts, the exception being 240 V. Even the largest 16" Makita is rated 15 AMPs on 120 Volts. so there is no increase in HP over a 7 1/4" 15 Amp saw. It will just cut thicker material, as Jim said:

Makita 5402NA 16-5/16-Inch Circular Saw


Powerful 15.0 AMP motor delivers 2,200 RPM for enough power to cut through pressure treated lumber
  • Large capacity blade cuts 6-1/4"" at 90 and 4-3/16"" at 45
  • Electric brake for maximum productivity
  • Low noise level at only 87dB for quiet operation
  • Blade stabilizer for stable blade rotation and superior cutting performance
  • Large depth control lever for convenience and secure adjustments
  • Weighs only 32.1 lbs. for ease of operation

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)
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post #12 of 24 Old 05-01-2016, 11:12 AM
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Quote:
Originally Posted by woodnthings View Post
With rare exceptions, most circular saw are designed for use on 120 Volts, the exception being 240 V. Even the largest 16" Makita is rated 15 AMPs on 120 Volts. so there is no increase in HP over a 7 1/4" 15 Amp saw. It will just cut thicker material, as Jim said:

Makita 5402NA 16-5/16-Inch Circular Saw


Powerful 15.0 AMP motor delivers 2,200 RPM for enough power to cut through pressure treated lumber
  • Large capacity blade cuts 6-1/4"" at 90 and 4-3/16"" at 45
  • Electric brake for maximum productivity
  • Low noise level at only 87dB for quiet operation
  • Blade stabilizer for stable blade rotation and superior cutting performance
  • Large depth control lever for convenience and secure adjustments
  • Weighs only 32.1 lbs. for ease of operation
Note the last line in the description:

"Weighs "only" 32.1 lb "for ease of operation". :)

Jim G
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post #13 of 24 Old 05-01-2016, 12:13 PM
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We use a Skilsaw wormdrive when we can, but the Makita's when we need something bigger...
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post #14 of 24 Old 05-01-2016, 01:38 PM Thread Starter
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Thanks for the great responses! The Skil 7-1/4" saw I have runs at 1-3/4 HP. The Makita I am considering to buy has a 9" blade and a 2-17/25 HP. The Makita's rated power is thus 1.5 times higher than the Skil, and according to Jim's calculation it should have a higher cutting force (at a proportionally smaller RPM). But as you point out, it's sure going to be heavy!

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post #15 of 24 Old 05-01-2016, 01:40 PM Thread Starter
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Quote:
Originally Posted by woodnthings View Post
With rare exceptions, most circular saw are designed for use on 120 Volts, the exception being 240 V. Even the largest 16" Makita is rated 15 AMPs on 120 Volts. so there is no increase in HP over a 7 1/4" 15 Amp saw. It will just cut thicker material, as Jim said:

Makita 5402NA 16-5/16-Inch Circular Saw


Powerful 15.0 AMP motor delivers 2,200 RPM for enough power to cut through pressure treated lumber
  • Large capacity blade cuts 6-1/4"" at 90 and 4-3/16"" at 45
  • Electric brake for maximum productivity
  • Low noise level at only 87dB for quiet operation
  • Blade stabilizer for stable blade rotation and superior cutting performance
  • Large depth control lever for convenience and secure adjustments
  • Weighs only 32.1 lbs. for ease of operation

It is a beast!

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post #16 of 24 Old 05-01-2016, 08:02 PM
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Quote:
Originally Posted by JimGnitecki View Post
It is very important to recognize that the diameter of the blade and the power of the motor are two different things entirely.

A saw with a larger diameter blade, but having the same motor power as a saw with a smaller diameter blade, has LESS cutting torque at the teeth! Let me explain.



Jim G

Redo your math and just to keep things simple stick to comparing the 16" Makita to the 7 1/4" Makita (both having the same power motor) and explain how that huge blade has 'less' torque than the smaller one once it is up to speed...

The smaller Makita has an RPM of 5800 as compared to 2200 on the larger one. (you will need that info for your calculations I suppose)

If you really wish to do accurate math here you may wish to consider the following in your figures as well:

Quote:
The greater the inertia, or the greater the resistance of the flywheel to the torque applied to the spinning flywheel, the greater the energy that can be stored. The inertia within a flywheel, I, is directly proportional to its mass, m, and to the square of its radius, r. This is given by equation (1) :


The rotational energy stored within a flywheel, E, is proportional to its inertia, and to the square of its angular velocity, ω. It can be calculated by:

Personally, I have no desire or need to do all that math. I have used and do use both regularly and know the difference.
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post #17 of 24 Old 05-01-2016, 08:18 PM
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Quote:
Originally Posted by OnealWoodworking View Post
Redo your math and just to keep things simple stick to comparing the 16" Makita to the 7 1/4" Makita (both having the same power motor) and explain how that huge blade has 'less' torque than the smaller one once it is up to speed...

The smaller Makita has an RPM of 5800 as compared to 2200 on the larger one. (you will need that info for your calculations I suppose)

If you really wish to do accurate math here you may wish to consider the following in your figures as well:



Personally, I have no desire or need to do all that math. I have used and do use both regularly and know the difference.
I stand by the accuracy of my math.

Do note that some manufacturers rate their power more optimistically than others.

That's why I said "rated".

Yes, inertia has SOME benefits, but those benefits only occur when a blade encounters a BRIEF obstacle - higher inertia helps it get through a BRIEF obstacle. But when the obstacle is extended, or an entire hard board, it is of no help.

Jim G
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post #18 of 24 Old 05-02-2016, 01:26 AM
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All the math calculations don't mean anything when the saw is stuck. Everything changes under load, too. I don't think your solution is a larger circular saw. We may be assuming you are cross cutting but ripping is another matter. If the cut isn't clearing sawdust and is closing in on the blade, you need to slow down and use wedges, like stips of cedar shingles. Tap them into the kerf behind the saw as you go. Use a coarse, low tooth count blade, rip style if you can find one. Another possible option is a track saw with a riving knife. The big Festool only cuts 2 3/4" thick but there is an 18 tooth rip blade available.
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post #19 of 24 Old 05-02-2016, 11:20 PM
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Quote:
Originally Posted by JimGnitecki View Post
I stand by the accuracy of my math.

Do note that some manufacturers rate their power more optimistically than others.

That's why I said "rated".

Yes, inertia has SOME benefits, but those benefits only occur when a blade encounters a BRIEF obstacle - higher inertia helps it get through a BRIEF obstacle. But when the obstacle is extended, or an entire hard board, it is of no help.

Jim G
I 'could' provide you with blade weights and Amp draw info to further add to your 'math' problem...



You can 'stand by the accuracy of your math' as long as you wish. My advice in this thread is based on MY experiences of the 'real world' differences of the actual tools being discussed from a guy that actually uses them on occasion to make his living. Not some junk I read on the internet and then had to go 'search' to find pictures of or gather info about...



In my experience I have learned this much - Some guys NEVER break scroll saw blades lest they are doing it on purpose.
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post #20 of 24 Old 05-03-2016, 05:46 AM
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Quote:
Originally Posted by OnealWoodworking View Post
I 'could' provide you with blade weights and Amp draw info to further add to your 'math' problem...



You can 'stand by the accuracy of your math' as long as you wish. My advice in this thread is based on MY experiences of the 'real world' differences of the actual tools being discussed from a guy that actually uses them on occasion to make his living. Not some junk I read on the internet and then had to go 'search' to find pictures of or gather info about...
. . .
The "junk" I learned about physics was learned decades ago, long before The Internet, in an Engineering school, and reinforced by plenty of experience helping The Old Man in his real world income earning business of building high end kitchen cabinets, remodeling homes, and designing and building homes, so take your unwarranted insults and stuff them. :)

Jim G
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