Stupid question, but have you checked the tiny screws holding the pulleys to the motor shafts?
I had one a bit loose and my circles were not round.
sorry Ebr but after adjust it you can make perfect circle? can you make a try for me? can you make for example a perfect round circle 40mm x 40mm ?
Sure I can try. Not today, though. Time for bed on my side of the planet. 
I’ll get back to you
I did make a hole to fit a 40mm pvc pipe a couple weeks ago and it was a nice tight fit.
Those set screws and the pulley are loctited to the shaft , the motor shaft also has a D shaped shaft as well.
Giavonni,
since we are all throwing darts here i’ll step up and throw one too.
While trying to locate my x-y zero for a jig i made to hold some material, i had homed the spindle. Then I jogged it out x .9 y .9 to where the x0,y0 was for my jig. I reset the material x-y zero’s then moved the spindle out of my way using g28 position which was x-max (30) y-max(30) . Then i had the spindle return to 0 from the g28 position. I had a 60 degree v bit i was using to locate the offset and when it returned i noticed it was off just barely noticeably in the x + direction. i jogged the spindle back to g28 pos and it returned to this same location that was off from where i set it by just a tiny bit. if i re homed and reset the work zeros it did this same thing every time. i’m talking just noticeable by the eye small. I think this has to do with backlash in the system somewhere so now before i set my work position i follow this procedure - HOME , then G28 position ( Far rght hand back corner) , Then return to 0 then set my work position x-y zeros. something you might try. hope it helps out.
whats mean “using g28 position” ? sorry really im new on x-carve experience…
Lorenzo,
G28 is a reference point you can set up for your machine.
You set it up by moving the machine to the location you want the reference point to be. then in ugs on the command line you type g28.1 and press enter.
this sets your g28 position. then when you want to move the spindle out of your way you can use a command like g28 z-.5 in the command line and this will raise your z axis .5 then move to the location the spindle was when you used the g28.1 command.
I use this sometimes to get the spindle out of my way while i’m changing materials.
you can also search for g code on google and you’ll find a lot of information.
hope this helps.
If you have already adjusted your X, Y, and Z potentiometers, then you need to calibrate your steps per mm. Voltage that is too low will cause missed steps… steps per mm that are not set to an accurate value will put the spindle in places that you do not expect.
also i check all the belt and are strong tension, also the i check the screws on the pulleys and are ok.
I increse by 1 the potentiometer for x and y.
the resulta is the same, the circle are not circle but oval, difference arount it its about 0,20-0,30mm
you means check the $100 and $101 only right? or there are other adjustment that i can do?
quite near to solving now i can make round circle i cut it now 39.97mm to 40.15mm i think taht is ok no?
anyway i loose all the v-weels was all to tigh and put both $101 and $100=40.1
Yes. I am talking about the $100, $101, and $102 values. Specifically the $100 and $101 is you are not seeing perfect circles. If you haven’t measured the actual movement of the X and Y axis to check the accuracy, then the 40.1 you changed the settings to is not necessarily correct.
I use a V bit as a pointer in my spindle and measure the actual distance the axis travels with a good ruler with etched markings. For example, if I jog the axis 450mm, then the formula I use to calculate the precise setting needed is this: [450mm (the distance I specified) / 449.3mm (the actual measured distance)] x [40 (this value MUST be the current set value of $100 (for X) or $101 (for Y) at the time you send the jog command.)] In this example the setting for this axis to enable precise distance movement is 40.062
(distance you specify / actual distance traveled) x (current steps per mm setting) = new steps per mm value
In your case, if you tell the axis to move 700mm (for example), and you measure the actual distance to be 702.7mm, then you would calculate: (700/702.7) x 40.1 = 39.946. Your new setting for that axis only will be 39.946 steps per mm.
Repeat for each axis you wish to calibrate.
how can i proceed in a 500mm x-carve? i want try your suggestion this evening
and also another thing so the X and the Y value must not be the same?
Lorenzo,
calibrate using a distance for the movement that fits your machine, say 200mm.
Robert made an excellent video demonstrating the procedure.
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yes i see it and also i have a good metal ruler but really for me is impossible understand how can he see the exactly measure over 0,5mm. I can see in ther uler 10.4mm for example but for me see 10.45mm is impossible.Im searching some elctronic istrument to do this
For the 500mm X-Carve, get a nice accurate ruler that measures mm and fits on your waste board. I would suggest something like this on a budget, but the finer the mm scale the better…
http://www.homedepot.com/p/Empire-18-in-Stiff-Ruler-27318/202035334
Put a small V bit in the spindle to use as a pointer. Then place the ruler squarely along the axis you wish to calibrate. Zero the tip of the bit on the zero mark of the ruler. Issue a command to move the axis your specified distance. Use a value that will allow travel for most of the distance on that axis. In your case, choose a distance close to your maximum workspace size of 300mm. For this example I will use 250mm. Once you have moved 250mm, then get a precise measurement at the tip of the V bit. You will need to estimate the measurement if it falls between scale markings.
Let’s say you sent the command to move the X axis 250mm, but you actually measured 252.1mm. Then:
(250mm/252.1mm) x (40.1 (this is the setting you currently have for $100)) = 39.766
Issue the console command $100=39.766 and this will set $100 to your new value of 39.766. Then re-check your measurement along the axis to see how accurate your steps per mm measure. You may need to make a couple changes until the axis is truly “dialed in.” Repeat this process for the Y axis.
If you are not familiar with how to access the command console for sending gcode commands, you can use Easel or Universal GCode Sender. I assume since you changed your $100 and $101 values to 40.1 that you already know how to do this.
Also helpful to know, the GCode command to move is: G90 G0 X(value in mm). So from a console command line you would enter G90 G0 X250 to move the X axis 250mm. Change the “X” to “Y” for the Y axis.
There are a couple helpful videos posted on the forum that demonstrate this whole calibration process.
perfect and well understand i try in this way this late afternoon.
Just do your best at estimating the fraction over or under the mark. Enter your change and then measure again. If you were not accurate then it will show up in your resulting measurements. If it’s not perfect, then repeat the process until you get it just right. I had to change my settings twice until it was spot on.