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IndustryArena Forum > MetalWorking Machines > Uncategorised MetalWorking Machines > Recommended Spindle Power for Heavy Milling
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  1. #1
    Join Date
    May 2010
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    122

    Recommended Spindle Power for Heavy Milling

    I'm not sure what is harder to mill than steel... I'm sure there's heaps of stuff out there but assume I want to get a spindle that is able to mill some really hard stuff... what spindle wattage would I be looking at? I don't have any materials in mind at the moment, however I'm thinking more for the future... maybe I'll bump into something that is harder than steel and it would be nice to buy a spindle that will be able to handle those kinds of materials.

  2. #2
    Join Date
    Jul 2014
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    215

    Re: Recommended Spindle Power for Heavy Milling

    You can mill about anything you want with 5-10 HP. With more HP you are able to remove material faster and use bigger milling tools and perhaps have a little less vibration due to larger mass of the spindle head. All other things being equal.

    When you say heavy milling do yo mean from a commercial point of view or a home hobbiest point of view.

    For heavy commercial milling you ought to have 15-40 HP depending on how much material you need to remove and how fast.

    For a home shop 5-10 would be very nice and allow you to do about anything you wanted at slower but still respectable feed rates.

    Typical Bridgeport type manual knee mills only have about 1-3 HP and they can machine most metals and composites. The limiting factor is the rigidity of the machine. With a very rigid machine you can make the most use of the power you have because little of it is lost in vibration energy. For the home machinist they should concentrate more on making the machine they have or build very rigid since they are not likely to have much more than single phase 240 volt power. Which you can do up to about 5 HP with and have a fantastic machine for home use. Big commercial machines are likely to use 440 volt 3 phase power which is not usually offered to residential customers.

  3. #3
    Join Date
    May 2010
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    122

    Re: Recommended Spindle Power for Heavy Milling

    Thanks, yep just hobby so 5-10 ballpark it is.

  4. #4
    Join Date
    Jul 2014
    Posts
    215

    Re: Recommended Spindle Power for Heavy Milling

    Quote Originally Posted by Atomic_Sheep View Post
    Thanks, yep just hobby so 5-10 ballpark it is.
    Just for information sake. Most small hobby benchtop mills have less than 1HP. And the more robust benchtop mills have about 1-2 HP. If you had a home mill that had a nice 5 HP spindle and was pretty rigid it would be a deluxe hobby mill indeed.

  5. #5
    Join Date
    May 2010
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    122

    Re: Recommended Spindle Power for Heavy Milling

    Yer mine is about 0.4hp at the moment so needs an upgrade.

  6. #6
    Join Date
    Jul 2014
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    215

    Re: Recommended Spindle Power for Heavy Milling

    I'm in the early stages of building a manual vertical mill and I plan on using a 3 HP DC treadmill motor and controller which I can do for around 250 USD. I haven't figured out how to do 5 HP for a reasonable cost with a heavy duty motor. But there are some large RC DC motors that can do 5 HP with the right controller but I'm not sure how robust the motors would be at machining heavy steel since they are designed to be light RC airplane motors. The shafts on them are kind of small and the motor shaft can have significant back stresses on it. I just broke the motor shaft on my mini lathe cutting alloy steel at a shallow depth so I know that the motor shaft can have significant energy put into it if there is any vibration that causes backlash to the motor.

    Part of the problem is that I didn't have my ways dialed in tight enough but now I am going to have to work on those parts of the machine. It's a learning experience. I had always worked on large engine lathes that had been properly set up and I didn't have to worry about maintaining the lathe myself.

  7. #7
    Join Date
    Jan 2005
    Posts
    1943

    Re: Recommended Spindle Power for Heavy Milling

    Motor power isn't the only variable. Putting a large motor on a small machine is useless because the machine won't be stiff enough to take the cuts that the motor is capable of. If you only have 0.4hp, then you probably could get away with putting on a 1 hp motor, but more than that will require substantial stiffening of the machine to enable using the motor to full potential.

  8. #8
    Join Date
    Apr 2004
    Posts
    5728

    Re: Recommended Spindle Power for Heavy Milling

    Horsepower is a function of torque and speed. A motor can go slowly but with lots of torque; that's what you want for milling steel. Other motors, like the RC motors you mention, go very fast but have little torque. These are less useful for milling, unless you're using very small tools, which need to go faster. With a pulley cluster you should be able to get the treadmill motor to go even slower, which would give you the torque you need to mill steel with a fairly large tool, assuming your home-made frame is rigid enough for the task. Hardened steels, or alloy steels, need to be treated as special cases - you might need carbide or even diamond tooling to deal with them.
    Andrew Werby
    Website

  9. #9
    Join Date
    Jul 2014
    Posts
    215

    Re: Recommended Spindle Power for Heavy Milling

    Quote Originally Posted by awerby View Post
    Horsepower is a function of torque and speed. A motor can go slowly but with lots of torque; that's what you want for milling steel. Other motors, like the RC motors you mention, go very fast but have little torque. These are less useful for milling, unless you're using very small tools, which need to go faster. With a pulley cluster you should be able to get the treadmill motor to go even slower, which would give you the torque you need to mill steel with a fairly large tool, assuming your home-made frame is rigid enough for the task. Hardened steels, or alloy steels, need to be treated as special cases - you might need carbide or even diamond tooling to deal with them.
    Yes, this is all good information. The mill I'm building will be very stiff by home hobby standards. So I think it will be able to use most of the 3 HP motor that I am planning on. I do plan on gearing down the motor at least 3:1 or more. 10 x 10 inch column filled with EG and steel reinforcement.

    This is an older picture. I have scraped the Bridgeport type adjustable head for a stiffer CNC style and will shim the bed if necessary.

  10. #10
    Join Date
    Jul 2014
    Posts
    215

    Re: Recommended Spindle Power for Heavy Milling

    Quote Originally Posted by 109jb View Post
    Motor power isn't the only variable. Putting a large motor on a small machine is useless because the machine won't be stiff enough to take the cuts that the motor is capable of. If you only have 0.4hp, then you probably could get away with putting on a 1 hp motor, but more than that will require substantial stiffening of the machine to enable using the motor to full potential.
    Agree with all of this completely. I even dare say that the machine stiffness is more important then HP as long as you have enough for what your doing.

    Here is an updated picture of my manual mill concept using a Grizzly cross slide table. I think you could make a stiff DIY CNC mill this way to, by converting the Grizzly cross slide table. The Z axis is already well suited for CNC conversion.

    My plan is to use this manual machine to help me build my CNC machines.

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