Help calculating power please?

[Oldmanandhistoy]

Could some one point me to some information about calculating what power I have going into my cutting tool?

So far the only information I have is the motor is 350W and 240Vac I think, two mechanical speed reductions and a variable electronic speed control. It’s the X2 mill and I would like to know what power I have to calculate feeds, speeds and depth of cuts using ME Consultant 2.0.

As always any help or advice is very much appreciated,

John

[MicroMill]

I think 746 watts generally = 1 HP. So you starting off with just a shade under 1/2 hp.

The voltage is really not a factor. Of course you can calculate current drawn by the motor using the formula: I (current) = P (watts) / E (voltage). Nice to know information if you are wiring it into a breaker panel, but useless in your problem solution. Here's a handy link. http://www.the12volt.com/ohm/ohmslaw.asp

[bruno.chaparro]

Hi,

firts what do you want to cut? Steel, Aluminium, foam, wood?
second: dimension of maximum mill tool (10, 20, 40 mm)
thirth: deep of each pass (2, 3, ...10 mm)

Bruno

[gar]

070528-0920 EST USA

Oldmanandhistoy:

Do you want to measure the power going into your cut, or do you want to do a theoretical calculation of what that power is?

To measure the total power input into the work, tool, and chips measure torque applied to the chuck or collet and the spindle RPM. Then calculate the horsepower from the equation HP = T * RPM/5252 where T is in #-FT.

By measuring torque at the chuck you eliminate all losses up to that point. Windage of the chuck and part is the principal loss not eliminated.

To get the distribution of power into each of the three components - part, tool, and chips - is more difficult.

If you can not measure torque at the chuck, then you need to measure power input further back in the electromechanical path, and estimate the efficiency to get the power at the part-cutter interface.

The furthest back point is the AC power input to the motor drive. You need a wattmeter for this. Volt * current is not a real good estimator.

If you want to run experiments on relative cutting efficiency of different tools, and materials, then input wattmeter measurement would be relatively satisfactory.

If you hold speed constant then power is a good measure. If you want to make comparisons at different spindle speeds, then use energy per unit volume of material removed. Energy is the time integral of power.

.

[Oldmanandhistoy]

Hi all and thanks for replying,

I have attached an image from ME Consultant below.

I have as yet not used it in practice just learning the ropes. Looking at the picture where I have circled in red it gives you the power needed at the cutting tool (I think) to do the cut as it is set up in all the other boxes. So if I know what power is getting to the cutter I can make the necessary changes to keep power needed within the range of my spindle and machine. I think I will have to make some changes to the program to fine tune the setting to give more accurate figures but I am hoping they will be a good starting point.

John

[Oldmanandhistoy]

A quote from the help document

“HP
This value can't be changed directly.
It shows the machine power, expressed as horsepower, required to satisfy the current machining parameters.
The calculated HP value is based strictly on the material removal rate for the active material. No adjustment is made for the type of tool being used.”


John

[Oldmanandhistoy]

Sorry about the multiple posts.

First I need to know if a motor is rated 350Watts; what the actual power is coming out of the motor.
Then I can work out from the mechanical speed reduction what will be getting to the cutter.
So the only thing I need to know now is how much power is lost using electronic speed controllers?

John

[Kipper]

Originally Posted by Oldmanandhistoy Sorry about the multiple posts. First I need to know if a motor is rated 350Watts; what the actual power is coming out of the motor. Then I can work out from the mechanical speed reduction what will be getting to the cutter. So the only thing I need to know now is how much power is lost using electronic speed controllers? John

Don't forget the mechanical losses and the fact that manufacturers often quote wrong numbers. Personally I don't care about the figures and just use RPM/type of material/depth of cut/dia of tool and let Mach do the hard work then increase the speed till it cuts nice

[gar]

070528-1202 EST USA

Oldmanandhistoy:

You will never get more power out of any system than you put in. The law of conservation of energy. However, in a mechanical system you can change the mechanical advantage from input to output. Thus, you can adjust your gear ratio to get more torque, but not more power. In fact as you increase the torque output by increasing the gear ratio you will get less power output because of increased inefficiency.

If your motor is rated as 350 W of mechanical output power on a continuous basis at your ambient temperature, then that is 350/746 = 0.47 HP out of the motor. Now assume 50% to get to the actual cut and you are at about 1/4 HP.

If you want a deep cut, then gear down and feed slower. But this may not be optimum. Suppose you want to cut Rc 60 with a CBN bit, then you want a lot of heat at the cutting interface.

.

[MicroMill]

Oldmanandhistoy:

Find an AC current meter and measure you input current to the motor. Measure the actual input voltage and perform the power calculation I gave you. 80% is probably a more realistic figure to apply for a power factor. As you see, the program has already factored in the efficiency. The .8 is of course 80%. Finding a "power" meter is easier said than done. You get into peak power vs RMS power vs 3 phase vs single phase, and on and on. For your basic calculation, an AC current meter works fine. As far as calculating all the ancilliary components, the sum of all the losses of power, cannot be more than what you started with.
That program looks pretty slick.

[Oldmanandhistoy]

Thanks for the help

If anyone would like to give ME Consultant a try; you can get it here as freeware http://www.freedownloadscenter.com/B...onsultant.html


I suppose the only information I really needed was; how does an electronic speed controller affect torque?

I will go and do some searching for this particular information; I would guess it’s out there some where.

John

[Al_The_Man]

John, This may answer some of your questions as I assume you are using a Universal motor with Triac or SCR control which is tyical for these motors.
http://www.faqs.org/faqs/woodworking/motors/
Al.