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I have been building a router for a sometime and after months of building I am starting to run some gcode and start the debugging process. For now I am just using a sharpie marker connected to the spindle to draw some lines on a peice of foam to check my tool paths. My test in the picture below is drawing a body mold for a small jumbo cutaway. For the most part the test looks to be fairly correct. Anyways, at this point I need to verify if the machine is really moving where it is supposed to and check the machine accuracy. I am working if anyone has any good test gcode programs that help me verify that everything is moving as expected. Any ideas?

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Brad
Avon, OH

Brad no test programs, but I can tell you how to test it. You will need to cut actual parts now though rather than use the marker. Program for a 1" square, 3" square and 6 " square. Keep in mind tool offset etc and the cut the parts. Measure them to see if they are indeed square and correct to size. With the PC router you may have some run out in the spindle so for now you may not get exact results, but that is something you can deal with later....(kinda)! Next cut some circles and measure them to see if they are round and correct.

This will at least let you know if you are in the ball park or not. Be sure to cut these in something hard enough to hold a good edge, i.e. not foam. Mdf, or hdf or better yet some lumber that is harder than either.

Mike

What control software are you using? Is it Mach3, or something else?

Mach3 comes with the now famous "roadrunner" g-code file, which you can test. As mike mentions, it is important to just cut some parts, and also make sure circles are indeed round (mach3 has some specific settings for this). In addition, it is important to check the "repeatability" of the machine...in other words, issue a command to say move the x-axis 10 inches, and then issue the command to go back to zero...does it always stop in the same spot? This will help determine any backlash on the screws.

As such, you can also use a digital caliper, to make sure that your steps per rev are set correctly in the control software...in other words, when you tell the machine to move 5 inches, in any axis, does it in fact move 5 inches, or something else above or below?

Another item to check, is to make sure that everything is square...in other words, all axis should be at 90 Deg to each other, and square to the table. Do not worry to much if the table has some low or high spots for now...you can later surface an MDF spoil board with a large diameter surfacing bit, to make it flat. You can easily check squareness with some good machinist squares.

You can use dial calipers, and digital calipers to "dial it in" and then if you measure your backlash, there are ways of dealing with that through software (to some degree).

Let us know what other questions you might have, and we can go from there....

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-CyborgCNC
http://www.cncguitar.com
https://www.facebook.com/CncGuitar

A good check for square is bolt a piece of mdf to your table and machine the front and side edges square.

Clamp a second sheet on top of the first and repeat this procedure for the second sheet. Flip the second sheet over and line up the front edge perfectly. The sides should line up perfectly too. If not your gantry isn't square by 1/2 the outage.

When squaring the sheets you should probably take cuts in both directions to eliminate backlash errors.

Thanks for the suggestions. I am using Mach3 software so I will have to check for the test gcode file. I checked my y and z axis and they are fairly repeatable but when I jog .100" I am seeing about .101". I thought there was an area that you could calibrate but can't seem to find it. Any ideas?

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Brad
Avon, OH

Brad if you are .101 for a .1 move, you will be 1.01 for a 1 inch move and 10.1 for a 10 inch move. The errors are cumulative, and you don't want that. This can be corrected in the motor tuning....I think. It has been so long I can't remember. I know when I set my machine up on Mach 2 (yes 2) that I had to set my steps per inch at a fraction to get exact repeatability. You will likely have to do the same, but there is lots of help out there for anything Mach.

Mike

I will have to check if the effect is multiplying. I thought Mach3 had a calibration area that you would run the machine in a certain distance and then measure the distance. The difference was put into the calibration area somewhere. Not sure were I read about it but I can't seem to find this. Does anyone else know?

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Brad
Avon, OH

Brad, going from memory here, but click the settings tab and look for something called axis calibration. There's also a function called screw mapping, but I've not been able to figure out how it works. The Mach forum is usually pretty helpful, but last I checked there wasn't much about screw mapping there either. There's also a backlash compensation, should you need it.

Bob

Thanks...I will check it out and see what happens.

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Brad
Avon, OH

Yes, under axis calibration, you tell the given axis to move say 1 inch. You then actually measure how far it moved (A digital caliper here is almost a must) and then input that number. mach3 will then tell you the steps/per/rev you need to input into the motor tuning screen.

Another useful action, would be for you to move say the x-axis, and then monitor the speed on the mach3 screen while moving. if there is ANY fluctuation in the speed, it could mean that you are loosing steps, and then you need to tune the motor/computer for that NOT to happen.

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-CyborgCNC
http://www.cncguitar.com
https://www.facebook.com/CncGuitar

Here's the way I calibrate my steps.

First I will use say a 1/4" end mill.

I will jog X axis positive (important to eliminate backlash by loading the screw in a direction) and zero it. Then I will lower Z for a 0.125 depth of cut. I then use the MDI (see below) and move X axis by 4 units/inches. I raise Z and using calipers measure the distance cut. Remember to subtract the diameter of the end mill. I then go to the settings page and run calibration (see below) for 4 units. It will then move the axis and ask you how far it moved. I then put in the distance (measured) when asked that it traveled and except the new step units. I do this several times in order to fine tune the steps. Do this for all axis.

Next Time I will try and explain the method of finding backlash that I use.

Hope this helps.

Mike



MDI Screen



Settings Screen

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I'm outside looking in, just farther from the window than most.

Thanks for the help with axis calibration. I have a few belts on order that I am hoping to get tomorrow and then I can put everything back together and start calibrating. I will let you know how it comes out.

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Brad
Avon, OH