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Forum topic by mikeber posted 05-21-2020 12:54 AM 660 views 0 times favorited 17 replies Add to Favorites Watch
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mikeber

35 posts in 1629 days


05-21-2020 12:54 AM

Topic tags/keywords: question bandsaw tablesaw electric motor power rating

One issue that always baffles me are power ratings of bandsaws and tablesaws. I see some bandsaws rated at less than 1hp. Most medium sized bandsaws are 1-1/2hp. The same with table saws. Yesterday I was looking at an expensive Sawstop cabinet saw and it’s rated at 1.75hp….

The question is why so low? I have a plunge router (which can be used handheld) that is rated at 3-1/4 hp. It costs about $300 and comes with many accessories. So what’s the problem installing 3-5hp motors in bandsaws and tablesaws? Such machines, sold at above $2000 cannot be equipped with a more powerful motor? What’s the cost difference? Cannot be huge…


17 replies so far

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jerseygeorge

7 posts in 1761 days


#1 posted 05-21-2020 01:46 AM

The horsepower ratings of motors so screwy. Much of the world compares kilowatts of a motor. 1 horsepower equals 745 Watts. And amps times volts equals watts.

But on a deeper dive, industrial type motors are rated for their “continuous duty”. You can take the motor and run it at that horsepower theoretically all day long and will not exceed it’s rated temperature rise. Ie it’s a safe assumption you could take the SawStop you mention, put a stock feeder on it, and rip continuously at that horsepower.

Now – the high ratings on your routers, etc. They are mostly brush type motors and you are getting the “develops” rating. Think of “develops” as the point where the motor will burn out in a short period of time. The develops rating is not a continuous rating.

I think most of this correct, its a while since I explored this subject. I am sure others can add.

-- ... once a Force in tools...

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Jared_S

351 posts in 729 days


#2 posted 05-21-2020 11:14 AM

Because of marketing Lies.. universal motors rated in hp are mostly straight out Lies and misleading information.

120v only has so much available to do work, and at 20 amps it’s about 1.75hp in a induction motor.

View Fred Hargis's profile

Fred Hargis

6233 posts in 3263 days


#3 posted 05-21-2020 11:55 AM

When you see the accurate motor ratings (usually on the induction motors) and wonder about the low ratings (like the SS you mentioned) it’s usually to allow the tool to stay on 120V service. That way those without 240V can still buy those tools….240V is typically needed on anything rated 2 HP+.

-- Our village hasn't lost it's idiot, he was elected to congress.

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theart

192 posts in 1324 days


#4 posted 05-21-2020 12:57 PM

The very idea of rating electric tool motors in horsepower is backwards and pointless. A 120v motor is going to generate a fairly constant amount of torque (which depends on motor type and how many amps it’s drawing), with power then being a function of how fast it’s spinning. The motor in a direct drive table saw is spinning at around 3,000-5,000rpm. In a router it’s 25,000. So, even the same universal motor drawing the same current is going to look like it has “more power” in the router because it’s wired to turn faster.

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jamsomito

547 posts in 1195 days


#5 posted 05-21-2020 01:23 PM

Without getting into the weeds on math, speed, volts, amps, power factor, slip, etc… A simple response would be induction motors (TS, BS, etc) are rated for continuous power and universal motors (router, lunchbox planers, etc) are rated for peak power. If you run something at peak power continuously it will burn out. It’s a different metric – generally speaking a little universal motor in a can cannot put out the power a big induction motor can with the “same” rating.

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clagwell

246 posts in 562 days


#6 posted 05-21-2020 03:14 PM

In the US the only spec I’m aware of that covers motor ratings is NEMA MG-1. It’s an industry standard. There is no law that says it has to be followed. It’s use is market driven. It applies when there is a contract between seller and purchaser that requires it.

What we see as hobbyists is that the induction motors that we can buy directly are usually labeled to NEMA standard while universal motors aren’t. It’s market forces that that cause that. MG-1 applies equally to both induction and universal motors. There’s just no market demand for consumer products to be specified that way.

For you spec mavens, note that Horsepower is not a measured parameter in MG-1; it’s a test condition, along with applied voltage and frequency. Measured and calculated parameters are RPM, current, power factor, efficiency, and temperature rise.

-- Dave, Tippecanoe County, IN --- Is there a corollary to Beranek.s Law that applies to dust collection?

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therealSteveN

5746 posts in 1343 days


#7 posted 05-21-2020 03:35 PM

Interesting thread.

Motor basics in a 3 minute read. Who knew Schwarz was so smart…...

https://www.popularwoodworking.com/techniques/what_you_must_know_about_motors1/

-- Think safe, be safe

View mikeber's profile

mikeber

35 posts in 1629 days


#8 posted 05-21-2020 07:43 PM

Thanks everyone for the response. I do understand that there’s a difference between the type of motor used for continues work, vs those used in tools like routers.

However one question still remains: what’s the difference in cost (to the manufacturer) between a machine with 1hp motor and 2hp? Why are they so reluctant to equip all their machinery with higher rated motors? We should remember that unlike a router such machines are sold for $2000 or more. Why still bother with inadequate power?

View Aj2's profile

Aj2

3071 posts in 2567 days


#9 posted 05-21-2020 07:56 PM

Wouldn’t it be a waste of materials and power to the consumer if a machine was equipped with a motor bigger then it needs to be.
Bigger is not always better.

-- Aj

View clagwell's profile

clagwell

246 posts in 562 days


#10 posted 05-21-2020 08:30 PM



However one question still remains: what’s the difference in cost (to the manufacturer) between a machine with 1hp motor and 2hp?
- mikeber

The cost difference is huge, at least in terms of lost sales. A 240V machine has a small fraction of the market potential of a 120V tool. It’s all marketing. Anyone who goes to the trouble of installing 240V power in their shop wants top of the line equipment. There’s not much market for a cheap tool that requires 240V.

-- Dave, Tippecanoe County, IN --- Is there a corollary to Beranek.s Law that applies to dust collection?

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mikeber

35 posts in 1629 days


#11 posted 05-21-2020 09:41 PM


Wouldn’t it be a waste of materials and power to the consumer if a machine was equipped with a motor bigger then it needs to be.
Bigger is not always better.
- Aj2

No it won’t. The common problem is with tools that bog down when performing their task. For example – someone on another forum just complained that his tablesaw (rated at 1.75hp) bogs down when ripping 2.5” maple. Another couldn’t resaw a 6” oak board on his 1hp bandsaw. You can read many similar issues. However, I didn’t read complains such as “my tablesaw is rated at 3hp, but it could perform the job with only 2hp…what a waste!
To solve problems with underperforming machinery, the usual recommendations are: “try feeding the wood at slower rate” or “is your blade perfectly sharp”? or “try a thin kerf blade”…. But with more powerful motors such issues won’t be a problem.

View CharlesA's profile

CharlesA

3430 posts in 2567 days


#12 posted 05-21-2020 11:43 PM

A good 1.75 motor is pretty much at the limit of what 120v circuits will handle. So more power means 240 v circuits. For most part f us, that means $200+ investment in the electrical circuit before you consider the additional coast of the saw. For most of us, that means we get the 1.75. If you really want to be blown away, check out the 6 hp Shop Vacs running on 120!

-- "Man is the only animal which devours his own, for I can apply no milder term to the general prey of the rich on the poor." ~Thomas Jefferson

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runswithscissors

3097 posts in 2794 days


#13 posted 05-22-2020 01:16 AM

It may be worth noting that Europe, Australia, and much of the world employs 220-240 voltage for everything—even your electric toothbrush. By sticking with the 120 volt standard, we have imposed unnecessary limitations on ourselves.

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

View Aj2's profile

Aj2

3071 posts in 2567 days


#14 posted 05-22-2020 01:59 AM

Wouldn’t it be a waste of materials and power to the consumer if a machine was equipped with a motor bigger then it needs to be.
Bigger is not always better.
- Aj2

No it won’t. The common problem is with tools that bog down when performing their task. For example – someone on another forum just complained that his tablesaw (rated at 1.75hp) bogs down when ripping 2.5” maple. Another couldn’t resaw a 6” oak board on his 1hp bandsaw. You can read many similar issues. However, I didn’t read complains such as “my tablesaw is rated at 3hp, but it could perform the job with only 2hp…what a waste!
To solve problems with underperforming machinery, the usual recommendations are: “try feeding the wood at slower rate” or “is your blade perfectly sharp”? or “try a thin kerf blade”…. But with more powerful motors such issues won’t be a problem.

- mikeber

I see what you mean could it be they are expecting too much from the class of machinery they bought. My tablesaw has a 2hp Dayton motor I’ve not felt it lacking. It also has a 12 inch blade so I can cut 4 inches tall.
I think it’s better for a persons expectation to change.

-- Aj

View AndyJ1s's profile

AndyJ1s

323 posts in 524 days


#15 posted 05-22-2020 04:02 AM



It may be worth noting that Europe, Australia, and much of the world employs 220-240 voltage for everything—even your electric toothbrush. By sticking with the 120 volt standard, we have imposed unnecessary limitations on ourselves.

- runswithscissors

Yes it would be better. Even better if it were three phase, instead of single phase power. Three phase motors are cheaper and more reliable than same HP & RPM single phase motors, and they do not exhibit torque ripple.

As more and more electronics come with dual-voltage power supplies, maybe it won’t be so expensive to switch over to 240V single phase, but there’s an awful lot of existing last-foot wiring and receptacles to replace too. And so many appliances that don’t have power supplies, and will not run on 240VAC.

The end state would be better, but the transition would be painful.

-- Andy - Arlington TX

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