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Cordless (Battery Operated) Circular Saws - Your Opinion?

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Forum topic by BDFan1981 posted 645 days ago 1524 views 0 times favorited 26 replies Add to Favorites Watch
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BDFan1981

96 posts in 961 days


645 days ago

Topic tags/keywords: circular saw cordless circular saw battery operated moto-tool

Here is my theory of why the cordless (and I mean battery operated) circular saws don’t work well: With regards to the OSHA standard that the maximum blade tip speed limit that is 18,000 SFPM, a max RPM of 1000 on the smallest saws in the category don’t do justice.

Henceforth, for example, would you have envisioned a cordless saw with a 3-3/8” dia. blade as having its motor spin 20,000 RPM to equal the efficiency of the larger, corded saws? I repeat: 1000 RPM is not enough and especially so for a blade size as small as 3-3/8”.

Case in point: even cordless battery-operated “Moto-Tools” can spin between 10,000-30,000 RPM easily.

SAW BLADE SPEED CHART (all figures calculated using the max of 18,000 SFPM)
3-3/8” (86 mm) = max RPM is 20,372
4-3/8” (111 mm) = max RPM is 15,715
5-3/8” (136 mm) = max RPM is 12,792
5-1/2” (140 mm) = max RPM is 12,501
6-1/4” (159 mm) = max RPM is 11,001
6-1/2” (165 mm) = max RPM is 10,578
7-1/4” (184 mm) = max RPM is 9483
8-1/4” (210 mm) = max RPM is 8334
10-1/4” (260 mm) = max RPM is 6708

Is there a reason that the early cordless motors can’t do 20,000 RPM efficiently (on the 3-3/8” cordless saws)?

~Ben


26 replies so far

View Tennessee's profile

Tennessee

1447 posts in 1146 days


#1 posted 645 days ago

Ben:
Agree with you, I somehow ended up with two in kits I bought, a PC and a Ryobi, and they both suck. When I do some work around my house that requires me to outrun a decent extension cord, I haul both out there with all four batteries charged and hope I make it through the project.

That being said, 20,000RPM is certainly achievable in a battery powered motor, but with the needed amps to kick through say, a 4X4, you would deplete the battery in very, very short order. So they slow it down and make the blade smaller and up the amperage. You end up with a sub-standard effort that is OK for some basic cuts, with you still changing batteries faster than your charger can keep up.

-- Paul, Tennessee, http://www.tsunamiguitars.com

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joeyinsouthaustin

1245 posts in 704 days


#2 posted 645 days ago

The corded skill worm drive saw only does 4600 rpm no load, the de walt 18 volt does 3700 rpm no load…..
That osha standard is a limit for construction of blades, not alot of saws actually run the blade at that speed.
Here is my theory of why the cordless (and I mean battery operated) circular saws don’t work well:

I see a problem with your premise as well…. As an owner of 8 different battery powered saws, They work excellent, and because the evaluation depends on the task, sometimes much better than corded, and sometimes corded much better than battery powered.

Is there a reason that the early cordless motors can’t do 20,000 RPM efficiently (on the 3-3/8” cordless saws)?

A 3 hp delta uni saw on 220v only does 4700 rpm blade speed. That makes it’s spfm only 6157

The skil 4365 and the dewalt 3514
I haven’t seen any cordless saws list ed below 3700 rpm so far….

So please clarify your point.

-- Who is John Galt?

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hoosier0311

355 posts in 657 days


#3 posted 645 days ago

I have often though one of these would be handy for places where I need to bob off the end of a board and am out of range for a cord. One of these days I will happen across a deal on one, until then,,,I have about 500 ft of extension cord.

-- I'm only deaf in one ear,,,,,I just can't hear out of the other one., Denny, Indiana implant, living in PA

View Tennessee's profile

Tennessee

1447 posts in 1146 days


#4 posted 645 days ago

I have to keep all my wood in another room, so I used to use mine for cutting up planks. Too many times I ran out of power, and one day I looked up and saw the receptacle in the ceiling…and bought a Rockwell Versacut, which I am not thrilled with, but it gets the cut done.

-- Paul, Tennessee, http://www.tsunamiguitars.com

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ETwoodworks

92 posts in 1325 days


#5 posted 645 days ago

I love my 6 1/2” makita. I guess i just accept its limitations. You really cant expect a battery op circular saw to run forever on 1 battery.

-- Building quality in a throw away world.

View crank49's profile

crank49

3373 posts in 1602 days


#6 posted 645 days ago

”Delta Uni Saw, on 220v only does 4700 RPM, that makes its spfm only 6157.”

I assume you meant sfpm (surface feet per minute).

10” diameter blade X pi = 31.416” circumference.
(31.416” cir. X 4700 RPM)/12 = 12,304.56 SFPM
Don’t know where you got 6157.

But, in any case, the manufacturers had to keep battery drain down to a level that would not fry the batteries.
That was done by smaller, thinner blades and running them at less than optimal RPM.

The Milwaukee 6 1/2” with a 28volt battery does a fair job, but to get the kind of power out of a 28 volt saw to compete with a 15amp 120 volt saw, the battery would have to put out 64 amps. The battery would weigh about 50 lbs; ain’t going to happen.

-- Michael :-{| “If you tell a big enough lie and tell it frequently enough, it will be believed.” ― A H

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joeyinsouthaustin

1245 posts in 704 days


#7 posted 645 days ago

I used radius instead of diameter .262×5x4700 = 6157
.262×10x4700=12314 But I made the same mistake for all three saws…(measure twice, multiply once?? ;)

I still am trying to grasp the theory and also defending cordless a little.
My point being. If your theory is that cordless saws don’t do well because of speed, I am not to sure about that. There are many cordless saws that run the same speed as corded saws. Corded saws with smaller blades are also going to generate slower tooth speeds. Speed in a saw often means power due to inertia, 1000 rpm is plenty for a lot of tasks that a small blade would be useful for, especially if it keeps its speed. The early battery powered saws used thinner blades, and lower running speeds as a trade off for power to make up for the lower inertia of the smaller, thinner blade. Also, too fast can be bad as well. Circular saw cutting is, to me, always a balance of speed, power, and heat (smaller blades, I might argue need lower speeds in part because they can’t dissipate heat as fast) I won’t argue that there is no a trade off for the versatility of going cordless, but I would defend the cordless also by saying that these tools are more specialized than how the argument treats them.

It may also help if you defined the qualitative part of the argument…
That is, What is “not well”. In my experience they cut great. The weakness is stamina, batteries run out, and power, not always needed. This is debatable between saws and how much power is needed per task.

I always keep both with me, ready to use for their specific purposes…. But I did notice the moment I got my first cordless saw, I started reaching for it more often, for more purposes. That is to say it is my goto when I need a saw and I only find my self using the other less, as the more specialized saw, and that I now have three times as many cordless circular saws than corded.

-- Who is John Galt?

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Loren

7424 posts in 2279 days


#8 posted 645 days ago

I had a cordless miter saw for awhile. Great tool in terms of
punchlist portability, but the blade spun too slow to do the
sort of chopping we get used too… I had to go slow like
when cutting metal with a corded tool.

Before the widespread availability of AC power there were
treadle powered table saws. I’m sure the rim speeds
were real slow compared to what we are accustomed to
these days.

-- http://lawoodworking.com

View Tennessee's profile

Tennessee

1447 posts in 1146 days


#9 posted 645 days ago

Joey, to be honest, I think we all would in one way or another like to kick the “cord” habit. But some things we get used to, like having more than enough power to run a circular blade through a piece of wood. Why would anyone want to haul a Skil worm saw around? What horses. Like moving the table saw, instead of the wood! I bought an old 68’ Skill worm at a garage sale for $2, cleaned it all up and that thing will easily cut through railroad ties without losing any RPM. (Within the limits of the blade depth, of course.)

But I don’t use it for daily things. It actually is a bit too awkward for my old hands. But the sheer torque would never, ever be matched by any battery unit.

-- Paul, Tennessee, http://www.tsunamiguitars.com

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joeyinsouthaustin

1245 posts in 704 days


#10 posted 645 days ago

Don’t tell that to the chevy volt crowd…they are working very hard to match it every day.

Besides, my next cordless saws will be either solar or hydrogen fuel cell :)

P.s. I understand the power and stamina sides of the idea, just not the theory that speed plays into it. They are already generating speeds comp. to corded saws. And that many of the newer larger cordless saws far out perform the first entries into the market.. which, ironically, I use the later most because they are smaller.

-- Who is John Galt?

View dhazelton's profile

dhazelton

1173 posts in 928 days


#11 posted 645 days ago

They are trim saws. You aren’t going to rip 2X material along it’s length. They serve a purpose and mine has been extremely handy.

View Tedstor's profile

Tedstor

1369 posts in 1264 days


#12 posted 645 days ago

In my mind, noise is the only advantage of cordless circular saw. The cordless saws I’ve seen in use were half as loud as their corded competitors. I considered buying one for that fact alone. I abandoned the idea when I realized that I only use my current circular saw about twice per year. It terms of performance, the cordless saws seem to work well enough. But I only used them to cut a handful of 2×4 and 1×4 softwoods.

Of course, I doubt I’ll ever buy another cordless tool ever again. Unless I need a quieter tool or find myself working someplace with electricity issues. I never work more than 10-20ft from an AC outlet. I don’t find rechargable batteries to be any less hassle than dealing with a cord. And I have more confidence it the reliability and longevity of a corded tool. JMHO.

View nwbusa's profile

nwbusa

1016 posts in 918 days


#13 posted 645 days ago

I love cordless tools for the convenience and portability, but as others have said, they do come with limitations. I use my cordless circular saw often to break down sheet goods and it does a great job at that. You just have to pick the right jobs for the tool.

-- John, BC, Canada

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47phord

174 posts in 869 days


#14 posted 645 days ago

The reason they don’t work well is because you can’t generate enough power with a battery to cut through anything-that’s the real reason the blades are so small, an 18V motor would have a helluva time running a 71/4” 20T blade through the air let alone through a piece of wood.

View Viktor's profile

Viktor

447 posts in 2050 days


#15 posted 645 days ago

RPM and torque is irrelevant here. With proper motor and/or gear ratio you can have them anything you want and at top efficiency. The limitation here is battery energy capacity. Unlike drills, circular saws are much more energy thirsty. Ripping 2×4 might require several hundred watts. A 3Ah 18V battery will last about 5 min of continuous use with that kind of energy expenditure. As a result cordless saws are designed small and for light use.

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