Testing and tuning OF for accuracy

Thanks Alex, much appreciated

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Excellent suggestion Alex - never occurred to me to shim the router. I was focusing on the router plate.

@TMToronto - I will run more tests for tonight. When I mentioned backlash earlier, I should have noted I was getting highly repeatable results with the machine returning to the same position, but I did not measure it beyond eyeballing the position. And I learned that precision is for measuring systems - the appropriate term for motion systems is repeatability. TMYK :wink:



I ran a quick pass in X and Y after getting set up, but to be honest, not to the extent of @cyberreefguru Though now I might. lol. I used a 22 degree engraving bit. Checking for tram on the router I used a small machinist square, and a block of granite. I shimmed the granite to level in X and Y. Inserted an endmill (old one) upside down, and used the square against the endmill and a flashlight. I can just barley see any light in the X, and the Y is as spot on as I can see.
So not the precision ( or probably the proper) way of doing things, but in a pinch. lol.


@TMToronto et al -

I did some more testing over the last 2 days, and unfortunately I don’t have anything exciting to post as a result. I ran a number of tests sending the machine various distances at various speeds and returning it to the same known location. I tested the return location using a dial gauge. Each time the machine returned to the same location within a fraction of 0.001 - the resolution of my gauge. I’m not convinced the little ‘slip’ I saw wasn’t due to the gauge moving on the router a little. But was literally like 0.0001 each move, after 5 time back and forth, I could barely tell the dial was moved from zero (and it might of just been my angle, though I tried to view from the same angle each time). So that’s all great news on repeatability as well as accuracy.

Starting Position

Ending Position after 3 Runs of 100mm Left and Right

I’ve also posted a short slow motion video of the machine returning to zero position.

More to come as I get into the machine and build more experience.



Thank you very much for doing these tests and posting the results. The fact that your findings show very good repeatability is great news.


I promised I would write the procedure I used to test and adjust the accuracy of the OF, so here it is. Decided to add it to this thread rather than create a new one.

Things you will need:

  1. OF Woodworker (same process for machinist, but adjust sizes)
  2. an accurate 36" ruler (a mm rule would be easier, but I didn’t have one)
  3. 1/4" shank, 1/4" 45 degree v-bit (larger bits will work, but makes it more difficult to see)
  4. Blue tape or masking tape
  5. Optional - fine grained 12" machinist ruler


  1. Put the v-bit into the router collet and tighten down
  2. Home the machine
  3. Jog the machine back (Y-) 100mm, and right 100mm (X+).
  4. Tape the 36" ruler to the waste board in the X direction.
    ** Ensure the ruler is parallel to the Y axis, or collinear with the X axis (your choice ;))
    ** Place the ruler near the front of the waste board, but not so far forward the bit won’t reach the ruler
  5. Jog the machine so the v-bit is centered over the 1" mark on the ruler. This is your starting point.
  6. Zero the X and Y coordinates
  7. In the MDI section of the OF controller, type the following commands, pressing play after each one.
  • G91
  • G20
  • G1 X30 F100
    ** G91 sets the machine to relative positioning mode
    ** G20 sets the machine to imperial (inch) mode
    ** G1 X30 moves the machine right, 30", feed rate of 100 in/min
  1. Check if the v-bit is completely centered on the 30" mark of the ruler.
    ** If it is, congratulations, the machine is well calibrated in the X direction. Jump to step 18
    ** Assuming the machine needs some correction, continue on in the process
  2. Using the machinist ruler, measure the distance from the v-bit to the 30" mark. This is your error or offset. Let’s assume the error is +0.125".
  3. In the MDI section of the OF controller, type the following command and press play
  • G1 X-30
    ** this jogs the machine back to the zero position we set in step 6.
  1. Calculate the offset for the error discovered in Step 9.
  • Adjustment Factor = Fa = (Distance Traveled/Distance Commanded)
  • Example, Fa = 30.125/30 = 1.004166666666667 = 1.004167 (distance traveled = 30" + 0.125")
  1. In the OF controller SW, click the menu expansion icon in the top left and click on ‘Motor 0’
  2. Scroll down to the option “travel-per-rev” under the “Motion” section. You need to adjust this value to compensate for the error.
  3. The default value for the travel-per-rev is 10mm. Multiply the value times the offset (Fa).
  • 10*1.004167 = 10.04167.
  1. Enter the new value (ex, 10.04167) into the text box and click Save in the top left.
  2. In the MDI section of the OF controller, type the following commands, pressing play after each one.
  • G1 X30
    ** G1 X30 moves the machine right, 30"
  1. Remeasure the offset, if any. If there is still an offset, restart the process at step 10.
  2. If no offset, then repeat the process for the Y direction with the following changes:
  • G1 Y30 instead of G1 X30 for step 7 & 16
  • G1 Y-30 instead of G1 X-30 for Step 10
  • Motor 1 instead of Motor 0 for Step 16

I hope this is helpful for folks and if anyone has questions, let me know.



Thank you for this! I don’t have my machine yet (recently ordered it, so have a bit to wait…), and this is my first CNC machine, but I’ve stashed this away for when I can run through this. Appreciate the detail and clarity!


Thank you for taking the time to post this. I will try it once I receive my OF.

Thanks for posting this, Tom. Very useful. Reading through the instructions, I think I spotted a small error. If you zero at the 1" mark and then jog over 30" the bit should be at 31". In steps 8. and 9. the measurement should be off the 31" mark.

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Thanks Tom, my machine is scheduled to arrive this month. I will be following your procedure.

#2. An accurate ruler. Is there brands guaranteed to be accurate? I have 3 that were used in my old work’s print room, each from a different manufacturer. None of them line up to each other by the time you get to their ends. Some stainless, some aluminum. I’ve never had much trust in rulers after seeing that.

Anyone have a good source for a metric version in the states?

@cyberreefguru Great walk though, and awesome for including the gcode and calculations.

Got out yesterday and decided that I would check things out. I used a thirty-six inch ruler, taped to the bed, and a Whiteside SC50 22 degree carving liner. I centered the tip of the bit to the one inch line. If I moved five, fifteen, or whatever inches when it stopped it was dead on. At least as much as my old eye could tell.

Hi Chad - I have a Woodpeckers ruler and I got a machinist ruler from Amazon - they line up to each other. Are they accurate? I hope :wink: Both were fairly expensive (for a ruler) so I’m not sure where to source accurate yet inexpensive rulers. Maybe others here have suggestions.

Rick - that’s great. Mine was very close out of the box (1/32 x, 1/64 Y) - again, within the limits of my failing eyes as well.



I bought a $3.48 aluminum 36" ruler from Lowes yesterday. It has inches and mm. Considering this exercise is “by eye”, I’m hoping it’s good’nuff.

Maybe I’ll take my WP ruler into the store and do some spot checks :wink:


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That Woodpecker metric set, I’ll put that on my wish list after the wife calms down from how much I spent already. :smiley:

If anything, I’ll use this method just to make sure X travel = Y travel equally, so a circle is truly a circle, a square is a square, etc. Or to match the travel that my laser does so they can be used with each other easier. That won’t require an accurate measuring device, just some transferred marks.

Thanks for the tutorial!

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I am quite new, so feel free to tell me if/why this would be inaccurate.
I taped a cm ruler to board. Lined machine up to home position. Then jogged y axis 100 mm.
Seems spot on.

“Accurate” is a relative term - someone doing rough framing will have a different definition than a steel-working machinist. For CNC work in wood, what you’ve done is certainly “accurate enough”!

@Spes - the farther you travel, the more error there will be. My machine was off about 1/16" across ~30" of travel in both x and y. Not a big deal, but worth correcting IMHO. If I only tested 100mm (~3.9"), the error would have been imperceptible to the human eye - something like 0.005" rather than 0.0625". If you don’t need max precision (or don’t care so much), then you should be good to go out of the box. The only reason I did the test is because my SO2 (and X-Carve) was off by over 0.25" over 24" - that needed to be corrected for proper operations. Hope this helps.


How did you go about squaring up the actual attachment points of your machine though?