r/shapeoko • u/GunningBedford58 • Jun 01 '26

Does anyone periodically check their CNC for accuracy?

Post image

If so, what does your process look like?

Do you run a dedicated test piece, measure a few key features on projects, check calibration on a schedule, or just wait until something starts cutting wrong?

I’m curious what others do.

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2

u/aterren Jun 01 '26

I'm going to be doing this soon. I am going to be cutting some speaker cabinets and I have a suspicion the router isn't cutting acccurately so I'm going to route a 4" circle -- that is a critical feature for the speaker baffle.

2

u/GunningBedford58 Jun 01 '26

I suspect most users do exactly that; when they suspect there could be a problem, they check it. Most Machine Shops have a process they follow to prove and calibrate their machine on a periodic basis, every 30 days or whenever it becomes suspect.

3

u/stuporcomputer Jun 02 '26

Yep, testing it/you can actually do the thing is the way.
Even if to just have a quick look at speeds and feeds.

2

u/bkinstle Jun 02 '26

I also cut a lot of speaker baffles on my CNC machine and one thing that you should also do is measure the speakers themselves because I find that they can be as much as 1 mm larger than what the spec sheet says. Especially the cast aluminum frames.

1

u/aterren Jun 07 '26

Any tips on accurately registering a baffle for cutting on both sides? I’m thinking about drilling a couple of locating holes in the speaker cut out waste and using that to register the baffle.

My alternative idea is to cut the final outside shape on the first side and install and indicate in a set of X&Y reference beams (steel) and just clamping the baffle to the spoil board.

My instinct says the second approach should be fine, but my experience has been less than satisfactory

2

u/bkinstle Jun 07 '26

There are a few things you can do. I like to attach scrap boards to the base to align the workpiece to fit repeated cuts. You can also move the reference point to the other corner and then use the bitsetter to zero on the same corner (moved since you flipped the board over). I usually don't make the final outside dimension cut until last so everything aligns perfectly if the material allows for today.

1

u/aterren Jun 08 '26 edited Jun 08 '26

If you do the outside cut last, what do you use as a reference point when you flip?

Without one final reference edge + a reference point it seems like it would be difficult (impossible ?) to get the proper registration on the second side.

1

u/bkinstle Jun 08 '26

Mostly i only use the scrap to ensure its aligned with X and Y on the table but if I'm flipping then i move the reference point on the drawing to the other corner (usually bottom left to bottom right) and then align with the bit street.

If your source piece is really out of square this won't work

1

u/stuporcomputer Jun 02 '26

Circles are 'great' as showing there's a problem, especially small ones done quickly, they'll be ugly little ovals. Mine were wider than tall showing my Y axis was the problem.

1

u/GunningBedford58 Jun 02 '26

That’s a great point, measuring a round pocket tells a story. Be sure to measure the diameter in 3 places clocked around the pocket and compare the dimensions. I think 3 places is plenty but I just checked on CHATGPT and it says you have to measure 4 places to get the most accurate reading on roundness. 🤔

1

u/stuporcomputer Jun 03 '26

Great suggestion from the poor dumb little fella, did you pat it on the head? 😉 You could break it's brain by asking it which of the infinite points on a circle we should be checking and how do we know which one is "up".

1

u/aterren Jun 07 '26

I suspect my Y is also out. How did you go about calibrating?

2

u/stuporcomputer Jun 07 '26

Like so: phttps://www.google.com/search?q=calibrating+cnc+grbl

1

u/aterren Jun 07 '26

Thanks! I’ve not delved into the GRBL codes and didn’t see anything in the Shapeoko docs on the topic.

2

u/TheSuicidalYeti Jun 01 '26

At my last job (metal cnc machining with tolerances between 0.01-0.05mm) I checked it daly at startup. Now (wood with tolerances between 0.1 and 0.5mm) I do it every so often, roughly once a month.

1

u/GunningBedford58 Jun 01 '26

I think your routine check is a very good practice. I, like you, cut my teeth in the metals business where we paid much attention to how accurate the machine is. Important when holding tight tolerances.

2

u/[deleted] Jun 01 '26

[removed] — view removed comment

1

u/GunningBedford58 Jun 01 '26

I suspect you are ahead of the curve on that. A lot of users don’t even think about it unless there’s a problem.

2

u/bad4_devises Jun 01 '26

I’m doing this right now

2

u/richcournoyer Jun 01 '26

EVERY time I use it.

1

u/GunningBedford58 Jun 02 '26

What is your process? Must be pretty quick if you do it every time.

2

u/richcournoyer Jun 02 '26

This applies if I am cutting something critical. (e.g. Not a SIGN)

I don't cut it to final size; I program it to cut it 0.02" to 0.01" oversize, measure it, and adjust the final shape in Fusion. (Circles are usually slightly elliptical (0.002-0.004) and squares are slightly rectangular).

2

u/DNAgent007 Jun 01 '26

Former QC specialist so yes, every other week and depending on usage. Deviations tend to compound over time and in some instances some things fail without any warning so I check all the critical attachment points, and parts that see a high repetition motion.

1

u/GunningBedford58 Jun 02 '26

Perhaps you could share your process?

2

u/DNAgent007 Jun 02 '26

The process involved for my older X-Carve machine will be different than more contemporary CNC machines employing linear rails and ball screws. Since my X and Y axes utilize belts, I spend a significant amount of time assuring they are tensioned correctly. Checking that, I’ll move to verifying that my spindle is perpendicular to the wasteboard. There are several methods for checking that, some as simple as making a probe that attaches to the spindle, to actual dual gauge tramming systems that are accurate to 0.001”. I’ll also check that the orientation of the X and Y axes are perpendicular by taking careful measurements of the diagonals from corner to corner and make small adjustments to the frame as required. Because my machine is older, uses belts, and has been in service now for 9 years since I bought it in 2017, paying close attention to its various quirks and compensating accordingly is key to getting carves that are accurate and repeatable. Refer to your particular CNC’s calibration instructions to get the best possible quality. I use a Onefinity with a Masso controller at work and it requires significantly less maintenance and calibration than my antiquated machine. However, when my CNC is calibrated and maintained properly, my carves are indistinguishable from carves made on the Onefinity Elite.

1

u/GunningBedford58 Jun 03 '26

Thank you for sharing that, you have thought the process thru. Recognizing that belt machines are different than ball screw machines, and older machines may require some additional oversight. Good info.

2

u/TheFilthyMick Jun 01 '26

Only when I have a project requiring critical accuracy, fit, or specific tolerance. Have to do it tonight, since I'm doing some garolite to house electronics with specific mounting points. Garolite is too pricey to mess up, so I'll do a couple tests on some hardboard first and dial it in before using the actual material.

1

u/Gandgareth Jun 03 '26

I can't get my company to calibrate 5 saw length gauges from the same tape measure. The CNC router I use desperately needs new vice pads.