4th Axis Calibration

I have my 4th axis up and running and can jog it both directions.
Now I have a question I have searched for on google but cannot locate.
When I calibrate the standard linear directions on the x,y,z I use a precision ruler. How do I get the rotary axis to do the same so I can get it to rotate precisely?

Disclosure - I havent tried a 4th axis myself yet.

Since the 4th axis is a rotary a step/degree is the parameter to use.
Calculate the step per rotation (360deg) then do a 10 and 100 revolution test to see accumulated difference.

I never used one either, but I’m thinking about it. If this is a lathe turning thing, I’d turn a 1" diameter cylinder and then measure the circumference by 3.1416 ( pi) with a tape measure or piece of paper with a printed scale on it. That should work out to 3.1416" or the metric equivalent. Printers can print pretty accurately. A piece of packing tape on both sides will reinforce the now flexible ruler. Adjust your steps per as you do linearly.

Are you asking about getting the rotation angles to be correct, or are you asking about assuring that the rotation axis is exactly parallel to the X and perpendicular to the Y and Z ? Or perhaps how to zero off of the center of the A axis?

I assume you are meaning if it is rotating the correct degrees. I put a pencil mark on a cylinder in my chuck…tell the axis to rotate 360 degrees…check my mark…adjust steps as necessary.

I just did this a few times until it was dialed in.

Put in a small v-bit to help see if the mark is lined up.

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What I am trying to do is calibrate the rotation. If I ask it to rotate 360 then it should do that perfectly with the size of the stock I have in there. I have never seen any calibration tool for doing this and no online source suggests how to do this.
I use a machinists ruler for the standard xy axis but I do not have a flexible ruler for the rotary. :confused:

Place a V-bit pointing at your back plate disk, command a 360deg rotation and see if the display stop short or beyond the start point. Dial that in, then repeat a 10revolution test and recalculate if needed. Try a 100.
Finally try several back and fort 10rev tests to see how the system perform.

You dont need a ruler at all :slight_smile:

Just found out that the job I attempt to send to Mach3 causes the chuck to rotate 3 times when its given a 360 degree command.
Trying to figure out what is wrong. :confused:

You can fix this using Mach Settings. This is likely due to Mach thinking that your stepper has a different number of steps per rotation than it actually does or there may be gearing in your axis (mine has reduction gearing) and Mach is not set the same way.

If you have a licensed copy of Mach, I hear their tech support is quite helpful.

I do have a licence copy and they claimed I had a cracked version. :confused:
I am not sure what other proof they need. I took a screen shot of my copy.
I have not heard back and you cannot call them by phone as I do not have the newer version.

I sure hope to hear back soon.

I wonder if you changed the settings to 1/3 of what it is now whether that would do it.

This video isn’t any help as its showing linear axis and not rotary.

I did what this guy did and even used his excel calculator.

I haven’t messed with my mach settings in years but I do know you calculate a number by 200 x TPI in there. If you divided that TPI setting by 1/3, I wonder if that would do it?

I didn’t do anything with TPI as I would have to take off the cover to see the teeth.
My 4th axis is a 1:6 gear reduction.
I used the spreadsheet from the author of the video I posted.
Using the same method in that video is what I did.

I’m talking about the motor tuning section. Threads per inch. If you have a 10 tpi lead screw, the number would be twice a 5 start lead screw. Scroll down to the motor tuning section and look at the screen shot of motor tuning.


There is no lead screw.
This is not a linear axis nor a worm gear driven axis.

The 4th axis is a motor with a belt and 2 gears. There is no TPI. No worm gear or lead screw.
Didn’t you even look at the video I posted? It does not show any lead screw or worm gear.

I didn’t look at the video because I know what a 4th axis looks like :slight_smile:

OK watching the video.

You’ll notice he talks about that in the video at about 1 min 30 seconds in. Steps per degree.

From an ebay ad:

MACH3 setup instructions: 1 degree required Pulse
The formula is: 360 / subdivision stepping angle * Drive * Transmission ratio / 360 = MACH3 Pulse

Now in the video he said his ratio is 2:1. He uses the number 8.88 steps per degree. I wonder if yours should be 26.54 in that spot?

So if you use my logic. 200 steps per rev. x 6 reduction ratio x 8 microstepping=9600 total steps per revolution of 4th axis.

9600 total steps /360 degrees per revolution= 26.666 steps per degree

Our set-up is the same…I will check the settings on my mach3 tomorrow when I get home from work and post it.

I followed that tutorial in the video.
I took in account the ratio and yet 26.54 was put in the Steps per in motor tuning.
The issue is that when I run a job the value A300 goes over a single revolution. (spins around over 3 times)
It should not go that far around. It should fall short of a full rotation.
If I put in 71 in the set steps per rev. Then it will turn one full rotation.

Thanks Erik.