Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Mr.Chips on September 02, 2008, 04:53:55 PM
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Using Mach3
Am in the process of fine tuning my CNC and have hit a snag while setting my “Steps Per Unit” in “Axis Calibration”.
I have been air cutting and using a pen to draw the various Gcode files, everything was repeating and running smoothly except that everything was half size. Sounds like I need to adjust the Steps Per Unit. My drivers are set to "Full Step" And in "Motor Tuning" the Steps per Unit was showing 2000. I am using a 10 TPI Acme so this sounds correct. ? ? ?
I went into the Settings Tab and selected “Steps Per Unit” in “Axis Calibration” then the X axis, deleted the 0 and input 2”. Ran that and measured and it was 1”, input that figure and saved it. Did the same I think for the Z axis.
Went back to the Motor Tuning the Steps per Unit was still showing 2000. Hmmmm Thought this should be a different number now after what I did above.
Tried a X and Y axis manual jog and the stepper makes about one revolution and stops, and buzzes if I hold the jog button. It does this in both directions. It does this every time I press X jog.
Tried Z axis manual jog and it moves a few stepper rev. but only about 1 turn in the down direction every time I hit jog.
In the Diag screen each axis moves toward home slowly as long as i hold the button.
As I said everything was OK before I tried the “Steps Per Unit” in “Axis Calibration” utility.
Any Ideas on how to fix this?
Thanks
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The buzzing is undoubtedly the stepper stalling because you're trying to step too fast. You doubled the steps/unit, but didn't change the max speed, so the step rate during jog was doubled, and the motors can't handle it. First, reduce the max speed on the motor tuning dialog to a low number, like 10IPM. Then check the jog operation. I think you'll find it works fine, just slow. While you're there, check the move distance is correct. Once both of those are OK, then play with max speed and acceleration, and set them low enough that the motors don't stall.
But, sounds to me like you're really in half-step mode, not full step. Either that, or you have a 2:1 mechanical reduction you've left out of the calculation. For 10-pitch screws, full-step 200PPR motors, steps/unit *will* be 2000 in inch mode.
Regards,
Ray L.
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The buzzing is undoubtedly the stepper stalling because you're trying to step too fast. You doubled the steps/unit, but didn't change the max speed, so the step rate during jog was doubled, and the motors can't handle it. First, reduce the max speed on the motor tuning dialog to a low number, like 10IPM. Then check the jog operation. I think you'll find it works fine, just slow. While you're there, check the move distance is correct. Once both of those are OK, then play with max speed and acceleration, and set them low enough that the motors don't stall.
But, sounds to me like you're really in half-step mode, not full step. Either that, or you have a 2:1 mechanical reduction you've left out of the calculation. For 10-pitch screws, full-step 200PPR motors, steps/unit *will* be 2000 in inch mode.
Regards,
Ray L.
Thanks Ray,
I slowed all the axis IPM from 40 (I had ran at 40 for days without any stalling) to 10. And they all moved normal but naturally slowly.
I am in full step. And steps set to 2000 per in. I input 2" and it moved 2"
I have a fixed gantry machine.
With the steppers turned off the amount of force required to turn both the X and Y acme threads by hand is about the same. However on the Y axis it will now JOG at 100 IPM no problem, but the X axis stalls at over 40 IPM. If I run the X axis at 30 and jog it is impossible to stall it by pushing on the axis as it moves, but set it to 40 and I can push on it an dstall it easily.
That is strange all I did was slow the axis down to 10 ran all the axis, now i can run the Y at 100+ without any hesitation????
What should the acelleration and G force be? Or is this a factor?
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Acceleration is a function of the motors, the machine, the drivers, etc., etc., and will be different for every axis, and every machine. X will generally be quite different from Y, because it's fighting a higher mass and hence inertia. Start low, and work your way up, checking at each step that it will reliably rapid to the correct position. If you go too far, you'll find you lose position randomly. There's really little to be gained by going to max acceleration except for bragging rights, so I wouldn't push it.
You may also be hitting mid-band resonance. Are you using Geckos? If so, you should adjust the resonance compensation. It will be different for the two axes.
Regards,
Ray L.
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Acceleration is a function of the motors, the machine, the drivers, etc., etc., and will be different for every axis, and every machine. X will generally be quite different from Y, because it's fighting a higher mass and hence inertia. Start low, and work your way up, checking at each step that it will reliably rapid to the correct position. If you go too far, you'll find you lose position randomly. There's really little to be gained by going to max acceleration except for bragging rights, so I wouldn't push it.
You may also be hitting mid-band resonance. Are you using Geckos? If so, you should adjust the resonance compensation. It will be different for the two axes.
Regards,
Ray L.
How will I know when I'm hitting mid-band resonance? I am not using Geckos but would a damper work, I have been reading about this on the CNCZone
I would post a photo but an new and don't know how.
Background: 200 in/oz steppers, Probotix isolated BOB and drivers 24V PS.
My homemade CNC is a fixed gantry, with a 24" X 24" work area, using 1/2" 10 TPI, 1 start acme screws, the X axis is running on 1" dia fully supported lin brgs, It is moving the Z axis and a wood router. My Y axis is running on gas pipe with roller bearings on the top and side of the pipe, the pipe is supported under the X axis travel area. I am a wood hobbyist and this was the most rigid machine I could make and have the lightest loads on the steppers. I have linear bearings and ball screws for all axis for my next machine and it will be a movable gantry with each side screw driven. That is if I ever get the bugs out of this one and enough confidence to start cutting parts.
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Nice looking machine! Mid-band resonance occurs at moderate speeds, and when you hit it, motor torque falls drastically. One way to deal with it (sometimes) is to just power your way through it - accelerate fast enough that you get through it, to higher RPM, before the motor has a chance to stall. But, that isn't always practical. Mechanical dampers are another way to deal with it, and can be quite effective. Micro-stepping can also help, as it reduced vibration. From what you've described, I do think this is likely your problem.
Regards,
Ray L.
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MrChips,
The power supply min amperage should be at least equal to the sum of all the amps required for x,y,& z
along with proper voltage output. That said:
Would set the X and Y at the lower speed of the two. Think I am correct in that Mach will default to the lower speed of the two axis's when doing circular moves. Reliable movements are more important than speed. If there are minor differences in the acclerations between two axis set the x & y at the lower of the two.
As the stepper speed increases the torque goes down. It is a trade off, faster speed with less torque or slower speed with more torque. So if you are cutting some wood and say you hit a knot you'll need some power to get thru it. Power is
a function of speed and torque. So you run at a feed rate which leaves some reserve while cutting.
As far as acceleration goes, start low, increasing by 2x until your motors skip, then set at say 60% of that acceleration value, then tweek up or down to refine.
Just some thoughts ,
RICH
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Nice looking machine! Mid-band resonance occurs at moderate speeds, and when you hit it, motor torque falls drastically. One way to deal with it (sometimes) is to just power your way through it - accelerate fast enough that you get through it, to higher RPM, before the motor has a chance to stall. But, that isn't always practical. Mechanical dampers are another way to deal with it, and can be quite effective. Micro-stepping can also help, as it reduced vibration. From what you've described, I do think this is likely your problem.
Regards,
Ray L.
I have changed the step from full to 1/8 step and changed my step units to 32,000. (With my Probotix drivers I can go down to 1/16 step would this be considered Micro-stepping) On a command of 2" it moves about 2 1/4" I am afraid to go into the “Steps Per Unit” in “Axis Calibration” because this is where I ran into trouble last time. I can just test and measure until I get in shape.
When I moved from full to 1/8 step I could no longer run the Y axis at 100 had to drop to I think 60. Why would that be? I also lowered the acceleration to 20. Also in the Motor Tuning page is Step and Dir Pulse, it says 1-5, currently it is on 0, as it was the default, what should this be set to? There are so many options in Mach 3 and I tried watching the videos, but seems some are missing, I printed the manual but what I would like to see is a typical setup for a machine of a given machine type.
I know high speed is just bragging rights, but I was kind of using speed as a proof of good alignment and i would like to have a not too slow jog speed.
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MrChips,
The power supply min amperage should be at least equal to the sum of all the amps required for x,y,& z
along with proper voltage output. That said:
Would set the X and Y at the lower speed of the two. Think I am correct in that Mach will default to the lower speed of the two axis's when doing circular moves. Reliable movements are more important than speed. If there are minor differences in the acclerations between two axis set the x & y at the lower of the two.
As the stepper speed increases the torque goes down. It is a trade off, faster speed with less torque or slower speed with more torque. So if you are cutting some wood and say you hit a knot you'll need some power to get thru it. Power is
a function of speed and torque. So you run at a feed rate which leaves some reserve while cutting.
As far as acceleration goes, start low, increasing by 2x until your motors skip, then set at say 60% of that acceleration value, then tweek up or down to refine.
Just some thoughts ,
RICH
When you say "until your motors skip", you mean loose steps don't you? What would be a good test for this? Cutting MDF (because of the consistant composition) at say 1/4" deep with a 1/4" 2 flute bit, and I'm guessing 20 IMP with my setup.
Thanks Rich
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When I moved from full to 1/8 step I could no longer run the Y axis at 100 had to drop to I think 60. Why would that be?
Because Mach3 can't output steps fast enough, unless you change to a faster kernel speed.
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When I moved from full to 1/8 step I could no longer run the Y axis at 100 had to drop to I think 60. Why would that be?
Because Mach3 can't output steps fast enough, unless you change to a faster kernel speed.
Where does it show the kernel speed? And what are my options?
Hey Gerry you really get around. Guess that happens when you are knowledgeable and in demand
Thanks
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Sorry about that,.... loose steps.
Nothing magical, just try different materials and cutting depths and see what works. Try the 1/4" dia x 1/4 deep at say 10 ipm, then 20
or whatever, won't take too long before you know what your machinie can do.
Before you make test cuts, get your motor tuning done.
RICH
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1/8 step should be 16,000 steps, btw. 8 x 200 x 10
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1/8 step should be 16,000 steps, btw. 8 x 200 x 10
I am so Confused Stupid or Both.
Start settings:
1/8 step at 32,000 steps settings X1 draws a line 1" long
I go into Motor Tuning and change the steps/unit to 16,000 for all 3 axis, saving each axis.
Now i get:
1/8 step at 16,000 steps settings X1 draws a line 1" long
What it wrong? At 16,000 steps/unit shouldnt the line be 1/2" long?????
What am I doing wrong???
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On a direct drive 10tpi lead screw with 200 step per rev steppers set to 1/8 microstepping 16000 steps per inch is the correct setting, no idea how you got 32000 to work.
I set my steps per by calculating it and then tested at low acceleration and speed, then did the top speed and acceleration to suit, my mill is set way below what it's able to run but I'd rather have it cutting right and take a little longer about rapids than loose steps.
Mine is a mill though and doesn't have the travel your router has, however I bet it weighs a bit more :)
Steve
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I am setting the steps in "Motor Tuning, Steps Per".
Is this the correct place to define the steps?
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That's the right place, make sure you hit the ENTER key whenever you change it though.
RC
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I always hit the enter as well as the SAVE SETTINGS button. Had trouble early on with settings not "Taking".
RC
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I always hit the enter as well as the SAVE SETTINGS button. Had trouble early on with settings not "Taking".
RC
YES hitting "Enter" is the trick!!!
Now I have another question now that the "Motor Tuning, Steps Per" is working.
I wrote GCode to draw a 1" square. Results below.
Why is the 32,000 run way off size and a rectangle. I was expecting it to be 2" Any ideas. I know this is off topic, and I know how to draw a 1" square now, but it doesn't make sense.
At 32,000 it draws a square that is 1.026" X 1.104 Not square
At 16,000 it draws a square that is 0.986"
At 8,000 it draws a square that is 0.489"
At 4,000 it draws a square that is 0.224"
THanks
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The square could be out due to backlash in one or both axis, when you generated/wrote the g-code did you offset for half the cutter diameter?
Kristin
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Now I have another question now that the "Motor Tuning, Steps Per" is working.
I wrote GCode to draw a 1" square. Results below.
Why is the 32,000 run way off size and a rectangle. I was expecting it to be 2" Any ideas. I know this is off topic, and I know how to draw a 1" square now, but it doesn't make sense.
At 32,000 it draws a square that is 1.026" X 1.104 Not square
At 16,000 it draws a square that is 0.986"
At 8,000 it draws a square that is 0.489"
At 4,000 it draws a square that is 0.224"
THanks
Something is very wrong with the 32,000 setting. However, since it's the wrong setting anyway, I wouldn't worry about it. 16,000 is the correct setting, but it's off a little, so you need to adjust the number a little. If 16000 = .986, then 1" should be about 16,227 steps. Try that and see what you get.
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You could also run the "Axis Calibration" feature on the Settings page.
(Hello Jim P. ::))
RC
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Problem is, his error is not constant, even if we ignore the 32000 setting. If it were, he should be seeing 0.986, 0.493 and 0.247. Something is very wrong there. As he reduces the steps/unit, the error, as a percentage, is increasing!
:(
Regards,
Ray L.
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MrChips,
Change it to the 16227 as Ger 21 suggests
.986/1=16000/X its a ratio to find how much to increase your steps
.986X=16000
X=16000/.986 = 16227 that should very close and if not calculate it again ( probably not linear)
( Another way is to make a longer travel if you can measure it accurately, but the inch travel should surfice)
RICH
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I am not too concerned about the actual size of the squares that I ran at 4,000, 8,0000, 16,000 because I was using a ball point pen that was loosely floating inside a piece of copper pipe with a weight on top, and it had quite a bit of wobble which in itself will make the size of the squares inaccurate. When I actually put a known size bit in and cut wood that will be the proof of the pudding. And yes I will cut the largest square that will fit on my table. Then run ¼ table size squares in each corner, this should be a good test.
The 4,000, 8,0000, 16,000 were the same in the X and Y direction, however when I upped the speed to 32,000 it made a rectangle, one of the posters said that to run at 32,000 you needed a PC with a high GHZ rate, I really think that was the problem when I tried to run at 32,000. Anyway around 16,000 is the ballpark I need to be in not 32,000.
I really want to avoid using the Settings utility where Mach 3 takes the number you actually measure after a fixed move and it sets the step rate. This utility has caused me many problems, the last time I used it the steppers would not jog more than a couple of revolutions when holding the job button down. Another member also cautioned me about the utility. When it is time to set the steps I will do it by trial and error until I find the magic number for my machine.
Today I installed the table hold down track and sacrifice table and made a crude dust shoe, and cut my first piece of wood with a ¼” Zip bit and a “V” shaped router bit. Things worked as expected.
Tomorrow I start to work on my dust collector, dust, especially fine dust in the 2 3 micron range is a killer.
Thank you all again, I had all my questions answered.
Mr Chips
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"When it is time to set the steps I will do it by trial and error until I find the magic number for my machine" - That is a horrible idea! There is one, and only one, correct number, and it is determiend by the hardware, and should be precisely known. If it isn't, then *something* is wrong, and just finding a number that seems to work will not give you a reliable, properly operating machine. The proper setting for your machine should be 16,000. If that doesn't work right, then figure out why!
Regards,
Ray L.
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OVERLOADED - THANKS FOR INTRODUCING ME -
Mr Chips - I fail to see what your problem is, and how you can possibly put all these diffrent numbers into "steps per unit" and hope to get anywhere.
Steps per unit, and we are talking of Config/Motor Tuning - bottom left hand corner, is a finite fixed number. It is not something that can be measured, guessed at, adjusted or anything else. We have covered this many time n this forum - and we still get the same old arguments popping up.
Steps per unit is asking you to say how many pulses the computer has to put out to move the axis by 1 inch (if in inches) or 1mm (if in millimeters). You must calculate this.
The thing most people seem to have difficulty with is the pitch of the leadscrew. I converted my old manual machine and here the pitch was 1/10th inch, i.e. 10 turns per inch - easy. You must find out accurately what the pitch of your leadscrew is. If you don't have a leadscrew - say a belt drive, it still comes down to the same thing - how many turns of the cog wheel produces 1 inch movement. If your leadscrew is in millimeters, then I would set up the whole machine in millimeters, it is easier.
Most motors are 1.8 degree per step these days, so therefore 200 pulses are required to turn them one rev. All drivers do microsteps , and 8 microsteps are the norm - so settle for 8, it gives a good combination of smoothness and power, and is well within the capabilities of the standard P.C. Multiply 8 by 200 = 1,600 steps per 1 rev of the motor.
If you have any gearing between the motor shaft and the leadscrew shaft, then this is added now - mine is 3 to 1 (steel cutting lathe) - so the equation is now 200 x 8 x 3 = 4,800. The only thing left is the leadscrew - I said mine is 10 turns per inch - therefore my result was 200 x 8 x 3 x 10 = 48,000 steps per inch.
This is a fixed number - it cannot be altered - particularly not to adjust your supposed shortfalls - the fault will lie elsewhere.
This is entered in Config/Motor tuning/(select the axis) - bottom left hand corner. Make sure after you have entered it you press the "Save Axis Setting" before you leave that axis, otherwise the figures will revert to the previous entries. Whilst on this page I would also set the speed at a modest 4 inches per minute and acceleration at 0.5. You want accuracy at the moment - not speed.
The way to check this for accuracy, if you must, is not to muck about with squares. Simply move you axis using the MDI line.
Make sure backlash compensation is OFF
With the table central on the machine, zero the axis DRO. Type in G0 X1 and the axis will move 1 inch. Do not try and measure this - it was only to get rid of backlash (and do not believe anybody who says they don't have backlash). Set up your measuring equipment and zero it (I use digital calipers) and then type in G0 X2. The axis will move another inch - and this you should measure and it should be 1 inch. (Give or take a couple of thous either way - because accurate measuring is impossible unless you have really specialist equipment.
If the answer is not 1 inch, then you have a problem - and you will have to come back to us.
While you have the measuring set up, the type in G0 X1, the axis will return 1 inch - only it won't - and if you check your measurement then the shortfall is backlash - make a note of it.
Repeat with the other axis.
You can then enter the backlash into Config/Backlash and switch on Backlash compensation. Set speed at say 50%. Backlash compensation sounds very disconcerting when you first use it, but it is accurate - and adds that little bit extra on each change of direction to take up any movement in the gears etc as the get their shoulders down to pushing the other way.
You could now try your 1 inch square.
You can now try motor tuning !
Gradually increase the speed on each axis. (Dont forget to save axis settings each time) You will reach a point where the motors stall as they start up - back off from this point to your last safe setting. You can try the same with acceleration. Don't try and get to the moon - I need accuracy - not super fast speed.
My motors, at first would not get past 4 inches per minute - 220Ncm motors, wired in series at 24 volts. I wired them in parallel and changed to Gecko drivers - and I can get up to 40 inches per minute (although I have reduced this for accuracy - they keep stalling on a couple of tight spots on my lathe bed) and my latest improvement is using 36 volts for the drivers.
Setting up the "step per" and speed and acceleration and backlash is an exact science - not something you can find by trial and error.
Sorry about the big post - but I had to get that diatribe off my chest (again)
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Jim,
Thanks for taking the time to explain accurately and in detail. It is always best not to assume that I know anything, in this case you are correct. He He
I am using Acme 1 start ½” 10 TPI, direct drive. Stepper motors are 200 oz/in with a 24V PS.
My configuration is a fixed gantry so I don’t have to push a big heavy gantry around.
Thanks for the detailed step by step instructions for eliminating backlash and getting accurate results on distance traveled.
When you say “Gradually increase the speed on each axis.” Do you mean air cutting or cutting the typical material that I will be using?
Regards
Hager (AKA Mr.Chips)
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Here are the test procedure and results from measuring the X and Y axis. As you can see all the results from moving 1” came out to be 0.996” on all three tests that were ran on each axis. I am using ½” 10 TPI 1 start Acme rod. All three axis were cut from one piece of rod. This is not a high precision piece of iron.
After setup I did not have to touch the indicator, it came back to zero every time.
I will try and attach the spreadsheet with test details.
What do you think of the test results?
What would be my next step?
Regards
Hager
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Hey I'm ready to cut but want to drill a hole through my work table.
When you use the Wizards in Mach 3 such as circle cut and hole drill, do you position the Z axis bit down and just kiss the surface to be cut then press the Zero axis button and then Press Start??
Thanks ???
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Hey I'm ready to cut but want to drill a hole through my work table.
When you use the Wizards in Mach 3 such as circle cut and hole drill, do you position the Z axis bit down and just kiss the surface to be cut then press the Zero axis button and then Press Start??
Thanks ???
Yes thats exactly what you do :) The top of the workpiece is set as zero and all cuts are negative numbers.
Hood
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Thank you Thank you Thank you. Two Gold Stars for You!
I looked it up in the Mach 3 mill manual and it talked about running the Wizards but not this very important point.
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Here are the test procedure and results from measuring the X and Y axis. As you can see all the results from moving 1” came out to be 0.996” on all three tests that were ran on each axis. I am using ½” 10 TPI 1 start Acme rod. All three axis were cut from one piece of rod. This is not a high precision piece of iron.
After setup I did not have to touch the indicator, it came back to zero every time.
I will try and attach the spreadsheet with test details.
What do you think of the test results?
What would be my next step?
Regards
Hager
I would be suspicious of the accuracy of whatever indicator you're measuring. Either that, or your screws are not reall exactly 10TPI. Do the measurements again, using a different indicator. If you get the same result, then you're screws are off, and the solution is to simply re-calculate steps/inch based on 10 turns = 0.996 inches. If you get a different result, (hopefully 1.000"), then you know you have at least one lousy indicator.
Regards,
Ray L.