Inaccurate cuts on the x and y axes

Hi there,
I’m having some problems in the accuracy of the cuts on the x and y axes and I can’t figure out how to fix it. From the photos you can see the problem, the cuts should all have the same size, 3.2mm but they change a lot according to the position in which they are located. I’ve already squared the CNC and it looks fine, what else can I or should I check?



How are you holding the wood down? It looks thin
If its just in that back left corner the wood could have a bow in it so when the bit is coming up the wood comes up with it.
If it cut the back left section last the wood has lost some of its rigidity because of all the cuts in it.
The wood gets weaker with each one that you cut out so with the bit cutting and applying pressure the
wood may flex some.
Have you’ve ever seen someone cut groves into wood so they can bend it around a shape? The wood moves and bends easier with the more cuts you put in it.
Hope that makes sense.
Russell

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Thanks for you reply Russel,
Yes, the playwood i use is quite thin (4mm more or less) and this is one of the problem and the reason why i’m looking for a pressure foot (but i’m not able to find something for the x-carve). So far i’m not holding the wood because i cut big pannels (75x75cm) and many of them (7 or 8 per day) and using the double side tape it will make me loose a lot of time. But it can’t be the only reason because i have this problem on all that pieces (not only the one i marked in red) in the same spots, i have some problem also if i have to cut small circular shapes, (2 or 3 cm diameter) they often aren’t perfectly circular but more oval. I think there is some kind of adjustment that i can’t think of. Is it possible that maybe the movement on one axis is more fluid than on the other and this translates into less smoothness and correctness in the movements?

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That’s possible, try adjusting the eccentric nuts. I just saw where Seth posted about this.
The eccentric nuts keep the V wheels tight.

Also even belt pressure and of course calibration. If you have a mm ruler you can jog the machine 500mm and see if it goes 500mm on the X and Y.
There are a few videos on calibrating the XCarve, PawPaw has one.
PawPaw has some good videos on adjusting and maintenance on the XCarve.

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Probably a good practice to just check the eccentric nuts before each carve, they do have a tendency to get loose. I always check mine before each carve. I keep a small wrench right by machine for this. From the pic it looks like the z axis nuts are loose, and you were likely cutting this a little fast, at it just caused the z axis to kind of wobble on those cuts since the nuts aren’t tight

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If the eccentric are moving by themselves, I’d tighten the Nyloc nut at the end onto the screw tighter and that will squeeze the eccentric in place better and will make it tougher to rotate on its own out of position.

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Thanks Russel for you time and tips, i will try what you suggested and see if i can fix those problems

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Thanks Johnathan,
Checking the machine is a good practice that I have to admit I don’t do often, I certainly will insert it in the workflow so as to do a quick check of the main components. You are also right that maybe I cut pieces too fast, I got the milling data from the company I bought the cutters but i will try to slow down the cutting time a bit.

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Thanks Seth for your reply,
i will check them, How can I know when I have tightened them correctly and not too much or too little?

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Excerpt from the Manual:Calibration and Maintenance - X-Carve Assembly

To properly position the adjustable v-wheel, take an open-ended wrench and slowly turn the eccentric spacer to the point where it takes a little bit of effort for it to spin. Do this slowly to ensure you do not over-tighten the v-wheel. This can cause the wheels to crack. Now repeat this step for every pair of v-wheels. Finally, test the wheels by moving the carriage using the Jog Controls in Easel. If the wheels moves along with the carriage without much effort, then they are properly tensioned.

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ok i tried to do some checks on the v-wheels, one of them was a bit loose. I also stretched the belts a little better. I did a cutting test and the situation has improved a little, but the smaller the rims the more imperfection is seen to the point that the smaller ones (15mm and 10mm in diameter) are no longer circles.



In the middle picture the row on the left has a couple good circles, did you do anything different when cutting those?
How deep are you cutting?
How fast are you running?

You don’t want your belts to tight, that will cause them to break. I broke a couple becasue I was setting them to tight. Take one finger and pick up on the center of the belt, you should be able to raise it an inch without much resistance. Jog the gantry all the way to the back when picking up on the belt and to either side for the X axis.
Are you cutting with a 1/8" bit?
Russell

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Check your play in the Z axis. Grab the bit and see how much pressure it takes to move it by the amount of offset you are seeing. I had the out of round issue with my X-Carve, but I was cutting AL. I improved the issue some by beefing up the X gantry, locking the y gantry to the waste board, and replacing the Z gantry. You can always slow down and take lighter cuts once you have the play as best you can get.

I would also use the blue tape and superglue method for holding down your work. Its possible that the material is flexing rather than the z axis. The blue tape should hold the parts in place while being cut. You can find lots of examples of this hold down method on YouTube. Good luck.

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