# Thread: Torque for Spindle Motor

1. ## Torque for Spindle Motor

I have been looking around at Servos Motor to use as a spindle motor... What kind of torque (oz/in) would i be looking at to run 12mm (1/2) inch cutter comfortably in aluminum, brass, steel and so on. Found some BLDC servos that run to 5000RPM no problem.

2. 5000 RPM is SLOW for machining aluminum.
The torque you need for machining steel is quite substantial.

Assuming you plan to gear the motor properly to make best use of available torque, healthy cuts in steel with a 1/2 cutter will need at least a few KW.

Matt

3. Something like a 1:2 up to 1:2.5 ratio will be used to get higher speeds... which will decrease the torque by a factor as well

4. You have to decide for yourself what "running comfortably" is.

Milling Horsepower Calculator

For aluminum, especially with smaller cutters, your ideal speed will be 20k or more. For steel you are looking at around 1-2k RPM.

Most knee mills have a low and high range with the low range about 50-500 RPM with lots of torque and the high range being 500-4000 RPM or so.

You MUST have torque or you cannot cut steel. Aluminum will still cut fine at slower speeds, just will take longer than it has to.

The rigidity of your machine and the size of the axis components will dictate to some degree how much power your spindle can handle.

Matt

• The answer to your question is somewhere between 0.1 and 200 foot-pounds. It's kinda like asking "How big an engine do I need for a car?". There is no good answer with so little information provided.

First question is what machine are you running on?? Then figure out what materials you plan to cut, what tooling you plan to use, and what kind of removal rates are you expecting. THAT will determine how much power you can actually make use of, and what type, and size, motor makes the most sense. If you plan to drill 1" holes in stainless steel, then you'll need a big motor with lots of torque at the low end. But if your machine is an X2, you have to get used to the fact that you simply won't be able to do it at all. On the other hand, if you will be using small cutters in aluminum, then having high speed will be far more useful, and a lot of torque won't be required. Putting an over-sized spindle motor on a machine can be a recipe for serious personal injury.

Regards,
Ray L.

• Originally Posted by HimyKabibble
The answer to your question is somewhere between 0.1 and 200 foot-pounds. It's kinda like asking "How big an engine do I need for a car?". There is no good answer with so little information provided.

First question is what machine are you running on?? Then figure out what materials you plan to cut, what tooling you plan to use, and what kind of removal rates are you expecting. THAT will determine how much power you can actually make use of, and what type, and size, motor makes the most sense. If you plan to drill 1" holes in stainless steel, then you'll need a big motor with lots of torque at the low end. But if your machine is an X2, you have to get used to the fact that you simply won't be able to do it at all. On the other hand, if you will be using small cutters in aluminum, then having high speed will be far more useful, and a lot of torque won't be required. Putting an over-sized spindle motor on a machine can be a recipe for serious personal injury.

Regards,
Ray L.
If you maybe read my first post again, i am pretty much saying what i want to do... up to 12mm tool cutting aluminium... The machine shouldn't really matter (in reality it does but that wasn't my question)... I am asking what torque i should have, if it is a 5ton machine or a small one the force on the cutter will be the same, if the machine is ridged or not has nothing to do with torque. What feeds i can run the machine at yes i can understand that can have something to do with it lets say max is 500ipm...

Yes i understand that putting a oversize (powered) spindle motor can result in personal injury (again that wasn't my question), but thank you for pointing it out, as everyone who cuts metal should be careful and wear eye protection don't put your hands in it when the machine is running, and yes i did learn that in school.

• Whether the machine is rigid or not has EVERYTHING to do with torque! That is what determines how much torque you can actually make use of. A rigid machine can take MUCH more aggressive cuts, with the same tool, than a flexible machine. So the amount of torque you can actually USE with a 1/2" endmill on an X2 is radically different from the torque you can actually use on a knee mill. On my knee mill, I can cut 1/2" wide, 1/2" deep at close to 20IPM. On an X2, you'd likely not be able to go any more than MAYBE 0.025-0.050" deep at that width, so sizing the motor to do the 1/2" deep cut will be a waste of money.

Now, I am assuming, from your signature, that you are looking for a new motor for your G0704? If so, then you're unlikely to be able to make use of more than maybe 1 to 1.5HP under any conditions.

Since Torque(in ft-lbs) = HP / 5252, you need to decide how much torque you need, at what RPM to do what you want to be able do, in terms of MRR, by deciding the width and depth of cut, feedrate, and tool and work materials you need to be able to handle, keeping in mind that it will be the machines rigidity that ultimately determines what MRR you actually CAN achieve on any particular material. Optimizing capability will require several gear ratios, as any given cut in steel requires ~4-5X the power required to make that same cut in aluminum. If you optimize for steel, you'll have a machine with lots of low-RPM torque (achieved through gearing) but it will likely be near useless for cutting aluminum, and vice-versa. There will be a LOT of compromises involved, and only you can make those compromises.

Regards,
Ray L.

• Thank you for this information, i will be mostly 99% aluminium and brass... not so much steel for that i will go on a real CNC a Haas that i have access too... Thank you again for the info.

• This video by Hoss is a 1/2" end mill run by a 600 watt motor in aluminum. Looks good enough to me.

http://www.youtube.com/watch?v=iXG8idjegDg&feature=player_embedded]G0704 Aluminum Hoggin music - YouTube

• ## 200W Motor with 5.4:1 gearbox

Hi

I'm considering running a 200W EC 4 Pole Maxon Motor with a Maxon GP 22HP 370686 5.4:1 reduction gearbox. By my calculations I will get 0.6Nm of torque with that gearbox. I'm happy to run with small (6mm max) cutters but I want to cut Aluminium do you think it will work?

Kind Regards

• ## 600w motor can do that??

Thanks for posting the video 109jb.

I am new to this and i am building my own cnc machine.

I am really surprised that 600w spindle motor could do that. Reading from the different post i came away with the impression that I could not do any thing useful with less than say a nominal 2hp motor etc.

Thanks for showing that rigidity counts!

Can i make the following assumption from the video seeing that it was cutting at 2500rpm that:

600w motor with drive train efficiency of say 80% but has a say 2:1 drive thereby giving 600w*.8*2=960w at the spindle with the motor spining at 5000rpm.

This is a simplistic computation (sorry I dont know much about these things nor the measure of these things)

Is that a realistic assumption? if so then i dont have to kill myself trying to find a small enough 2hp motor and still fitting a belt reduction drive to make power at spindle at 3.2hp based on the same assumption (2hp*0.8*2)

I will be cutting mostly nonferrous metal 95% of the time with some mild steel etc. but most of all i like big cuts because i hate waiting. Had enough of taking ginger cuts with my sherline which now i want to move up from to a nice machine.

appreciate any comments.

Cheers
fgc

• damn it I almost got suckered into posting in an old thread! oh wait..

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