Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: native34 on August 20, 2007, 06:04:47 PM
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I am having a problem with my Z axiz stalling. I just converted it to ball screw from the manual feed cnc. I didn't have any problems with the old setup as far as the axiz diving into metal without stalling but since the conversion i can't seem to get it to feed into the metal without stalling
My motor is a Sanyo Denki 720oz in motor 12-300VDC 6.0A with a 20 tooth gear on the motor and a 33 tooth gear on the ballscrew i have the steps per set at 16500 which is giving me the correct accuracy i just lost all sorts of torque what can i do to get this back
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What is the drive and what do you have for the current setting on the drive?
Thanks
Brian
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My Drives are Gecko G202 and i have the current set for the motor which is 6A the resistor that it calls for is 285K ohms but they don't make a 285K ohms resistor so i used the next closest which is 270K ohms
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I can't believe that no one has any answers to this problem
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Sorry Native,
Give us more details about what you had before and what you have now. Is the only thing you have changed recently is the ballscrew or the whole way the z is driven? Do you have any before pics? Give us a pic of the whole machine so we can get a better idea of your setup. What voltage are you running the motor at now?
Brett
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My setup before was i had the same gears going to the fine feed the motor had 20 tooth the fine Z feed had 33 tooth 1.65:1 reduction ratio. I was able to drive down into metal under 20 IPM until the cows came home with that setup but my overall goal is to convert everything to ball screw better tolerances.My powersupply is 60VDC. So i started with the Z axis i made a ballscrew setup like the one similar to Jeff Davis at http://homecnc.info i used the same gears 20 tooth on the motor and 33 tooth on the screw 1.65:1 gear reduction which is the same gears as on my x and y axis. Now when i drive the Z axis down it will cut into the metal but it will only go in a few thousandths before stalling and chattering. I will try to get some pictures when i get home from work. The only thing i can think is that there is enough resistance coming from the original return spring in the Z axis to stop the motor when diving into metal i will have to check this when i get home
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Was it the same motor before?
Brett
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Yes i used the same Motor Sanyo Denki 720oz in 6A stepper i see on the Tormach Website that they use 640 oz in motors direct drive and they have plenty of torque i just can't figure out why i have such little torque with a good sized motor
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WHat were the threads per inch on the old screw vs the new screw
Double and triple check that the drive is properly set up to output 6amps, measure it to verify it.
Double check the motor wiring for correct polarities
With the power off does the screw turn easy throughout the movement
(;-) TP
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The motor wiring and output is the same as it has alway been as i never touched these areas just the screw and pulleys. The Screw leads on the old setup is ".1" and the screw lead on the ball screw is ".2"
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OK, that helps a lot. You have half the torque you use to have.
Brett
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Plunging into aluminum at close to 20 ipm is pretty fast, I try to plunge at half the speed I cut at, and for a non flood coolant machine you are working it, must be a pretty rigid machine. But, you now have half the thrust you had with a .1" pitch leadscrew, the ballscrew being .2" pitch, this is a large difference I'd say, and the source of your problem.
Dave.
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Sorry Brett, I should have refreshed before posting, you got there before I did!
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NP Dave, thanks for helping.
Brett
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How can i fix this problem now that we know it is from the ball screw pitch being different than acme lead screw. Right now the reduction rate is 1.65:1 do i need to reduce it even more say 2:1 or 3:1. Thank you everyone that has been helping me with this problem
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My setup before was i had the same gears going to the fine feed
Were you driving the fine feed before and direct driving now? If so, we have to do some more math. If not, to get the same torque you will need to gear it 3.3-1.
Brett
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Yes i was driving the fine feed before with the same gear reduction that i'm using now 1.65:1 20 tooth on motor 33 tooth on fine feed screw. How do i figure this out. I consider myself to be very mechanically inclined but i am not very mathematically inclined.
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OK, you have to figure out how many revoloutions the motor had to make before to move the z any determined distance. 1/2 inch, 2 inches, no matter. We can figure it out form there. If you were driving the fine feed before and only driving a ball screw now, you will need to know the reduction of the fine feed. You can figure this out. I have sent you a personal message.
Brett