Saturday, 9 June 2018

How to calibrate your CNC machine - episode 213

This video is a natural sucessor to the previous one on squaring your machine.
If you do not calibrate your machine then noting you make will be the right size. The larger you make an item the larger the sizing error will be. Depending on what you make with your CNC the lack of calibration may or may not be an issue. If all you do is cut 3D models then any sizing error will go unnoticed but if you are cutting inlays then the penalty for an inaccurate machine is parts that do not fit as they should. Fortunately there is a simple way to fix this problem. 
Mach3 and UCCNC have built in calibration that allows you to check real world movement against the calculated movement and then they calculate new steps per unit values automatically for you.


Click to watch

 Calculations
The calculations can be a bit daunting and to make things easy for you I have created a spreadsheet you can download that will calculate everything for you.

 http://bit.ly/2JFs4Yk

Only the figures in red can be changed.
While the Leadscrew part of the spreadsheet is straight forward please read the Notes section at the end of the Rack & Pinion calculation to select the correct value to enter into your machine.
If you find an error please let me know and iI will correct it ASAP.

Assumptions
Unless you are using precision components it is likely that you will see errors in the real world measurements and just because you are using the same components in on various parts of the machine doesn't mean that they will give the same result. This is especially true of Rack and Pinion. My X & Y are identical but the calibrated values are different. Only slightly but different none the less.

Sanity
While it is nice to get everything perfect there are limits to how perfect you can get things using rulers and pointed sticks. I do not recomend using a dial to set the X & Y axis unless your machine is very small indeed. The larger the measured distance the more accurate your final result will be on a large axis. The error reduces as the item you cut becomes smaller.Measuring over a large distance take into account any non linear error in your leadscrew or rack.
Remember that this is a hobby machine and do not take this to extremes.

Making the pointed stick
If you didn't see the previous video I have put a link below to take you to making the pointed stick I used for calibration Quick and easy to do.

https://youtu.be/lU0iZKajpoo?t=3m11s

Square your machine.
If you haven't already done so then I recomend you watch my last video on squaring the X & Y axis on your machine. Unless you do both the calibration and squaring your machine will not cut properly. You can conbine both processes and have the whole lot done in under an hour.

I hope you have found this useful and I will catch you next time.
Feel free to leave a comment either here or in the video comment section.
I always enjoy hearing from viewers.

Cheers
Peter