[moana]

Hey all,


New to the forums and new to operating a cnc.

We started creating a vacuum table and for some reason the channels are not spaced evenly like they should be. We cut this on multiple small trials on different material, mdf..etc and it is consistently cutting unevenly. In the mach3 preview window the spacing is perfect as it should look and every time we cut this happens

The weird thing is the spacing is exact between every other one but as you can see one gap in the channel is bigger than the other.

Excuse me if this is obvious but I've done a lot of searching and cannot really figure it out. We do have a "hobby" machine if you would call it that, it is not heavy duty but I do not think this is a deflection/backlash issue since the material is not very dense and we are running it smoothly... my understandings of those may not be entirely correct either but I really need to get this figured out as right now we do not need exact cuts to make this vacuum fixture work but we will need very accurate cuts soon. What is weird is that it is even in the error so it makes me believe it is a setting somewhere.

I also tested the motors to make sure they jogged the correct amount on the DROs with a measuring tape on the gantry so it seems like it isn't a tuning issue... help!!? haha

I attached a picture to show on a test piece of particle board what I am talking about.

If this thread needs to be moved to another section please do so. Thanks for your help


Attachment 267816


~moana

[ger21]

My first guess would be deflection.
Is the bottom left corner the end of the cut? If it is, then it's most likely deflection.
Can you post the g-code?

[awerby]

To me, it looks like your CAM program isn't set to cut down the middle of the lines you laid out, but it's cutting to one side of them. The error you're looking at is too regular to be lost steps or a mechanical problem, and it seems to be off by a factor that's pretty close to the radius of your tool.

[joeyjrc]

Try running the program only .010 deep, if it does the same thing then its not a deflection issue. It may be a cutter comp. issue. Look at the g-code, is it switching from a G41 to a G42.

[moana]

Thank you for the replies everyone

The above picture is when we tried cutting the vacuum channels with a 1/4 inch bit. The spacing between each channel was supposed to be 1/4 inch but it ended up having 3/8 inch for the wider width and the smaller one is 1/8 inch wide.

The g-code posted below was when we decided to run the channels with a 1/2 inch bit on a sheet of mdf. I do not have the measurements of these channels but they were inaccurate and consistently off just like the 1/4 inch bit was on the particle board picture.

I know the machine we are using isn't rock solid like some fully welded one but we didn't run these at ridiculous feeds and it is the same freakin consistent inaccuracy each time. I am about to pull some beard hair out haha! It is off on both ends of the sheet of mdf the same amounts!! AHHHH!!!!

N0010 (Filename: vertical vacuum channels.txt)
N0020 (Post processor: Mach3.scpost)
N0030 (Date:07/02/2015 Time:18:05:40)
N0040 G20 (Units: Inches)
N0050 G40 G90 G91.1
N0060 F1
N0070 (Part: vertical vacuum channels)
N0080 (Operation: No Offset, Default, T6: Mill/router, 0.5 in diameter, 0.25 in Deep)
N0090 S1000 (Mill/router, 0.5 in diameter)
N0100 T6 M06
N0110 G43 H6
N0120 G00 Z0.1500
N0130 S1000 M03
N0140 X47.0000 Y1.7500
N0150 Z0.0197
N0160 G01 Z-0.250 F11.811
N0170 Y95.2500 F2834.6457
N0180 X46.0000
N0190 Y1.7500
N0200 X45.0000
N0210 Y95.2500
N0220 X44.0000
N0230 Y1.7500
N0240 X43.0000
N0250 Y95.2500
N0260 X42.0000
N0270 Y1.7500
N0280 X41.0000
N0290 Y95.2500
N0300 X40.0000
N0310 Y1.7500
N0320 X39.0000
N0330 Y95.2500
N0340 X38.0000
N0350 Y1.7500
N0360 X37.0000
N0370 Y95.2500
N0380 X36.0000
N0390 Y1.7500
N0400 X35.0000
N0410 Y95.2500
N0420 X34.0000
N0430 Y1.7500
N0440 X33.0000
N0450 Y95.2500
N0460 X32.0000
N0470 Y1.7500
N0480 X31.0000
N0490 Y95.2500
N0500 X30.0000
N0510 Y1.7500
N0520 X29.0000
N0530 Y95.2500
N0540 X28.0000
N0550 Y1.7500
N0560 X27.0000
N0570 Y95.2500
N0580 X26.0000
N0590 Y1.7500
N0600 X25.0000
N0610 Y95.2500
N0620 X24.0000
N0630 Y1.7500
N0640 X23.0000
N0650 Y95.2500
N0660 X22.0000
N0670 Y1.7500
N0680 X21.0000
N0690 Y95.2500
N0700 X20.0000
N0710 Y1.7500
N0720 X19.0000
N0730 Y95.2500
N0740 X18.0000
N0750 Y1.7500
N0760 X17.0000
N0770 Y95.2500
N0780 X16.0000
N0790 Y1.7500
N0800 X15.0000
N0810 Y95.2500
N0820 X14.0000
N0830 Y1.7500
N0840 X13.0000
N0850 Y95.2500
N0860 X12.0000
N0870 Y1.7500
N0880 X11.0000
N0890 Y95.2500
N0900 X10.0000
N0910 Y1.7500
N0920 X9.0000
N0930 Y95.2500
N0940 X8.0000
N0950 Y1.7500
N0960 X7.0000
N0970 Y95.2500
N0980 X6.0000
N0990 Y1.7500
N1000 X5.0000
N1010 Y95.2500
N1020 X4.0000
N1030 Y1.7500
N1040 X3.0000
N1050 Y95.2500
N1060 X2.0000
N1070 Y1.7500
N1080 G00 Z0.1500
N1090 M05
N1100 M05 M30



Once again, thank you for any help you may offer! I am ever grateful and would love to show you guys what we are doing if I can get this cnc accurate!!

Best,

Moana

[cfunderburgh]

First off I would test cut on something that cuts good like mdf not laminate, that's pretty hard stuff. Second I would look at your tool run out. And lastly check your backlash.

[moana]

Per my last post we did run through mdf. Same issue with the 1/2 inch bit on that.

Testing backlash, going to have to get a how-to on that although I'm sure there's posts on it. Tool run out..it isn't wobbling?

[cfunderburgh]

From experience I've learned that the collets that come with most routers are anything but precise. The second issue could be if your router is perpendicular to your table. Manually plunge the bit down and move it a set distance in both x and y. Measure the widths as well as the lengths of those two slots. If your bit had runnout both slots will be oversized the same amount. If the router isn't square to the table the slots will probably be different sizes.

[bhurts]

Try making the cuts all in one direction and see if that changes the spacing. Also what bit are you using to cut with?

Ben

[ger21]

The circled area all indicate deflection. It looks like there may be other areas as well, but it's hard to tell from the chipping.
With the spindle off, and no bit in the collet, grab the collet and push and pull in all direction. See if you can find something moving, or if the entire machine is flexing.