Fine tuning the machine.

[Derek the Admin]

I thought you guys and gals might like a little spreadsheet that can be used to fine tune the movement accuracy.

For instance, you might cut a 100x100mm square and end up with a 100.25 by 98.65 square.

This sheet allows you to type in the actual versus modeled dimension of a feature and get a corrected value for the steps per mm setting in Grbl (your machine's control firmware). You may want to run two or three test, but I find that a couple adjustments is about all you need to get within about 0.1 to 0.15mm consistently.

See attachment and feel free to share it wherever fellow CNC nerds are found.

Steps per mm adjustment.xlsx (28.79 KB)

Edit:
Don't forget to tighten the V wheels so they sit snugly against the rail and to square the machine and plumb the router for best performance.

[aforww]

Awesome! I was wondering how to go about accomplishing this awhile back.

[Derek the Admin]

Yup. It's handy for sure and really lets you dial things in.

[markwisniowski]

Coming back to the drawing board on this one! Been really busy with work and projects and would really like to fine tune the M3. I'm reading the instructions in the XL doc and it states:

X Expected Distance 100.00
X Actual Distance 99.80
Programmed X steps/mm 40.00
X Percent Error -0.20%
Corrected X steps/mm 40.080 Type in $100=40.08 in the command line to set this

Why does programmed X steps/mm = 40? What is that value?
What actually happens when you type this command "Type in $100=40.08"?

Does my gcode program (bCNC) remember these settings for all future projects?


Can't wrap my head around this

[wozzan]

I believe the "X steps/mm = 40" is the number of steps that the stepper motors use to move the drive 1mm. If you are slightly out, you need to turn the motor a fraction more or less than the "40 steps" to get exactly the right distance.
I've been using UGS, so I am not sure about bCNC, but
$100 = X-axis travel resolution, step/mm
$101 = Y-axis travel resolution, step/mm
$102 = Z-axis travel resolution, step/mm
and by updating the value it remains in UGS for future use.
Also on the CK its 200 steps/mm
You may need to check on the actual setting for bCNC as it may be different to UGS

[Derek the Admin]

That's correct on the steps, wozzan.

Also, for what it's worth these settings are stored in the Uno board itself, not in UGS or bCNC. They just read and report what is on the board.

[Bruce]

Great info Derek.
Question: You mention how to square the X gantry with the Y rails in the assembly manual, but in checking the router plumb I don't see an explanation but I'm guessing it is done with the eccentric spacer adjustment? The only way I've noticed the router out of plumb is when I surface the material with a 1" surface planing bit. Is there an easier way to check the plumb of the router?

[markwisniowski]

Thanks for the explanation everyone!

[Derek the Admin]

Oct 18, 2017 14:33:59 GMT Bruce said:

Great info Derek.
Question: You mention how to square the X gantry with the Y rails in the assembly manual, but in checking the router plumb I don't see an explanation but I'm guessing it is done with the eccentric spacer adjustment? The only way I've noticed the router out of plumb is when I surface the material with a 1" surface planing bit. Is there an easier way to check the plumb of the router?

Just use a square placed on the bed to make sure that the router body aligns with it. You won't be able to put it right against the router, but you can close one eye and see that if it aligns or not. If it's rotated about the X axis then you can loosen the X rails ever so slightly and rotate the gantry to bring the router plumb. If it's rotated about the Y then it's best to just adjust the router mount until the router is plumb.

[mrkandangi]

I ended up having to calibrate my M3 using the new app. I had to perform this a few times in order to get the resolution correct. Right now the x and y are within .003-.004" of each other. I have a couple questions:

1. Is this what is I can expect for tolerances with the M3 or can I tweak this further to get it perfect?

2. After performing this adjustment my work position will not show zero in the x and y , see image below, is this normal?




3. When jogging in x and y from machine position after issuing $H, say 10mm, the the read out in the work position does not show -10 but rather -10.01 (x) and -9.99 (y). I would imagine this is because of the calibration I performed?

Mark

[Derek the Admin]

3 or 4 thousandths is getting pretty close on the M3. I'd personally be calling it good at that point.

The "won't show zero" thing is normal. You've gone from a nice, round 40 steps per mm to something like 39.985, for instance. This makes the display math a little wonky.

The 10.01 and 9.99 thing is normal as well.

[notso]

This is a little old however should I still be tweaking my steps?
I only have 3" caliper so I used Easel and made a 50mm square and when ran the X and Y are both at 50.8
Can it do better or is this good enough? (M3)

[Derek the Admin]

It can definitely do better. Have you measured the end mill and confirmed your cam settings aren’t “leaving stock”?

[James@fireaxe]

Whats the smallest movement the motors on the CK can make?

[Derek the Admin]

0.005mm