Comparing power in different table saw types - Woodworking Talk - Woodworkers Forum
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post #1 of 10 Old 09-16-2019, 04:55 PM Thread Starter
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Comparing power in different table saw types

Hey everyone. I was hoping to get some help. I have a cheap table saw I've built into my workbench: https://www.homedepot.com/p/Skil-15-...0-02/204504286. I built it about 8 inches in and built my own fence for it. Honestly it's been pretty good for me up to this point but I'm getting more into woodworking and have been shopping around for a new saw, something a bit nicer and heavier. The biggest issue I have with my current setup is power. It gets really bogged down cutting 1" hard maple and fairly bogged down when ripping pine 2x6's. Now for the technical bits. How can I choose/compare the power I need? I read that in electrical applications, horsepower (1hp = 746 watts) is calculated based on the power INPUT to the motor, not the power out of the shaft. Using this math/logic, my cheap skil table saw would have a ~2.33hp motor. I have a hard time believing that my current saw would cut as well as a 1hp or a 1.5hp jet table saw. Is there any comparison to be made here? Do the contractor/hybrid saws put out more torque per watt? Would 1.5hp be a reasonable amount of power to cut (on occasion) 1.5" hard maple?

Side question: Will performance change if running a compatible saw on 220v instead of 110v?
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post #2 of 10 Old 09-17-2019, 10:44 AM
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The HP calculation for an induction motor is not the same as direct drive. I'm not sure how its done, may be based on torque, but I know a belt drive motor is totally different regarding power.
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Last edited by DrRobert; 09-17-2019 at 11:09 AM.
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post #3 of 10 Old 09-17-2019, 11:43 AM
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Quote:
Originally Posted by Garrett Jensen View Post
...Side question: Will performance change if running a compatible saw on 220v instead of 110v?
Hoping to get more oomph out of the same electric motor by simply changing from 120 to 240 is a myth. By doubling the voltage you cut the amperage in half (ref Ohm's Law: V*A=W). It is only if you have a motor made specifically for 240 that you will see an improvement. Example, I had a Ridgid R4512 that claims to be around 1.75HP. I used it on 120 but I think it can be rewired for 240. I believe it draws around 12 or 14 amps. It is nothing compared to the 3HP 240V motor on my new Grizzly G1023RL that also draws around the same amperage. It is because of the combination of both volts and amps.
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post #4 of 10 Old 09-17-2019, 03:22 PM
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As I see it:

HP ratings in general these days are nothing much more than numbers to compare to another number in a similar tool.

A 2 HP bench top motor will be more powerful than a 1 HP bench top motor.

Hybrid, Contractor and Panel Saws have a different style motor, which is inherently more efficient than the bench top motor so a similar HP rating of that motor will be more powerful. So a 2 HP motor will be more powerful than a 1 1/2 HP motor, etc on those types of saws.

To add to the confusion, if you convert a 2 HP electric motor driven air compressor to gas powered you will need a 5 HP gas engine.

And don't even start looking at shop vacs. 😊
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post #5 of 10 Old 09-17-2019, 10:05 PM
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Slight issue with the HP calculation; Horsepower is just a different unit for measuring power, and yes, it is equal to ~745 watts. That said, measuring power going into a motor will not tell you how much power you get at the shaft. The problem is inefficiency. No system will take in 100 units of power and give out 100 units of power, its not possible with humanities present understanding of thermodynamics. Universal motors, the kind powering your saw, generally have an efficiency rating of 50-70 percent, probably on the lower end in this particular case, so 1hp is a much more accurate rating for what youre getting at the shaft.

Problem the second is again with how horsepower is calculated. The equation is HP=(RPM*T)/5252. Where RPM is obvious and T is equal to torque. RPM is how fast something spins, torque is how hard it is to stop, and as you can see in the equation, you can raise one, lower the other and get the same number at the end.

Now, to illustrate this, your saw is rated to consume 15 amps, which should theoretically work out to 1.5hp with the inefficiency factored in, so far so good. Then you get to the blade rpm, 5000rpm. Plug that equation and you get 1.5=(5000*T)/5252, which means that torque is equal to 1.5756ftlb, assuming Wolfram Alpha did the math right because im lazy. For the same of comparison, lets use the more common 3600rpm that most induction motor saws spin their blades at. So, 1.5=(3600*T)/5252, T=2.188.

So, Tl:Dr version of all this is that yes, torque is the issue. Your saw doesnt have the torque needed to power through the cuts, which is why your saw is bogging down on heavier cuts

Also, Chickn already went through the math but switching to 220v wont make more power magically appear. The formula for wattage is W=A*V. The wattage consumed by your motor wont change, so either way your equation will look like 1500 (or whatever) = 120*A or 1500=240*A. Only thing that changes is the amperage, which could be a plus as lower amperage is healthier on the wiring,but that wont give you any more power
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post #6 of 10 Old 09-18-2019, 02:24 PM
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HP and Torque explained:
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post #7 of 10 Old 09-18-2019, 04:02 PM
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epic, gave a very good response. There is so much BS associated with consumer tools that you can't trust any of it. Sears/Craftsman stuff was notorious for their claims. All the rest of the cheap sellers followed suit. Something left out of the equations are "duty cycle." A lot of cheap tools will over heat rather quickly if required to put out their claimed power. Induction motors will be 85 to more than 90% efficient and the better ones will have a service factor of 1.1 or better. Bigger motors & 3 phase tend to be more efficient. An induction motor at idle will consume about 50% of its full load rating.
It is too bad that, in the US, 3 phase is not available to the home. It is in many European countries. For the home you can put in a phase converter if needed. Many years ago I built one from scratch that worked fine for years. Simple to build and that way you can run used 3 phase tools.

Some people will tell you to just slow your feed rate if your tool doesn't have enough power. True to a point but slower feeds will often cause excessive heating of the tool and work. I have 5 circle saws in the shop: 5, 9, 10, 15 & 15hp. All but the 5hp are 3 phase.

Depending on what you do I'd start with a 3hp cabinet saw. Much better than the "contractor" saws. Widely available used.
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post #8 of 10 Old 09-19-2019, 03:00 PM
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A lot of good info here, but #1 Make sure you blade is sharp, even carbide blades get dull, and if it is the one that came with the saw, it is probably not one of the best blades available

There is no app for experience
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post #9 of 10 Old 09-25-2019, 04:45 PM Thread Starter
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Seriously, thanks for the info guys. This really helped guide me decisions. For any future readers, I ended up upgrading to an old craftsman 113 (belt driven with cast iron top and wings) with a 1.5 hp motor. I was still worried about power, but after getting it all cleaned up and aligned I ran a piece of 5/4 hard maple through it and it cut like butter. I was able to maintain a steady feed rate without any burning which is wildly different than the skill saw. Major thanks to @epicfail48 for all the math. I'm a math oriented person so this was much appreciated! I also wasn't clear on the differences between the different motor types so thanks to everyone who helped clear that up as well!
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post #10 of 10 Old 09-25-2019, 04:49 PM
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That type of saw has been used by many of us, great bang for the buck.

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