Re: [CAD_CAM_EDM_DRO] Re: Declining motor torque with lower voltage.

Polaraligned wrote:

>
>
>
>>If you need 1000 Pounds of linear force (cutting force + friction +
>>acceleration)
>>then 1000 *0.0318 = 31.8 In-Lb, or 508 In-Oz. That would presumably be
>>the PEAK torque requirement for X and Y on a mill. But, it could be
>>close to this
>>as the CONTINUOUS torque on the knee, unless you had a counterbalance
>>system.
>>
>>In the above examlple, if you had a 250 Oz-In peak torque motor, then
>>you'd want a
>>2:1 belt reduction ratio, at the minimum.
>>
>>Jon
>>
>>
>
>So Jon, what your are saying is that I could direct couple my 600
>oz-in (peak) servo's and they would produce 1000+ lbs of linear force
>on my Bridgeport. And 1000 lbs is a good value to be at for the
>X and Y axis. I would also then get 240 ipm rapids.
>Am I correct? Everyone seems to be using a lot more power to the
>table than this.
>
>

Well, it depends. First, the lack of torque is very rarely going to
cause a stall
during a cut, unless the motors are really weak. What it means is you can't
deliver extreme accelerations to the table, so corners may get rounded off a
bit. Is that a big concern? It totally depends on the workpieces
you'll be making.

I've got some pieces here where I could see this effect :
http://jelinux.pico-systems.com/artwork.html

But, that's about the only place I've found it to show up. Those are
programmed
as hard right-angle turns. And, this is on a Bridgeport with a 9x31"
table, and 1/8 Hp
motors which give about 4.6 In-Lb continuous, and I'm guessing about 18
In-Lb
peak. That is a bit less than 300 In-Oz peak! I will note that I have
snapped off
a 3/8" end mill in the collet like it was a balsa stick, and the servo
amps didn't even
trip! (That was while setting up, with the spindle off.) I can get 100
IPM rapid feed
with no problem, and if I had a little more power supply voltage, I
could do 120 IPM
with a bit of reserve margin.

This performance is plenty for me, for a home shop that does some commercial
manufacturing. Now, if you insist on being able to make a sharp
right-angle corner
at 300 IPM with a radius of .01", you are going to need a LOT more
power, and
probably 2" or larger ballscrews.

Jon