Newton power

[pit202]

Hi all,

I`m thinking about a new machine , and I am thinking about something like VF3 , this machine has about 100Nm without gearbox and 330Nm with one , do I need a gearbox ? I know , that noboby knows what I am doing , I self don`t know what I`ll be doing tomorow , mostly I work in steel, so I don`t ask what a machine will be better for me , more I`m curious what can I do with a machine with 100Nm and with 330Nm , what are those machines abilities , lets compare this with a milling or planing a steel , what sizes and what depth are possible ?
Maybe power isn`t so important , maybe riggity is the border ?

many thanks ,
Piter

[gar]

080129-0938 EST USA

pit202:

Do not confuse torque and power.

If you plan to do heavy cuts below about 1200 RPM, then get the gear box. Around 1200 RPM is the usually setting, but it is changeable, for shifting the gear box.

For a motor producing 1 HP at its ouput shaft at rated speed the output torque is
T = HP * 5252 / RPM in #-ft = 5252/RPM .
If the motor power output is held constant and you add a gear reducer, then the power out of the reduce will be slightly less than the 1 HP from the motor, but the torque will be higher than at the motor shaft.

Note: most electical motors can be consider as constant torque limited vs speed because torque is proportional to current, and largely the heat losses in a motor are I*I*R. Internal power dissipation inside a motor determines its rating. A gear box or belt reducer with relatively high efficiency increases the torque but lowers the speed.

If you use a 1/16" endmill you do not need the gear box, a 3" facemill will require a gearbox.

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[Geof]

I think you need to consider rpm as well. Without the gear box you have 100Nm, (about 80lb-ft?) but at what rpm and how does the torque decrease as you go to a lower rpm? As an example when you use a face mill often your rpm is low because the diameter is larger; you want a large diameter to remove material as quickly as possible. The problem is you have two things that conflict very badly: The peak torque is at a speed of around 1100rpm I think and the torque becomes less at lower rpms, you may need the lower rpm when you are face milling steel with a large diameter cutter to keep the peripheral speed correct for the material, but the large diameter cutter needs a lot of torque to drive it because the cutting edges are a long way from the center of rotation. Just at the time you need a lot of torque your machine is giving you only a little bit.

With the gearbox I think you will find the maximum torque is at a lower rpm so already it is more suitable for using large diameter cutters, and the torque does not decrease as much as the rpm decreases.

Maybe do some experimenting with small face mills on your MiniMill. I have 1-1/2" (4cm) dia. and 2" (5cm) diameter face mills and can only use the small one with steel on the Super MiniMill. With the larger one I have to use a lower rpm and the machine does not have enough torque to take a good cut.

[gar]

080129-1040 EST USA

pit202 and Geof:

See VF-3 20 HP vector motor Speed Torque curves for both power and torque vs speed at

http://www.haascnc.com/pdf/brochure/VMCBrochure.pdf page 10 on .pdf viewer. Page 11 in the printed version. Title is More Spindle Torque.

In low gear 250 #-ft from 0 to 500 RPM, then diminishing power and torque to 1200 RPM. At 1200 RPM shift to high gear. In high gear 60 #-ft from 1200 to 1600 RPM, then slopes down to maybe 20 #-ft at 7500 RPM.

.

[Geof]

Originally Posted by gar ....In low gear 250 #-ft from 0 to 500 RPM, then diminishing power and torque to 1200 RPM. At 1200 RPM shift to high gear. In high gear 60 #-ft from 1200 to 1600 RPM, then slopes down to maybe 20 #-ft at 7500 RPM. .

What is missing from the graphs is how the torque falls off at low rpm without a gearbox; that is what I was getting at. I know it does, and drastically, because I have stalled both 10,000rpm and 7500 rpm spindles using face mills at low speed. Just for interest sake one time I even put a smooth piece of 1" stock in th spindle and gripped it by hand; at around 200 rpm as I recall, I could push the spindle load to something like 100% just with the friction from my grip, the machine was not delivering much torque at this speed.

[pit202]

true is true , I understand this theorie, but this wasn`t my point. I know that an 80mm face mill can kill my TM-1 in few milimeters in aluminium, or riggit thread M16 can get 100% of spindle, I wish to know what can Kill a 100Nm VF in milling steel what sizes and what depths are possible with this torque.

[Geof]

From the Haas website.

The TM is; 45 Nm @ 1200 rpm

The VF3 without gearbox is; 102 Nm @ 1400 rpm

The VF3 should be able to drive twice the diameter with the same rpm, depth of cut and feed as the TM, or the same diameter with twice the depth of cut and the same rpm and feed.

But it still depends on how the torque falls off at lower rpm. If the torque on the VF3 goes down quicker than the TM you might find that when you are at 700 rpm the two machines are almost the same.

[gar]

080129-1138 EST USA

pit202:

Go to
http://www.spindlemax.com/
for e-mail link. The web site does not provide much technical information.

The owner is exkenna at www.cnczone.com . You could go there and send a PM.

Maybe the question to ask is what tool will remove the most material per unit time given that the machine is a VF-3, with and without gear box, and which motor speed. Specify your material. Additionally you may want to specify a need to use a large face mill, vs faster hogging with a smaller milling tool.

Your question is more related to other factors, than HAAS, except that you need to know the HAAS specifications to intermix with the other factors.


Geof:

In the past HAAS has had better curves displaying torque vs speed than what I could currently find. With an induction type motor there will be much greater problems at very low percentage speeds than with DC motors or synchronous motors with a fixed magnetic field in the rotor.

I do not have an easy way to torque load and measure any of our machines. It would be an interesting experiment.

.

[gar]

080130-0738 EST USA

pit202:

Check out this post
http://www.cnczone.com/vb...d.php?t=150946
A reverse calculation indicates he is using about 7500 RPM. I do not know the HP or torque capability of his Fadal. Apparently he was overloading it. Also not specified is whether the 1/2" endmill was anything special. Removal rate was 23 cubic-inches/minute.

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