Ive noticed recently that on larger pieces cut on the CNC (Stratos Pro) that the longer edges have a bit of an arc to them. If I take the pieces cut side by side and flip 1 on top of the other line up the corners Im noticing approx 1/16" offset in the center point of an 8 ft piece. Ive tried replacing my bits thinking that it might be deflection but that hasnt helped. What could be the cause of this?

Nathan

What you are seeing is most likely tension released in the material. It is unlikely that it is a fault in the cnc. You could try a first pass with allowance of .05" then second pass to final size for large parts with the offending sheet goods.
I have experienced this only with melamine on the saw and only every once in a while. Maybe try a different board supply

I do leave an onion skin on all my parts and then a final cut with an .03 offset. The diffrence between the cut pieces is pretty consistent and that leads me to think that it might be the cnc.

One or both axis?

So far I`ve noticed it only on the X axis

So if the X axis is drifting it's likely something loose in the Y axis drive or the X axis linear bearings. Check all the bearings on the X and the lead screw on the Y. It could be as simple as a loose bolt somewhere. A sixteenth is enough that you should be able to move manually by pushing/pulling/prying on the table and gantry to see.

Any recent crashes?

Is the arc in the same place every time?

Is this on panel stock or individual boards? It could be a hold down issue.

BH Davis

I did have a crash where the fly cutter to surface the spoilboard got jammed in to the table, so that could be where the issue originated from. This is on panels, its defintly not a holddown issue, I did some further investigating and found that my bigger parts are slightly offsquare as well. Ill have to get a tech in to have a look at this.

Could be the spindle or the plate that the spindle mounts to is a little loose. Had that problem on my old Anderson a couple of years ago.

Have you tried a climb cut to see if it still does that

Try running a straight cut the full length of the table. Just kiss the surface though........perhaps 1/32" deep. Then see if that cut is straight.

If it is straight then you have some sort of shifting issue when under load. If it is curved then it's most likely an adjustment of some sort.

BH Davis

I had a similar issue an Omnitech Selexx. I would check the drive belts on the X axis and make sure they have proper tension. If not, retension them. Be careful not to turn the servos, or they will need to be syncronized.

Possible reasons for this issue could include:

1. Machine calibration: The CNC machine may need recalibration to ensure that it is cutting accurately along all axes. Over time, vibrations, wear and tear, or changes in temperature can affect the machine's accuracy.

2. Tool deflection: If the cutting tool is not rigid enough or has worn down, it may deflect slightly during the cutting process, leading to inaccuracies. Trying different cutting tools or replacing the current one may help solve the problem.

3. Workpiece clamping: Insufficient or uneven clamping of the workpiece can cause it to shift during the cutting process, resulting in inaccuracies. Make sure the workpiece is securely fixed in place to minimize any movement.

If the CNC is not cutting straight than the edges of the separated pieces would fit/follow each other perfectly, no matter the path of the cut; if one edge is concave, other should be convex and they should fit each other without a gap. Since there is a gap in the middle, that is most likely infamous “banana cut”. I get them all the time on melamine boards that are cut on a slider, regardless of the board’s manufacturer.
The reason is the stress/tension embedded in the board during manufacturing process, or so they say. Interestingly, it always results in a concave, never convex, shape. Either both sides of the cut would be concave, or one side would be concave and other straight.
Once the 4’x8’ sheet gets divided into 2-3 crosscut pieces it’s no longer an issue with subsequent cuts, but those first two cuts are oversized by about 1/4”, so I can straighten the edge with a final cut.
No idea how to fight this on a CNC.