Calibration Help

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Calibration Help

Postby Schifty1 » Thu May 03, 2018 6:19 pm

HI Support,
I am a very confused newbee to CNC machining and am trying to setup my DIY machine. It has the following “parameters”:
1. I am using the UC400ETH controller, it’s working fine.
2. Using Std. NEMA23 steppers with direct coupling to the lead screw
3. Lead screw is standard 1605 with a 5mm pitch (5 turns/inch)
4. I am using DM 542H drivers on the steppers. They are set to 128 microsteps
5. Your software calculates and puts 10152 in the steps per unit box. This makes the machine “sing” a high note. Obviously, the wrong value.
6. Putting 1000 in the steps per unit box speeds up the machine and increases the distance traveled by ~ 5 times.
My questions are:
1. It appears that I am using the WRONG microstep number What should I change it to???? How is this determined??
2. None of these adjustments changes the x/y/z position display numbers. How can I make the position readout display in inches/mm and not units???
Thanks in advance for your help and understanding in teaching a novice CNC’er.
Regards Jeff
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Re: Calibration Help

Postby beefy » Thu May 03, 2018 8:03 pm

To give an example:

My stepper motor is 200 step/rev.
Stepper drive is 10 microsteps.

200 x 10 = 2000 step pulses / rev from UCCNC

My leadscrew is also 5mm pitch, so 2000 step pulses cause 1 revolution, which causes a linear movement of 5mm

Therefore steps/mm is simply 2000 divided by 5mm = 400 steps/mm.

You have not stated what steps/rev your stepper motor is but let's assume it's 200 steps/rev.

200 x 128 microsteps = 25,600 step pulses for one motor revolution which causes a linear motion of 5mm

Divide 25,600 by 5mm to get 1mm worth of steps = 5120 step pulses per mm.

Anyone please feel free to confirm my calulations. Just got out of bed and need to rush out to work.
beefy
 
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Re: Calibration Help

Postby Schifty1 » Thu May 03, 2018 10:18 pm

HI Beefy,
Thanks for the quick reply.
Did those calculations and also came up with the 5120 number. When I put that in the "steps/unit" spot, the machine quickly goes to a location and then has a high pitch whine for a bit before settling at the location.
The real issue is, I don't think I should be using 128 microsteps, but don't know what to change it to, question 1.
Also you did not address question 2, the issue of the readout reading in inches or mm instead of units.
Thanks Jeff
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Re: Calibration Help

Postby ger21 » Thu May 03, 2018 10:32 pm

Do you want the machine to be set up in mm's, or inches? You need to choose one or the other. UCCNC will always say "units", as units can be either inches or mm's, depending on how you set it up.

Set the microsteps to 2000.

If you want the machine to be set u p in mm's, then use 400 steps/unit.
If you want it set up in inches, then enter 10,160 steps/unit.

The high pitched squealing is your motors stalling.
Lower the acceleration and velocity until it stops stalling.
Gerry
UCCNC 2017 Screenset - http://www.thecncwoodworker.com/2017.html
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Re: Calibration Help

Postby beefy » Fri May 04, 2018 4:07 am

Hi Gerry,

could I just confirm that what you meant is set the microsteps to 10 so that with a 200 step/rev motor, UCCNC needs to output 2000 step pulses to make the motor turn 1 revolution. Just so the OP doesn't get the wrong message and goes looking for a microstep setting of 2000 on his drive LOL.

Schifty,

when I was first learning, it was recommended to set the microsteps to 10, and there's not much advantage in going higher than this.

I don't know the motor theory behind it but microstepping basically "splits" the normal single step movement into 10 smaller movements. Thus you effectively get more resolution.

Now if I've got this right, then firstly there's not as much torque capability with microstepping, and secondly the resolution increase is at the cost of accuracy per microstep, i.e. if the normal single step distance is not perfectly divided into 10 equal lengths.

I believe my Gecko drives actually "morph" during operation from single stepping to microstepping and back as needed, but their maximum microstep amount is 10.

And as Gerry said about the acceleration/deceleration and max velocity. Through testing, find out what the "breaking points" are then back off a safety margin. Be aware that if you have any tight spots on your machine and you haven't tested at those points, your machine may run fine until it hits a tight spot then the motor(s) stall. The best solution of course is to find and sort out any tight spots.
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Re: Calibration Help

Postby A_Camera » Fri May 04, 2018 7:03 am

Schifty1 wrote:1. It appears that I am using the WRONG microstep number What should I change it to???? How is this determined??


The higher the microstep the lower the torque. In a CNC you want very high torque, so 128 microstep is just too high. A CNC is very nosy by nature, especially when cutting real material, not just air, so there is no benefit of using high microstepping values, quite the opposite. There is also no benefit of high microstepping regarding the resolution. Your machine is never going to get that accurate for many reasons, so it is not realistic to believe that just because you have high microstepping you'll be able to mill with higher accuracy. Set microstepping to 10, that is high enough for smooth run and will provide you with good enough torque, assuming you have motors and voltage/current for the speed and torque needed.

Schifty1 wrote:2. None of these adjustments changes the x/y/z position display numbers. How can I make the position readout display in inches/mm and not units???

The machine has no idea about the units you are using. It is not displaying mm or in, it is simply unitless. You have to decide which units you are using, can't mix units, and once you have decided you will have to imagine the mm or in after the digits displayed. It is important that you are consistent in your mindset, if you decide for inches then EVERYTHING must be set for inches, speed, acceleration as well, so you may need to do some basic math, manually converting between units to get it right.

BTW, your screws are 1605 which means 16mm diameter and 5mm pitch, which means 5mm ( 0.1968503937 in ) move in one 360 degree turn. That is NOT 5 turns per inch but 5.08 turns. In a CNC accuracy of units used for calculations is important if you are interested in good work results.
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Re: Calibration Help

Postby ger21 » Fri May 04, 2018 10:41 am

beefy wrote:Hi Gerry,

could I just confirm that what you meant is set the microsteps to 10 so that with a 200 step/rev motor, UCCNC needs to output 2000 step pulses to make the motor turn 1 revolution. Just so the OP doesn't get the wrong message and goes looking for a microstep setting of 2000 on his drive LOL.


Yes, 10 microsteps. A lot of chinese drives seem to list the steps/rev, rather than the microstep amount, so a setting of 2000 on those drives would be 10 microsteps.
Gerry
UCCNC 2017 Screenset - http://www.thecncwoodworker.com/2017.html
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Re: Calibration Help

Postby Schifty1 » Fri May 04, 2018 4:02 pm

HI All,
Thanks very much for the information.
I will adjust the microstep value to 10, and then do the calibration steps. This will take a few days since I have to disassemble the machine to get at the stepper drivers.
I understand about choosing one measurement system and sticking with it.
The thing I am still not clear on is the readout. How do you adjust it so that a movement of 1.0000" (from a zero) shows as 1.0000??
Again, THANKS for your quick responses and help.
Regards Jeff
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Re: Calibration Help

Postby beefy » Fri May 04, 2018 8:17 pm

Schifty1 wrote:The thing I am still not clear on is the readout. How do you adjust it so that a movement of 1.0000" (from a zero) shows as 1.0000??
Regards Jeff


When your steps/unit are set correctly, your DROs will automatically show exactly how far the axis moved.
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Re: Calibration Help

Postby Schifty1 » Wed May 16, 2018 7:23 pm

Hi All,
I just wanted to thank you for your help and support.
My machine is up, running and calibrated.......
Now on to building my first project.

Regards Jeff
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