sizing motor questions

[Goldhunter_2]

sorry if this is partly a double post form one of my other threads but there are so many forums over here I never know if I am in the right section and just saw this one with direct support

quick history; I have a old kempsmith #4 mill that has been converted to vertical it works fine for what I do now but want to convert it to CNC for other projects and I'm having my first problems of many I am sure trying to size my stepper and/or servo motors

Ok I used the formula in the Gecko FAQ section (someone posted a link for me thanks) and I think I must have done my math wrong or the assumed IPM of 120 is just to much to ask for a big machine like I have, I am not really sure now. I'll put my math below if someone sees a error please point it out to me. I lowered the one IPM to 90 and still seems high RPM/watts . What are everyone else's large mills normally running IPM? 120 IPM is allot faster then I could every turn by hand but I assumed that was the average for CNC since it was shown in gecko's formula....... I know I should know better then to assume anything but I did it anyway

My table side to side has a original 6" wheel (3" form center) but on my in & out , up & down they use a home made arm that is 10"diameter (5" form center to handle)

(up/down) 10lbs is 160oz x 5" movement arm = 800 in-oz of torque
10 TPI x 90 IPM = 900 RPM 800 in-oz x 900 RPM/1351 = 532.938 watts

(side to side) 10lbs is 160oz x 3" movement arm = 480 in-oz of torque
4 TPI x 120 IPM = 480 RPM 480 in-oz x 480 RPM/1351 = 170.54 watts

(in & out) 10lbs is 160oz x 5" movement arm = 800 in-oz of torque
5 TPI x 120 IPM = 600 RPM 800 in-oz x 600 RPM/1351 = 355.2923 watts

Is my math wrong? Is my IPM just to high? or does it look right and I just need to throw some gears into the equations ?

[judleroy]

I would look in to something like this http://www.kelinginc.net/CNC34ServoMotorPackage.html and use a 3-1 timing pulley to the screw. Are you using ballscrews? Why are you calculating the oz-in needed off a moment arm when the screw will be direct drivin without the moment arm? Do you have a way to eliminate backlash in the screws? Do you have a link to info on the machine and pics of the vertical head setup? It would help people to know what your dealing with and what issues you need to overcome.
Judleroy

[Goldhunter_2]

judleroy,
I'll attach a picture of my machine (don't laugh I keep it on the trailer so I can move it out of the garage when I have another big project to work on , my indoor space is very limited) I don't use the old Horizontal shafts for anything as you can tell it isn't pretty but it is what I have . I only have a 1.5 hp motor though I ave thought about putting a larger one on there if I ever started doing more steel instead of aluminum

Originally Posted by Judleroy I would look in to something like this http://www.kelinginc.net/CNC34ServoMotorPackage.html and use a 3-1 timing pulley to the screw

so gearing maybe what i want I had planed a 1:1 gear to connect so changing to a 2 or 3 to one ratio is easy

Originally Posted by Judleroy Are you using ballscrews?

I am trying to use the standard screws in the machine ideally I am wanting to change as few of parts as possible

Originally Posted by Judleroy Why are you calculating the oz-in needed off a moment arm when the screw will be direct drivin without the moment arm?

well for lack of a better reason I assumed I had to........ I assumed the motor needed to provide at least the same amount of in-oz torque as I do with a handle weather it is direct drive or geared .........is that assumption wrong?

Originally Posted by Judleroy Do you have a way to eliminate backlash in the screws?

Honestly I am still trying to figure out the proper size stepper or servo motors for my conversion and I have not given backlash much consideration yet it has never been a problem for me using the mill manually and I don't know if the CNC increase backlash or what I could do to prevent it but I am open to suggestions

[Goldhunter_2]

Can anyone tell me what a slow, a average and a fast IPM is for a mill?

[Goldhunter_2]

I know its Sunday and should wait for a answer But figured I would rephrase my question a little

Is there a limit to how slow the CNC can control the movement? or does that create a whole new problem?

The first time around I used the 120 TPI in the Gecko FAQ I assumed that was supposed to be average I have since decide that must be a excessively fast TPI so I timed myself manual turning the cranks and this is what I got (much faster then I expected)

Manual turning:

side to side 60 sec timer = 86 turns per minute & 22" max table movement

up & down 60 sec timer = 79 turns per minute & 8" max table movement
(with head on)

in & out 30 sec timer = 30 turns per 1/2 minute & 6.5" max table movement

Automated Formula at manual speeds: (I'd be happy)

up & down 10lbs is 160 oz x 5" movement arm = 800 in-oz of torque
10 TPI x 8.6 IPM = 86 RPM 800 in-oz x 86 RPM /1351 = 50.925 watts

side to side 10lbs is 160 oz x 3" movement arm = 480 in-oz of torque
4 TPI x 19.75 IPM = 79 RPM 480 in-oz x 79 RPM /1351 = 28.0680 watts

in & out 10lbs is 160 oz x 5" movement arm = 800 in-oz of torque
5 TPI x 6 IPM = 30 RPM 800 in-oz x 30 RPM /1351 = 17.7646 watts

Automated Formula at 3 times manual speeds:

up & down 10lbs is 160 oz x 5" movement arm = 800 in-oz of torque
10 TPI x 25 IPM = 250 RPM 800 in-oz x 250 RPM /1351 = 148.03849 watts

side to side 10lbs is 160 oz x 3" movement arm = 480 in-oz of torque
4 TPI x 60 IPM = 240 RPM 480 in-oz x 240 RPM /1351 = 85.27 watts

in & out 10lbs is 160 oz x 5" movement arm = 800 in-oz of torque
5 TPI x 18 IPM = 90 RPM 800 in-oz x 90 RPM /1351 = 53.2938 watts


with these numbers to me it looks like the project just became much more affordable I could even use direct drive coupler if it wasn't for waning to keep manual operation for one specific type project and needing the handle to still fit with out removing the motor

Big question is can the CNC operate at such a slow speed? if not what is the slowest IPM speed?