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Any Way to CheckTorque on Lead Screw.

Any Way to CheckTorque on Lead Screw.

Postby jeff » Thu Apr 01, 2010 9:09 pm

Was wondering if there was any way that anyone knew of to check how much force it takes to turn my lead screws? I have googled this and cant find nothing on it ( maybe I am not wording it right). Not really important but just like to learn things. I thought of maybe using a torque wrench only in reverse fashion, say setting it to 1 pound then turning the screw then so on till the screw turns with out clicking. I know this wouldnt be to accurate. Anyone care to school me? I have purchased the 425 oz motor and I am100% positive that my lead screws wont require that much torque. Just curious??

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Any Way to CheckTorque on Lead Screw.

Postby keltic88 » Thu Apr 01, 2010 9:37 pm

I don't know if this is exactly what you need, but there are some calculators on this page:
http://www.cncroutersource.com/calculators-and-charts.html
I'm thinking of the Forces of Acceleration, Friction, and, External (inch) calculator near the bottom.

Hope it helps & cheers,
Red

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Any Way to CheckTorque on Lead Screw.

Postby jeff » Fri Apr 02, 2010 3:33 am

Thanks

Jeff

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Any Way to CheckTorque on Lead Screw.

Postby PHoodDaniel » Fri Apr 02, 2010 5:52 am

Torque is the force applied at one unit of measurement from the center of the shaft to turn the shaft. For example, with the oz-inch unit of measurement, it will take ?? ounces to start turning the shaft when the force is applied at one inch from the center of the shaft.

Remember that this is not considering static coefficient, but this may not be important in your quest for the torque measurement.

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Re: Any Way to CheckTorque on Lead Screw.

Postby woodenduck » Sun Jun 20, 2010 11:43 pm

This is my first post on this forum, but I felt it a good opportunity to get my feet wet, and probably put my foot in my mouth.

The stepper motors used in our systems do not really have a "holding torque value. This is mainly due to being an "open loop servo" and not a "closed loop servo". The difference is the positioning feedback that would normally return to be compared with the target position and the current position, as pulling the rotation of the motor to check the static torque value will take the servo out of the target position. With open servos, there is no feedback to compare the positions to, so the holding torque is a matter of the microstepping factor chosen when setting up the drivers. The lower value of microstepping...the lower the torque value.

With closed loop servos, we used to tale a inch-pound torque wrench and turn the screw until either the servo tripped out because of excessive following error, or we got a reading of the breakaway torgue value. On smaller milling machines the value was less than 25 inch pounds normally to pull the servo back into position. The more force applied to take the servo out of position, the more current applied to the motor to bring it back. Like I mentioned before...it is possible to exceed the excess (following) error and trip out the servo.

The microstepping motors will consume more current and have less torgue with the microstepping set to smaller values, also. This is normal, because of more pulses/second for higher resolution.

So, getting back to your original question, the torque value of a micro-stepping motor with no feedback for a closed loop, if positioning is an issue with NEMA 23 then go with a NEMA 34 motor and a more powerful driver.
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Re: Any Way to CheckTorque on Lead Screw.

Postby crawlerlogger » Fri Jul 09, 2010 3:02 pm

I would say that if you could control the current going to the motor, you could turn the current limit down until it can just barely move forward. Then disconnect the motor from the machine, using the same current limit setting and measure the maximum torque the motor can produce at that current.

It would be interesting to know how much torque is really required to traverse an axis at different speeds, whether it is cutting or not, whether you are using a threaded rod, acme screw, different backlash nuts, or ballscrews.
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Re: Any Way to CheckTorque on Lead Screw.

Postby PHoodDaniel » Thu Jul 15, 2010 5:05 am

Don't forget that the torque is generally related to the amount of current that the driver will allow the motor to draw. The top speed is generally related to the voltage and is proportional to the current. Make sure that you have sufficient voltage and current to allow the motors to get to the speed that you need.
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Re: Any Way to CheckTorque on Lead Screw.

Postby robd » Thu Sep 23, 2010 9:52 pm

Yes, there is a way to check the amount of torque on a leadscrew. Use a Torq-O-Meter (snap-on brand analog torque gage) in the inlb, 1/4" drive version. A needle is provided on the gage display that will capture the maximum torque. To measure "break-away" torque, place the gage at the end of the lead screw and slowly turn until the shaft begins to move. This is will provide the amount of force required to overcome the mass moment of inertia plus static friction. Make a second measurement by watching the gage while the shaft is being rotated to determing the amount of force required during motion. btw, the stepping motor should be de-coupled during your measurements...if that wasn't obvious from the start? Also, keep in mind, the speed of the table ralates to acceleration and the force required to turn the leadscrew from static through acceleration is never constant...F=M*a (Force equals mass times acceleration), i.e. if you know the mass of the gantry and the speed then you can determine the force required to achieve the result. hope this helps.
Rob
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