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Dimensions Problem ... Help Please
« on: November 24, 2013, 06:56:03 AM »
Hello,

I have finished my DIY CNC router for wood working and I am using Mach3 software with it. But I have faced a problem which is that there is a difference in dimensions  between designed dimensions in CAM software and  executed dimensions on the machine. The difference are 8 mm increment in Y axis and 6 mm increment in X axis.

I mean that I draw a square ( width = 10.00 cm ) on CAM software ( like Artcam & Vectric Aspire ).  After finishing the job on the machine and when I measure the dimensions of engraving square, I find them are 10.8 cm ( in Y axis) and 10.6 cm ( in X axis ).
Or if I make a circle diameter 25 cm, the measured diameters after engraved are 25.9 cm ( in Y ) and 25.68 cm ( in X ).

I have used
KL-5056D Digital stepper drivers from www.automationtechnologiesinc.com
SFU1605-C7-1055 Ballscrews from www.automationtechnologiesinc.com


In mach3 settings, I have set the value of ( steps per unit ) in motor tuning as the following :
( 200 * microstep of uses drivers )* (1 / ballscrew pitch in mm) 
( 200 * 2 )* 1/5 = 80

And then I have set the axis calibration from ( alt + 6 ) as usual.
But the problem still exists.

Can any one help me ? How can I cancel this increments ?

Thanks a lot for any help..

Offline Hood

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Re: Dimensions Problem ... Help Please
« Reply #1 on: November 24, 2013, 07:41:48 AM »
I would suggest you use more than 1/2 stepping, Gecko drive say 10 is the optimum, so if you set it to that and set your steps per unit to 400 and see how you get on.


Hood
Re: Dimensions Problem ... Help Please
« Reply #2 on: November 24, 2013, 11:54:27 AM »
Thanks Hood,

Initially,  I have set it at "8" microstep . Then, I changed it to "2" to solve this error,  the error still exists. But I didn't use 10 before.
I will try that.

Offline Hood

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Re: Dimensions Problem ... Help Please
« Reply #3 on: November 24, 2013, 01:26:52 PM »
I am not sure if it will help with the actual oversize but it will make for a smoother setup which is always a good thing.

Are you sure the cutter is the correct size compared to the one yopu are programming for?
Hood
Re: Dimensions Problem ... Help Please
« Reply #4 on: November 24, 2013, 01:57:05 PM »
Yes, the used endmill bit has the same specifications that in CAM software.

What worries me is that the error increases when I increase the work dimension.
 In a small works the error be small ( about 2 or 4 mm ) and with the large works the error up to 9mm or 1 Cm with itself bit.

I set the drivers on 10 microstep now and I doing the calibration to try it.

wini

Offline Hood

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Re: Dimensions Problem ... Help Please
« Reply #5 on: November 24, 2013, 02:04:31 PM »
Something is not adding up if your oversize increases as you go bigger on part size.
Are you sure of the ballscrew pitch you have? Are you direct coupled from motor to screw?
Hood

Offline Hood

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Re: Dimensions Problem ... Help Please
« Reply #6 on: November 24, 2013, 02:06:18 PM »
BTW calibration should not be required, you should be fine with calculating, in fact it should be more accurate than calibration as that will only be as accurate as your measuring capabilities which I dont think will be as accurate as hardware.
Hood